Monitor Amps - Class A Monster Madness ?

[madswitcher]

can anyone see the jpg I attached - it seems to have screwed up somehow

 

[ruffrecords]

Not visible here.

IAn

 

[alexc]

Hey Mike - thanks for the description. Photos aren't linking right tho'.

Sounds hot! ... literally   50Wrms per channel of JLH is ..  something like 150W of heat per channel dissipating ?

I'm looking forward to getting mine going ... 30Wrms max  per channel off +/- 25Vdc supply.

Not regulating here either  - I like  the 'brute force' method of filtering 

I'll be keenly interested in the thd figures I eventually get. 0.1% THD over at clip over such wide BW is pretty good performance.

...

Of course, the method of measure is also important - at this stage, I just do THD measures at 1KHz till I 'dial it in' then take readings at 20Hz and 100Hz at the bottom end, 10KHz and 20KHz at the top.

My app of choice, REW - as well as a  million great features,  now has a 'headline THD figure'  for 20Hz-20KHz  BW displayed in real time (ish)  8) 8)

That's way, way cool - not yet, tho', does it 'headline' the extended BW that the system generally supports ie 10Hz-48KHz.

But even at the provided 20-20KHz BW  it's a huge milestone in getting 'aggregated' thd measures - I like to think of it as 'fanfare for the common man'

Thanks mr REW for the 'killer audio measurement app of all time'    ;D ;D ;D

...

ANyway - JLH is crazy but cool. I see it as the logical extension of classic Neve class A circuits ... but to a hot level of LOUD!

 

[madswitcher]

I give up - I cannot seem to add attachments - its a plain jpg

Any thoughts anyone?

Mike

 

[alexc]

SO now I'm once again doing some JLH class A stuff  

Got my sum bus units squared away
Forward tube projects primed for the winter's diy season
Hifi test rig  up and running'
Recalibrated my baselines  .... 8)

Parts are in   and its Time for Some Late Summer  Fun  8)

----

Just  built up some more cheapie ebay modules    ....

-  instrument input with discrete fet preamp/eq module
- main mix bax style 3band eq with make up module
-  refined version of the headphone amp
- medium power JLH power amp  5 to 10Wrms per channel

- discrete, adjustable  bipolar regulated supply, low-ish current  200mA at +/- 15V
- discrete, adjustable  bipolar regulated supply, high-ish current  2A at +/-25V


in preperation to the big cahuna ...  the 25Wrms per channel  jlh heat monsters  + psu

....

So all that is soon to become  ...    a 'pre amp 2ru box', a 'distribution amp 2ru box'  and a  'power amp'  ;D

The 'preamp' box is a personal recycle  (#3 I think)  - it's meant to mix an 'instrument' input plus a bunch of pedals  into  a  main stereo balanced  outputs  ....  to feed the apie-micpre-style sum bus unit I recently did.

Interesting  things are :

- 4 stereo unbal inputs at rear panel, switched after local sum
- 4 mono unbal inputs at front panel, switched after local sum

- 1 selectable HiZ/line/mic input  at front panel  with a  'direct' unbal out at rear panel

All that sum'd  stereo and feeding a chip class A Bax EQ with variable gain

feeding a stereo headphone amp module  ...  with Haufe traffo balancing pair  ..  as well as an  unbal 'alt' pair.

Target price would be in the 2hundreds us in parts I would say. Maybe 300 if I get real fancy at the input end

...

The 'distribution amp box' is the  medium power JLH 5 - 10Wrms  as the distribution amp; and again, I am using a bax+pre  module to drive it. super cheap maybe 150us parts, again recycling a previous build (#1).

---

The 'power amp' is the high power JLH module and psu  - it  is a 150W stand alone heater for driving a 25W monitoring stereo speaker setup    .. bit more expensive but no too bad .  500usd I think with some premium components.

.....

Here's a pic of the startup of the first unit ... ClassA DI+Mix  box 

 

[alexc]

Once again I'll be keeping an eye on the performance ..  as I go ..  with my updated test setup and baselines.

