GroupDIY

General Discussions => The Chamber => Topic started by: alexc on November 06, 2018, 11:16:19 PM

Title: REW Update
Post by: alexc on November 06, 2018, 11:16:19 PM
The fabulous Room EQ Wizard (REW) application from John Mulcahy and team   has a new update!

[  REW is the business for audio real time analysis, especially distortion measurement  ]

https://www.roomeqwizard.com (https://www.roomeqwizard.com)

SOme interesting improvements and extras, and so far everything I have  is working great with it.

Thanks REW for services to audio measurement-kind  :)



Title: Re: REW Update
Post by: ruffrecords on November 07, 2018, 02:39:17 AM
+1 for REW as an audio measurement tool. The correlated white noise source is a boon for measuring frequency response. The distortion pop up show THD, THD+N and harmonic levels up to about 7th. Noise measurements are more or less direct and include A weighting if you want to indulge in specmanship.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on November 11, 2018, 06:41:44 PM
Of most  interest to me - the main RTA window  THD and Noise measures are more detailed,  and one can now set the BW of the thd measures.

Also, there  is now control of 'stepped sweep' from the RTA window, and the option of 'dBc' amplitude unit.

Plus much wider basic bandwidth .. up to 384K sampling rate - I think with the current generation of 120dB SNR audio interfaces out there, one can really go to town !

One day I hope REW adds :

- calibrate-able dBu unit for RTA amplitude
-  intermodulation distortion test measures
- a second 'measurement cursor' with the difference between them displayed ... like my Tektronix CRO  :)

Just a fantastic piece of software engineering.

Title: Re: REW Update
Post by: EmRR on November 11, 2018, 10:44:45 PM
I really gotta find the time to explore this....
Title: Re: REW Update
Post by: alexc on November 12, 2018, 02:52:13 AM
I spent another half-day noodling with REW 

..  trimming up a simple 6SL7 in a variety of ways  ..  single gain stage with cathode follower, parallel'd gain stage, cascaded gain stages with/without nfb  etc.

You can really dial in the desired perf with quite a lot of dexterity ..  and compare with the data from the 'LoadSim' calc-er.

btw, I finally tested some of the russkie sl7 type against some modern tung-sol  ...  the modern tung-sol was streets ahead in hum performance   ...  didn't bother testing further   .. something like 10dB diff in hum , albeit at some little more dB gain.

I was surprised .. maybe I have some poor examples ... Also tested up some '6L6 equivalents' from the old soviet days  ... against some modern TungSol types.

Once again, no contest - this time mostly due to really poor match in so called 'matched pair'  ..  10mA diff!

A pair of modern TungSol 7581a  basic-match were less than 1mA different (single spud SE amp, 6K-8ohm 50mA output traffo).

The crapola sino SE traffos in my 'spudster test platform' crap out way before the finals, tho', so the poorer performers don't make much difference at the end of the chain. 'Its all good!'

....

And what a fab tube the  6SL7 is.

One of the greats.  I have a few variants and they can be really stellar, both vintage and modern (even more so).

 I want to combine it with a modern hi-perf power amp module, just to see if I can preserve that beautiful spectra to a pair of 30W speakers.  Sort of a   6SL7-with-straight-wire-power kind of thing.

I have a tiny pcb module with that  super hi tech Texas Instruments 'amp driver chip+heatsink'  and a pair of power bjts onboard.

Just add a large heatsink, even a little fan, plus some high current bi-polar power rails and voila! Award winning audio   ;D

And just for kicks, a 6SL7 driving a JLH 10W bjt class A module   :)

. ..

Have to find how close I can get to that pure 6SL7 spectra at decent levels!

..

REW really shines a light on audio stuff for those with only half-days to noodle away!
Title: Re: REW Update
Post by: ruffrecords on November 12, 2018, 03:39:30 AM
Higher hum level is usually a sign of poor heater cathode leakage. Often occurs with age in tubes. One reason I do not buy NOS tubes any more. Sometimes it gets a little better if you run the tube for a day or so. Sometimes heater elevation works.

Regarding REW the one feature I want is to be able to set the zero reference level on the RTA graph to an arbitrary input level so I don't have to keep remembering to add 7.7dB or some similar figure to the noise measurements to get absolute values.

Oh, and automatic Q measurement of EQ plots - and Bode plots with phase response as well as amplitude.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on November 12, 2018, 03:51:27 AM
Higher hum level is usually a sign of poor heater cathode leakage. Often occurs with age in tubes. One reason I do not buy NOS tubes any more. Sometimes it gets a little better if you run the tube for a day or so. Sometimes heater elevation works.

Good points Ian, thanks.

I had quite good results with the soviet era el84 equivalents, which did perform very well.

I guess, as always, one has to hunt for the perf.  I just can't resist the Russian tubes  :)

Before REW, the lens for selection was much coarser.
Title: Re: REW Update
Post by: trobbins on November 17, 2018, 05:39:22 AM
A key aspect is the on-going development and bug fixing - amazing for such a detailed app.

It is also worth checking on the rew forum about wish list improvements - it may seed a future addition, or get an informative response.
 
Btw, what intermodulation distortion function is lacking?  From a vintage perspective it provides the common standard techniques that were in use.
Title: Re: REW Update
Post by: alexc on November 17, 2018, 06:43:54 PM
There is a facility in the sig-gen part of REW for multi tone generation, but as far as I know, there are not Intermodulation
Distortion calculations anywhere - IMD measurements are the only thing I still do in Rightmark.

Another fairly advanced thing I'd like to see are 'distortion residuals' ... 

There are a ton of features that I don't use - I most only use the sig-gen/RTA/sweeps.

Title: Re: REW Update
Post by: trobbins on November 17, 2018, 07:05:17 PM
IM is reported in the distortion window (for the given test signal configuration chosen in the tone genertor).  The distortion window identifies the harmonic residuals and there levels, and automatically identifies them on the spectrum plot.
Title: Re: REW Update
Post by: ruffrecords on November 17, 2018, 07:18:58 PM
IM is reported in the distortion window (for the given test signal configuration chosen in the tone genertor).  The distortion window identifies the harmonic residuals and there levels, and automatically identifies them on the spectrum plot.

I didn't know that.Must give it a try.

Cheers

ian
Title: Re: REW Update
Post by: alexc on November 18, 2018, 01:33:33 AM
Oh snap!

Thanks for the tip !

With the 'Dual Tone' signal selected in the Generator window, the RTA window's Distortion panel does indeed show Intermodulation Measures  :)

Exactly what I was looking for!


Title: Re: REW Update
Post by: Tubetec on November 18, 2018, 08:21:07 AM
I ran up REW yesterday for the first time , superb for measuring the dist on my Hp200cd sine gen , with a few replacement components, Im now able to get  a thd figure of less than .5% which is on spec , frequency is rock solid and settles in 3 instead of the allowed 5 seconds . Amplitude was a bit up and down also , a clean of the output att pot seems to have improved matters a bit here .

I used the standard soundcard mic/line in , it was very easy and intuitive to set up ,  overdriving the sound card input with the oscillator harmonics up to about 9th appeared in the window ,as expected the noise levels were poor as the sound card can only accept a few hundred millivolts .

For anyone who wants too but hasnt tried it yet , get stuck in , you should be up an measuring stuff in no more than a few minutes ,between download ,install and set up . It reminds me a bit of Reaper in terms of intuitiveness and ease of use .
Only thing missing for me in it was no scope ,or at least I didnt find one . I reverted to YMEC audio tools for its scope abillity and sure enough the 200cd is cranking out a nice clean sine , the limitations of the inbuilt soundcard I used were very plain to see with anything over about half a volt causing the waveform to 'flat top '

I feel a bit stupid now for procrastinating so long before trying REW , Ive barely scratched the surface but the abillity to see how the proportions of various harmonics change with level is fantastic to have .

Title: Re: REW Update
Post by: trobbins on November 18, 2018, 01:35:26 PM
I used a scope app for a while, but a spectrum plot tells me so much more, that I don't get the urge to swap over much nowadays.
Title: Re: REW Update
Post by: Tubetec on November 18, 2018, 02:29:16 PM
Theres no doubt about it the distortion panel in Rew gives great indication whats going on in your circuit , much more than a simple waveform on screen can say . the whole thing has me wondering if a digital scope is even nessesary , all the math functions you need are built into Rew ,  a simple old fashioned analog scope would do for waveform indication .
It seems to me the REW is much more versatile than just a speaker test program , its just as good with line inputs and using external signal sources ,as opposed to mic input , I cant help thinking the scope of this program is somewhat limited by its name, functionally its much much more .

Anyway big thanks to John Mulcahy , quite an Irish sounding name , I do hope the free(donation) business model is giving a return for all the work put in .

The other thing is I ran the program up on  single core 32 bit based windows 3 Gig ram , its works great despite the lack of number crunching power , Mac, Windows or Linux platforms means just about anyone can run it as well.
Title: Re: REW Update
Post by: ruffrecords on November 18, 2018, 03:24:35 PM
A scope will tell you things REW won't, like if your circuit is oscillating in the MHz region, what your square wave performance is like, if there is a dc offset on your output and so on. They are both tools that help you design and debug your circuits.

Cheers

Ian
Title: Re: REW Update
Post by: trobbins on November 18, 2018, 04:57:41 PM
Yes it is "horses for courses".  For valve amps, it can show parasitic feedback resonances coming out of the noise floor well before they would ever show up in a waveform.  And with 96kHz bandwidth, i reckon i would see anything amiss from an 807 acting as a radio tx, as something would fold back in to tha audio band.

But i get the scope out for X-Y low frequency phase shift and resonance effects - it can be fun trying to use various tools to gain a better awareness of some topic.
Title: Re: REW Update
Post by: Brian Roth on November 18, 2018, 07:09:24 PM

The other thing is I ran the program up on  single core 32 bit based windows 3 Gig ram , its works great despite the lack of number crunching power , Mac, Windows or Linux platforms means just about anyone can run it as well.

What OS are you running?

Bri
Title: Re: REW Update
Post by: alexc on November 18, 2018, 10:38:03 PM
I routinely run a 'high voltage' probe as an input to REW ....

I did up a small alu box with a connection for the probe, and a parallel BNC connector to feed to my CRO. The box has a dc blocking cap feeding a high impedance network with a  6 way rotary switch to vary the attenuation of the probe ac signal.

So I can measure (unbalanced) ac signals of up to 450Vp-p both on the CRO directly and/or  in REW, with that signal suitably divided down so as to suit my soundcard's balanced input, a range of 0 to 10Vp-p or so corresponding to -130 to -3 dBFS in REW.

There is some loading effect by the probe of course, but it is reasonably minimal ..  I can check a signal's true value on the CRO by simply disconnecting the ac probe and using the standard CRO probe alone.

ANYway, the point is one really needs *both* a CRO and REW at all times!

The best thing about my modest Tektronix is the pair of measurement cursors ...  I like to set one cursor  to the bottom div of the graticule, the other cursor about half way up ...  dial the CRO sensitivity to approx lie within the two cursors and then quickly adjust to get an accurate reading of the CRO screen. 

Beats counting divs any day!

I'd like similar on the REW RTA .... one cursor is a line at the 'hum floor'  and the other at the 'return signal peak' with each level displayed in a 'cursor window' as well as the difference between them. 

I do it manually when I do my 'snapshots' of the REW RTA window ...  my app is 'SnagIT' for Windows  .... lets me annotate and draw lines and what not in it's editor ...

Like this ....
Title: Re: REW Update
Post by: trobbins on November 19, 2018, 04:50:26 AM
Given the typical bandwidth limitation of soundcards, it does relax the need for top of the line probes. 
Even cheap 10:1 and 100:1 from fleabay perform nicely if their compensation range is acceptable. And even if they don't, it isn't too daunting to swap out the bulk cap typically hidden away inside the bnc end for a value that does allow flat response.  And even then, a simple calibration sweep could be used to 'iron out' grossly poor response as an easy way out.
Title: Re: REW Update
Post by: Tubetec on November 19, 2018, 04:48:26 PM
Its a bit like having thousands worth of hardware with a HP badge on it , but its all in software .

Maybe a hi-z input jack on an audio interface the would be more appropriate for direct to tube connection  with less loading effect .

Any good tutorials on REW out there ?

Is it possible to produce graphs of output level and distortion vs frequency ?

Looks like the program runs reliably on everything windows at least as far back as XP ,
Any old pc or laptop can be repurposed for this , even with a 2009 low powered single core mini pc  all the metering and general operation of the program is fast  and smooth , really this program deserves to run at all times on the test bench on its own dedicated little pc , what would be nice would be to take your idea Alex, with an attenuator box ,but add an ultra hi -z cathode follower input to  a 384khz capable A/D -USB , just like in the days of old the cathode follower input could be built into the probe itself , the USB housed with the psu in the enclosure .

It seems like the usefullness of the program in terms of electronic signal sources has barely even being explored on the site , a little  box with a hi-z probe and attenuator would make a great addition ,all of a sudden it becomes a serious test bench tool ,Once I explore it more its gonna be lots of fun tweaking my monitors on it ,but I think  its worthy of everyday bench use and not just speaker tweaking .



Title: Re: REW Update
Post by: MountCyanide on November 19, 2018, 10:48:40 PM
Thanks for hipping me to this. Installed and ready to go.
And if anyone from here does want to do a video tutorial on REW <in Los Angeles> I'd be more than willing to shoot and edit.

Cyrus
Title: Re: REW Update
Post by: alexc on November 20, 2018, 03:04:06 AM
Regarding measurement of high ac signals, like those at the plates of tubes etc ...

Because there is usually a large dc voltage present, it is safest to make up a box with a large dc blocking 600V poly cap - I use an orange drop type 0.22uF to  0.47 or so as I recall. 

It's required to prevent the dc at the 'test point' finding it's way to your expensive sound card inputs.

I have tried a simple attenuating CRO probe as the 'front end' for my attenuating box, but it's unsafe (crack! burned out/shorted) ..  small components easily fried with possible damage to the sound card.

I also like the seperation of a single-wire HV sampling part with the ground wiring in the box and breaking out on a test clip. It's best not to have the probe active tip any where near a ground (as they are on a conventional cro probe with the front hook removed)

One also has to remember to 'ground the probe tip' when not in use - to avoid unrequested discharge!

This is also the reason not to have to high uF in the dc blocking cap. 10uF electro is a no-no. That's a lot of discharge to go off.

As to accuracy, in most cases, the loading effect is a few percent; occasionally one needs to account for it but most often not.

Generally you can safely keep an eye on your noise floor as you go and prevent hum from getting away from you.

As far as using a HiZ input on a sound card for the probe - I do all my I/O balanced with XLR. I have various balance/debalance boxes and cables that I use as required.

It also pays to use an interface that is 'not too expensive' just in case you do somehow fatally spritz it  :o  For same reason, I don't recommend using one's computer's built-in soundcard facilties for this job!

....

I can't imagine not using REW to nail down performance at my plates  ..  and all over the place ...  checking the hash on power supply lines, B+, B1+ etc, grounding schemes   .....   its all there. ;D

For me, there's always been some pathway found to a significant improvement by spending some REW time.

I do annotated snapshots at each baseline of change in 'all my circuits' ... it's a discipline that pays off in terms of making informed decisions about  performance and tradeoffs.

I mean, if you can't demonstrate it (with a REW snap),  then it doesn't  exist, right ? Especially for nebulous small dB changes and what not.

The danger (of over reliance on 1st level measurements) is -  it can shape ones 'paradigm' towards 'less THD' ..  some times I thought I had a 'sound' that was exciting but on subsequent measurement-and-tweak, I felt I lost that 'thing'.

Not often though!  Still haven't come across a case where I prefer more noise.

Character, sure thing!   Hum and such - no, no, no.
Title: Re: REW Update
Post by: alexc on November 26, 2018, 01:16:13 AM
Here's a nice REW snap   :)

Its a tube build with a quad New York Dave One Bottle module  powered by a remote modular PSU with a heavy duty 7pin interconnect cable of 2m length using cheap and large-ish, eby 'aircraft' connectors.

Regulated HV and dc filtered heaters. The PSU is a 'twin' layout, each section is identical and independent with it's own interconnect to a signal rack.

The  PSU modules each do up to +350Vdc 100mA, +6.5Vdc 2.5A, +24V 1A, enough to do a decent signal rack or two.

Here is a REW snap for  one channel, with a nominal -20dBFS balanced send and using my 'hv ac probe' box to safely attenuate the return signal to suit my audio interface's balanced input range of around 0 .. 8Vpp.

Here, the probe box is doing something like 30dB of attenuation (on a rotary switch)  ie.   500Vpp divided down to 10Vpp or so

...

Fairly good performance from the nos Philco ...  minimum nfb setup   ...   57Vpp plate signal being measured  ....

ie.  a single av7 tube with 2 cascaded gain stages and nfb  ....    gain x57   

(driving a load consisting of a 15K/600 Edcor xsm output transformer)

0.4% thd+n, nearly all h2 with 87dB of signal-hum margin and +27dB of headroom  :)   Hum floor is at -96.0dBu. 

When I crank the input signal some, I get a 1% thd+n scenario with  >96 dB signal-to-hum margin ...   at a plate doing 120Vpp signal into 15K load.

That's a hum margin within 'sighting distance' of   typical opamp circuits that have some  gain.

Not bad for a modest AV7. The nondescript 'cascade-with-nfb'  beats any single tube gain stage I've seen ...

...

So, all that's pretty good I think!    And around 100usd per channel including tubes, signal traffos and  very quiet PSU.

.....

I estimate the PSU is more than 3dB quieter than my best regulated 'co-located' psu to date. 

Something like 9dB quieter than the psu in my typical 'amp head with rectifier+choke psu'  type builds.

Can't wait to do the 'limiter' and 'eq'  modules    :)   

.....

Modular, remote and regulated PSU  ...  rock the house big time for 'over the top' tube stuff.

[even more so if there are any signal traffos about]

Give yourself a 10dB noise break.    Go remote   (and modular !)
Title: Re: REW Update
Post by: alexc on November 26, 2018, 01:46:11 AM
Here's a pic of the biz ..
Title: Re: REW Update
Post by: alexc on November 26, 2018, 01:48:34 AM
and the NYD module   (from a great Group DIY pcb designer ! )

....

The modular psu also provides a dc rail for powering some class A solid state line amp modules - 'JLH Headphone Amp' modules.

Super cheap, small  with serious drive capability at figures hard to believe from just 2 small and 2 big transistors.

I'm using a heavy duty LT1083  regulator module within the signal rack to provide +24V at 1A, enough for 4 to 6 JLH line amp modules (biased for low current )  and needing quite a large, robust heatsink!

The idea is to get that beautiful NYD signature to line level without destroying either the wonderful harmonic structure or the exemplary hum margin.

When I rack it all up, it will be a small mixer ....  4 channels to stereo with direct outs and 2 independent pairs of stereo outs. 

I'm using unbalanced mix busses  with 4 sources and a tube sum amp   ....    'plate follower+gain' config driving output transformers. Once again, the modest av7 - they really are a nice performer, with a wide range of applicability.

The busses, like the input channels,  will be boosted with JLH line modules driving some 600:600 utc traffos.

It's a rack with 'tubes and transformers' inside  and  also on the 'top deck'   :)  All that extra space, you can do with.

At a rock bottom price, of course   ;D
Title: Re: REW Update
Post by: alexc on November 26, 2018, 04:49:33 AM
Yep - I surely measure flat-flat on my 'hv ac probe'box setup for the audio 20-20K

and even as far as around 48KHz or so before my signal chain and audio interface and uP horse power finish up.

And the low to mid  ratio matching transformers available, even at a budget, can measure super well for audio  .. re  Edcor XSM and similar. In static measures (at least) they do very well.


Title: Re: REW Update
Post by: trobbins on November 26, 2018, 08:42:03 AM
Where do you think the 50Hz ingresses?
Title: Re: REW Update
Post by: alexc on November 26, 2018, 06:01:13 PM
The 50Hz is the 'ripple' that the HV voltage regulator leaves  ...  around 1mVpp on 325Vdc  or around 0.3mVrms which shows up at -117dBFS on the spectra, up from -130dBFS 'ground hash' or background noise.

That's a pretty good figure as far as things go ... 

I am not quite sure why it's 50Hz and not the more expected 100Hz (post rectifier/resevoir caps). 

In this case, at least there is no appreciable  'induced' hum(from the psu traffo)  into the transformers and highZ parts of the signal unit ..  the psu transformers are way away.

Normally I get a certain amount of 50Hz, which is mostly 'induced' and a stronger 100Hz (+harmonics)  hum which is the B+ ripple.

I'll be monitoring it as I increase the loads on the psu ...  it's early days yet in the build.  But so far, so good.
Title: Re: REW Update
Post by: Tubetec on November 27, 2018, 06:32:36 PM
Do the mains transformers you use have an interwinding screen ?

I see a lot of modern transformers dont have it , but its very common on older stuff .

I read somewhere that using very large caps right after the rectifier can be problematic also ,as it forces the transformer to supply very high short term peak currents ,and that in turn can cause unwanted effects and coupling into other windings .

There are a few older guitar amps ,which seperate psu/power output  and signal chassis , even though the physical seperation is small , it does help ,as strong AC currents make it no further than the psu .

Just got gifted an old Ac-30 choke ,that needed replacing ,due to total breakdown of the wire insulation , I managed to strip it down and keep the bobbin intact , so I might have a go at rewinding it , I notice better quality chokes often use paper interleave between layers , this particular late 60's vintage one had no insulation between layers,just a big ball of wire , it measured .75 HY and 26 ohms resistance , as I unwound it the the degraded wire was easy to see , should have measured 20 Hy and about 260 ohms or so .
Title: Re: REW Update
Post by: trobbins on November 27, 2018, 09:55:58 PM
Winding wire insulation is just so much better than it was in vintage days. The need for inter layer insulation for a choke is likely rare. Main issue would be lead wire insulation and creepage between first and last layers, and to core.
Title: Re: REW Update
Post by: alexc on November 27, 2018, 10:56:49 PM
Some interesting insights guys - thanks.

My psu traffos at the 'affordable' end of the Edcor XPW  series - no 'screen' between the windings, I think   .. and also no copper 'strap' around the outside either.

Originally I used them in little amp head circuits  ....   but I did find them to be quite noisy!   At the time I felt the radiated hum into my signal traffos,  a UTC A series as well as a Magnetic Components  '6v6 deluxe style' ,     was very, very noticeable.

Unusable like.

I've since confirmed that *both*  the little Edcor psu traffo is a little 'splattery' (wrt radiated fields)  AND the utc a series (4K:500)  are quite prone to hum with even a whiff of HV ac nearby ...

Hence the push to 'external psu' units on my current builds  ....   *and* the utc  a-33    shielding cans (such as they are)   PLUS   some extra  heroic efforts for them to work well in the 'deluxe' amp head rev4 (now my daily practice amp)

Thanks to REW I did find these irons'   particular orientations  *and*  physical seperations necessary  to get it all hum happy.

Distinct from the 'remoting' of the psu,   the major contribution to hum reduction in a small amp head context,   has been the shielding/shadow  effect of a larger-and-heavier-than-usual  6v6 output transformer ....  in between the utc signal traffo  and edcor psu traffo  :)

 ....  to get an instrument amp with hum-noise margin at the 'high end'  of >85dB in typical usage

................

Nowadays I go all round  ..   serious shielding on signal transformers as well as as remote PSUs ...   to give my more ambitious creations a big starting advantage  and a reason to exist.

I've been lucky to get quite a bunch, like 10 or so ...   of some local 50's broadcast traffos for fair prices - heavy duty shielding including the 'cast, nested cans' types, reminiscent of the glorious US made originals.

The typical 6v6 pp plate-to-speaker transformer in these lines are huge! compared to the 'deluxe' traffo!

....

The downside is you need to make a bunch of large racks - I make mine oversize for good  seperation between units as well as for good cooling, despite the use inexpensive solid pine boards.

More like tables and open-back book shelfs, really. The light stained timber really showcases the more elaborate 'tubes'n'traffos on top deck' style of construction.