I'm keen to measure how well  (or not) some cheap pedal and ebay modules ..  can be cajoled together  .. in a hifi sum'd, class A jlh  context ... 

I've made up a class B mono module amp with the lme49811 + power_BJTs    ... as a 'test power amp'  - which should be able to keep my power measurements and thd profiles ...  honest  ...  and hopefully low in the 'triple 0' thd measures.

I'm thinking to beat my best performance to date  from the classB ....  and hopefully get close as I can (heat-sink) with the classA

And improve my measurement practice as I go 

...

IF I can keep towards  my lower boundaries of performance, I will get a better test-channel Motu  to go further down .. the rabbit hole 

 

[alexc]

and here is the little classB amp module : just add big ass heatsink and +/- Vsupply capable of whatever current you wish to slam thru.

The power amp front end chip, the TI LME49811 can take up to +/- 100V dc supply and can deliver up to 500Wrms into 8ohms    It has  a 'typ THD+N' of 'triple 0' 35% at 1KHz at an output of 30Vrms.

Of course, that is very dependent on the number of output devices, heatsinking and current availablility.

I am using for output devices, the TIP147, TIP142 congugate BJT pair with a TIP41 as the Vbe multiplier.

TI also has a similar  LME series chip tailored for  MOSFET type output devices.


I plan to do something like +/- 45V supply and heatsinking up to 50Wrms into 8ohms or so.

Plenty to provide me with a single channel of 'test amp' for comparisons and also that I can use in my winter 'tube amp'  builds.  ie. so I can more accurately measure tube finals' performance  and so on, driven by a big, clean waveform 

It was 23usd unassembled from ebuy and it took me about 30mins to assemble. It has about 7 smt 'spec of dust' sized resistors to solder and getting the TI chip into the little pin array takes some patience ..  if you need a magnifier, like me.

 

[alexc]

The first module in this box is cool  .... it's the OLC/RunOffGroove 'dumble-like' pedal preamp pcb - typical 5 controls  affair.

I think it cost me about 25usd to build up from a pcb I bought from their site.  http://www.runoffgroove.com/umble.html

So that should be fun to get going 

 

[madswitcher]

Here's a photo of my JLH high-power mono-block

Plenty of fins 

 

[madswitcher]

and the primary  PSU module

Lots of transformers (2 x 500VA) and pre-smoothing smoothing caps.

 

[alexc]

Those are some impressive builds there ..

That's the kind of thing I am aiming for pretty much, but of lesser output power.

So far, I have been collecting parts for the psu unit - 300VA toroid, pair of 22KuF, unregulated.
Plus a slow start module, large size iec filter.

My plan is get the psu going, get one amp box going with selectable mono (highest power) or stereo (half power).

If that seems so good that I want moar, then just duplicate for a 4xbox configuration 

I think that something like 15-20Wrms/8ohm will be plenty, so 2boxes will prolly be plenty

 

[alexc]

Interesting is your capacitance multiplier and post smoothing caps in the amp box.

It may be that I will need to do similar  - I should be able to do so if needed.

I had thought to use main reservoir caps in the psu box and an LCR filter in the amp box.

For comparison of supply ripple effects , I am also making up a 'test' regulation module - it's a large-ish module with a lot of heatsinking and uses high power  LT1083 low drop out regulator chips in a bipolar config.

That should give me a good idea of the performance envelope.

 

[madswitcher]

Hi Alex

The output on this model is about 45 watts just before clipping with a distortion of about 0.05%.  I am just about to retrofit the next version of the main board which takes the distortion down another 26dB to about 0.002%.  Noise is down at about 120dB.

On the build plan, I use 18,000 uF after the diode block to get rid of most of the ripple and then another 30,000uF inside the amp enclosure before the cap multiplier, which then makes all of the noise just disappear.  One of the things I love about this build is that you can put your ear again the speaker and hear absolutely nothing. 

You mention that you want to get about 20 watts or so, you could do that with a single output pair and rails of about +/- 22 volts, but still leave the path open to a higher power version later with +/- 30 volt rails.

However, you have to be careful about pcb layout connections etc., earthing etc.  If you are interested, I am writing up a bit of a document on it for my own pleasure.  It is work in progress, but you are welcome to a copy for yourself to help along the way.  Let me know if you are interested and I'll pm you a pdf of it so far.

Kind regards

Mike

 

[alexc]

Thanks Mike - I'm always keen to learn from someone who's well trodden the paths I like to go down.

PM'd

 

[alexc]

Gosh, where does the time go?

A couple of months more have passed ...  I have some more parts  ;D  for my Class A projects, but sadly winter is here and it's time to hibernate ....  away from the bench ...  and into the Lounge Room  .. warm like ...

I got thru a lot in these last couple of months ...  a pair of sum boxes, re-worked all of my remaining speakers  AND finished up maintainence/restorations on my old and neglected guitars ... all spruced up and fine sounding

AND reworked my singled ended 6L6 hifi amp for better performance in it's role as 'most often listened to'  ...  'low watts' monitor amp  8) 

Thanks to Real EQ Wizard (REW), I tweaked up from 'sub 3' to 4.5Wrms for 4%thd. It took a lot of work - tube rectifier vs diode plug, plate voltage/current/thd  measurements for the 6L6 se final ... but the diff was big! After that, I reworked the speakers to handle the extra power.

The thd profile at the speaker still showed a dominant h3 over h2 and significant higher orders, but a fairly big improvement in the 'regularity' of the distortion products ..  was enjoyed by all

Now I have to upgrade the single 6sn7 gain stage (no nfb) where it is now,  to a mu-follower stage for more gain at less thd, driving the final to full blatt (75Vpp).

Hopefully I can reduce the driver thd a percent or so ..

-  the 6l6 ended up  +408V B+,  +370V plate, +364V screen at 47mA cathode quiesscent, fixed bias -35V  .. with decent 6l6s but decidedly  cheapo sino output se traffos (rated 60mA , 3K5 .. I think!)

- using 8ohm speaker with '4ohm tap'  yielded the best 'power at 4% thd'  results ... at a surprisingly low bias current.  .... I measured all the way up to 70mA)

For a small, dry 8" box, it reproduced the double bass in 'walk on the ____ side' very well  8)

All it needs  now is some decent output traffos! These guys start to bork pretty early.

This setup done proper could do quite a bit better

....

Putting together all the past summer's  work has been really rewarding, into a  'relaxed lounge'  rig ..  for to be using as good-ol lounge room recording.

I have my notebook with an M-Audio firewire box, feeding a nice wooden rack with my own api-styled sum box, the fore-mentioned 'se 6L6 stereo' amp and a pair of my worked-over  8" 2-way vintage paper-coned driver, smallish timber speaker boxes.

Augmenting  that, is an 80s Japanese hifi amp and another, bigger, heavier mdf boxed 8" pair; some modern 'peerless'  drivers + 'vifa' silk tweeters with  modified  crossover  in some old 'jbl' boxes   

THOSE two different monitor sets are combined so give some real 'deep spacious' feel to a low-ish volume listening environment of stereo 2 + stereo 2.

Into all that are stereo stems for  live , daw and vsti 

.....

SHort story - sounds super 'compelling' 

Listening to some classic stuff ...  'Angel of Ashes' by Scott Walker  really takes you back to the day  8)

Anything calling for seriously articulated double-bass, my standard for 'hifi',  is working super well.

I would say the se 6L6 amp is doing 3Wrms per channel on average with around 2.25% thd+n, and the ss yamaha amp is doing around 10Wrms at low distortion (< 0.1%)  - with the two balanced by ear for my positioning in lounge room.

The big innovation here was pairing my stereo build of Jakob's gPultec eq with the se 6L6 amp. Tick. Tick!