Further on that, I'm doing up a pine rack that is 'long' rather than high .. and can also take my standard RU chassis-es   .. 

It's really liberating to just 'let it all hang out' regarding the user control panel, and let the layout organically spread out for 'comfort'   .... as opposed to making everything fit in RU modules  ..  often each with their own psu and mains traffo and all.    :D

Going for an 'rca radio console'  kind of look, with big rotary faders and VUs and such   ..  and an  angled workbench leading to a couple of conventional style tall racks.

I having a try with some brass and copper  metal plate for my 'mixer' section - a bit different from the more usual alu.

To augment the proper old school VUs, I'm installing a couple of cheap eby led meters  ..  the kind that do some peak-hold on an array of 50 leds or such.


Title: Re: REW Update
Post by: ruffrecords on November 28, 2018, 05:25:51 AM
Talking of internal vs external power supplies, I found the biggest culprit was the 12V dc heater supply I used in my tube lunchbox builds. Big toroid followed by big bridge and reservoir cap followed by LDO on big heatsink. The toroid is asked for some serious current pulses by the rectifier. When fitted in a rack with four tube mic pres, the 50 and 100Hz hum level reduces as you move further away from the supply (REW was great for quickly comparing outputs). The electronics was in a screened box and I even invested in toroids with mu-metal screens which helped but hum was still affecting the noise floor (I think some was being picked up by the the unscreened Carnhill output transformers) . Almost in desperation I replaced the linear heater supply a Meanwell 12V SMPSU. BIngo, no more hum. REW  measured the best noise floor I have ever achieved with a tube mic pre.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on November 28, 2018, 06:33:49 PM
Thats interesting Ian - may I ask what is LDO   (I know now  ..  Low Drop Out regulator chips  :)

So the regulated dc heater is doing a fair amount of current at 12V and was contributing to hum   ... and the system  was quieter with a switching psu.

I guess it has to do with 'dirty current' return from the heater circuit getting into the audio ground ?

Or a case of the large current spikes spattering em fields which are being induced into wires/signal traffos ?

...

This is my first external psu and it can provide about 5A of dc filtered heater at +6.5V from both psu modules ...  no sign of anything so far hum wise from this source.

But I've only just started 'chaining' signal racks off of it.

I *did* notice a big difference with either 'ground referencing' the dc heater negative at the signal unit or at the psu unit or just floating.

I was trying to determine if heater current would contaminate audio ground  and if floating heater was useful.

I found the best by far was 'ground reference' the heater at the psu unit. Not much different was doing it in the signal unit. 

Really bad was 'floating' - again not sure why! It was a significant broad hash of noise across the hum region.

It could be that there is no 'return path' for the heater current ... ? Maybe it leaks into the cathodes to ground or something like that because there is nowhere for it to get 'to ground'.  I don't know.

The tube was amplifying fine  just a frightfull wideband hum.

One day, I also have to measure and compare :  ac heaters floating, ac heaters with centre-tap grounded, ac heaters with one leg grounded (as is common in amps), dc filtered floating, ground referenced and/or  regulated      ;D

....

For now, I will be keeping on eye out with REW as I load up the psu with more (and more) tube stuff,  then to also ding the 24V winding at 1A of JLH goodness   8)

....

Modular PSU #2 is my current attempt at a higher powered psu and has a much more serious set of psu traffos. It is intended to power some tube monitor amps on one side, and a mastering chain with major tube limiters  on the other side.

A 2RU with modules on the inside, toroid inside and big Edcor and filter caps on top. Again with 2 cables but this one having individual power and standby switches for each connected cable and it's associated psu traffo.

One psu traffo, the large Edcor,  will be providing some 6A of heater for the amp rack, of dc filtered with seperate windings for the finals and the preamp stages.

The other psu transformer  is a 100VA 2x 12V toroid for heater on two windings for seperate heaters amongst the mastering chain units.

I expect this PSU unit to be doing 11A of heater all up. The HV will be a combo of unregulated for the finals' some 250mA worth, and regulated for screens and preamp/gr amp sections able to do 150mA   ....

A serious psu but quite straight forward and hopefully ..  robust. So I'll be   REW-watching   as I go.

....

And a final bit of kit .. invaluable when racking these kinds of powerful amounts of heavy metal .....   one (or more)  standard rack 'tray' s   made from heavy duty steel plate  ....  4RU, open at the front, tapering to a 40mm high rim at the back which is quite deep, like 400mm or so  with a floor of same  ...  that nice old yellow coating on steel   ...  2.2mm or so thick.

They used to be cheap in the old days. Great EM shielding and does indeed make a diff to the noise bottom line  in the right circumstance.

You stick that above the psu #2 with plenty of space underneath it, on the underside of a shelf, then on top you start  with the amp module, leaving plenty of space above it too .. and so on.

...

At this point, with PSU #1 looking really good, I'm not sure if I can do any better - I suppose, some more improvement could be had but I can't imagine it more than a dB or two.

Theoretically, the hum could go down about 12dB more,  till it is buried in the noise floor;  which is -130dBFS in my measurement system.

- better HV regulation module ?    I get 1mVpp of hash with no sign of modulation at all on my $20 eby hv reg module.

It already uses a high speed error amp in transistors around a good quality power mosfet. The rectifiers are 4x hexfred diodes which have no 'snubbing' capacitors across each.  That would be my next thing to try.

- IEC filtered mains inlet connector ?  The next model I have a really heavy duty one of them, japan manu :)

- regulation of heaters ?  possibly, but I've never been a fan especially at any significant current. But is is possible to get beefy linear reg modules and also switched mode psu modules.   It is an area I'd like to try some more.

- seperation of modules ?  Already done

- better layout of signal modules ? Surely a plus

In general terms, with no 50Hz ac anywhere near the signal unit,  its more about high amplitude audio buzzing from one part of a circuit to another  .. from the output end into the front end and/or left-right channel seperation  etc. Not much impact on hum  at 'silence' really.

That and of course, grounding ...  always the grounding and the shielding. Return currents and seperation of etc. Shields and seperation from audio grounds, except of course, when they is not.

- better interconnect cable ? Possibly an even heavier ground line would help. I'm already using an interconnect with wires that are heavy gauge.

- better performing tubes ? No doubt!  Some tubes are better than other tubes.

There could well be a couple of dB still of better signal-hum margin for a specified THD to be had from 'tube selection'.   Rolling tubes is, after all, the 'last refuge of the simple'  :)  That would be me, for sure.

I have a set of around 20 candidates to have a look at in this signal module ...  av7 and at7 types   ..  so far, it's a close spread, within a dB or so.

My next signal unit is the fun one ..  point-point wiring, with some octals as well as the smaller 9pin types   ...   so I can go to town and chisel on down,  past the 100dB margin of the old low THD tube hum  ..  and  into the great beyond.

There, I'll need cooling; like liquid nitrogen,  to keep out the cosmic rays  .. that might impinge on my grids.

......

I  haven't even looked at other forms of noise apart from 'hum' to date - there's also a world of 'switching transients' type of noise related to rectifiers, as well as  'hiss' type  noise and a good many other things so far not even on my personal radar! 

....

Anyway, even if 'that's it' regarding hum performance, with this psu #1, I'm happy to have REW'd (subdued) the tube beast even to this level!

Next up ...  JLH mini-modules all round  :)     

....

Here's a snap of my 'opamp test rig' silence noisefloor ....  basically  a variable straight-wire gain with balancing/debalancing using some of the quietest chips around ... LM49860 for debalance, another for gain and a DRV134 balancer,  with an Alps potentiometer set for unity gain at the non-inverting opamp.

All that x2 for stereo. And with a groovy machined alu 'shield' for the gain opamp!

It's about 2.5dB  22.5dB   better at hum than the tube getup I showed above.   ** correction : 20dB measuring error!

[I confused the real-world figures with a 'scaled' figure ...   sorry! . Explained later in thread. ]

That opamp cct 100Hz spike is still about 10dB higher than the ground hash of -130dBFS   .... the test rig is powered by a 'JLM 3way' regulated linear psu at +/-16V.

The 25VA toroid that powers it is 'co-located' in same 1RU but this isn't much of an issue for builds without signal transformers, and using low voltage rails and lowZ chip circuits.

I have some 'toroid shielding strips' that I use here and there ...  in this case they make a tiny difference, some 1dB or so I recall ..  once the toroid has been 'rotated' and so on for min hum.

TheyJLM 3way modules work well, but  simple lm317/337 regs are not the quietest thing available, in terms of ripple and so on. And they're best suited for the lower current requirements even at these low voltages.

I since have acquired some psu modules, similar in size to the jlm that I've generally used up to now - these are cheaper and have discrete voltage regulation circuits - they claim to be very quiet, so I'll be checking that too.

For Class A circuits especially, a really low noise supply is much better - in small current apps, little discrete 'Class A regulator' circuits should do really well.

For the bigger jobs, they can scale up or one can go to LT1083, LT1084 based linear regulators which I believe have a tighter performance spec as well as much increased power ratings.

I have one module that does +24V at 5A easily with large heatsinking - for those intermediate level JLH and Neve styled requirements   ;D

....

I did some REW tests of my dual channel gyraf pultec eq .... bye-bye to the tube psu and make up gain module!

So much ripple, hum and hash  from the co-located psu  ... ... when boosting the bass freqs   >:(

I tested the unit  after the removal of the psu + make up amp modules  ...  using this opamp test rig   ....  the filter results were really good and the eq sounded totally clean and quiet  with the opamps doing the make up and line amp duties.

I'm keeping the 600/600 input traffos and adding some more at the output end.

It was a blow tho' - those Lundahls in those modules cost a lot and aren't much use without a pcb >:(

Give me an old school traffo any day - you can recycle, and recycle and on and on no probs.

Just finishing up some 'ssl mic pre' pcb modules now to do that peq makeup+line  job and finally realise the full potential of the thing, after 10 years!
Title: Re: REW Update
Post by: ruffrecords on November 29, 2018, 04:07:38 AM
My problem was definitely induced because I remoted the supply and the hum disappeared.

I always reference the heaters to analogue only at the power supply. This is unavoidable for me because the heaters are elevated relative to analogue 0V.

If you float heaters you will always get hum. I am not entirely sure why but I have accidentally done it enough times to check it first if I get a lot of hum. Anyway it is not good for the tubes. They have a specified maximum heater to cathode voltage and resistance which floating most likely violates.

For the Mark 3 tube mixer I am going to attempt 100% SMPS for all supplies. I'll let you know how I get on.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on November 29, 2018, 04:22:05 AM
Thanks Ian.

I wish I was just starting out with the benefit of all the great insights and knowledge around this place.
Title: Re: REW Update
Post by: alexc on November 29, 2018, 04:40:23 AM
And to wrap up my commentary, here is a proper 'old school' piece of kit I just acquired for fair price ..

Genuine way-er  'down under' ...  affordable   ...  destined for front and centre of my test bench   8) 

This is how they rolled circa 1955   .. measurement amp style!
Title: Re: REW Update
Post by: alexc on November 29, 2018, 04:41:24 AM
and an angled front pic  ..
Title: Re: REW Update
Post by: alexc on November 29, 2018, 04:42:27 AM
 .. inner
Title: Re: REW Update
Post by: alexc on November 29, 2018, 04:43:11 AM
and oblique rhomboid ..

I'll refresh it  and just maybe, a few mods to the ins and outs .. a new 'probe-ulator' perhaps.

Lots of REWing for this one!
Title: Re: REW Update
Post by: alexc on November 29, 2018, 05:30:46 AM
And what's really ..  serendipitous, is that some old traffos have come up, that have a v.big step down to a super low impedance rating coil    .. like *scary* low.  Like a guitar DI traffo but much bigger and more crazy.

Most people wouldn't look twice.  But me ?  Yep.

A couple of years ago I was blabbing on about some grounded grid circuits  and all that ...  and how it would be hard to find an input traffo to suit.

These guys really would fit the bill to a tee.  And very much like  a small opportunity to be taken, I think. Historical, like.

I'll have to ask the guy if he has them still   ;D   I'm feeling a  little historic tonight.
Title: Re: REW Update
Post by: ruffrecords on November 29, 2018, 01:06:08 PM
The little 6AU6 is a good tube. I used them triode strapped in my very first mic pre. Only NOS available now and you have to select for low noise - maybe 20% are good enough for the first stage.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on November 29, 2018, 03:46:38 PM
I'm looking forward to going thru this 'Volume Indicator' box ...

Interesting the way the VU meter has some dc offset applied courtesy of some 1st stage cathode resistance ..  sort of a nfb loop of sorts I think and a 'zero adjust'  .. I suppose the meter has some rectifier in there ... it's not on the schematic that I can see.

Other than the vu meter load, and whatever efffect it has, it's pretty basic really  ..  quite a bit like the NYD One Bottle preamps above; 2 stages cascaded with nfb.

First stage for high gain and with nfb into cath, second stage in triode mode biased for some higher current.

I have used '6AU6 like' pentodes such as the russian 6K4P in triode mode for my 660 style limiter, without any real probs.

I'll probably move to them if needed - I have a bunch of them already tested up.

And the 6X4 is a groovy rectifier  .. I have one or two lying about.

I'll need to replace the electrolytic can caps of course ..  prolly I'll try that trick where one 'drills out' the content of the old cap and glues in a modern, smaller cap, saving the old aesthetics and mounting arrangement.

If it seems worthwhile and do-able, a small inductor wouldn't hurt for some B+ filtering.

Should the psu traffo traffo allow, I'd like to add another 9pin mini for a small line amp; it looks to be reasonable sized, but I don't have any details of current specs. Otherwise, some mods to use 9pin dual triodes all round.

It may not need, that second stage can do a reasonable amount of drive, possibly enough for driving a 15K or 20K winding sufficiently to  modest line level.

Freq response should be fine, perhaps a little bandlimited in the bottom end from the 0.047u coupling cap  ..   and not sure what the nfb network results in.

So all in all, an interesting little project for affordable $
Title: Re: REW Update
Post by: alexc on December 02, 2018, 12:56:27 AM
Some more testing today ....  finding any 'sensitive' wiring  .. in this Quad NYD preamp ... 

I've already done my best 'ground scheme', which is the 'sensible or common sense' scheme plus a tweak or two.  :)

Now that basic  'hum' is firmly placed in it's box AND a good 'ground scheme' is implemented and tweaked .....

The main 'twitchy-ness' is in the wiring       ie.   tapping/jagging wiring with a chopstick and watching for jumps in noise floor

the next most important factor wrt to noise, is  related to the front panel 'Gain' pot and 'DI jack' positioning.

So I watch REW while I find a stable orientation that gives best improvement, then I do a 'mock up' in alu strip to hold in the position I think is lowest hum. And check again!

Turns out there is 10dB right there ....

My new baseline for the humble AV7 mic pre is :
    > 93dB of signal margin over 'hum' at THD+N 0.35% nearly all h2
Title: Re: REW Update
Post by: alexc on December 02, 2018, 01:19:54 AM
I re-checked my 'calibrations'  for the M-Audio Profire 610 with balanced inputs and outputs, quite an affordable unit ..

I get the factor   'add dBFS + 12.7dB -> dBu'   

So that is included in my annotations to my REW snap.

Also, I added a factor for 'return signal scaling'  which indicates if any  'attentuation' is applied to the return signal  ..  like from the 'hv ac probe box'  I use to 'scale' down high ac signals, like at tube plates.

In this snap, I'm not using any scaling of the return signal, I'm driving an edcor xsm10K/600 with a 2K2 secondary termination - this is the 'normal load' for this build - that goes to XLR connector and on to the M-Audio and REW.

So I add the note 'no return signal scaling'  in the green box in the annotated snap.

Normally for 'scaled return signal' measurements of a tube plate, I use a -37dB 'scaling factor'  which maps something like up to 500Vac signal down to 0 .. 8Vac or so.

So for those measurements, I add the annotation 'signal return scaling factor -37dB' in the green box.

That 'keeps me honest' with respect to tracking the gain structure of my device-under-test and my measurement setup and how it relates to both  'absolute voltage' measurements (with CRO) and REW readings.

....

While on that subject, and during my 'calibration' measurements, the effect of loading needs to be considered ...

The hv probe doesn't do much, a couple of percent,  *but* the process of switching from a standard line level return to the 'hv probe' return makes a large difference to proceedings.

ie. my M-Audio interface has a large-ish input impedance, like 10K per phase differential ...so it doesn't load down low Z signals under test, much.

But when you disconnect that M-Audio balanced input from the  'output of the circuit under test',    the output of the 'circuit under test'   jumps up    because you now have an open-circuit load.

SO one should 'terminate the circuit under test' such that the output amplitude remains reasonably steady when connecting/disconnecting the M-Audio interface bal input, while watching the signal on a CRO.

In my case, I have a 10K/600 output traffo ... terminating the secondary in 2K2 means that when I connect/disconnect an xlr to the M-Audio (20K input Z more or less)   the output signal stays similar  ...  as measured by a CRO.

NOW when I switch to my 'HV ac probe', I don't get huge jumps in the 'circuit under test' output  due to  connecting/disconnecting of my measurement probes (and their associated loads)

....

When all that is measured up and taken into account, my 'gain structure' calcs all line up  :)   I can compare a signal using either a 10K/600 output traffo with no other scaling, or my 'HV ac probe' which has a -37dB scaling.

...

Of course, all that is flip-flopped when considering balancing/debalancing calculations   ...  those ol' 6dB  factors that crop up.

One needs to figure out how the software application, like REW, interprets 'balanced' or 'unbalanced' lines.

For this, one can use a dual trace CRO, with each trace giving a 'phase-to-ground' voltage measurement. You then 'INV' one trace and 'ADD' both traces for a correct 'unbalanced' voltage measurement.

Basically, I find that 'REW' coupled to M-Audio Profire 610 reads 'unbalanced' voltages, rather than balanced.

That's fine, you just need to account for it if you want to calculate gain structures and then link that up to REW readings  :)

That's why I always do 'signal margin over hum' calculations ...  that doesn't change by much in all of these 'level shifting'  types of measurements ...  for a given THD.
....

It's a little confusing, but the maxim is test, measure, verify, calculate    and repeat!  Till you think you know what's what!

Then do it again.


Title: Re: REW Update
Post by: alexc on December 02, 2018, 01:56:31 AM
And finally, all that is why it's good to have a 5-position rotary attenuator on the 'hv ac probe box' . ..

You can select the 'scaling' factor or attenuation and tailor it for the amplitude of hv signal under test.

ie. you want to maximise your return signal on the REW rta window ...  the closer it is to the maximum allowable signal in REW (-3dB from full scale), the more accurate your measurements are.

maxim is you don't want to attenuate your signal more than the 'hum floor' peak is above background noise.

ie. you can reduce a signal, and it's amplitude *and* the hum floor will both reduce.  Until the hum floor peak drops below 'background noise'. 

Any further attenuation is just throwing away signal-hum margin, a big no no. You can't get 'quieter' than background!

Sooner or later, you need to rise above the floor  and then you have to pay the piper. There's no tricks.

..

I did that trick, when matching a 'tone stack' loss to a gain make up circuit  ...  you don't want the tone stack's  typical   'loss' to exceed the  driving stage's   'hum peak  margin above background noise'     otherwise you are throwing away margin.

If you get it right, you are rewarded with exemplary performance over hum ... vitally important when chaining in some EQs and Limiters   :)
Title: Re: REW Update
Post by: alexc on December 02, 2018, 02:16:27 AM
Now that I have my 'boundaries', I can do some rollin' of tubes and transformers ....  and find the best suited to this circuit.

I don't think I'll do much better with this preamp build ... 93dB margin is not bad .. in typical low THD use.

edit .. some days later ...

I did compare a bunch of av7 and at7 ...both nos and modern ...  rca, ge, eh, philco    .. I checked about 10 from a field of 20, mostly bought as 'sleeves' of 5 ...

Very tight spread .... in this NYD One Bottle application (with minimal nfb setting)

-  output variation between av7s  was less than 0.2 dB
- thd varied from 0.35 .. 0.50 %, nearly all h2 with the h3 varying from around 0.015 to 0.005 %.
- AT7 had something like 0.3dB more gain than the AV7 both at the peak and the hum floor
- hum floor varied less than 0.3 dB all round

So, I stayed with the philco set of 4 that I began with   

The general best were the nos ge, almost identical among the 5 and consistently at the low end of the thd scale.

Obviously, the nfb present, even though it is at the minimum in this test, irons out the variations across tubes.

I could take out the nfb and repeat, but here I'm just looking for a good set of av7.

...

UNfortunately,   when I previously  said I was 'closing in on opamps' - wrong!    Sadly, I confused myself when I conflated  the 'scaled down' hum floor with the regular 'unscaled'

**mea culpa  - got that measure 20dB  wrong *** I'm still remaining well away from the fabled -120dBFS barrier.  :-X

BUT, yes, closer than ever before.   Still 22dB away from that wonderful  op-amp noise floor.   

...

I may exceed the 100dB margin with a really low distortion tube,  but that 'hum floor' looks like its a hard one. Like titanium.

Now I'm looking much more sharply! I have my 'Hubble' vision going.

....

HOWever,   the Quad NYD with Edcor  does sound very nice. Very, very nice.

Not even a hint of hum from my  regular  hifi speakers ...   from a hifi stereo amp  into 8ohms at > 15Wrms levels.

I may find a slightly more optimal way to drive it, by twerking the   'send level' and 'nfb Gain' control to maximise my margin over hum ...  at the lowest possible resultant THD.

...

But it will have to wait until my next tube build to make a serious assault on the '100 dB signal-hum margin'  barrier.

I'm pretty sure the best single   'tube-gain'  stage -biz I've ever seen,  is something like 103dB margin over hum  at 1.5% THD+N   ....    the plate of a 5751 tube into 1M load or such.

...

So that's the goal - mostly better tubes, better transformers and better component/wiring placement, I think, to get me there.

PSU and grounding  is now about at my basic  limit,  as far as I currently know.

As always, it's that last couple of dB that is the hardest.

That, and honest accounting    ;D      Only REW stands between one's wavy opinion and reality!
Title: Re: REW Update
Post by: alexc on December 02, 2018, 03:26:14 AM
And all of this fixation with hum floor is *historical*  and  *geographical* , in my case.

....

When I first came to this place, down here,  way down south, I found the electricity supply has a low level 'tick' at 1Hz or so.

Rarely noticeable, but with distortion pedals and compressors doing lots, which I did do a lot of the time!  , it's bad.

Maddening it was,  when I first transitioned from the city,  and their city-clean elec supply!

I did measure that tick with a storage cro .. it was there. Not just my imaginary tinnitus or my actual tt.

...

But what do you do, except learn to live with the outrageous impingement on one's personal e-noise floor!

That and measure, quantify and educate one's self!

...

Nowadays I don't run into it much ...  I've lowered my own noise by 10dB  and I get out in the orchard a lot more!


Title: Re: REW Update
Post by: ruffrecords on December 02, 2018, 03:39:13 AM
The one addition to REW I would really like is the ability to alter the dB scale to something meaningful.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on December 02, 2018, 04:29:25 AM
I'd like a nice 'active' and 'smart'   probe box  ...  a robust thing  that you can attenuate at will  and  load the way you want!

You really have to be vigilant on performance measures ... even if you are only a part time player!

Title: Re: REW Update
Post by: trobbins on December 02, 2018, 06:27:21 PM
The little 6AU6 is a good tube. I used them triode strapped in my very first mic pre. Only NOS available now and you have to select for low noise - maybe 20% are good enough for the first stage.
Ian, was that a change in hum harmonics, or noise floor level (and was that mainly higher or lower f range)?
And was that a typical triode strap, or the special 6AU6 hum minimisation triode strap?
Title: Re: REW Update
Post by: ruffrecords on December 03, 2018, 01:15:03 PM
Ian, was that a change in hum harmonics, or noise floor level (and was that mainly higher or lower f range)?
And was that a typical triode strap, or the special 6AU6 hum minimisation triode strap?

It was a change in noise floor alone. No hum because for those tests the 6AU6 heaters were powered from batteries. In those days I was not measuring noise spectrum only rms level so I don't know in which frequencies it changed, However, it is fairly well known that the most likely noise variable amongst tubes of the same type is in flicker noise so I suspect that is what it was. It was a regular triode strap because I was using dc heaters. No need for the clever 6AU6 strap using the screen grid as anode and grounding the anode.

Edit: I may still have the original results somewhere if you are interested.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on December 04, 2018, 12:01:57 AM
I have noticed one new thing in REW I don't like - if you exceed the max input level of -3.2dBFS or so, it ceases to function (everything) while displaying a message, requiring acknowledgement by clicking a box, then requiring switching the sig gen back on.

And it does it after 3secs or so everytime until the input signal is reduced.

Pretty painful when you normally have your attention of your circuit under test, to have to stop and 'go fix the analyzer'.

It's not like an input signal overload is uncommon, after all. Why all the hoopla ?  (in this new revision).

Oh well, small matter in the grand scheme of things.

A few other unser interface quirks still there .. like when using two monitors ..  REW can't figure that out so one has to 're-arrange' the second screen each time. Never seems to remember sig-gen output assignments either .. always have to select the same thing on startup.

We're never happy, are we ?   ;D
Title: Re: REW Update
Post by: ruffrecords on December 04, 2018, 03:25:56 AM
I have noticed one new thing in REW I don't like - if you exceed the max input level of -3.2dBFS or so, it ceases to function (everything) while displaying a message, requiring acknowledgement by clicking a box, then requiring switching the sig gen back on.


Is this only with the latest version? I am a couple of revisions behind and I have never had this problem. Have you reported it to the developer? He is very good with bug fixes.

Cheers

Ian
Title: Re: REW Update
Post by: trobbins on December 04, 2018, 03:36:38 AM
I am pretty sure my in and out driver settings are kept between sessions, but can revert to a default - i think that was when the program wasn't closed properly, or the usb device was powered down before the app.
Title: Re: REW Update
Post by: alexc on December 04, 2018, 09:03:39 PM
No - not the basic 'i-o' assignments in the 'setup' window - I'm talking about the 'sig gen' window where you have to have the outputs checkboxes assigned. It remembers the 'test signal' out but not the 'reference' - I always have to select it on startup.

And the 'overload nanny' seems to be a new thing ..  exceed -3.2dBFS return for about 1s or so and it pops up the 'nanny overload'  and will do so until you reduce, stopping the whole show until.

If you are 'zoning in on the max' things can sometimes be twitchy on a vol knob ... easy to overload ..  and with a basic RTA refresh latency of praps 1/3 of a second, it can take a few adjustments to get back on track .., meaning can take a couple of 'nanny taps' to resume what I was doing ..,  plus a couple of seconds to regain my 'unit under test' focus of mind and eyes!

WHen you are squizzing about with a CRO and HV and such, with probes probing  and chopstick tapping  ...  focus is everything, right ?

There should be an 'nanny opt out' setting   ;D ;D   It's a deal breaker for my testbench, so back to the previous version I go.

I can still use the new version on some other machines, where I don't do such 'hands inside' testing ...

....

Another thing I dislike, but in this case, I may be doing it wrong. After doing a 'measurement' sweep, I can't return to 'plain old' rta realtime mode. I have to shut down REW and restart   and  resetup the sign gen and then move all the windows over to my 2nd monitor ..  which is next to the cro ... 

I need the monitor close otherwise I can't read each of them ...  old eyesight is not so great anymore.

It may be me being clumsy, and not noticing that a 'measurement' run is active in the LHS tree view of historical runs or something like that.

I check some more.

One other thing I get, is *glitches * in the realtime rta ...  like a 'buffer overrun' kind of thing. The spectra jumps to crazy high and then returns perfectly . about 0.5s in duration.  Not that often, perhaps once every minute  or so ... but consistent, in a random-ish way.

It happens on all versions, as far as I can recall ..  on most all my machines.

Other asio apps don't do it ..  like cubase, media layer etc .... these are all music machines, with asio etc and very little issues. I have measured that latency biz with that applet and there are 'dlp interupt' thingos going on, but it could do it a little smoother.

.........

Relatively benign things , but in a world class app, like REW is approaching ...  well there's always work to be done, isn't there. Mostly though, it's unbelievably wonderful to use.
Title: Re: REW Update
Post by: alexc on December 04, 2018, 09:08:41 PM
And here's a snap of my M-Audio Profire 610 balanced inputs and outputs, driving my 'Opamp Test Rig'

Its an opamp rig +/-17V with 317/337 regulated psu, a JLM  5way ...

It has   LM49860 debalancing -> Alps Rotary 100K log dual gang pot -> LM49860 non-inverting gain stage -> DRV134 balancing

It's my  'real life' unity gain scenario or 'basic starting point' for opamp work ...

....


Now when the 'unity gain' scenario has say +15db added (to normalise it with my baseline NYD One Bottle), I would get an expected hum floor or around -114.7 dBFS. 

In practice, it's a little better than that... maybe -5dB of 'extra traction' to be had .. 'seredipitous gain', I call it.

.....

So that means my NYD One Bottle, with it's 'real-life'  -98.7 dBFS hum floor (from earlier snap) is +16dB (to 20dB) worse hum.

SO  16dB 'to go' ..   downwards  ... on my quest to see low I can go   8)    ...  in tubes.   

.....

In the 'regulated HV' category, so far the  winners are :

LOWEST HUM

1.    NYD One Bottle Edcor xsm 10K/600 + ModPSU with 2m cable .. and  ebay reg module  -   is the clear winner 

...  by about  2 dB more or less     ... over the similarly historical . ...

2. Orange86  ...  cast shield output traffo ..  with onboard semi-reg and co-located psu spacious-rack- with-shielded-toroid

.. yep, it overcomes nearly all the obstacles in a rack unit  ..  but magic traffos do help a bit!

LOWEST THD

1. Orange 86 - by a long way, lower THD and it sounds like it ..  very pro

2. NYD - very charming h2 ...   hard to resist ....   but higher measuring

....

Going forward, I think I can do -3dB better from wiring,  at best , before I get over 'it' regarding basic stuff.  :)

The foundations of it all are psu and measurement. Then craftsmanship!  After that, magic components and topolgies.

And I can live with that. Just as long as I know 'what is'.   

...

Thanks Mr  REW.  I'll be doing a small contribution for Xmas.
Title: Re: REW Update
Post by: alexc on December 04, 2018, 09:26:10 PM
The great news is that this M-Audio Profire 610 is more than 10dB quieter than my previous Motu 328Mk2  ..  which had developed some late life 'hum' problems of it's own!

Possibly as a result of being my bench interface for a couple years.

A juicy >10dB spike at 100Hz creep-ed in in it's last days.  And the firewire was never right either .. always with the clacking in and out and what not.  Eventually it checked in ..  but not out.  Must have done about 8yrs of service or so.

...

The M-Audio is super cheap, so it's a good choice for this kind of  'hazaardous' work   ..  a touch more THD than the Motu had, but a hugely superior noise floor and generally very stable even on my 'older' machines  :)

I think the M-Audio was already around 6 or seven years old when I bought it.  It's one year bench time and going strong  8)

(time to get another one !)

...

Looking back over the years of my measurement 'baselines' is really interesting ..  like the DIY audio equivalent of 'family' snaps.

I can see some great improvements and also a convergence of results in the last few builds ... 

Some good refining trend which I can revisit and  reference myself to,     without too much effort.

That's what these REW snaps and annotations  are all about.
Title: Re: REW Update
Post by: alexc on December 06, 2018, 05:39:43 PM
Here's a snap that I'm playing about with now ...  it's a 15 dollar eby module ...   an stereo  preamp with bax style 3 band eq ...  uses ne5534 chips for the front end and a discrete  JLH style back end  ..  with onboard +/- psu circuit

I haven't optimised anything ..  it's a first test; I think I can improve the psu hum a bit ....  and use it with some other modules added ..

Huge signal margin over hum ...  generally low THD  ...  that h3 spike is from the eq section, I think. JLH generally have h2 dominating.

Pretty interesting for cheap   - the eq is really quiet and works really easy and the JLH can drive 600-600 traffos with ease.

Title: Re: REW Update
Post by: alexc on December 07, 2018, 04:26:23 AM
Next test is some JLH 'mini modules'  ...  pcbs about 5cm square .. 12usd each eby ...

These are the 'old school' JLH .. single supply rail .. 12 to 24V usually .. at anything from 100ma and up depending on bias and what not.

4 transistors, with the 'finals' edge mounted for easy heatsinking. I'm using tip41c for current drivers and a moderate decent heatsink. Intended as line amps driving some 600-600 traffos.

In this test, I'm using a   'class a' discrete regulator pcb of some 12usd or so.  Enough to to 200mA if the voltage drop isn't too crazy. I'm driving that psu module with another psu regulator mosdule so I can experiment some  .. and not burn everything up!

::)   So hopefully I will get that thing ...  essentially a 'tube's tube' ...  better thd, lower hum and mighty output power, early JLH style.

We shall see.

Title: Re: REW Update
Post by: trobbins on December 08, 2018, 08:33:04 AM
John updated the beta version - may be some benefit, so worth a check of the changes imho.
Title: Re: REW Update
Post by: ruffrecords on December 08, 2018, 09:05:34 AM
John updated the beta version - may be some benefit, so worth a check of the changes imho.

I just got an email about this. He has added a dBu and dBV scale with calibration to the RTA. Perfick! Also dBA weighting to distortion for the marketing department.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on December 08, 2018, 05:43:09 PM
Awesome!
Title: Re: REW Update
Post by: ruffrecords on December 09, 2018, 04:16:35 AM
Awesome!

Yes, I am very pleased. I have sent him a couple of donations. Well worth every penny.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on December 12, 2018, 10:13:41 PM
The beta REW addresses all my concerns ..  has the 'input overload warning' opt out (thanks!) and a huge number of added functionality.

The dBu handling and calibration capability is top shelf! 

Even more info in the 'heads up displays' of distortion and rms input aw well.

Wow what an upgrade   8)
Title: Re: REW Update
Post by: ruffrecords on December 13, 2018, 03:56:53 AM
Wow what an upgrade   8)

I agree. It is a great product for audio testing now. Better IMHO than any of the other PC based ones.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on December 13, 2018, 10:41:39 PM
I did the REW calibrate procedure with my bench MAudio Profire 610  today ...

All went well ..  took a couple of goes to line everything up.

Here's a handy link for dBu conversions .. there may be some out there who don't use this ... :)

http://www.sengpielaudio.com/calculator-db-volt.htm (http://www.sengpielaudio.com/calculator-db-volt.htm)  Thanks 'Tontechnik-Rechner - sengpielaudio'

I used a CRO to measure the output voltage of my audio interface 'balanced out'  .. 

I measure the xlr  'hot' pin to ground with the cro, an 'unbalanced' measurement for brevity. 

The audio interface balanced line outs have voltage waveforms which are symmetric about 0V and in opposite phase   ..  as one might expect - but always one needs to check. So if measured differentially, there is a +6dB level shift.

Also, there is a small amount of 'loading' that is common when measuring the audio interface output voltage when 'looped back'  (ie. output connected to input) - I do all my voltage measurements that way (rather then not connected/open load)

So - did the loop back with one xlr shell open, measured 'phase-to-ground' off the CRO, in 'peak-peak' volts,  converted to RMS volts (div 2.83) and entered that into the cal dialog.

If all goes well, then that's that  .. almost  .... it took a few goes to get it right ...  no matter. It does work!

There are two other places where the calibration factor can be entered  ...  in the sig_gen 'readback' field  as well as the RTA 'readback field'.  One needs to make sure they both end up correct as you work thru your own cal procedure.

Here's a snap of the first baseline after the cal ...
Title: Re: REW Update
Post by: alexc on December 13, 2018, 10:55:31 PM
The above snap is the '0 dBFS' loopback scenario ...  maximum output and input levels.

That is a hum floor of -120dBu and a margin of +129.7dB  ...  of course the thd is a little higher at this maximal level.

By the way, it's great that REW lets you work right up to 0dBFS now .. :) 
 .... big plus for those 'maximal levels' measurements ..

and of course, calibration.

......

It turns out that my interface has a 0dBFS = +9.67 dBu. 

This is a little different to my previous measurement of +12.7 to convert -  still looking at that ....  approx 3dB diff in my 'pre-v5.20beta'   calcs!

...

Anyway I triple checked,  and it all lines up as it should ...  in both dBFS and dBu, both sig-gen and signal return as well as my CRO and some conversion math.

Thanks double plus Mr REW.

And just like that, a huge step forward! Direct dBu measuring with no 'fussing or fighting'.

...

Here's a 'nominal +4dBu' scenario ...    THD is well down on the previous 'max level' scenarios as expected.

Hum floor at a touch below -120 dBu with a signal margin of +125 dB at super low THD and very low noise.
Title: Re: REW Update
Post by: alexc on December 13, 2018, 11:19:01 PM
It's good to note the basic accuracy is fantastic - I get limits of 0.1 dB across the inputs, outputs of the signal and reference channels.

...

The usual 0.5dB 'factor' between the 'rms input' heads-up display and the RTA dB cursor measurements remains ..  this is not an error, but an 'rms vs peak-frequency' kind of thing ...  others can explain it better than I  :)

It also manifests in the 0.5dB difference between the 'levels window' display for 'out'  level vs  the 'in' and 'ref' levels.

Interestingly, the new 'peak sample dBFS' reading kind of  indicates that 0.5dB 'factor' ..  if you do the math with the dBFS/dBu conversion.

There is also a factor in the 'hum floor' line depending on whether there is a peak signal present, or not ..  I call it a 'hum floor crest factor'   ..  and it can range from 0.5dB down to 0.1dB.

...

It's good to note all these things are self-consistent and very high quality! 

So much so, I'd like to see  the 'dB measurement cursor' that you can 'nudge'    ...   to half the current increment. 

You use the '+' or '-'  key stroke  to 'nudge' the dB scale horizontal measurement cursor and get around 0.2dB increments, as far as I can get.

I wish there was a 'shift +' /'shift -' key strokes combos that would shift it half of that to 0.1dB   (100m dB)

The underlyings already support it (0.1dB); I suppose the RTA window dB cursor will soon catch up.
 
Today's cal is the first time I've noticed it! 

....

I have to do some rearranging of my windows, however ..  with the improved sig-gen window, the larger size needs to be accommodated so I don't lose my 'levels window' to the overlapping and such.

Never happy, are we  ;D ;D)   But I say that with respect and awe for the updated  power of REW.

Another feature or two and I'll have to get a modern hi-performance  interface ..   and really REW into hyperspace.
Title: Re: REW Update
Post by: alexc on December 19, 2018, 02:00:44 AM
Nearly have my bench 'tube rig'  reset  for the latest and greatest REW tests. 

Hopefully I'll get some readings on my latest 'tube choices'  soon ... I'm using my 'remote psu' unit for powering.

First up is to check :

-  a couple of pentodes including the noval  e83f in se
-  some moderate powered finals, including  the  octal 7591a  in pp

It's a real luxury to have a bench 'tube test rig' with a remote psu of regulated hv and well filtered dc heaters.

It's like an air-conditioner for the soul   8)   Working now on a 'mk2'  bench   'tube test rig'    remote psu ...

Including an easily variable Vreg, seperately mains-fed heater-transformer and   an external 'varactor' transformer unit  for the HV    ...   to vary my primary ac around   the nominal  240Vac   ... 

I'm quite excited to finally get me one of them rotary transformer units for my bench!

It's getting to that point now, what with the fine-fine  measurement capabilities of 'REW'   for audio DIY testing.

pic ... a bit blurry, but you get the drift.  I'll do a better one shortly, along with the diagram of my 'hv probe'.
Title: Re: REW Update
Post by: alexc on December 19, 2018, 06:07:40 PM
Here's the signal unit of the 'tube test rig'  ..

It has a basic 10W pp output to voice-coil transformer (deluxe style), an Edcor 10K/600 plate-to line output transformer [on the under-side - they are great performers and cost effective  ..   but could use an aesthetic do-over!]     ....  then a little DI traffo at the front end,  from a cheap tube mic ..

*And* a  small-ish  se  plate-to-voice coil    output traffo - an old telefunken 12K prim  radio unit   .. good for a watt or two  of old time se fun  :)

There's a bunch of tube sockets for octal, noval, loctal and 7 pin (septal ?)  ....  some are in pairs, for pp and vari-gm blocks , some are singles for class-a blocks etc.

I also have some jacks for input, insert/return, output plus a pair of xlr connectors.

...

Everything one needs to do some entry-level  tweazing of some basic tube modules ..  it's made from materials and parts recycled or left over from other things  ... the alu was a previous attempt (#3) of a little amp head;

I'm just making up some wood frame for it to sit on and similarly for the new bench psu - the timber is from an old futon!
Title: Re: REW Update
Post by: Brian Roth on December 22, 2018, 10:51:29 PM
I should RTFM.

Does REW have an X/Y mode to do  Lissajous measurements for tape head alignment or monitoring the "phase" when cutting lacquers?

Thanks!

Bri

Title: Re: REW Update
Post by: alexc on December 22, 2018, 11:31:25 PM
Not that I know of - I don't think it has a 'cro' mode of operation.
Title: Re: REW Update
Post by: alexc on December 24, 2018, 12:29:26 AM
I have my tube test rig prep'd   for some REW'ing ...

e83f pentode, medium height 9pin, 300mA heater at 6.3V and plate,screen limits of 2.1W and 0.35W respectively - pretty standard spec except for the larger envelope - a small signal pentode.

....

First test is simple - triode mode with 275V supply and 100K resistive plate load driving an easy load, say 1Mohm.

I have some cathode voltage trimming with a pot+resistor, some bypass cap jumper-ing too.

Driving with a variety of means .. including with a debalancing traffo or not ...  and a few different ground schemes till I get the stage working happily.

---

I'm hoping for a good measurement turnout ...  :) It is Christmas after all.

but realistically, some of the popular modern hi-gain types can be very hard to beat ...

These were around 10usd each in a sleave of 5 - early sixties I would say. [could be wrong - this kind of thing was well sorted in the mid 50s I think]

Pretty standard fare  from them in that day ...  looks to be superb construction inside ...  mesh plate with substantial structures .. I can just picture the workers painstakingly doing their bit to build up the whole.

In the days that I recall, it was always the women who were the best at soldering and wiring ..  let alone micro-brazing and such

If I were a tube, this would be it.

...

I'm kicking off a new round of REW snaps   ...  in dBu  and with my refined 'annotation' 

.. so people with less browsing time can get something useful from them.

Tally ho!
Title: Re: REW Update
Post by: alexc on December 24, 2018, 01:04:41 AM
and a good pentode pic  :)
Title: Re: REW Update
Post by: alexc on December 27, 2018, 09:50:55 PM
I have my first results for  the  small signal pentode  E83F   .. 

I'm running it in triode mode with a B+ of 280V regulated, dc filtered heaters, remote psu 2m away

I have a plate resistor of 13K5 at present and a variable bias resistor.
Also, 470K grid leak resistor, 2K2 grid stopper and 2K2 screen stopper.
Driving an edcor xsm 10K-600 output transformer terminated with 2K2 across the secondary

It's running a plate current of around 6mA and a screen current of around 1.3mA for a total cathode current of 7.3mA -  less than half the rated power or so.

....

SO ...  varying the bias to +4.1V gave me the lowest THD with a nominal 1Vpp input signal, sine 1KHz

THD was very low (no nfb)   at 1.15% nearly all H2.  Hum floor super low -120dBu. Hum margin -119.35dB  note - this was due to excessive LF rolloff - now corrected for -113dBu hum floor

Which is (still) s really good - especially so given I haven't yet got it humming at it's best ....  I need to vary B+ and the plate resistor :)

The input and output transformers together are adding around 0.1% of thd  ....

....

This small signal pentode (2.1W plate) has a high gm at 9000 mA/V  and it shows in the very low noise. 

Of course, the remote, regulated psu is really important - this one (eby kabota hv reg pcb) is great - easy to vary the Vreg with a trimmer and no issues of any kind so far.  I've standardised on these, so a few more on the way!

If I tried this with an 'amp head' type build with just choke-cap filtering it would be at least 12 db worse hum floor, all the time ..  bottom line - a  case of significantly higher B+ ripple *plus*  likely  em-induced hum into the signal transformers *and* ground lines   ...   from the psu.

And anything less than a 47K plate load resistor - in a similar circuit  in an 'amp head'  -  is asking for hum.

....

Gain is reasonable, even in triode mode with this low-ish plate loading. I'm still tweaking on that, so I'll wait for more data!

I definitely haven't noticed any sensitivity or undue microphonics - rock stable hum floor. 

Even with my odd-wooden-blocks 'wobbly' test rig  :) But the wiring is solid ..  I mean, the psu is 'way away' !

I haven't even optimised grounds or anything yet, and there's a few things to route better - but this is mostly affecting the 'mids'.

ed.  (so far! - I have to check I'm not 'band -limiting'  the bottom end with that quite small coupling cap  ..  till tomorrow, it's a possibility :)

Update : sure enough, my low freq extension *was* being curtailed by too small of a coupling cap from the plate to the edcor xsm 10K-600.

I checked the freq resp of a range of values ...  I'm settled on 4.7uF ...  a big wima

I now get 20Hz at -2dB or so and 22KHz is less than -1dB - so the response is now good!

My noise floor is now -113.4dBu with +28.3dB gain ...  (worsened 6dB from previous low-rolled-off 'prelim'  measurements)


....

Early indications are showing this tube performs better than anything yet I've tested, and by a *modest* margin.

Margin over hum is +116dB - previous best (JJ 5751) was 105dB margin with similar distortion  ...   in an 'amp head' type build

[discounting the 12 dB of worsened hum margin with 'amp head' vs 'remote psu'  .. brings things (re.  prev best)  to within  1dB of today's result - very nice --  but until I do the 'head off' testing between the 5751/6922 historical standouts and newcomers, who knows wth ? ]

When I push it to 3% THD, the hum margin rises to  122dB.    Thats for a 2Vpp input, x26 gain, 52Vpp at the plate.

It all amounts to   'less sensitive' than a 5751 stage ..  with super low noise  ..  sparse harm.dist. spectra, albeit with slightly increased thd  ...   with 'that  diff' made up of   ..  increased h2  .. arguably a good thing   8)   

To the tune of only 1dB and maybe 0.3% thd  diffs  at the end of the day, over the prev. personal best   ..

Still it is significant, especially given my 'prototyping' build qualities :)   ...   and in it's way, rewarding the right. efforts

....

As to the audible diffs, not so much, really - although I haven't yet 'listened'   ...     that's another thing altogether.

Ask someone with good hearing!

...

But all very interesting to figure, no doubt.  If this world truly is a 'sim' wth does it mean to chase 'tube stuff' seven decades after it's heyday ? Who knows.

....

This tube shines as an single-ended  output tube, no doubt ..   I suspected as such, given the obvious construction quality and the high gm.

And it performs pretty well as a first-stage tube too!   Plus anything in between, I would say.

The onset of distortion should be gradual ...  this tube likes to be biased somewhat cool  ...  +4.1V bias for 1Vpp input signal showed a thd minima. 

A good thing too (cooler bias) .. this tube likes to run a decent amount of current (>10mA) given half a chance.

The challenge is to reduce the currents whilst increasing gain without losing the thd or it's spectra ..  along the way.

 .. it's a 5-way tweaze where the hours fall away as you try to find your current 'best'. (and take a snapshot!)

So I'll spend some time tweaking in triode mode for max gain, min current  etc   ....  and after all that ...   with a really high quality output transformer. Much better a one , than I should  hope for.

Then continue with some pentode tests - I think they will be very good results.