A match made in heaven and the first time I've been really knocked out by either!  They really complement each other perfectly.

I spent some time getting this eq  build the way I like it - 2 channels in a 3ru box, with shielded toroids and some changes to the tube (6dj8) circuit to  suit my choice of input (haufe) and output (lundahl) traffos.

Super low noise, super articulate. SUbtle until you push it

Now the SE 6SN7/6L6 spud amp has some  real kik and sizzle 8) in those dry paper timber bookshelfers ..

 

[alexc]

ALong with all that, and feeding into my sum box, are a couple of 'instrument' channels ...

.

First, is my build of a  'drip la2a+fender pre' in a 3ru box. It's pretty well tweaked out now, haven't changed it for several years. It has 4 signal transformers and 6 tubes all up  Plus a pair of Triplett meters.

I wish I could redo this whole box in my style with point-point octals  ..  and external psu. But alas, the years get by and I'm 85% happy with it . Only thing it could use is a few more dB noise performance.

And noise performance is everything in a proper limiter!

This was my first one but still stands the test of time.

........

The other 'instrument channel' box I am using in this 'lounge studio' low-watts 2.2 listening environment is *again* Jakob with the  Gyraf g9 

My build has a bunch of 'extensions' to the standard version and here it is really working out great.

ANd again, I underestimated the Gyraf g9 all these years - it is actually quite a good balance between 'hifi' and 'tube' characters  with easy to 'dial in'  distortion.  (  ie.  0.1% .. 2% thd ).

...

For quick recording, I'm using a small Tascam DR-40 sdram recorder - the bal outs from my sum box for inputs as well as live-to-air with it's in-built mics -  is giving great results.

I can has it on my net in a few minutes and playing back on the tv

....

WIsh it was all that easy 40 years ago when I first started messing about with audio ...

 

[alexc]

And the 'proper' recording is cubase 5  ..  an hp i7 and an  m-audio fw1814  .....  pretty 'cost effective'  ie inexpensive!

I have one for the DAW functions and another one just for VST instruments and effects.  ;D

Been using the arturia keylab 49 for a while and I have to say it's super awesome. The Solina instrument is just amazing. I could noodle away a couple of years just with that one keyboard!

It has some pretty decent app support for mapping knobs-to-keys ..  light years ahead of how it was when I spent most time in front of cubase ...  that was kurzweil's, akais and midi  what nots ...

 

[alexc]

The kicker is that my re-wirings and 'return to original ' work on my old guitars have made them way usable again ... quiet wirings, smooth pots, jacks and switchers  ..  just awesome.

I cleaned them up, over a few days for each, into as nice and clean condition as could be  Took the time to print some notes on their history and left a leaflet in the case of each.

I'm sure they sound and feel better now than when I found them

Have a bunch of active pups and electronics now to eby 

 

[alexc]

Back onto the 'instrument channels' ....   

Three (3) channels seems to be the charm for me - one dual channel and a single channel 

I added my build of the 'Poorman 670' limiter to the G9 - all good; combining with a LRBaggs acoustic guitar pre (for the peizo), a Jensen DI box and a couple of pedals  ..  sonic bliss somniferus 8)

And

Finally, adding a tube sdc mic to the G9/Poorman .... ready to roll to .. tape!

So far, so good - it's kind of like a 'diy-love-inn' ...  near the wood burner .. for a few months

 

[alexc]

I have the Finalizer on the sum box; it's a fine stereo gate especially when using a bunch of limiters  ..

The net result is fairly intimate - a couple of stems from the DAW , a couple of live instrument stems and even a few live fx sends thanks to Guitar Rig asio plugin

The latency in the live fx is easily blended out with live stems and all sounds pretty together ... for a smalliswh lounge room  8)

.....

I use a Korg electribe drum machine to round out proceedings - it's a pretty deep little box, in a not-too-difficult-to-use kind of way ...  with a midi link to cubase, and a decent 'loop' pedal ..  it's very satisfactory.