Finally, I plan to try the 'enhanced triode'  or 'screen drive'  mode ....  where the grid g1 is grounded and signal is applied to grid g2. This tube has a reasonably high gain[g2g1] which is a parameter of interest for doing this.
Title: Re: REW Update
Post by: alexc on December 28, 2018, 12:17:50 AM
And the practical application of all this is *of course*  tube limiters :)

Having an extra 12 dB of hum-free-ness  'in hand'   to 'spend'  on even more excessive gain-reduction, is ..  well, it is.

After I get thru the characterisation of this nice tube, I'll be looking at the 'remote cutoff' version   ... the 6eh7 in typical diff. stage with varying bias-es. It's a very interesting one, for stupid high starting gm with a truly panoramic slope to the deck.

I've done a few vari-gm tube stages now and I've recycled a few too!  I'm looking for this next one to really shine. 

This 'tube test rig' is just the thing to grind on tube functional blocks ... some good results also motivates to chase the next level of esoterica.

Like cathode follower vari-gm stages, grounded grids, constant-current-sources, active loads *and* aikido cancellations!
Title: Re: REW Update
Post by: alexc on December 28, 2018, 07:10:50 PM
More grinding on the E83F pentode in 'triode mode' ...  with a 4u7 cap to edcor 10K-600

Increasing plate load resistor to 47K is good ..  gain increases 1 dB or so, bias  down from the coolest 4.0  ..  thru 3.5  and to this +2.5 V   ..  for a nominal 1Vpp signal to grid.

THD is now at 1.53% nearly all h2  - the increase (around 0.4%)  is due to the now-properly-extended low end.

Margin over hum is 116dB rising to 120dB at 3% thd

Increasing  B+ supply voltage doesn't change much the figures ...  decreasing it increases THD.

Increasing beyond 47K isn't doing much good ...  increased gain is offset by maintaining bias voltage.

So it looks like this is the best I can do right now - about right for a 'medium mu tube'  ...   in this operating scenario    mu=49 approx  (gain x26)

E83F in triode mode still wins 1st Place for margin-over-hum at 'low THD'  :)     - even though the hum floor is 'only' -113.4dBu and the THD is 'moderate' at 1.5% mostly h2.    (x26 gain)

Low freq extension is -2dB at 20Hz and the high is better at -1dB at 22KHz   - a good baseline turnout.

...

I think 'ideal' for this config   is -120dBu hum floor, thd 1% h2 and 125dB margin over hum with +/- 1dB 20Hz .. 22KHz.

I doubt I'll ever get there, for a simple grounded cathode gain stage  'gca'  -  but I'll keep on trying.  A l.o.l (labour of love)

It wasn't that long ago that I would be capering with joy at the figures I've just measured.

Such is the impact of REW Audio Analysis   wizards' tools.

The maxim 'measure, then measure, then do it again'  does apply ...  to rein in the early results' exuberance envelope.

Then wait another day .. and 'do it all over again, this time flip-flopped'    ...   (and with tracability!)

...

Whilst I still have a few tricks to try here, my next  'new exotic choice' would be the C3g tube ... it's kind of grabs attention in the sims sims. But it's crazy exe (pensive) ..  so pass. 

I think I'll try a few others instead ...  6EJ7 grabs me (very similar to the e83f), as does 12BZ7 (of citation fame), EF80  (popular in german stuff)  ..  and of course, the venerable  usa great  ...  the  6AU6.

And I'll be comparing pentode performance of this e83f with my more usual choices ...  6AK5 (great for mics), 6BC5 (unglam little tv pentode)     

 and  ..   the  humble  6J13P (russkie ef86 type), my previous best small  signal  pentode  ..  which is now  teetering precariously from it's exalted and high 1st place ....  but not until I do some proper tests.



....

To finish up testing on this mode of operation, I'll check my batch of 8x  E83F  to get a 'feel'  for the 'spread' of key performance indices

(kpis - used to do this alot back in my Quality Assurance Engineering days in biotech!)

....

Now for some wire - jagging   ...  for sensitivity checks, particularly on the input/output wiring and routing/locations. This has always been fertile ground for the grinding.

In this case, however, I don't expect any improvements - they're mostly 'tapped out' and 'simplified away'  .. in my 'Tube Test Rig'.

'Remoting, regulating and dc filtering heaters'   psu neatly eliminates most of the usual dross. 

Now it's mostly about  'input signal - output signal couplings' and  'short signal paths'  where some gains can be made.

It's certainly a novel (for me)  and a very pleasant place to be.   I'm sure this is,  I want,  going forward!

I would expect a righteous layout could do a little better ... maybe a dB or three for a real wiz.
Title: Re: REW Update
Post by: alexc on December 29, 2018, 12:27:13 AM
And here's the 3% spectra ...  quite nice.
Title: Re: REW Update
Post by: alexc on December 29, 2018, 04:45:10 PM
Tested up all 8x e83f ...  these are  all holland made branded amperex (x5) and sylvania (x3).

spread of  thd was tight ...  the one I was using turns out to be the worst of the 8, at 1.5%

I get a range of 1.17% .. 1.29% with two out-riders at 1.45% and 1.5%

Gain, spectra and hum floor are all virtually identical.

So, I have a close matched set of 6  with really low thd   ...   and a matched pair with a bit more.

I sound a bit like tube 'flanders' I think!  (glass half full)

I'll continue testing with the 1.29% tube  ...  a nice little reduction in thd ..  for a little modest judicious 'tube rollin' selectionism.

My new baseline   1.29% h2 with 116dB of margin over hum.

...

Right then ..  now to reconfigure for 'enhanced triode' mode :) 

Also described as 'screen drive'  ..   and with some sand-state support,  the term  'crazy drive' has been used by some :)

I'll be playing around with this kind of circuit ..  thanks kindly to 'Black Tom' for this interesting implementation!
Title: Re: REW Update
Post by: ruffrecords on December 29, 2018, 06:46:32 PM
@alexc

I notice all the spectra you have included have a rising noise floor as frequency increases. All my tube circuit measurements using REW show the opposite - noise increases as frequency decreases. I notice also that your spectra are rather blocky at low frequencies so I wonder if this is an artefact of the RTA settings you are using?

Cheers

Ian
Title: Re: REW Update
Post by: trobbins on December 29, 2018, 10:27:13 PM
i just use the spectrum mode setting, rather than an RTA setting like 1/48.
Title: Re: REW Update
Post by: alexc on December 29, 2018, 11:51:51 PM
Hi Ian,

I've always seen a rising noise floor as frequency rises, at the top end.  I thought it was simply that there is more noise energy in the 'bins' at the higher freqs than lower  ...  and it takes off at 5K and up. I could well be wrong!

That includes many years with TrueRTA before I started using REW's RTA,  and with several different interfaces.

So, I think it is a basic characteristic of RTA apps ...  but I'm not an expert.

...

I have seen the differences in the REW 'spectra' mode (vs  '1/48'  mode) ...  they don't show the  'increase' except beyond 15K or so.

I prefer the 1/48 RTA display, personally.

Do you have a snap you could show ?  I'd be interested in your results.

...

My current REW rta settings are :

24bit, 44KHz sampling, RTA 1/48 display mode, 64K FFT, Hann windowing 50% overlap, 20Hz-22KHz BW filtering

I use update interval of 1, no averaging, no peak hold, and no historical traces ...


Title: Re: REW Update
Post by: alexc on December 30, 2018, 12:17:13 AM
Here's a spectra of a G9 using pro gear  (not mine)

It doesn't have the rising noise response at high freqs that I always see     ..  just the opposite, like yours, I guess   ...

...

The answers are requiring more brain horses than I can muster! 

Maybe one of our more knowledgeable members can shed some light ?
Title: Re: REW Update
Post by: ruffrecords on December 30, 2018, 02:58:59 AM
Can you list your RTA settings?

Cheers

Ian
Title: Re: REW Update
Post by: alexc on December 30, 2018, 03:04:35 AM
I thought I did ?  a post above I think.

Here's a pic of the latest biz   .   50ohms to 100K and reverse .

One a smaller, for input.
Title: Re: REW Update
Post by: alexc on December 30, 2018, 05:34:27 AM
And one a larger, for output.

For a 'grounded grid' input amp - in a differential setup, and  for cathode following.

The ip traffo is  planned to feed  a   'vari-gm cf' gain cell if I can get it working. I wrote about it a few years back. My thing is a hack of the real article ... it's hard to find those 'feed forward' delay cells with any kind of fidelity.
...

The ouput traffo ...  well it's kind of a 'high impedance speakers' kind of thing. 50ohms output driving a series string of speakers.

They do exist! Like that Bose from many years back  ..  8x mini full range drivers in a secksi cab  ...  all working happy like.
Title: Re: REW Update
Post by: ruffrecords on December 30, 2018, 06:58:23 AM
I thought I did ?  a post above I think.


Oops, sorry, completely missed that. I will check them against my settings and get back to you.

Cheers

ian
Title: Re: REW Update
Post by: JohnRoberts on December 30, 2018, 11:16:28 AM

The ouput traffo ...  well it's kind of a 'high impedance speakers' kind of thing. 50ohms output driving a series string of speakers.

They do exist! Like that Bose from many years back  ..  8x mini full range drivers in a secksi cab  ...  all working happy like.
FWIW the popular Bose 901 used 9 full range drivers in series parallel (3 series strings of 3 all in parallel) to maintain 8 ohm load...

You will notice such approaches use prime squares like 2^2, 3^2 (901), 4^2 (sweet sixteen), etc.

Later Bose tooled up their own speakers with 0.9 Ohm voice coils so they could be wired in series and still deliver 8 ohms.

JR
Title: Re: REW Update
Post by: trobbins on December 30, 2018, 11:35:20 AM
Sort of like inter-leaved secondary windings on an output transformer  - but for your ears  :)
Title: Re: REW Update
Post by: ruffrecords on December 30, 2018, 03:19:25 PM
My REW settings are attached. This is an older version so there are less options but the only real difference is I use a spectrum rather than 1/48th octave and I use a longer FFT.

Cheers

Ian
Title: Re: REW Update
Post by: trobbins on December 31, 2018, 06:56:25 AM
I'm more with Ian on settings, and vary the averaging to suit the application.

I think the shape of the noise floor is more about the soundcard you are using - the floor level can vary if your soundcard has gain controls (like my EMU 0404 USB).  It may also change if you auto-calibrate for a flat frequency response (which I don't typically have engaged).
Title: Re: REW Update
Post by: ruffrecords on December 31, 2018, 05:23:25 PM
I think I know the reason for the rising response. it is because you are using the 1/48 octave mode rather than spectrum. If you use spectrum mode and set the generator to pink noise, you get a steady decrease in amplitude as the frequency rises as expected. If you then change to 1/48 octave mode the line becomes horizontal. If you now change the oscillator to white noise but keep 1/48 octave mode you get a rising response. Keep the white noise and switch to spectrum mode and the line goes horizontal again.

So basically the 1/48 th octave mode shows the energy in different bandwidths and by definition the bandwidth gets bigger at higher frequencies. So as white noise has the same energy at all frequencies, 1/48th octave mode show it as a rising curve which simply reflects the larger bandwidths at higher frequencies.

The reason for the blockiness is unrelated to the above. It is caused simply byu checking the 'use bars on RTA' option in the RTA tools menu.

The interesting thing is that measured values (distortion. S/N etc) seem to remain unchanged.

As an aside, the periodic white noise (white PN) will lock to the FFT only if the window is set to rectangular. This means you can get an easy frequency response plot using spectrum white PN noise and a rectangular window.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on December 31, 2018, 07:34:30 PM
Thanks for the observations Ian - I think that jibes with what I thought.

With respect to observing unchanging thd measures etc  with the different modes ...  that is interesting, because I have generally observed (slightly) different results depending on the RTA settings  ...  certainly with different sample rates and window types, but even with some parameters like fft-length and fft-bit-length.

Not so much nowadays, as I've settled on my preferred settings with a 'high degree of comfort'   ...  but for sure,  a couple of years back, I would have a couple of different settings-scenarios and would have to check on each ...  to give myself confidence that was what being reported was 'sane' as well as improving my understanding of the measurement system as a whole.

...

Trobbins, I don't think the basic phenomenon of  '1/48th RTA mode  gently rising hf noise floor' is related to the audio interface or even choice of RTA app.

I see the same thing on all my interfaces (and there are a few) with this kind of spectral display (1/24th and 1/48th octave) and consistently with both TrueRTA and REW for many years.  Other RTA apps I have used, don't have the detail required to even notice it.

I do agree with the assertion that the audio interfaces can have (slightly) varying noise floor signatures across the 'mids' and the 'highs', but this 'issue' is something else I think. At the 'low' bands, modern interfaces 'hum' noise seems to have converged to very, very low levels. Older interfaces that I have, not so much - they can be pretty ordinary with big diffs in hum harmonics.

..

I mostly don't use the 'spectra' mode because the averaging that seems inherent in the hf display ..  it just muddies up the 'instantaneous' picture of things,  imho.

I like to 'take an action' and see the effect in 'real time'  (more or less, with maybe 1/3s delay)  and decide 'better or worse'  :)

Once I get to the end of testing, I do then apply some of the averaging and historical traces and what not.

The capabilities of REW in this area  ..  of 'multiple historical data set handling' and 'post processing display'   is pretty superb.
Title: Re: REW Update
Post by: alexc on December 31, 2018, 08:11:10 PM
I'm getting very excited now  :)  re. 'screen drive' mode for e83f

I've just knocked up a simple CF from an 6922  to set up the bias conditions ...   took only a couple of minutes to cobble it in.

I'll have to tune the CF cathode string,  to get the required grid and screen bias voltages at the e83f  ..  it's a little weird that way.

There also another slightly different way of arranging the screen-drive pentode, which I'll have a look into after I get this going ....

(circuit is a few posts back)

....

Just love the luxury of a 'tube test rig'   ..  it's pretty fast to get some results action  ...  which is just what's required ..

as my attention span doesn't support proper 'craftsman' values   ..  at the best of times, let alone when 'exploring' or 'baselining'  tube stuff. I'm more of a compulsive 'baseliner' than a true explorer, tho'. I just love standardised testing!

Here's where my topside is up to  ...

.....

I added the single triode 9pin 6S4A  next to the old  'telefunken 12K-6ohm se output traffo ...  that's going to be fun.

The 6S4A is my ultimate small power triode ... only the 6V6 beats it, and it's a sound thrashing too  ...and it does so with substantially increased plate rating and 30% less heater and more gain to boot. The 6V6 triooded is not as good on rp,  however.
And of course, the octal is a lot larger. 

6S4A is my choice for a 'm parallel se' amp   ...  I like 6 of them together, per channel, wired up with little 'bus bar' wires - it can be quite tidy if done right. Prev. best is 4 of them - it's the last two that really make it!   

Good if one has a switched mode supply for heater. I just do a series + parallel string with a 100VA toroid  at 12Vac.

One can even get 4-way 'bias adjust' pcbs on eby cheap .. small enough in size to use several ..  basically little trimmer networks for the cathode circuit of each parallel stage. 

Always a good idea to try to match those idle currents as best as you can and adjusting a little resistance helps fine tune to a very good degree.

...

Also to note, the big output traffo   ..  affordable, old 'medium fidelity' local unit 'A&R' with a nice cast can,  mid 50s-60s -  I would say  ... it's 5K, 3K primary for 15Wrms push-pull with a secondary taps from 500ohms  down to 100ohms. 

It cost about the same as a pair of edcor xsm from 10 years ago  ...  it kind of picks up, testing wise, where the edcor leaves off. It can take some decently high voltages a bit more safely than the humble edcor  with its exposed terminals and fragile wiring attachments.

It's not bad,  so far ..   I have a lot more detail testing to do with it.  It's just begging for a pair of 7591a  '19W plate' finals.   
:) 

Happily, they are right there, in place, glowing and ready to go.

Speaking of which, one of a quad nos 7591a (octal 19 watt plate, 800mA heater) turned out to borked  ...  I can't get any heater glow from it, but the heater still shows continuity. But heater wise, it's dead.  I couldn't believe my lying eyes  ..  I'm half believing I got it wrong.  I hope so, these old GE aren't cheap! 

-> update  ..  partial better .. not borked, just with the centering pin snapped off and wrong insertion.  D'oh!
-> so - better than borked but not as good as proper   ...  time to get another.

Oh well, s**ff happens  ..  I fritzed plenty of stuff myself, in my life, that's for sure!

I figure I'll buy a modern set (much less exe) and go forward from there ...  I'm interesting in seeing (and hearing)  how these compare with a high-power   6V6gt (14w plate) nos GE  (just awesome sounding) ,  and, the modern, higher-voltages-rated variant -   the fab and affordable   JJ 6V6s  ..  which I really like.

Other modern 'moderate  plate rated'  6V6gt  can be very fine also - I think I've used most of them at one time of other   ..  eh, sovtek, tung-sol, jj.

The 7591a can take some very high voltages and the screen can take a good beating  ..  just like the JJ 6V6s  ...  but at even higher currents. 

Of course the 7591a has nearly double the heater, for those extra ratings  ...  more like a low-powered 6L6  ie. 5881 and the like.
 
I'm not sure if the el34 is comparable, being a true pentode vs a beam-power type. These distinctions can get a little hazy  ..  at least in my mind.

I tried out the old russkie 'little 6L6'   type  ...  not impressed unfortunately ... prolly just bad luck (I only have 2) but the prices have increased a lot for them and it's just not worth bothering with.

Nothing beats the modern Tung Sol 7851a 'super 6L6' for 'big power' hifi greatness   ...  at a reasonable price  and with a very reasonable heater current of 900mA and  a generous 35W plate rating. 

It just gets in under the bar before one looks at kt88 and larger :)

Testing at those high power levels will have to wait until I 'bolt-on' a 'variac' and finish my Mk2 psu  :)   This Tube Test Rig has limits around +370V at 150mA or so ...  but I have two of them available  ..  in my 1RU (+ 3RU of upper space required)

This current PSU has easy variation of HV to some degree, but one has to be very careful not to dial it down to0 far if HV current consumption is significant - the heatsinking needs to be up to what you demand of it.

I am running a fairly low regulator voltage drop, with low currents, so no probs.

For the Mk2, I'll have a 'higher power hv' cct seperately done  with the 500VA variac  ..  and the rest of the lower powered stuff can be done  the same as now.
Title: Re: REW Update
Post by: alexc on January 01, 2019, 07:08:50 PM
So ..  onwards with trying to get a result on 'screen drive' ..

So far  .. no good    :o  ..  but it's early hours yet ..

.....

I have a 'CF driver'  set up with a series string of resistance in the cathode to setup the required conditions    ...  but there is a lot of tuning to get it to work  - as I have read.  This is my first attempt to cobble together.

 i) bias voltages (dc)  for the scrn_drv pentode  ie.  g2, g1, k
             -> some very particular values req'd

ii) ratio of signal voltages at g2, g1
             -> some very particular ratios req'd

For now,  I have  ..

-  ball park currents flowing in both the cf driver triode  and the screen-drv pentode

- 6922 driver cf is working fine at 1.5mA or so  with amazingly low thd  at 0.079% or something like that :) even with the rough and ready bias conditions I have and the small-ish 1Vpp starting signal  :)

-  the  scr_drv pentode is flowing current fine around 5mA or so

-  no 'gain' to speak of, at the the plate output,  of the scr_drv pentode.

The pentode output spectra looks like a regular gca stage but with it's grid at a low-ish Z,  mostly 'shorted out',   ..  resulting in a relatively tiny output signal   ...   in other words ..  not screen driving at all. Just a very crappy gca   >:(

The basic gain structure is :

 -  x1 into the driver cf,  about x0.95 out of the driver CF at the cathode

 - cf driver cathode dc and signal voltages are divided to ground in a particular ratio
    like 60% to scrn_drv g2,  and 40% to scrn_drv g1 - so one is losing 6dB or so into the next stage g2 and even more into g1

-  scrn_drv plate is usually driving an se traffo primary at good high volts as is usual typically 3K or 5K to 10K and so on - I'm doing a plate load resistance, not a traffo and so my scrn_drv plate is way too low etc.

....

SO a *pitiful*  turnout for today   . ??? ..  except the eh 6922 triode stage as a simple CF.  Phew! It's a truly great performer, even in the crude hands of a  gardener  like me.

Time to hit the studies again tonight   ....  regroup for the next attempt  :)

A bit like with those rock monkeys in 2001,  really.  REW is my 'monolith' and the Tube Test Rig is my  'whirling sky bone'. 

And sure, I like  'tapir' just like any.

The golden teacher of experience will surely inspire me,  to somewhere interesting. I have no doubt.

It does tend to ramble, however  ..  I do know that.

....

*Attached* is another design along these lines posted from 'diyAudio'   ...  it shows an (the) alternate way of handling g1

It uses a 'totem pole' driver  and shows the scr_drv pentode's grid grounded thru 100K  (rather than the lowest leg of a resistive divider in the driver  cf cathode circuit - usually 10K or so).

That's basically the two main ways, afaik,  to get into this mode.

Sometimes the cathode voltage of the scrn_drv pentode is 'augmented' with a connection to a dc bias 'boost'  ..  coming from just about anywhere in the circuit that's handy. 

...

Here's a comment from 'diyAudio' contributor regarding why 'some pentodes are good for screen drive and some are not'.   

Note this is generally in the context of  TV 'power pentodes' with 'lower max screen voltage rating'   generally known as 'sweep tubes'.

ie. very high plate voltage rating, but quite low screen voltage rating and as well, a low-ish screen power rating.

..  I'm trying first with small signal ones to jump start my thinking processes  (needs several days notice at least!)

----

The critical factor for practical g2 screen drive, is the transconductance of grid 2. (high gm2 best) You just want reduced grid2 drive voltage basically.

gm2 = gm1 / Mu

This will generally show up in datasheets as a low max g2 voltage spec or a low g2/g1 Mu.

The g2/g1 Mu of 6L6 and similar KT tubes is around 8. While the more practical TV Sweep tubes have a g2/g1 Mu of around 3 or 4   and   so require about half the grid2 drive signal Volts of the 6L6 types.

----

So - I'm still pondering that   those things.
....

On top of my many  other  incorrects, I think I also  just have the wrong kind of pentode .. and that is compounding  things  ..  resulting in a very low gain at the plate output.  e83f has a high  'mu g2-g1'  spec of 38.

I don't just mean the disparity between 'power pentodes' and 'small signal pentodes' - it's more like low mu triodes vs hi mu triodes. But in pentodes.

Not quite sure - more data needed.

Either way, I still need to think a lot more about it :)   I have a few more basics to cover  .. the se traffo for example.

I could try to find a more suitable pentode from 'stock'   ...  at least I have several available 'tube socket' types on hand to play with.. 

otherwise I could try to get hold of a couple of sweep tubes and  get a 'contributed circuit'  going 'as shown'  ( read the manual  for once!)

I'm not game for a 'top cap' anode type except for in a 'proper build'  ...  I have a few candidate if I have to buy in.

I figure best to get some results first with what I have here :)
....

Screen Drive is very  intriguing and I know it does work  ..  but takes time and skill I guess.  The diyAudio guys like to publish 'scrn drive curves' which they use to properly bias  .. in detail.  Regular data sheets don't have these kinds of data.
Title: Re: REW Update
Post by: alexc on January 02, 2019, 06:38:22 AM
and heres the prototype choice for a potential cheap 'buy in'  more suitable for screen drive  ...  in a 'lesser' el84 prototype as far as I can currently determine   ie. from my 'computer seat'

el86 with the 'low' mu g2-g1    mullard and other nos .. ge, rca  etc

Funnily enough, this one was quite popular down here in Aust (Oz) and us nos are still available  for better than soviet prices - a case of 'who cares'  :)  the el84 is better!

There are also  a few old soviet types based on this 'slightly less statured' el84 avail affordably ...   6p15p, 6p43p, 6p18p.

These nos Soviet types  do have their staunch adherents,  as  regular moderate 'power pentode' types  ...  especially in triode mode ... where they have been touted as being very linear.

Not sure if they 'spec'  the mu g2-g1 parameter    ..  only the mullard, brimar  and a couple of holland pentodes seem to mention it.

Another one with the low mu(g2,g1) is the 6aq5  at 10..  which is like a standard 6v6 in a really little bottle 7pin.

Also el34 with low mu(g2,g1) at 10
Title: Re: REW Update
Post by: alexc on January 02, 2019, 06:40:09 AM
and the el84 proper which I have 'in stock'  ...   apparently not as 'meritorious' in this metric  .. even discounting the operating conditions somewhat.

..  and the e83f is 'less' still more, with  mu g2-g1  at 38,  quite a high-ish value apparently

Its all very curious, really.  A reasonable low cost tube pursuit :) for those with time to  ...  pass.
Title: Re: REW Update
Post by: abbey road d enfer on January 02, 2019, 07:07:20 AM
I think I know the reason for the rising response. it is because you are using the 1/48 octave mode rather than spectrum. If you use spectrum mode and set the generator to pink noise, you get a steady decrease in amplitude as the frequency rises as expected. If you then change to 1/48 octave mode the line becomes horizontal. If you now change the oscillator to white noise but keep 1/48 octave mode you get a rising response. Keep the white noise and switch to spectrum mode and the line goes horizontal again.

So basically the 1/48 th octave mode shows the energy in different bandwidths and by definition the bandwidth gets bigger at higher frequencies. So as white noise has the same energy at all frequencies, 1/48th octave mode show it as a rising curve which simply reflects the larger bandwidths at higher frequencies.
I'm actually quite surprized that such a basic mistake could be done.
Spectrum is based on a linear frequency scale; the bins have a constant absolute width (i.e. same f2-f1 expressed in Hz) and thus are dedicated to working with a noise source that has also constant Hz width, which is the definition of white noise.
OTOH, RTA is based on a constant relative BW (i.e. same f2/f1 ratio), which implies the use of noise with the same characteristic, i.e. pink noise.
REW is a very nice tool, but as with any tool, one must learn to use it and how not to misuse it.
IIRC there are enough explanations in the Help, but again who does RTFM?
Title: Re: REW Update
Post by: alexc on January 02, 2019, 05:44:42 PM
So what does this 'rising hf noise'  amount to ?

Is it fair to say the '1/48 RTA'  apps that I and others have observed  (TrueRTA, REW) are doing things not quite optimally?

I used to post snaps from years back where I would annotate this 'gently rising hf noise signature'

My own 'gut feeling' tells me that it is reasonable to expect the trace to do exactly that - there is more energy in the hi freq register of the noise floor and the log display makes it inevitable that this should show up reasonably dramatically.

If the trace were 'flat' all the way out to the high freq limit, I am sure I would think that was 'massaged'.

....

Again, I've not compared with the pro types  ..  just the best of the low or no dollar PC based apps with a variety of converters and interfaces.

The few snaps I have seen of the pro types don't seem particularly detailed one way or another.

But I'm a complete newby in today's high dollar hardware 'pro analyzer's.

Maybe one of our group with access to such, could post a snap of a simple loopback 'silence' in a similar display mode ?

..

And up till now, I've mostly been concerned with the quite simple sine type testing with a focus on the  'hum' region, whereas now I am interested in the rest.

I can't recall using white-noise or pink noise tests much, so I don't know if some types of analyzer are more tailored to that kind of thing.

....

Maybe we need software  filter or some kind of 'pre-emphasis' to 'flatten it out'  :) 

I think someone mentioned an 'auto-cal' type of function somewhere   which does such  ... 

I suppose that would amount to a kind of 'normalisation' function. 

Perhaps  an   'RTA Mode  Raw/Normalised'   button :)  which could be useful for the purpose of 'baseline' performance measures that I like so much.

..

Here's an annotated  snap from TrueRTA of 6yrs back  ... 1/24th RTA I think ..  same thing  .. Motu 828MkII Analog Loopback

- you can also see that damnable hum spike I lived with for several years before binning that interface   >:( >:(

Today I would quit rather than live with that!

..

OK - off to read the manual.
Title: Re: REW Update
Post by: abbey road d enfer on January 02, 2019, 06:04:21 PM
So what does this 'rising hf noise'  amount to ?
It just shows that the analyzed signal is closer to white noise than pink.

Quote
Is it fair to say the '1/48 RTA'  apps that I and others have observed  (TrueRTA, REW) are doing things not quite optimally?
I think it's not fair to implicate the tool when the issue is likely to be an operator's mistake. My understanding is that someone tried to evaluate a frequency response  and noticed a difference between Spectrum analysis (in fact a derivative of FFT) and RTA. Both are usable but they must be used in conjunction with the correct stimuli: white noise for spectrum, pink noise for RTA.

Quote
Again, I've not compared with the pro types  ..  just the best of the low or no dollar PC based apps.
The big issue with those is they don't come with the necessary metrologic knowledge.


Quote
Maybe we need a filter or some kind of 'pre-emphasis' to 'flatten it out'  :)
No, one just needs to use the proper settings according to the type of measurement.
BTW the difference between white and pink noise is just a 3dB/octave low pass filter.
Title: Re: REW Update
Post by: alexc on January 02, 2019, 06:49:50 PM
In the meanwhile, I want to rattle off some '6922 footprint'    gca REW snaps ....   in this brave new world of uber-measurement :)

I'm thinking some comparisons of the usual suspects   ..  eh6922, some amperex, some nos russkies.

Once I get the bias dialled in, it should be fairly quick to get an updated picture of this family.
Title: Re: REW Update
Post by: alexc on January 02, 2019, 07:03:03 PM
OK I think I get it a bit better now, here's my current 'take'  on the issues     ..  still struggling a little, so thanks for the patience Abbey  :) 

I do think you have the important things here very correct and I do want to understand the measurement process better.

.....

Because of the kind of  testing that I like to do    ..  ie  'single tone'  and   'noise floor' signatures  ... 

which are closer in their 'nature' (energy distribution in the  freq domain)

to 'white noise' ,

I should use settings in the analyzer which are best suited to that 

ie. 'spectrum' mode rather than 'rta mode', as an example - I'm guessing there are others ..

that does not 'obfiscate' results in the  'hi freq' register ,  leading to a more 'reality based' interpretation of the data

...

That does make more sense to me now  - thank you. 

I can do some more reading of the manual and do some more exploration of the different settings available in REW to get a better understanding of the measurement capabilities - particularly in the area of these baselines that I like.
Title: Re: REW Update
Post by: alexc on January 02, 2019, 08:44:47 PM
I had a read of the manual regarding the 'spectra' and 'rta' modes  ..

It  all seems reasonable, as does the rest of their details on how to setup REW ...

....

For this specific type of profiling of   'line-in/line-out testing : single tone and silence' for a 20-20KHz view

I still think it basically comes down to a preference of the displayed detail.

I tried most of the options out, windows and such - I still think 'my settings'  give the most useful interpretation of what I'm trying to measure.  :)

Especially in an 'instantaneous' type of view with the desired 10Hz to 22KHz viewed as the default 'zoom' setting.

I can tweak the 'averaging' and 'windowing' and 'fft-len' within each of the spectra/rta modes and see varying details come into or out of focus sure enough.   

Certainly, when one zooms in on smaller displayed freq ranges, 'detail' and 'resolution' issues can come into play a lot more  .... 

but with a standard view, such as my settings give, well I think :

..

 'what's there is actually there'

 in a given 1/3 of a sec or so and to an amplitude error of 0.1 dB when everything is stable 

-  there can be some uncertainty to the tune of 0.3dB (when stable) rising thru 0.5dB and up to 3dB  ..  when the bottom end is twitching about   .. from an unstable diy-under-test

- it's that 'hum floor crest factor' (my terminology)   I go on about  ..  and it is a good measure of just that  ..  low freq stability  ..  it part-answers the question 'apart from  (subtracting) the peak, what is the relative importance of the  low end in the schmutz that remains  ?'

- as does  the 'peak-rms-factor'  (my terminology) figure in the floating 'rms input' headsup windowlet

- if things are going right each of these are very low  ...  approaching 0.1dB or so  ..  saying literally 'nothing, apart from the peak, to see here'.

I'm pretty sure that's as good as one could ask for, generally speaking. I would say I'm 0.2dB to 0.3dB now, in 'real life test' like here.
 
..

The basic signature of the hi-freq register noise floor,  at the end of the day,  is different for the two modes - consistent within each mode but distinct from each other.

I get no refinement to answering the basic question of 'what's my unit *really* doing, noise-wise,  at silence, right now ?'   

by using one mode over the other. 

Visually, and with making the most of the 'single measurement cursor'

....     apart from the obvious difference  in the  'envelope' of the hi-freq response,   all that 'shaded black' trace to me is not useful and masks where any real instantaneous action might be happening - it amounts to more 'averaging' as far as I can see.

....

SO - one take's their pick of 'mode',  then tweaks 'settings' within it to suit their testing scenario as best as possible for today and the near future,  and carries on. 

Who knows where it (REW)  might go  in another year or two.  I'm sure there are better instruments for metrology, but using *this* one I don't think I'm demonstrating any operator error  .. nowadays  :D 

I sure have, without question, historically - but *now* I think I'm getting good results and have always enjoyed putting them out there for others to look at.

I know there are better 'protocols' and 'supporting external test tools' to improve overall test methodologies for sure

.....

Remembering, my objective is to do  'long term collection of baselines'  of noise, single tone tests and thd measures and frequency response sweeps so as to 'keep it real' and 'with traceability'  for my diy stuff as best I can. On the cheap!

....

Of course I remain really interested to see how other analysers, particular the really good ones, handle a similar display RTA mode.

I would definitely expect them to have various normalizing functions - as to their way of handling what I think is a basic property of the 'RTA mode' and similar implementations - allowing some amazing and comprehensive (ai ?) dataset mining, baselining, cross-correlating  and ultimately, convolutions thereof ... no doubt.

'Gold standards' and metrologists are always great while you can keep your hands on them - they don't come cheap. I used to have access to them alot for medical instrumentation  when I was working for a living. Nowadays, not so much.

...

This 'diy thing of ours' is much more fun, although just as detailed in the required info levels.

Thanks to all the people  who likes to discuss this diy stuff and share their knowledge!
Title: Re: REW Update
Post by: abbey road d enfer on January 03, 2019, 02:17:26 AM
For many years, designers have relied on sensitive voltmeters and dedicated weighting filters for noise optimization.
Spectrum analysers, whether RTA or FFT-based) simply were not commonly available, and actually nor really necessary.
Most noise in analog audio gear is either Johnson noise or hum residuals. Assessing them just takes a sensitive meter and adequate filters.
Distortion can be assessed satisfactorily for most needs with a distortion analyser, which is, after all, a glorified notch filter.
Spectrum analysers have the advantage of providing a more detailed array of data that allow extracting the ususal single-figure results we're used to see.
However, this takes a little math.
The single-figure result is the integration over the desired BW of all the individual bins (FFT) or bands (RTA).
The more bins (FFT length) or bands, the lower the level in each.
In fact, many RTA's use an actual FFT and some math.
The availability of FFT has made the analysis of distortion much easier,prompting a new interest in tube distortion.
Title: Re: REW Update
Post by: alexc on January 03, 2019, 02:46:32 AM
All very true.
Title: Re: REW Update
Post by: ruffrecords on January 03, 2019, 04:29:11 AM
For many years, designers have relied on sensitive voltmeters and dedicated weighting filters for noise optimization.
Spectrum analysers, whether RTA or FFT-based) simply were not commonly available, and actually nor really necessary.
It is said a picture speaks a thousand words. An FFT plot from an RTA with derived values  contains a host of information not available from voltmeters and filters. You can see 1/f noise. You can see mains hum harmonics so as to determine if you have a ripple or screening issue. You can see all distortion harmonics and their values. Using a periodic white noise generator (which REW has built in) you can see a direct plot of frequency response and see exactly how an EQ changes response as you alter its controls. And of course you can save and print the display so others can see.

I started out with an audio millivoltmeter and a distortion analyser that gave only THD. I later bought a tuneable one so I could see individual harmonics. Now I have REW I would never go back to them.

Cheers

Ian
Title: Re: REW Update
Post by: abbey road d enfer on January 03, 2019, 04:53:30 AM
It is said a picture speaks a thousand words. An FFT plot from an RTA with derived values  contains a host of information not available from voltmeters and filters. You can see 1/f noise. You can see mains hum harmonics so as to determine if you have a ripple or screening issue. You can see all distortion harmonics and their values. Using a periodic white noise generator (which REW has built in) you can see a direct plot of frequency response and see exactly how an EQ changes response as you alter its controls. And of course you can save and print the display so others can see.

I started out with an audio millivoltmeter and a distortion analyser that gave only THD. I later bought a tuneable one so I could see individual harmonics. Now I have REW I would never go back to them.

Cheers

Ian
I certainly don't disagree with that; spectrum analysis is a powerful tool, but, as it is with any tool, the more powerful it is, the more competence it takes.
I've seen too many cases of spectrum analysis yielding incongruous results because of misinterpretation or improper setting.
One should be alert to the many caveats.
For example, evaluating an EQ with an RTA is a very common mistake. Or assessing a HPF with a 1024-point FFT.
Clearly, you're one of those who read the manual before plugging; this is far to be the case in many instances.
Title: Re: REW Update
Post by: ruffrecords on January 03, 2019, 11:33:52 AM
I've seen too many cases of spectrum analysis yielding incongruous results because of misinterpretation or improper setting.

Me too. I rememeber one case where an audiophile published the spectrum of his new tube preamp. It had the noise floor bumping along at -100dBu. This, he claimed meant his preamp had a -100dBu noise floor. I explained that  was probably as much as 43dB out but I did not receive a reply.

Cheers

Ian
Title: Re: REW Update
Post by: abbey road d enfer on January 03, 2019, 11:49:53 AM
Me too. I rememeber one case where an audiophile published the spectrum of his new tube preamp. It had the noise floor bumping along at -100dBu. This, he claimed meant his preamp had a -100dBu noise floor. I explained that  was probably as much as 43dB out but I did not receive a reply.

Cheers

Ian
Alas!  :( That's a perfect example of what an abundance of resources, shed on lazy Philistines can generate.
In the past, only a few idle rich could do that, and were easily identified. Today, thanks to democratization, there are so many of them it's much more difficult to filter them.
Do I sound elitist?  8)
Title: Re: REW Update
Post by: ruffrecords on January 03, 2019, 12:27:15 PM
Alas!  :( That's a perfect example of what an abundance of resources, shed on lazy Philistines can generate.
In the past, only a few idle rich could do that, and were easily identified. Today, thanks to democratization, there are so many of them it's much more difficult to filter them.
Do I sound elitist?  8)

Thanks to the internet there is so much more of everything - good and bad. I would not be without it because it makes available a wealth of information but the price is exposure to a large number of idiots.

I remember back in the 80s when we first started emailing PCB layouts and mechanical drawings to manufacturers in the Far East. It seemed a revelation at that time. I also rememeber sending a customer a telex from my Commodore 64 around midnight on a Sunday. He was bowled over I was still working for him that late (in fact I had just had a light bulb moment so decided to put it on paper before I forgot).

When automobiles were first invented they were only available to a select few. Today out roads are clogged with them.

When I think about the technological progress in the last few decades (in 1980 I ran the project that developed the Dragon 32 8 bit home computer for the UK, then Europe than the USA) I wonder what the next few decades will bring.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on January 03, 2019, 05:30:47 PM
One of the things I most love about the 'real time' responsiveness of REW, is tuning the harmonic structure of a tube stage and with amazing dexterity.

The e83f is a fine tube ..  I think a 'precision' one, so to speak.   I've run about  a tenth of   it's different capabilities so far.

Its a privilege to have a nice one under the the lens of REW. Truly made for each other!

In a typical gca type stage, with a 500ohm trimmer in the cathode circuit, it's amazing how one can turn up or down the harmonics  ..  the even set and the odd set.

I like to find the minima, then adjust around there for the least odds, generally.

Also of interest, the effects of different B+ voltages on thd ...  varying at the hv regulator module and adjusting the bias to hold .. while watching REW and how gain changes, harmonic structure, hum etc.

Of course, be sure to use a   'well insulated screw driver'   for those pcb trimmers ..  one slip and who knows where the tip might land.
Title: Re: REW Update
Post by: alexc on January 03, 2019, 05:55:55 PM
Just for some basic education, Abbey ..  could you elaborate a bit on the problem with using an RTA for some kinds of eq testing ?

I could use a refresher :)

I mean I know that doing any sort of eq increases thd  ..  by definition , generally speaking.

And also the log scale of the frequency axis can scale the characteristics of a filters slopes.

Are there issues with doing basic sine freq sweeps with eqs ?

I suppose this is where one starts using the more advanced (from my perspective) capabilites  ..,

... white noise, pink noise and so on.

Thanks
Title: Re: REW Update
Post by: abbey road d enfer on January 03, 2019, 06:50:59 PM
Are there issues with doing basic sine freq sweeps with eqs ?
Sine sweep is actually the most accurate measurement for filters, provided the sweep rate is low enough to allow the whole circuit to stabilize (that includes the meter's rectifier). If the sweep is too fast, the measurement is actually that of a past event.

Quote
... white noise, pink noise and so on.
Spectrum peasurements imply the existence of one or more filters. Their slope comes in addition to the slope of the DUT, so the resulting graphs are always too wide.
It may look like FFT does not suffer this, because the BW is split in numerous individual narrow bands, but in fact a 1024 point FFT has a BW of 19.5 Hz, which means the 20Hz bin has a relative BW of one octave.
Title: Re: REW Update
Post by: alexc on January 03, 2019, 07:21:47 PM
Nice  ..  I indirectly knew of those things but it's always good to do some 'relinking' of packets of info.

I think REW does allow durations of sweeps, so I can do some trys of that.

On my bench, I have the 'filter' section of a gPultec racked up awaiting some new makeup amps ..

I think I'll hook that up to my tube test rig and try some of the white/pink and variable duration sweeps.
Could be quite nice with this ef83 I think

....

It's always good to consider  the filtering aspects of the spectral analysis ..  and what it means in practice. I'm relearning this stuff. I did study it but that was 35yrs ago and mostly now 'archived'.

I have the book 'Scientists and Engineer's Guide to DSP by Steven W Smith  1997'  which is *way* better than the texts for signal analysis were in 1984 when I started that study.

....

I did use those studies, at one period, and wrote some 'vibration analysis' tools .. similar to the more basic  RTA type tools  ..  for the rail system in aust.

We (engineering teams where I was a 'cadet') would wire up trains of 4 to 6 locomotives and about 1km of various trailing stock  ..  like coal carriers etc  ..  every transducer imaginable, kms of wiring, combining networks, multitrack recorders and our own digital converts  ( I did that once too).   

Then 'hit the outback' for weeks at a go   ... there were sleeping carriages for the staff and we could pull up anywhere we wanted to breaks and meals etc.

You haven't really lived as a 'wire jagger' until you've 'roadied' inside the engine compartments of a 3000hp diesel electric loco going strongly ..  and I don't mean idling  ..  pulling a huge train. 

It's extremely hot and noisy next to a V16 super charged with a blower half the size of my car.  The 'perks' was to get a much desired 'seat' in the loco cab most of the time  ..  air conditioned, air cushioned with space to nap some.

And then later, back in the labs to analyse it all  ..  vibration analysis was the main thing but also all the electrical parameters and many mechanical and hydraulic things as well.

Literally 50 or so engineers, techs, loco drivers, signals guys  ..  metallurgists    ... the works.

There were even 'pyro engineers' who were incredibly expert in all aspects of 'burning stuff'.
Title: Re: REW Update
Post by: alexc on January 03, 2019, 10:44:42 PM
and back on the 'screen driven pentode' thing  ..

Here is attached an article from 25yrs back ....  mr Tim de Paravicini of EAR  ...  he published the design and so on back then for 'people like us'   diy folk.

It's prolly the most well known example of this kind of thing ..

...

has example with the el509 power pentode, with grids grounded thru 10K and screen driven from a totem pole driver.
Title: Re: REW Update
Post by: ruffrecords on January 04, 2019, 05:22:02 AM
Spectrum peasurements imply the existence of one or more filters. Their slope comes in addition to the slope of the DUT, so the resulting graphs are always too wide.
It may look like FFT does not suffer this, because the BW is split in numerous individual narrow bands, but in fact a 1024 point FFT has a BW of 19.5 Hz, which means the 20Hz bin has a relative BW of one octave.

Does anyone use 1024 point FFTs any more? REW allows ones two orders of magnitude longer.

Cheers

Ian
Title: Re: REW Update
Post by: abbey road d enfer on January 04, 2019, 05:42:02 AM
Does anyone use 1024 point FFTs any more? REW allows ones two orders of magnitude longer.
That is true; there are still apps and hardware that use 1024 points. My comment was to illustrate the fact that all systems have their limitations. I haven't even started on windowing.  ;)
Title: Re: REW Update
Post by: ruffrecords on January 04, 2019, 10:30:39 AM
That is true; there are still apps and hardware that use 1024 points. My comment was to illustrate the fact that all systems have their limitations. I haven't even started on windowing.  ;)
Windowing is a whole other ball game.  For instance, I have discovered the REW periodic white noise only works properly with a rectangular window.

Cheers

Ian
Title: Re: REW Update
Post by: abbey road d enfer on January 04, 2019, 11:00:10 AM
Windowing is a whole other ball game.  For instance, I have discovered the REW periodic white noise only works properly with a rectangular window.

Cheers

Ian
FFT misunderstanding is a subject that comes so often on the LTspice group...
Title: Re: REW Update
Post by: alexc on January 04, 2019, 11:38:34 PM
I just congratulate the new 'young persons' recently getting into music and audio and diy and engineering and the biz.

You'll never know, a world without REW ...

Everything is just so much more detailed nowadays and at the fingertips,  and in every field, all the time.

Often for just the investment in time and study and practice.

I couldn't believe how smart and accomplished, the youngsters at my last work place were. And that was a decade ago.

Back at the start of the eighties, the world of tech was like the flintstones in comparison.

Imagine *actually* recording to strips of plastic tape with rust etc ...   and bank books that the 'tellers' would just write in and *stamp*.

My greatest encounter as a 15 year old was a big teac (tascam)  4-track 1/4"  at the local tv tech shop  :)

btw how complex are those tube TVs ?

Whoa   :o  I still try to understand some the schematics .. the kind that would unfold into huge diagrams like maps on a ship's light tables  ..

I figure it will take me at least 10 years to just check all the tubes from my past, just to see the change.

< pic of tube tv insides to post >
Title: Re: REW Update
Post by: ruffrecords on January 05, 2019, 03:58:35 AM
FFT misunderstanding is a subject that comes so often on the LTspice group...

I do wish LTspice would turn off compression by default. IMHO it is the biggest source of errors in its FFT plots. We are no longer so short of memory/storage that we need it and it is a PITA to remember to include winplotsize=0 or is it plotwinsize=0. I always have to check an earlier file to check the syntax.

Cheers

Ian
Title: Re: REW Update
Post by: abbey road d enfer on January 05, 2019, 05:43:21 AM
I do wish LTspice would turn off compression by default. IMHO it is the biggest source of errors in its FFT plots. We are no longer so short of memory/storage that we need it and it is a PITA to remember to include winplotsize=0 or is it plotwinsize=0. I always have to check an earlier file to check the syntax.

Cheers

Ian
I agree, the syntax in LTspice is not always intuitive. But isn't it the case with most programming languages?
Title: Re: REW Update
Post by: alexc on January 05, 2019, 09:45:29 PM
I think so.

I used to love the ti tms dsps in the late 80s and later the sharcs in the 90s  ... talk about high powered lean mean machines.

It amazes me that apps with capabilities well beyond that are now common place in java  ... which I'm sure is quite optimised to run on most things nowadays ..   but it's a bit like a 'racing bus'  I think.
Title: Re: REW Update
Post by: alexc on January 05, 2019, 10:34:59 PM
I wonder where are some of the 'tube guys' from the day, working for tektronix [cro makers] and so  on.

If I had more time I'd like to read a book about the development of those.  Their products were the 'hi end' source of everything tech back then. In terms of tube circuits, they probably still are and always will be - at the 'top of the game'.

...

SO - one of these days, if an old tube cro comes my way, I think I'll take a look inside.
Title: Re: REW Update
Post by: ruffrecords on January 06, 2019, 03:03:36 AM
I agree, the syntax in LTspice is not always intuitive. But isn't it the case with most programming languages?

Indeed. The other thing that makes me smile is the latest version of LTspice will not run on my old Windows Vista laptop but it does run perfectly on my Linux box under Wine.##Cheers

Ian
Title: Re: REW Update
Post by: alexc on January 08, 2019, 01:02:04 AM
Not much done lately ....  it's 'grass cutting' season  ....  must  ..  make ..  hay  ..while .. sun ..shines  ...

[no big machines here .. I just have a couple of lawn mowers to do 4acres  :)  downunder in 'the land of grass'  - it's only chest high, after the 'summer rains'.  Meh - I've seen worse sans horsies.. ]

This year is a jubilee year   ..  hence the hand labour ..  fields after horses have been thru  ..  need lot of tlc.

...

Still looking at the wonderful 6922/6DJ8 family  with rew (!)   

.... but the hot weather makes me drowsy and less diy motivated  ::)  - well suited to grass cutting  ...  where I can think on stuff   ...   and the path ahead  ...  plus my objectives for the year 2019.  All those tomatoes in the orchard  .. with  bug sprayer  .. things.

....

New business, only a couple of purchases  ...  will take a month or so to get here, so I look forward to that.

- 10x  of 6p15p-ev 
  ->  (nice russian examples,  voltages uprated 6bq5/el84 proto - a 12W plate  and 330V plate/scr   pentode)  40usd  'to my door'

- 2x  of matched modern Tung Sol 7591a (also russian, octal beam power pentode 19W plate) 40usd each 'tmd'

I'm hoping the 6p15p are the 'last word' in 6bq5-speak  and I have a hankering to try 4x parallel push-pull  for the hell of it. The nos 6bq5 are sturdy but I want to really bash these ...   

Best to date, in my measurements  (lowest THD, most robust at 330V B+)  has been the 6p14p-ev variant  (the higher 14W plate but with 300V rated plate/scr - some say conservatively).

My average-ish nos sound good no question, but measure a little higher thd   ..  and I am not game at > 300V B+ in 'pentode' mode let alone at 'ultra linear' or 'triode' modes.

I'm interested in the diffs between the various players in this area  ..  there's quite a few variants.

If I had some 'lower B+' power supplies and some 'lower primary impedance' output traffos (any more, that is!)  I'd go for the el86.  But I have to 'pitch' for 'what's in stock'  now ....  more or less.

...

And just wanting  to do some compares of the modern and nos 7591a. As far as my own prefs are concerned, I think this one is prolly 'end of the line'  :) 

Maybe excepting the 6aq5  ..  a very nice little tube  :)

Title: Re: REW Update
Post by: alexc on January 09, 2019, 12:52:37 AM
There's been a couple more updates to the REW beta 4    ....   just trying out now.   

Mr Mulcahey and Team are pretty keen  ..  with the releases  :)   

It does remind me of the hurly-burly of the commercial world of 'science instruments' with the fast pace of innovation.

It's great to just be a 'user' :)   rather than one of the people who do the hard yards, software engineering wise.

The day I see two measurement cursors, well then I'll know  it's the front of the thing.

As 'Krusty' would say  'Hey-Hey' 
Title: Re: REW Update
Post by: alexc on January 12, 2019, 02:47:15 AM
Another day, another REW thing going ...

I updated to beta4 - everything mostly the same  : good start!

I'm doing some testing on the 6922 family  .... I have one going as a 'grounded cathode amp'  stage + cathode follower stage - a classic functional block and generally pretty good.

While I'm finding my bias points and what not .. REW  is as always, indispensible.

Nothing flash, just workman-like honing in on the zone.

....

SO - I used the 'stepped sine sweep'   button   from the  main RTA window  :)

Works quite well - it allows the duration of each step in frequency, with a settable interval period  as well as the usual parameters that were available in the 'measurement' functionality within REW previously.

I like it :) :)     The CRO shows the proceedings in detail .. all very nice and steady and stable like.  Pro.

It is a big step forward, integrating 'sweep' analysis and reporting,  from within the 'plain old RTA'  window.

The 'frequency response'  results are painted in real-ish time, complete with the fundamental, the h2 and the h3.
Quite intriguing to watch it progress - very engaging to the user.  Top marks for sure.

Once complete, (and with the RTA window inactive), the 'DR' readout  - I think it is 'Distortion Residual' headline figure   ...  is displayed  ...  and it makes sense (even to me). 

This area of 'residuals' is of great interest I think. I can only imagine where this kind of display and reporting is going to go in the future - clearly it's quite cpu intensive - on my 3yr_old AMD box it's pretty flash.   

'like far out man - this is crazy good!' - would be a reasonable approximation of my initial reaction.

After the 'stepped sine sweep measurement process' is complete, you can just continue on your way, RTA wise    ...  the resultant frequency response trace(s) just float at the top .

TOP of the class!

.......

I can see my newest  'annotated REW snaps' with the new capabilities. Hopefully a day or two.

......

The results of the sweep run 'drop in' to the 'dataset handling environment' for historical analysis and post display processing.

Just like before, as far as I can tell. 

This functionality is one  of the most impressive, imho,  and it puts REW on a trajectory akin to the sort of thing one uses in financial and biotech charting,  without question.
...

The other thing is    "how good the 'signal generator' updates are"    ..  the 'level' data entry is superb  ..  smooth and accurate, supporting the measurement thing rather than fighting it.  It's a pleasure to dial around on.

I could probably go for a 'slim mode display' with the big 'wave display' scaled down a bit ..  it's good for 'standard' users but 'advanced users' might like to tailor the display and so on   --  but these are low level suggestions  :)  All good as is!

Whoever worked on that (signal generator updates)  is (are)  (a) real artist (artists).  :) 

I love the dBu display, and the 'little dBFS readout' too    ...  sheer luxury.

Finally but not leastly, the 'input level window' ..  floating at top right corner ...  the 'peak sample' in  dBFS does indeed equal the 'headroom to 0dBFS'

Fan-***-tastic.  The fact it is there at all is very fine. And that is accurate and always-available  ...  well that's just more champagne in the glass.

....

Just another link in the REW chain.  This is what real innovation feels like for the 'common man'.

10 out of 10    tick

Title: Re: REW Update
Post by: alexc on January 12, 2019, 02:54:10 AM
And on the subject of REW innovations, it does appear to me that there is another kind of mode of display used in the 'RTA window stepped sine sweep' function ..

It's not the same as the 'RTA mode', but is much more like the 'spectra' mode  within REW.

But it's not quite the same as the 'spectra mode' either. 

It is similar in that it has a 'shaded envelope' display for the high freqs. It is different in that the envelope doesn't 'bounce around' but is more 'flat. It reminds me of some of the classic filter responses ..  the chebychevs and the butterworths and so on.

So, it looked to me like a 'spectra mode with flat hf extension'  kind of thing - not sure what I'm seeing yet; could be the device-under-test or could be the new REW functionality.

I'm keen to look further into it - I kind of liked it  ..  this 'spectra mode with flat hf envelope'   reporting  :)

Thanks kindly Mr REW  ... for all the newest capabilities in addition to the foundations previous.

...

Anyway, onwards and upwards  ....  I have to do more tweeking on the 6922 and so on  ... hope to have a few new snaps for you all shortly. 

I still have another 2acres of grassland to pulverize.

....

Title: Re: REW Update
Post by: ruffrecords on January 12, 2019, 04:34:43 AM
Make sure you fit grid stoppers to your 6922s. They can squeal in the MHz region.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on January 12, 2019, 05:19:30 AM
I always do  :)   ...

I wish I could really hone this great example of tube wonder  .. the 6dj8 / 6922  and extended family into modern days  ..  the russkie greats.

Even with all the refinements available, there's still only so many hours to experience it in a 'measurement' sense, let alone 'aurally'.

Still we do as we can.

Thanks Ian - Ruffrecords  ... you've always pulled for the 6922   .... and I can understand why. 

It's my great hope, with REW help, to find some of the other fine performers in the tube world.

...

Here's my initial snap for the 6922  setup as a gca + cf  functional block   ..   driving 4u7 wima into 10K/600 edcor xsm output traffo.

It's pretty good ... the  'low THD test'     gives   0.61%  thd nearly all h2 at the output of the cf.

The input traffo,  which is now a very cheap 10K/10K  contributes    around 0.1% of that   ....

- signal margin over hum is +107dB with 25dB headroom (to 0dBFS) and freq resp is extremely flat 20-20K     :)

I'm using 47K plate load for the gca stage, with a bias of +3.2V  (input signal is 2Vpp) ..   and the cf stage is cap-coupled thru 0.1uF and has  850R+22K  as the cathode load  .... with a 4.7uF wima to the edcor 10K/600 output.

....

The 'hv probe' attenuation or 'return scaling' factor  is approx -37dB 

ie.  47Vpp (unbalanced measured with cro) at the cf output is   ...    scaled down to approx    0.67Vpp   (div 71)    (psuedo balanced)

The 'psuedo balanced' send to REW   - is  interpreted as 'unbalanced' voltage.

As always, one needs to *check their '6dB factors' with respect to 'single ended' vs 'differential' measurements  *   :)

...

One other thing REW I noticed today   ...  when 'hovering' over the 'trace legend', the 'trace' that is hovered over  is  *highlighted* in the main window    ...  just another super nice touch from the REW crew!

The 'nudge' amplitude cursor increment remains at 0.2dB  ....   very good, but not yet fully  'REW-good'   (0.1dB) - the underlyings continue to support 0.1dB basic resolutions 'in spades.'
Title: Re: REW Update
Post by: alexc on January 13, 2019, 08:57:16 PM
So the 6922 is clearly a very good performer in this 'gca+cf' config   ..  especially given the relatively low B+ of 246V.

The cf section is very impressive ...  super low intrinsic distortion  ...  no probs whatever driving the load 

If I push it to say 1% thd, the signal margin over hum rises to > 115 dB  ....  and the 6922 still barely ticking over ...

My impression is that the e83f has more dynamic range but requires a much higher B+ to achieve it  .. and at significantly higher THD.

The 6922 has less THD at much less B+.  The gain of  the 6922 is around 2dB less typically, than the e83f triode mode with the same 47K plate load  ....... 

The downside for the 6922, is that it requires a decently high input signal to really shine  - like 2Vpp  to 3Vpp   or so.

More so than the e83f triode mode which seems to do better with the signal in the 1Vpp to 2Vpp range   .. even with discounting the 2dB  or so difference in gain 
....

However, I'm still refining my comparison  :)    and it all comes down to judgement calls  in a way  ...  both these tubes are very good performers ...  it takes the really small optimizations now,  to get any demonstrable improvs.

Nothing is ever straight-forward ...   so one must always check their apples remain apples, and their oranges remain oranges  ..  at all times.

...

I have to re-check my 'attenuation box'  numbers too ....  it may be that I can 'map' my HV probe voltage range  better  to my interface input range.

So far so good  and I find :

0dBFS = 2.357Vrms -> 6.67Vpp 

and   my 47Vpp signal (measured at the CRO) is mapped down to 0.67Vpp  which is div 71 -> -37dB return scaling.

I still have to check how 'constant' that -37dB scaling factor  (which is position 2 on my rotary atten box) is at either end of the voltage (amplitude)  scale.

It may not be as linear as I would hope.  So  more there to determine. TBD

The other thing is that a return scale factor of -37dB  may be pushing down too far into the interface 'noise floor'.

I'm pretty sure I only have 'about 20-ish dB' down there to 'scale down into' before any 'noise limiting' occurs.

It's best to attenuate only as far as the interface's fundamental noise limit ..   any more is 'noise limiting';  :)

The more I compare the results of the

-   'edcor xsm 10K/600 output balancing transformer with no further scaling'  standard
and
- 'hv probe unbalanced with attenuation scaling factor'   

The more I think I am skewing results a bit  ... my attenuation factor should probably be no more than 26dB   ::)

Basically, by not choosing the right attenuation factor, I'm downgrading the 'margin over hum' perf but not the thd measures so much.

Tomorrow I'll recheck and rejig  - it does take time and effort to really hone in on the zone ..  especially when one's frame of reference get flip-flopped  (for the better).

...

Here's a snap of the REW 'stepped sine sweep' in the 'RTA window'   doing it's thing  ...
Title: Re: REW Update
Post by: alexc on January 13, 2019, 09:12:58 PM
And when I try to 'LoadSim' the operating conditions, I get a reasonable match of the operating conditions, but nowhere close for THD ..  with a 2Vpp input.

loadsim  says nearly 2% h2   ....  Tube Test Rig  says  0.61%  h2   


Title: Re: REW Update
Post by: ruffrecords on January 14, 2019, 05:16:49 AM
Simulators are very poor at estimating distortion and they do seem to err on the high side. LTSpice is just as bad. Better to measure.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on January 14, 2019, 08:29:21 PM
Another day, another calibration run  ....  moved to an attenuator setting of -28.3dB (loopback measurements).

With  plate signals of 10 .. 100Vac my attenuator box 'factor' of -28.3dB is a bit more accurate in REW ...  with respect to the 'signal margin over hum'  or loosely speaking 'signal noise ratio'.

At that attenuation, my 'signal-under-test' noise floor is above the 'noise-floor of the measurement channel', so I'm not 'over-attenuating' and thereby worsening my 'signal under test' dynamic range.

I may need to 'rejig' my atten box to really hone in some more ....  my old -37dB is too much and -28dB is not quite enough  ::)
I suppose 33 is the magic number   ...   I may try a 100K-50ohm traffo too  ..  it's 33 for sure.

....

I reset my RTA display limits to best show this 'tightened up' view  ....   I can't quite get the display as I want ... I like to have the 'freq-response-sweep' trace fully visible across the top and not obscured by the 'thd display window'. So in order to 'clear' the THD window, I need to 'scrunch up' the RTA amplitude limits  a bit.   

I would like to see the 'THD window'  become  'long' sideways and 'short' downways.  It's a question of 'visual to noise ratio'  :)
No bout adout it.

*  Never happy are we :)   *

Also, not at all sure what the 'DR' is telling me .. in the 'peak present' displays.     In the 'silence' I get 'it' more,   and in the 'sweep' too - but the 'plain old RTA mode' THD display window DR field, I don't know what is.

...

I think I get about 2dB more 'accuity' from this ( -28.3dB atten) match of the 'measurement channel' to the 'signal under test'.

ie. signal margin over hum is improved around 2dB

It's a bit like when the optometrist switches the lenses  until he finds the best for your poor eyesight :)

....

The other thing I have to consider is the reduction in THD one gets in a simple test like this ...  when one sets the gca bias  colder   ...  wrt  to the chosen test input signal amplitude.

ie. 2Vpp sine at the grid   ....  bias at  +3.2V improves the reported THD  than bias at +2.8V.

- gain changes a little when I vary the bias (all other things being equal) ...  when bias 'colder' ->  less gain, THD is also reduced

My thing is to bias as I would in the 'real world' for the expected role ...  and go from there.   

ie. 0 .. 1Vpp range input     or 1 .. 2Vpp, 2 .. 3Vpp, 3V .. 5Vpp, 5 .. 10Vpp and so on

.....

With this in mind, I get a baseline thd of 1.0% from the 6922 gca+cf   at B+ 245V with  +3.2V bias with bypass cap .. 2Vpp input and 47Vpp output  ...  [driving my  '1M' atten box as load]

I could chase that back down to 0.61% by biasing for less gain ...  but it's kind of silly ..  one is generally striving for all the  *basic* available gain.

It's a bit 'artificial' or 'tailored for test' to   get too 'finely biased'     ...  not to mention easier  to go into overloaded grid condition when something apart from the test signal is encountered   ....  ie *music* :)

....

So now my two tubes types are converging in terms of thd ....  but the very big gulf on the B+ remains. 

The 6922 is designed for a lower B+ and in THD, shows 'no penalty for it'

whereas E83F-triode-mode needs a proper >300V B+ to get similar THD, but with higher signal-hum margin 'for the trouble'

I confess, I am a 'signal to hum' guy  ...  I like to blow any 'hum-gains' made, on 'tube limiting' repeatedly and wherever possible. 

As long as it's <1% that is.

This is what it takes to get there!

....

So it was worthwhile to spend an hour or so rechecking my 'atten factor' to suit the testing I'm doing and to make sure everything 'lines up' properly. It's the kind of thing one does at each test session   ;) to 'keep it real'.

Generally speaking, I get a maximum of approx  0.3dB uncertainty in the measured amplitudes of  I/O with the M-Audio-REW combo 'round trip'.

That's 0.1dB on the Send, 0.1dB on the Return and a further 0.1dB 'for good measure'  :)

Other items to account for are ....   [apart from 'circuit gain' and 'hv probe box atten+bal factor']

(in order of impact)

-  input debalancing transformer level shifting
-  insertion loss in the input transformer
- uncertainty in CRO measurements 
- loading effects at the audio interface send and return

With that lot in mind, you can really closely measure and compare-to-expectation  the gain structure all the way thru - very important.

....

And finally  ...   the 'takeaway'  :)

one can get a good match between the 'display', the 'gain of circuit under test' and the 'attenuation factor'  such that they mostly cancel each other out, giving you a 'measurement channel' which is nicely 'normalized' to the 'device under test' and with a 'traceable' degree of confidence.

....

Probably could do with a really great 'attenuator' overhaul  ...  not just the pitiful little lorlin with 4 positions in a 'stomp box' that I currently have   ;D

Might be a good time to buy a proper large multideck switch and do the thing properly.

All good! 

.....

Here's a pic of a suitable eb y   rotary switch for use as an attenuator     ...  12usd  ...  11pos, 4 deck  ..  large open frame


Tomorrow I'll really start to grind and snap   8)  but the 'attenuator box' upgrade will have to wait ...  maybe next winter :)


Title: Re: REW Update
Post by: alexc on January 14, 2019, 10:29:49 PM
And on this subject of 'attenuator box with rotary control and hv probe'  thingo ..  for the 'plate-ing' in REW

I wonder could it be done to use a mosfet as a    high but switchable variable input impedance, high voltage probe buffer with some more actives to do the variable attenuation and balanced 600ohm output ?

It would have to have a super low intrinsic distortion (< 0.1% at 1KHz)  and noise (-120dBu)  , however   ...   *and* be linear over a 120dB range of signal   8)

It would be quite nice if it could take a power feed from the 'tube build under test'  ...  further regulated for sure  ...  perhaps with a 'self powering' capability of sorts if really needed.

Fully variable 'attenuation factor' and with a calibrate-able readout of 'fine attenuation factor' please!

Of course, it would require a 'pass thru' to CRO  which can be switched to show 'pre' or 'post' or 'none' (unbalanced) voltages and have a cabled output [to the CRO bnc  input]  with the correct  'range set locating pin' if required.

In addition to that 'cro output' bnc cable, some 'multimeter' connectors might be useful too  ..  for watching on a true rms meter.

I'm very sure HP and Tektronix had this kind of 'supporting test equipment' available.

.....

I have seen things in this area but nothing that grabs me.   I guess it must be possible ...  I could almost do it in tubes  :)   

(say it in 'snow-board'  :)  )

Like the old 'volume indicating amp' from the 50s I have  ...  but with output to REW ]

Mosfets would be a lot sexier for this I think and without all the tube distractions. Could be a project  for one of our younger, more tech-savy (than me)  members.

...  sorry for the bad pic  [of my passive hv test probe with psuedo bal output]
Title: Re: REW Update
Post by: alexc on January 15, 2019, 01:30:53 AM
and one more Tektronix pic ...   good Lord these people  were good!

Title: Re: REW Update
Post by: ruffrecords on January 15, 2019, 11:15:43 AM
and one more Tektronix pic ...   good Lord these people  were good!

No, they were superb!!

Cheers

Ian
Title: Re: REW Update
Post by: alexc on January 15, 2019, 10:05:48 PM
You got that more right :)   

It's hard to fathom the build 'craftsmanship' in these Tektronix tube oscilloscopes - it's just a joy to behold such dedication to quality.

I suppose these Tektronix 511 series   were from the 1960s.  Must have been great to be a tech in 1965 :) 

...

Here's my 'latest and greatest'  REW snap for the 6922 gca+cf functional block ......  I have my new annotations and display style going  ... 

I'm getting closer to 'normalised' display formats ...  here I still have around +7dB or 'net gain'   end to end  ..  so my -7dBu 'send level' returns as 'near 0dB'   ..... which is easy for the eye  :)

I chose -7dBu because that results in a 2Vpp input to  the grid of the functional block  - it's one of my 'scenarios' don't you know.

You can see the basic 'input-output' uncertainty of 0.2dB   ...

I like to say another 0.1dB for 'good measure'  ...  like 0.2dB +/- 0.5dB is the basic 'roundtrip'  uncertainty.

.....

Headline figure is 0.94% thd at 116dB signal-margin-over-hum    ..  best yet! 

As I said, by 'biasing cooler'  say +4.0V changed from +3.1V, I can drive the headline THD to 0.61% at the cost of some 2dB in less gain. 

I'll stay with this 'scenario' as my 'standard' for now ...  I like +3.1V bias in a 6922 :)

I think that's about as good as I get for a 'basic setup'  ....  47K plate +3.1V bias on 1K Rk, 0.1uF cap-coupled ,850R+22K cathode

......

The frequency response is mostly influenced by my choice of input traffo  ..  in this case a 5 dollar sino 'altronics 10K/10K' weighing 100g  ...  small but not stupid tiny .. it's actually quite good - it contributes around 0.1% thd to the headline figure and has something like a 1dB insertion loss.

The Edcor xsm,  which is my usual standard,  trounces it in the low register ... it should do at 436g in weight  and  cost .. about twice as much in '2007 dollars'   (now more of course)     ....  but I'm all out of stock  ..  of this 10K/10K ratio.

I figure once I have my 'normalized'  test setup working correctly and 'traceably' THEN I go to the 'magic transformers'

I like to get my 'ducks in line' before parading the greats  :)

...

NOW ..  back to the E83F-triode-mode ..  which is still as I left it ....  around 1.53%thd for the similar signal-margin-over-hum at B+ supply of 325V  as I recall 

 (pre REW beta 4 world shaking release)

  ...   let's see how it 'shapes up'  with my latest and greatest 'normalised' and 'annotated' REW snaps :)

I predict a  THD 'smack down' in the favour of the 6922   ....  it 'sets the bar' 

  ...  by any account of performance that I have personally measured.


Title: Re: REW Update
Post by: alexc on January 15, 2019, 10:29:57 PM
I always like to end the day with another gratuitous pic posting  ..

Here's some Tektronix 535 series  ...    tube cro  ...  front panels   ....  oh man,  what class.
Title: Re: REW Update
Post by: alexc on January 15, 2019, 11:39:24 PM
And, being prone to editorialising my own narrations  :)   at the relaxing evening after the day's work ...

...

I nominate REW for the award of 'most wonderful quant tech for audio to date'   :)

It's getting a little    ..'scary' accurate, in my measurement world!   

Soon I have to go back to 'design' rather than just 'roughing things out'  on the bench  - that would be a first for me.

..  to get any more 'actual' improvements    [in my my own diy audio builds]

..

I may have to make up an award 'graphic' to commemorate what REW means to me, later of 4 decades chasing audio at the 'poorman' end of town.

<pic of rew 'award' Jan 2019 - 'services to audio measurement kind'>

 cue 'Dark End of the Street' as performed by Mr Gram Parsons and his band

followed by something like 'Afternoon Delight' ,  I think   8)   
Title: Re: REW Update
Post by: alexc on January 17, 2019, 07:43:21 PM
Just a little more info on tube testing with REW  .....  and 'HV Probe' stuff.

As I described, I have my    'HV Probe' with an attenuation of -26.5dB  - a value chosen to offset the overall gain  of the 'circuit under test'     -  thusly to give a reasonably 'normalised REW snapshot' -    with the return around the 0dBu (nominal)  - easy on the eyes.

I was testing the output of a 'gca + cf' functional block with no real 'loading effects' evident at any attenuation settings.

When I switched to a 'gca' functional block, with the higher output Z - the loading effect of attenuator set to 'minimum attenuation' becomes very noticeable. [the higher attenuation settings are, as usual, quite negligible, for loading]

SO - it is useful to have a CF at the front of the 'HV Probe'  ...  permanently

The super high input impedance of the CF buffers even the highest output Z of the 'circuit under test'

and the intrinsically low and 'known' THD of the CF doesn't impact typical tube measurements by much  ...  less than an impedance matching transformer, for example.

....

Hence, I will do a 'tube active HV Probe' unit  ..  going forward .. with an 11 position attenuator to really dial in the 'net gain/loss' factor as well as ensuring that loading effects stay well and truly in-the-box. 

It's worthwhile to do because I already have the remote PSU completed  and in use for my 'Tube Test Rig'

....

I'm thinking to try an 'Aikido' type CF circuit ...  perhaps now that I've got my basic tube performance 'in the zone' I will be able to measure a difference over say a White CF circuit, which would be my usual choice.

OF course it means another 'investigation' to do  ...  which tube is best for a CF ? 

Experience tells me that (again) the 6922 may be best   ... at least for input voltage swings that don't get too large.

For measurements with several hundred volts swing ... it will need something with a really high B+  ...  I think about 375V is my limit with this rig  ...  I would say a JJ 6V6 or even two :) in triode mode could be a good choice ...  for a 'measurement CF'.

At least, after the CF stage, the 'attenuation' is fairly easy to make ..   a combination of 'fixed' and 'variable' resistive attens in series, I would think  ... and also some nfb could do the job I hope  .....

.....

As soon as I finish this '6922' and 'E83F' comparison, I'm going to get right on it.

....

The other thing I need to figure out, is how to 'interpret' the changes in THD when switching from a 'higher attenuation' setting to a 'lower attenuation' setting on my passive 'HV Test Probe'.

ie. I can track the gain changes etc perfectly, but I do see a difference in THD which I can't account for.

eg. the -26.5 dB atten shows higher THD than the -37dB atten

It's not the analyser  ...  as far as I can tell

ie. normally if a signal is a bit too low in amplitude, then THD is reported some little amount higher, until a certain level, then no further.

It's not the 'circuit under test' it's a 'poor analyzer signal-noise ratio' kind of thing.

BUT this is something else  -  I think it's just that the 'lighter loading' of the attenuator when at 'high atten settings' means lower THD (despite the overall increase in level).

When using a 'lower attenuation', the loading is 'higher' and so the THD is also higher.

Once I have some more data with the 'CF buffered' HV Test Probe, I should figure it out. 

Early indications are that once 'loading effects' are reduced to a minimum, the THD should be reasonably steady at differing  atten settings.

Hopefully, the 'fixed high input Z' of the CF will not also increase my 'noise floor' too much!
....

Measurement is a deep, deep well ..  you can drop hundreds of hours in it before hearing an echo   :)
Title: Re: REW Update
Post by: ruffrecords on January 18, 2019, 03:41:50 AM
Regarding the difference you see in THD with different probe settings, just about all tube circuits produce more distortion with a lower value load. Exactly how this varies with load depends on the particular design but it is reasonable to assume that the probe lowers the value of the load so the distortion increases so what you measure is a worst case.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on January 18, 2019, 05:01:53 AM
Thanks Ian - that does agree with what I am measuring.

....

I'm looking forward to exploring the CF circuit as an input stage to my 'tube active measurement box'  MK2  :)

I'm very interested in what perf one can get from a 'power pentode' wired for triode mode ..   as a 'single stage' CF  and also, just for the learning ...  what a pair can do in a push-pull CF config   .... firstly a White CF and if I get any joy ..  an Aikido or Broskie type.

It will have to wait for my Mk2 remote PSU to get the real voltages going  ...  +475V and such [ as high a B+ as I am game to use]

I *do* like to measure plates in power stages   :)

....

So far, the 6922 as single CF is working out really well    ...  for signals to the grid of  up to 60Vpp or so  (B+ 235V)

I have almost done the E83F-triode-mode  gca stage measurements ...  they are similar to the 6922 gca stage measurements

 ie., for same input voltage, bias and plate load,   each has very similar gain and signal-hum-margin  with the same  CF as load.

   ....  just need to nail down a little excess 100Hz I'm newly seeing  ..  need to rewire a socket, I think  .

...

 And also,  just 'driving down' B+ for each,   to find a reasonable compromise with the increase in THD (as B+ decreases).

6922 is at  +235V supply and the E83F-triode-mode  is at +315V supply and they look pretty similar
Title: Re: REW Update
Post by: abbey road d enfer on January 18, 2019, 05:10:53 AM
I *do* like to measure plates in power stages   :)
Then you need a CF that is capable of swinging 1000V+, not a minor endeavour.
Title: Re: REW Update
Post by: abbey road d enfer on January 18, 2019, 05:12:30 AM
Then you need a CF that is capable of swinging at least -500 to +500V, not a minor endeavour.
Title: Re: REW Update
Post by: alexc on January 18, 2019, 05:19:46 AM
I like the way you think!
Title: Re: REW Update
Post by: alexc on January 18, 2019, 05:26:12 AM
Of course, I will retain my 'passive hv probe'  scheme .. particulary for the the really big stuff  ..  450V plate swings and such.

There, the 'attenuation factor' is much larger, meaning my 'loading effects' are reasonably minimal  ...   whilst still not attenuating below my 'measurement channel' hum floor.

So

->  an 'active CF HV probe' for as far as I can 'swallow input swing' for a B+  475V   - maybe 125Vpp  or so  ?
-> a 'passive HV probe'  for the signal beyond that   125Vpp .. 450Vpp

I think it's a nice challenge  :)
Title: Re: REW Update
Post by: alexc on January 18, 2019, 05:54:47 AM
And I don't have much idea of what some power mosfets  can do in this kind of application,

...  but I have some bunch of affordable IRF B20N50K  devices, which I'm using in HV regs    ...  I'm having some explore time with  ..  in very simple circuits  ...  I like the 'fet to tube' conversion kind of thing in these basic functional blocks.

Title: Re: REW Update
Post by: alexc on January 20, 2019, 11:38:21 PM
..  and here's the 'normalized'  E83F  scenario for 1% THD  ....  using the 6922 CF stage before the 'HV Probe' attenuator

At +315V plate supply, 47K plate load resistor    ...   with 2Vpp input giving 47.3Vpp output of gca  (+27.5dB)

This can be a direct comparison now to the '6922 gca'  which is my benchmark for this kind of config

...

Comparing the E83F and 6922 in these 'normalized' views,

..  the 6922 is a smidgeon better   ....    a  fraction of a dB more gain  ...  a tiny increment less THD  with same 'hum floor' and 'freq resp'  under these same loading conditions.

The E83F-triode-mode   - is more or less identical to the 6922 except for it's much lower supply voltage  ...  +245V vs  +315V for the pentode.

Each has a typical 'signal margin over hum' of +116dB at 1% THD (1KHz sine)  ....  rising to +126dB  at 3% THD

....

Each of these tubes can do a very nice job  :)    Not bad really ...  for the E83F  ...  to be close-run second to the 6922    .... so far   ;D

Beyond this very simple comparison, each goes on to diverse applications  ....

- the 6922 with it's 2x triodes in one envelope for low cost  ..  with 365mA heater at 6.3V ..  finds wide usage in 'front end' s
- the E83F for more 'output' oriented duties for 'more cost'    ...with 300mA heater at 6.3V  ...  'single ended driver' s

And so it goes!  Until I wire up my 'av7 style'  socket ..  and can bring that lot into the fray, that is.


Title: Re: REW Update
Post by: alexc on January 20, 2019, 11:43:45 PM
Next task is to get a 'power pentode' going as a cathode follower  ...  to get a feel for the THD one can expect at various input voltage swings - as some pre-work for my 'cathode follower input buffer' option for my Mk2 'HV Test Probe' .

....

And while I'm getting that going, I'm going to have a look at the 'spread' of performance with some more 6922, then with some of the 'extended family'  ... including some nos 'greats' and some russian equivalents ...

And of course, I'll do some more 'historical' runs and update my data on my *fav standout performer*s   in this area  ...

- the Orange86 and the New York Dave One Bottle pres.

Of course, I can only speculate what my other 'great',  the   Gyraf G9    would return in this 'test environment'   

My G9 is pretty good as built ..  but I can't help but wonder just how good it could get with an optimal psu

:)
Title: Re: REW Update
Post by: ruffrecords on January 21, 2019, 09:02:41 AM
There are two main current production sources of the 6922. One is the 6922EH by Electroharmonix and the other is the JJE88CC Back when I first started using the 6922 I tested a few of each. Generally they were both OK but the JJ types had some unusual harmonic harmonic structure. The EH ones had mostly H2 with the other harmonics steadily decreasing. All the JJ ones had quite a loss less H2, more H3 than the EH ones and thereafter steadily declining harmonics. I also had a couple of noisy JJ ones so in the end I 'standardised' on the EH ones.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on January 22, 2019, 12:46:24 AM
That's interesting Ian ...  I only have modern in 'eh6922'  ...  I've always felt they were better than I expected.

I do have more of the '6922' family than I need, but if I was going to try another modern one, it would be the JJ

But I don't think I could bare a 'more h3' tube anymore  ...  I  know, h3 is just as important in it's way .. what with the 'bright' and 'cut thru' qualities.

It's just that I'm a relatively simple person ..  h2 dominating is not so easy to come across 'in the wild'  and I just revel in it.

I should say, that it can get too much at times ... like a 'resonator' gone a bit too far  (long cardboard tube + kids)  :)

But  ...  yep  ..  I am interested to see the 'spread' of results   for the '6922' family that I have 'in stock'.

...

I find it amazing that once I'd given my best 'knowledge' plays *and* all the 'REW magic'  ... together  ..  giving me my 'best yet' results ...  that they wound up  neatly 'normalized' for the notional '1% thd +n (headline)' figure *and* centred about '0dBu' 

...  before I even knew what is 'really'  ...  measurement detail wise ..

But yes ..  it all pops out nicely ready for casual view-ment.

As the 'Small Faces' said (and oft afterwards) "Its All Too Beautiful"
Title: Re: REW Update
Post by: alexc on January 22, 2019, 12:57:04 AM
And with that, I'll be signing off for a while ...  some 'fire warnings' ..  abroad in the la nd  ...

Hopefully will be 'nothing' over  the next couple of days ..  but elsewise I'm glad to 'have a plan'.

....

The ire-net was mostly gone for a day or so ..  I think it will shutoff again  soon . ...   I have  4g connects to the local base-station ..  but the smoke is pretty thick now.

One can prolly expect the power to go off quite soon too. Water usually follows after that, if things get fully dire.

When it goes 'orange-brown all around' ...  it's time to head for the coastline  ... fortunately I can cycle there pretty easy.

Way down here in Southern Tas, it's reasonably sane weather -  compared to some mainland Aust regions  - and it's still quite early in the 'pre- fire season'.

As I once said before, it 'doesn't take much'  .....  etc.

bfn
Title: Re: REW Update
Post by: alexc on January 23, 2019, 02:06:36 AM
Luck for me, the fires turned away with a wind change  ....  they reached about 10km or so away from me.

Today is super nice again ... regular 25C temperatures, the UV 'burn' is way down, gentle sea breezes and all the smoke from yesterday .. gone! 

It went from 'eve of destruction' to 'pleasant valley sunday'  overnight.

Still ..  the fires are all going and this weekend is predicted to be a shocker ...  hopefully my area will just bypass the drama   .. as it has since the mid-60s   ..  which was the last time my township was severe with fire.

So far, so good!

....

I put together today a 6V6-triode-mode  cathode follower   ...  to test what range of input signal I can get with low thd  ...  +325V supply, and the cathode is expected to be around +180V or so, for 27mA of current  for around 8.8W of plate dissipation.

It's  self biased at around +27V and  (1K+5K3) resistors (high wattage!)  in the cathode circuit, bypassed with 100uF electro. 

Hopefully, I can get something like 200Vpp input capability at low THD ...  I'll then add some negative feedback ..  to give some attenuation as well as reduction in distortion.

Hopefully I can get some numbers tomorrow.
Title: Re: REW Update
Post by: ruffrecords on January 23, 2019, 09:03:31 AM
The thing about a cathode follower is the cathode follows the grid so the signal level can be very large without suffering grid current. So you don't need to bias  to a high current as you would with a grounded cathode stage.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on January 23, 2019, 11:13:25 PM
So far, I have the 6v6-triode cathode follower going, but not too well. 

I always get my operating point wrong  for CFs  8)   ..   forgetting to subtract the cathode V from the plate V on the sheets.

I measure B+325V, grid-to-cathode voltage of +17V (bias) with cathode at +112V   ... my 1K+6K4 cathode string has +95V across them.

Which does indeed 'measure up' on the data sheet  ...

....

But, I wanted the cathode to be at around +160V  or half the supply   ..   and at quite a few more mA  ...  25mA instead of the measured 17mA or so  ..  which is wrong by about '100 supply volts'   :P

Still have some adjustments to make  :) 

I can increase B+ to 350V, and decrease the 'self bias resistor' part of the cathode string ..   to coax more current ..   and increase a bit the cathode load resistor ...  for  higher V   ...   and as well as give it a 'defined load'   ..  and I may need a 'stiffer grid circuit resistance'   .. using 560K right now ..  prolly may need to go up to 1M ..  perhaps, that is.

That may all give me some +135V or so at the cathode ..  I think that should give 120Vpp or so capability.

..

I am getting quite a lot of loss of gain right now, which I should be able to fix ..  but it didn't seem to be a 'loading' issue. Instead of around gain of x0.93  it's more like x0.77, which is excessive.

Also, the hum floor is a bit higher than in the 6922 cf case ...  -111dBu vs -116dBu   ..  it's a 100Hz spike of 6dB ... can't seem to shake. Usually that is 'supply decoupling' issue ...

 ie. add a 'dropper resistor' into a stage's B+ line, with an electro cap to ground (47uF 450V)

and it usually goes away ...  but not this time.  We shall see, as I go forward.

...

Right now, THD is quite good ...  I am feeding the 6v6-triode cf from the e83f gca stage of previous  ...  basically 46Vpp at 1%.

That returns as around 0.76% THD at the output of the 6v6-triode cf   ..  when I increase the input signal to 'compensate for the lossy-ness', that goes to 1.0%  and with +110dB of signal-margin-over-hum.

Which is OK but not flash  ...  in line with my very lousy operating conditions!   :D

....

The other thing is that a CF made with a power pentode (in triode mode) should have the advantage (over say a 6922 cf) for 'higher input swing' capability, hopefully at low noise.

It does 'sort of'  ,  but to test properly,  I need now to rig up some more 'clean gain'  for it  ..  in order to verify it's low thd and large swing capability, as a low Z output.

Something like 100Vpp to 200Vpp at as clean as I can make.  Usually I use a step up transformer, but I should have some tube section standing by ..  in this  'Tube Test Rig'.

If I can get that missing '6dB' of signal-margin-over hum at low-THD  ..   with a stronger input signal, then all is well   ...  as a starting point.

....

AND, in parallel to the above, I'm doing the same thing again,   right next to the octal ..    but in a noval 600mA 6.3 heater  'single triode 8.5W max plate' 6s4a 

..  which is a fav of mine

Similar to the 6v6-triode cf  now and probably  better. It's early days ..  just 1/2 hr on the clock for the 6V6gt  !

The other thing I'll do, is try a 6L6gt in that octal position  too   ...  just for some additional data points  :)
Title: Re: REW Update
Post by: ruffrecords on January 24, 2019, 04:59:33 AM
The thing about a cathode follower is the cathode follows the grid so the signal level can be very large without suffering grid current. So you don't need to bias  to a high current as you would with a grounded cathode stage.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on January 24, 2019, 05:33:16 AM
I do follow you Ian  ...  at the 'first level' of cf understanding, as it were   - so a moderate current is ok .. I don't really need to overdo it ( current wise)  to still have a decent input signal handling  ..  at a reasonable thd into a reasonable load ?

Based on previous stuff, I think it's fair to say I've had better result (so far) with say a 6SN7 and/or 6SL7  in this regard ...

But it's all experience - so I'll do some more thinking :)
Title: Re: REW Update
Post by: trobbins on March 29, 2019, 05:57:26 AM
Oooooh drooool, beta 7 now with more scope!!!
Title: Re: REW Update
Post by: alexc on March 30, 2019, 02:13:17 AM
yowza !
Title: Re: REW Update
Post by: ruffrecords on March 30, 2019, 04:09:22 AM
I am constantly unpressed by the guy who develops this, especially as it is supported only by donations. I urge all users to send him a donation.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on April 02, 2019, 11:10:21 PM
Completely agree.  I'm happy to say I have, and will be doing so again in future  :)

I'm just having a look at the latest update now ...  have been nearly completely amazed by the improvements in the last couple of releases.

Useful scope stuff is very difficult to do on a personal computer, generally speaking, so I'm really interested to say the least.

REW's stable high sampling rate and asio capabilities may well make 'scope applications a reality ...  here's hoping!
Title: Re: REW Update
Post by: alexc on April 03, 2019, 12:21:21 AM
Five minutes later  [ with REW Version 5.20 beta 7 ]   ..

The 'Scope' function is very nice ...  I'm just doing some testing in my lounge for now, monitoring my guitar channels and such, but I have to say, the screen updating of the 'richly varying' analog signal is pretty satisfying! The 'Persistence' setting is very, very nice.

I like the 'Ch1-Ch2' capability, with a bunch of 'math function' to boot ..  very interesting indeed.

So that's my first 5 minutes  ..  awesome on the 'Scope' new functionality.

Double plus good with a fair chance of further upside!
Title: Re: REW Update
Post by: alexc on April 03, 2019, 02:38:10 AM
Triggering capabilities are quite impressive - with a musical transient (like a plucked guitar string) it is superb ..   the REW 'Scope functionality captures the transient amplitude envelope brilliantly  ...   and seems to use intelligent display choices to give a nice 'stationary' snapshot  ..  combined with pretty fast 'trigs/updates/refreshes/historicals' on tap, it makes for a very usable scope indeed.

I can't say I've seen such a 'great handling' analog waveform display on a pc before,  that so much does 'what I wan't to see'    (and not think about)

Sort of combines 'real time' updating, triggering and hold functions together with 'history' in a lovely way.

I could use a  'REW Gate with Hysteresis'  audio plug in right now  ;D

....

Looking forward to checking out my 'limiter'   builds'   transient performance with this  ..   on the 192KHz sampling rate.
May finally 'see' some real action for my '660 type fastest attack setting   :)

I can surely see a lot of potential for this tech in top shelf daw plugins, no doubt! 

...

I love the fine and responsive control for the vertical amplitude scales ... very snappy and updates the displays just like you expect.

I'm yet to check the 'Scope  against my bench  CRO, meters and such, but given REW's historical penchant for superb accuracy, I expect the 'mV/div' displays will be accurate to a very high level of confidence.

Ditto for the control on the horizontal time scale ...  time 'zoom' is super responsive.

...

Not to mention, is the nice overall  'sizing' that is available for the main  'Scope window  ....    again working just as you expect, refreshing the trace(s) accordingly, as you really open up the window  ... on the  big screen  :)

Love the 'draggable' vertical and horizontal  display     'position offset'     thingies too  ...  seriously cool.

And the 'mouse scroll wheel' on the horizontal time display is a 'pro' touch.

As is the 'dragging' of the whole display on the vertical amplitude scale  ...  I mean, wow.

...

Last but not least, some 'cursors'    ...   I can see some for the horizontal timebase, complete with read-out of  measurements of different types  (period, frequency)   ...  super great. 

However, not seeing any measurement cursors  for the vertical scale  or  readout of such, but can't expect the moon in just one release update now, can we ?

 [ that would be the piece-de-resistance both in this new 'Scope functionality
    ...   and how great it could be in the 'RTA' section too ]

UPDATED : found it!  The vertical cursor function is there and it's brilliant  8) 8) 8)

...

The  'Snapshot' capability looks to be good ...  for a first glance  ..  some editability ..  although for serious annotation, I like post-processing the snap with a really good 'snap' app  .. 

I like 'Snagit' on my win pc, with 'after edits' of the filename to indicate the baseline conditions and what nots  ..  for posterity   .. 'the ages' :)   ..  kind of like 'poorman cvs'   :)

....

One other thing, I need to check, but my impression is that there is also an improvement in the 'RTA' application ...  I fancy that the occasional 'buffer glitch' I would always see is no longer evident.

Have to check that out some more,  over a couple of different installs, however ...  I can be optimistic and say I'm not getting it here at all.     I'm using a 3yr old  pc :  amd cpu, fx 8 core 16 gb ram, ssd system drive with win7-64

....

So far, Mr Mulcahy and REW Team don't disappoint - what a cracking update, is this 'Scope' functionality  8) 8)

Sheer brilliance   :o   
Title: Re: REW Update
Post by: ruffrecords on April 03, 2019, 02:53:34 AM
Sounds good. Time to update I think.

Cheers

Ian
Title: Re: REW Update
Post by: alexc on April 03, 2019, 08:37:47 PM
Having a look now at REW 'Scope functionality with some steady tones  ..  sine, sq etc from the 'Generator (with analog loopback) ..

All look really good - no sign of 'jaggies' or other obvious display artifacts at all.

96kHz 24bit - all working solidly with no issues for me.  :)    [decade++ old  motu 2408Mk3 asio drivers on amd pc]

Here's a pic of the 'Scope with a loopback signal from the 'Generator, analog bal I/O (asio drivers) square wave of 1KHz with the 96K/24bit operation ...

Clearly shows the transient response of the square wave with the overshoots etc.  Not bad at all really. I'll be looking at my bench generator with this 'Scope shortly too.

Well, it was more 'square wave' looking befoor I zoomed and cursor'd for an exact 500us (1kHz)  view. Very satisfying.

...

Also, the 'Scope has the ability to freely move a captured display on the horizontal time axis, and anywhere within the entire 'trace buffer'  subwindow  ....  very nice indeed  ...  along with the cursor measurements ... makes it easy to focus on/manipulate and measure time periods of interest  ...  for any desired interval in the trace history  (which is around 743ms for this fs 44.1KHz)

...

Speaking of the  trace buffer length, I wonder if it is settable ?

Some more length would be seriously great for capturing the horrible 'mains supply tics', around my noise floor,  that have beplagued me for the last decade ..  they have a periodicity of near 2s and are very short duration ..  on my 'rural' elec supply  :P

Perhaps that 'memory setting' that REW asks for at install time, affects the trace buffer length. I'll check that tomorrow.

...

With the vertical and horizontal cursors plus measurement readouts, this REW 'Scope can give my analog CRO a serious run for most things   [ signals within the analog limitations of the audio interface, of course etc ]

REW 'Scope seriously exceeds my CRO in vertical sensitivity - it has no probs at all with 1uV / division 

....  whereas my CRO goes down to 2mV / div or 40uV / sub-div   (with 5 subdivs to the div on the CRO graticule)

SO, looking in great detail at noise signals becomes quite easy ..  you can clearly see  noise floor modulation, for example, and use the timebase cursor and display shifting to accurately measure the lf modulation period and hf osc freq.

That's going to be very interesting on some of my builds for sure!

...

Also, when displaying both CH1 and CH2, you can shift them vertically seperately, which is great to seperate them out for easy viewing, or you can shift them on top of each other   ...  just like a real CRO. 

They remain locked together in time with any timebase operations affecting them both.
Title: Re: REW Update
Post by: alexc on April 04, 2019, 12:22:53 AM
Just found the 'vertical' measurement cursors ....   brilliant!  :-*

Here's a snap of noise floor at 10uV/div with both CH1, CH2 displayed, shifted vertically for clarity and with both measurement cursors for time/freq and voltage.

There are 3 seperate vertical cursors available, one for each Ch1, 2 and a third for the CH1 math CH2 trace. It doesn't appear to maintain the 'last set cursor' values for each, however ...  it applies the 'current cursor' settings in turn to the selected traces  ...  no biggy.

And that's just the 'manual' cursor mode ...  the 'tracking' cursor mode auto sets the top cursor of the vertical measurement band as you move the time cursor along ...  to the waveform amplitude at the time cursor.

If you drag the whole waveform around (as opposed to the time cursor) it widens or narrows the vertical measurement band
 ie. both the top and bottom voltage cursors are adjusted.

Just amazing imho.


Title: Re: REW Update
Post by: alexc on April 04, 2019, 01:42:18 AM
All the waveform display machinations are way snappy with the updates - the overall experience is very responsive indeed - and that is no mean feat in any language, any where, any time   8)

...

I've been taking a break from the diy journey for the last couple of months ...  all that hot season rural fire hazard biz and some concurrent family things have had me ducking for a few months of downtime ...  worst summer ever  >:(

But I have to say, once again, this latest  'new REW tech'  has me keen to 'get on up' and get moving ..  one more time! ;D

'Over here, over there!'   

Tomorrow - back to the bench.

...

And another donation is well in order,  for this is really classy work from the team
Title: Re: REW Update
Post by: alexc on April 04, 2019, 03:45:16 AM
And how about the  'RTA function window   'list of vertical units'  available  ...  does  V/sqrt(Hz)  in freq domain !

It's just 'all too beautiful'  :)
Title: Re: REW Update
Post by: trobbins on April 04, 2019, 07:14:28 PM
There is a nice WIP for doing distortion level sweeps  :) :)
https://www.avnirvana.com/threads/feature-request-distortion-vs-power.1848/ (https://www.avnirvana.com/threads/feature-request-distortion-vs-power.1848/)
Title: Re: REW Update
Post by: alexc on April 04, 2019, 10:28:57 PM
I could use that! 

... addendum  :  donated another increment to Mr Mulcahy and REW Team .... dang it feels satisfying  8)
Title: Re: REW Update
Post by: trobbins on May 12, 2019, 01:44:05 AM
Just had a chance to check the scope function, and sure enough its a delight to have a scope window and spectrum window up side by side on my wide bench monitor - something I will do from now on when amp bench testing, especially to confirm the onset of peak clipping on any side of the waveform.
Title: Re: REW Update
Post by: trobbins on May 16, 2019, 10:54:37 PM
Just noticed the dither option on the sine wave generator  - hadn't really appreciated its effect on noise floor before.

https://www.roomeqwizard.com/help/help_en-GB/html/siggen.html#sinewave (https://www.roomeqwizard.com/help/help_en-GB/html/siggen.html#sinewave)
Title: Re: REW Update
Post by: alexc on May 16, 2019, 11:01:59 PM
re the dither function and noise floor ....  ditto here. I have to check that out some more.

Have the latest r20 download now and having a looksy ...
Title: Re: REW Update
Post by: Tubetec on May 24, 2019, 01:24:18 PM
Im only just getting my teeth into it  ,
Im using the centrance axe port pro  , with a most favorable position of the controls Im getting in the region of 0.002% thd on loop back , opperating at 96khz/24bit asio driver  ,the headphone output providing the signal source might be the weak link in this case I might try a discrete digital out with external D/A as my signal source tomorrow .

I couldnt get 24 bit opperation at all under windows 7 ,but this of course relates to my sound card and drivers not REW itself,on XP I was able to get proper asio Centrance driver  96khz 24bit ,and THD figures sharply decreased on loop back .

How the USB sound module is powered makes a difference in the performance in relation to noise ,it wouldnt power on usb bus power from the laptop , then I rigged a common usb mains 5 volt 500ma switcher supply ,then 4xNimh cells ,making physical contact with the metalwork of the interface lowered induced noise around 30db ,and battery supply showing less spikes and harmonics 

The Cal procedure worked very nicely ,and the stepped response measurements with H2 and H3 graphed off below  is great , but what seemed to be missing was the abillity to provide outside known cal references  . Visual Analyser for me still holds its own for its multimeter style gauges freely scaleable in v,mv,db etc ,and the easy way it had to introduce a known reference from an external source. Seems like VA is a few years without an update at this stage and my particular audio drivers dont seem to work well   ,REW's RTA is jaw droppingly awesome , Dist. panel  is a revelation in sound .

I think really it all comes down to analog front/back end as to what you can achieve in terms of 0.00...% and below thd ,

Passive analog filtering of the generator output might allow an order of magnitude better test signal .

Ive fantasized already about a usb based circuit probe for REW , axeport pro sorta does that , its about -3db down at either end of 20hz-20khz with a meter of co-ax  , noise is about -100db , the thing is down at this level of magnitude residual power supply gash impacts the %'s thd , I might try 6 cell battery pack regulated to (780)5 volts and ground next to see if the noise can be reduced further .
Title: Re: REW Update
Post by: trobbins on May 24, 2019, 05:21:59 PM
Yes I use 6V and 12V small VRLA monoblocs as I have them easily available.  I sit a battery in an aluminium baking tray, along with the non PC parts as a way of reducing background noise ingress.  I can battery power the USB soundcard, as well as a USB isolator.
Title: Re: REW Update
Post by: Brian Roth on June 01, 2019, 04:29:17 AM
I tried to watch this thread, but lost track of everything...lol!  Does REW run on older (XP) machines...and if so which versions?

A friend "gifted" me a WIN XP laptop ...seems to now have a minimal installation..which was GREAT so my ancient HP scanner is once again usable and I can again use the TubeCAD design app...both apps died going into WIN 7 and later.

Ian...you mentioned a Focusrite (???) interface that you use which connects via USB.

Lazy boi here....trying to not dig through many postings!

EDIT:  The XP machine will NOT EVER be connected into the Internet.  Anything in/out will be done with USB SneakerNet.

Bri
Title: Re: REW Update
Post by: ruffrecords on June 01, 2019, 05:06:14 AM

Ian...you mentioned a Focusrite (???) interface that you use which connects via USB.

Bri

Yes, I use a 2i2.

Cheers

ian
Title: Re: REW Update
Post by: Brian Roth on June 01, 2019, 05:32:26 AM
Thanks!

What would be the Nyquest frequency?

Bri
Title: Re: REW Update
Post by: Tubetec on June 02, 2019, 10:47:57 AM
Works ok for me on Xp ,
M audio transit with external conversion ,
Tried Centrance axeport ,but cant prevent a portion of input signal appearing on the HP outputs , there is a slider in software to reduce how much direct signal reaches the outputs ,but that seems to have no effect . Tried Asio4all using the inputs from the axeport and the outs from the transit , didnt work right but might be the settings ,more testing required . Distortion of about 0.002% was as good as I have been able to get so far .
Title: Re: REW Update
Post by: alexc on June 29, 2019, 02:46:07 AM
I've been using REW to test some win server installs   :)   

It's so easy to install/un-install, as well as being   very stable and well-exercising of the available hardware   ..  tells mountains about the platform 'horse power'.

Looking forward to test with a modern interface ...  I'm leaning towards a Presonus box right now.

While testing Win platforms for stability and throughput, I've gotten to like the 'Presonus - Studio One DAW'  application.

I'm using the free version from Presonus right now, which is nothing on the Studio One 4 Pro   flagship.
 
Very impressed indeed with the 'Presonus  Studio One'    sound quality and  especially,  the speed and the lack of bloatware   :)   

I'm sure I hear additional details on myself playing on 'takes'  from years ago

On my ancient Motu interface  (early 2000s pci-e card with asio)   and Win Server 2016 on   'yesterdays fast AMD hardware'

..the sound is      ..   brilliant  :)

Next stop  is an upgrade to some  AMD 'Ryzen 2700X'  action   :)   

SSD storage all round with   the  Presonus  ' usb3 192' interface and   Studio One 4'  DAW   combo.

That should do me for the next 20yrs   8)

Title: Re: REW Update
Post by: alexc on June 30, 2019, 09:14:16 PM
I also like (on paper) very much,  the Presonus Quantum interface, with the thunderbolt 2 ..  however, in the Win world, that's not so common.

thunderbolt 3 - sure thing - my fav Win mobo makers do proper 'tb3 add in boards' for the right price

So, my focus has sh*tfted upwards in price and once again Motu - I've been a user for decades  :)

Specifically, the Motu 828ES   series with Thunderbolt 3 / usb 2.0     ....    8)   

Very nice spec, a lot of improvements on this form factor which motu has occupied for ages.

Of interest is the 'ES'  designation, that 'ES Sabre' device family ... 

Reportedly to be handling some very impressive perf  ...  and hence as a 'REW Measurement System' , of great interest.

Prices are pretty good too ...   :)

---

For now,  I can get by while I look at platform related things ...  I have a new SSD in the mail, which I am setting up for a couple of different Win configs ...  some new data points   re    perf,  to look at.

Suffice to say, the baseline has shifted big time to the upside over the last 10 years   :)

Hopefully I can get the hardware and os   sorted out   while I decide the main event  ....  'daw application software' .
No to mention, time to 'fund the funds' ...  some selling to do post haste.

I've been''cubase' for ages ( at a relatively  primitive level )    but am really liking 'studio one'   for the slimline experience  ;D 

First impressions of Studio One (free)  are very favourable ..  fab sound, sensible interface, not too much 'overkill' and very snappy in use.  The basic efx plugs were really good .. even the super simple default ones.

My daw automation  'surface' is similarly ancient  -  being a nicely built german 'sac' unit - it's been a champ but very old now. 

Time to ditch it all, and go for a new platform, inteface, daw and surface.

I like the 'single fader' Presonus surface control  box - it's everywhere I want to be now!

Indeed the Presonus coverage of many 'bases'  in the PC world is impressive.

As far as proper digital mix console, I'm still a    Yamaha 03D guy ...  I think I bought it new in  '97 and it still goes strong.

If I was   (and I'm not!)   doing a 'do-over' again (for a second time),   

I would be looking more closely at the Presonus console series - they are easy to find even way down here (geographically speaking).
Title: Re: REW Update
Post by: alexc on July 24, 2019, 03:37:47 AM
So, onwards and upwards, as they say!

Now looking at some 'VMWare' which is a real cracker!   Just seeing  how far 'virtualisation'  has progressed, over the last say 10years ..  is an eye opener.

So of course, now I'm running an instance of win server 2016 with some vmware  managed environments   ...    and its super impressive.

The progressive imaging (snapshot system backup)  capabilities are good enough to think about in the same way as one might use some of the popular system archiving tools ..  like Acronis  products for example, which again, are the business.

OK, I need to get that next increment of raw horsepower with  some current model spending  but  its compelling enough for me to get going in the 'software development environment'  sense   and just possibly in some audio work to   ..  REW and DAW virtualised, forever together in the matrix tonight.

I like to have several 'virtual machines' available, as well as several physical machines ..  to get thru the daily tasks of life 'out back'  on the farm.

So far the VMWare is doing very well :)

....

Win Server 2016 does have it's own virtualisation technology 'in-the-box'  and I'm just starting to have a try of it.

It looks to be a similar thing but I'm sure there is a lot of depth there.  I just remember VMWare back from 'the day'.
Title: Re: REW Update
Post by: alexc on August 06, 2019, 03:50:48 AM
Not much progress with the virtualisation of some proper audio apps  ...  but not for any reason other than 'spring' weather has sprung somewhat early again this year ...  ie.  mid winter  (mid July) is like early spring (mid sept)  :)

I've been busy getting on top of  weeding my small orchard and even smaller vegetable patch(s).

The early great weather (winter)  is jim dandy right now, but I'm sure it portends for the summer.

....

Anyway, doing some more  'manual'  digging   ..   (vege beds),  while the weather is good ..  '10 days of hard labour then a rains a gonna f   ...'

On the up side, 'my place and me'  has been adopted by a family of large and healthy 'rosella'   birds    ... for the last 8 mths or so :)

They are all doing well and coming into their bright plumage for spring   (already!)    [green rosella sthrn tas aust}

I have been practicising my 'rosella calls'  [ whistling and carrying on]   ..  over the last few months ...   this crazy mob of birds (the largest of the rosella family - basically huge budgerigars)    ..   has taken 'this place' as their personal territory.

It's like I can't go anywhere without my own flock of incredibly colored crazy ass wild birds following me about.  [no joke]

They make the most incredible sounds .. like 'pings' and 'bells' overlaid with subtle melodic chattering of 'the crowd'    ..  It's very much like 'analog modem' kind of protocol for communicating - to them it's all 'mark-space' periods of bells  and whistles rising above the chatter  [like softly jangling keys and triangles]   ..   a bit like   'sonar modem speak for crazy parrots'    overlaid with the sounds of the 'rivulet'     [ creek or tiny river which roars to life 1 yr in 10]

Luckily, I spent years as a protocol droid in the field of telephony   ;D    And  it works - these guys go nuts around me ..  aerial displays of dazzling color  a metre or two   away ..  disappearing in a blur of pings and bells ...

Next moment .. gone   .,.  moments later  , right where   you are looking   [saying  lord pls show me]  ..  the whole family glides magestically into view and starts again with their lively biz   ..  chattering and grass-diving  ..  grazing for hours on end  [eating seeds in the low height grass fields] ..   under my window  :D

Even myself, I am amazed, I am.    But there it is.

...

Soon   I'll have my  little amp   with my bench Strat   ready  ...  bells and chimes is what the strat does  :) 

Its all in the mark-space intervals and the pure notes ..  plus bouts of avian lunacy followed by steathy stationary 'disappearing'.

..

So, I've already been teaching them more than the two or three phrases that I hear them use.  When I hear them chirp same back  ...   it's some positive feedback  ... for all the years of music  ..  and my own protocol squawks. I strive to be like 'raffi (sic) of the birds'  :)

They come for the roses, they stay for the conversation  8)
Title: Re: REW Update
Post by: alexc on August 06, 2019, 04:06:58 AM
The crazy thing is that the same thing was happening years and years ago, with the birds, and in particular   the 'rosella' birds

  ...   when I lived in the big city of Sydney   ..   in that case, it was 'blue-and-red rosella' birds, the same  of 'Arnotts Biscuit Company' fame   :)

There it got to 'hummingbirds'   duking it out in my garden (which I planted)   ...

So - if I know anything about anything, it's that hummingbirds are going to show up here pretty soon.

No doubt.  I mean, 'if you plant the trees, the birds  will come'.

-- pic credit at lower left hand side of image
Title: Re: REW Update
Post by: alexc on August 06, 2019, 06:28:04 AM
This girl  here   ..

. pic Wikipedia
Title: Re: REW Update
Post by: alexc on August 08, 2019, 07:33:37 AM
Of course, no discourse of rural birds would be complete without mentioning the 'gang'  ...   a large flock of 'currawong' birds that pass thru these parts at this time of year ... 

Amazing birds, like a fighter plane and a glider rolled into one   ..   they work together and  also compete with each other to secure an 'area' then get to work looking for their food, which is everything.   I've been learning their calls too.

They are quite different than those I was accustomed to ...  the Sydney 'Currawong' bird sounds much more  like the call of the  local Tas  'magpie' bird.   Same awesome 'Currawong' body plan, tho  ...  steath flight to the max.

They just 'turn up' and check everything out, turning over anything that is still and chomping anything that moves.

...

And there's at least a couple dozen other species that are happy to waste a few minutes each day to 'do my head in' with their biz.

Don't start me on the 'Red/Brown  Falcon'  ..  crikey that's a serious animal!   8) 

Around here they get  quite large and they have an endearing habit of flying alongside one's car ..  when the terrain is just right (high twisty forest road dropping steeply to wooded fields)   ....   they like to coast right up by your window (100kph) and look at you  for a bit before turning away   :o     In a convertible, like my (t)rusty old 450sl, it's quite amazing.

At my home, they [the hungry falcon] do swoop in on the 'sparrow's   shrub'  and do their thing ... seeming to like my garden fence gate as a 'lunching spot',  and it does get a little 'grizzly'.    I used to take pics,  but now I just watch the spectacle and marvel.

Nature doing her thing, each day as since forever  (sans me, of course!)
Title: Re: REW Update
Post by: alexc on August 08, 2019, 07:51:24 AM
The bird king of coastal forest, however is the large Black-and-Red Cockatoo   8)

Majestic, large and travelling in moderate sized family groupings, they have a beautiful, wistful call that just  hangs in the air ..

....

[nothing like the white cockatoo which is a 120dB screech-a-rama anywhere, anytime, always ..  particularly in captivity   >:( >:(]
[Pure Furry Freak Bros. level lunacy]

...

The graceful Black Cockatoo families waft on by, with their wing motions curiously like their plaintive cries ...

Here, they do hole up for a while, maybe a day or two in the area before going off on their business. 

Whenever I hear their call, I drop everything to see if they are close.
Title: Re: REW Update
Post by: kambo on August 10, 2019, 03:16:09 AM
this bird up here, has a smile :)

Title: Re: REW Update
Post by: kambo on August 10, 2019, 03:17:40 AM
looks like, all posing to camera...  :D
Title: Re: REW Update
Post by: alexc on August 10, 2019, 11:26:15 PM
The birds here are complete 'hams'  no doubt   ;D

One of the most theatrical is the 'Fairy Wren'  ..  female is forever enamoured by my old merc's chrome trim ...  the mirrors in particular  ...  at the right times of the year there is a 'mighty pile of poop' on the car just underneath the mirror surface.

They just love to make their call, which is a 'whole of body' affair, like a large rooster proclaiming defiance to everybody in earshot.

All their feathers stand on end, their tiny crests flaring as they do their high pitched, long and incredible loud  .. for such a tiny bird.    They are  a 'cotton ball with a pipe cleaner tail'   kind of size.

I'm lucky to have a good population of them here .. they're not that common  ..  a great, plucky, tiny little bird with amazing energy and smarts.

At least one fem is on duty outside my bedroom window at all times    ....    especially first thing in the morning to wake me up :)
Title: Re: REW Update
Post by: alexc on August 10, 2019, 11:27:52 PM
And the totally superb male of the species ..   my ones are much more superb  ..ie deeper azure blue,  and more finely feathered ..   they are the 7cm tall blue-headed flying lion of their world! 

Completely fearless they are, and fully absorbed in their crazy 'dance-off'  protocols with their equally 'twitchy' fems, plural.
Title: Re: REW Update
Post by: alexc on August 10, 2019, 11:33:19 PM
Whats funny about this location, is they (the birds) are not too 'fussed' by humans, responding with curiosity to the respectful observer.

Many of mine, although not all, seem to seek 'one' out.   

There are a couple of species which are very wary  ...   and one lot that always seems to know exactly when you are watching them -  no matter how still you stand etc'  -    then   quickly they slink away into the shadows  and fly away,  very low to the ground - these ones have  beautiful calls and are common here. I watched a family of these go from 'egg' to 'feisty ', one lazy spring.

..

Believe it or not, families of 'quail' birds live in my fields .. like ' the Partridge Family'   ....  they scare the hell out of you when they explode into the air flapping and with big sound if you get close!

...

My lot of 9 'green rosella'  [local wild parrot]  love to sit on the horse fence watching me 'pound earth'  [digging vege beds]  while they chatter excitedly amongst themselves, before effortlessly ascending to the top branches of the near 50m tall trees, all flouncy color and bells  .. for a nice sleep.

My rosella calls are fair in fidelity  but they laugh at me like I was just off the 'turnip truck'   ..  which in their terms, I surely am.

I do believe they see me as a big, dumb, flightless green parrot with poor manners     ..  kind of like that  recently discovered in New Zealand, from some 40M yrs ago ...  1m tall and 7kg in weight, estimated from the fossil record.

For sure, I know they see me as a 'gardener'  or 'grounds-keeper'    ..  and therefore 'OK'   ....    it must be  all the planting of trees and stuff, particularly 'roses' which they go bananas over.

My own private belief is that they are a fun part of that web of life that connects me to the divine  ...  sort of 'off duty angels' ..  doing  'a turn' in this physical plane   ...  for their own  personal reasons    ;D   mostly 'kicks' and 'nectar' I think. 

That, and the  'flyin' - how awesome would it be!


...

It does get a little 'weird' when a hundred or so 'Currawong' birds  blow into town! 

My place is 'on the circuit' for all the passing bird groupings around  these parts  ...  a legacy of hosting 'the horses' and the fine quality grains they are fed with  ;)    ...  everybody eats well when  fancy horses  and their people are aboot.

Stealth fighters they are  [Currawong birds]  - quite large, well 'beaked', superb fliers  very well organised in the 'flash mob' motif.   I stand there, watching them, watching me, watching them. When I make the 'call' they shuffle about uneasily  ..  not sure what I say in 'currawong'  :o   

They [Currawong birds] have quite a number of characteristic sounds which also happen to be very musical   ..  I try them out but they're not at all convinced. Tough crowd for sure!

My parrots clear out  tripelle quick with bells and whistles when they see any of these guys.   

It's exactly like the old Hitchcock film  .. 'the Birds',  sadly without Tippi Hedren or Rod Taylor for that matter.

...

And co-incidently, my favourite band of all time, bar none   [except maybe mr sinatra, elvis, bobby d and the fab4]  are also named for them, the birds   ..   'The Byrds'    8)   

Roger or 'Jim'  McGuinn and much later, the late great Clarence White   ....  were    everywhere I dream of guitar wise  .. 

Of course, the also late great Gram Parsons' contributions were a fine addition too to the whole Byrds' thing.  His 'solo' legacy  knocks me out to this day.

..

The crazy part is that the birds' calls  is very much like  'air traffic control' or 'cb radio'    type protocols [in sound]   ..  pings, bells, doppler, check-ins,  blatt-outs, flapping wind sounds  etc.   It's quite amazing to be sure.   

So I guess you could say I see the world as much as I can from the view of the birds [as far as I can]
Title: Re: REW Update
Post by: alexc on August 10, 2019, 11:42:13 PM
And for scale ...  currawong,  lovely tippi h.    and the NZ giant Sqawkzilla parrot.
Title: Re: REW Update
Post by: alexc on August 12, 2019, 12:41:08 AM
Back to REW  ..   I am just trying out version   5.20   beta  18   for  64bit Win 10 pro   ....   amd 8-core with  ssd    storage

An interesting new feature is the   provision   of a 'Secondary Output'  for the 'test signal' . Quite interesting ..  I'll look at playing with this at the bench, for sure.

It looks like there is something new by way of 'Calibration' - the ability to use 'cal files' -   need to check some more on this - I think it's new but I could be mis-informed.  Looks very interesting   ;D

In the RTA window, the heads-up display panel of THD and Noise figures looks like it has some new fields ... damn fine.

Also the Signal Generator 'amplitude panel' has more info fields than I remember ..  pretty useful too.

The Scope window is similar to how I remember it.

And I think an installation issue with a missing file is sorted too.

.....

That's what I see so far ...   some good enhancements as always and some intriguing new functionality, re 'cal' and 'secondary output'.

Fabulous.





Title: Re: REW Update
Post by: trobbins on August 14, 2019, 08:15:51 PM
Having some fun with REW over at diyaudio (https://www.diyaudio.com/forums/equipment-and-tools/341272-distortion-analysis-experiment.html (https://www.diyaudio.com/forums/equipment-and-tools/341272-distortion-analysis-experiment.html)) with the aim of making almost distortionless sinewave test signal by adding in harmonics to null out harmonics generated in the line output of a soundcard (or even an amplifier under test).

My EMU0404 USB provides about a raw 0.0009% THD at 2Vrms from its line output.  REW can be used to null the harmonics in that test signal to lower THD to around 0.00004% using a simple loopback test.

Although I haven't yet tried it, if the soundcard was used to drive an amp, then the amp's output THD may also be somewhat trimmable for lower THD.   Whilst not related to music reproduction, it is an interesting  topic for test instrumentation purposes.
Title: Re: REW Update
Post by: alexc on August 14, 2019, 11:26:53 PM
Thats super interesting ... I'd like to try some of that myself.