Mark 3 Vacuum Tube Mixer

[ruffrecords]

Does that matter?   

JR

Of course it does. There is something seriously wrong with a world where economy of truth is the norm. We should do everything in our power to stamp it out. I admit I am occasionally guilty of it myself but I do my best not to be.



Cheers

Ian

 

[bockaudio]

I hate to say this, but I can tell the difference between Bakelite and plastic with my eyes closed and I think most other folks can too.  Bakelite has a nice dry feel, whereas the plastic knobs feel almost greasy by comparison.  It is definitely not just about the shape or look of the knob, IMHO.

I'm not saying that your tube console has to have Bakelite knobs, but if it does not then perhaps stay away from that style to avoid disappointing people.  I still can't stand using a Tube-Tech EQ-1A because the knobs feel greasy and the pots feel so loose compared to a real Pultec.

Absolutely.

 

[ruffrecords]

Mark 3 blog updated:

https://mark3vtm.blogspot.com/

Cheers

Ian

 

[shot]

Mark 3 blog updated:
https://mark3vtm.blogspot.com/

Ian, this is fantastic info! Thank you for your valuable effort!
I wish you could test Z3003E transformer alongside those to see how it compares



Luka

 

[zamproject]

That's an update !!

Best
Zam

 

[ruffrecords]

Ian, this is fantastic info! Thank you for your valuable effort!
I wish you could test Z3003E transformer alongside those to see how it compares



Luka

The Z3003E seems to be the same as a Z3002E but without the split primary. The reason I mention this is that I tried the Z3002E several years back and as I recall I found it to be quite good. I am not quite sure what tests I did but I think I used them on the second tube mixer I made to provide a balanced in for the headphones amp.

Cheers

Ian

 

[ruffrecords]

Yet another blog update, this timing covering the most recent tube mixer I built in which I was able to test out many of the Mark 3 concepts.

https://mark3vtm.blogspot.com/

Cheers

Ian

 

[Tubetec]

That was an enjoyable run through of the transformer design and testing phase ,
The final  results as far as distortion ,frequency response and output level  must surely qualify as excellent by anyones standards. 
Will it be a matter of ordering from Electromag directly  or will you hold stock of smaller quantities yourself?

 

[ruffrecords]

That was an enjoyable run through of the transformer design and testing phase ,
The final  results as far as distortion ,frequency response and output level  must surely qualify as excellent by anyones standards. 
Will it be a matter of ordering from Electromag directly  or will you hold stock of smaller quantities yourself?

Electro Mag is a small local company so they do not hold stock. You can order direct but the minimum order quantity is 10 off. If you just want one or two I am happy to supply them at cost.

Cheers

Ian

 

[Tubetec]

You might pm me a quote on 1 PMM board , and a pair of output transformers ,
Im fairly sure I'll take them , but just to be on the safe side with my finances I wanted to check first .

 

[ruffrecords]

You might pm me a quote on 1 PMM board , and a pair of output transformers ,
Im fairly sure I'll take them , but just to be on the safe side with my finances I wanted to check first .

The EI transformers are £25 each. I don't know the PMM board cost yet. I decided the 5 prototypes I ordered would have blue solder mask for a change and I also decided on gold flash for the pads. They still turned out reasonably cheap. Then I got an email from DHL yesterday demanding payment of VAT plus a fee for collecting it. Their figures do not add up and I have queried the bill so for the moment it is watch this space. But I do not think the board cost will exceed £25 each. Plus shipping and Paypal fees at cost of course. I will let you know when I know.

Cheers

Ian

 

[ruffrecords]

It's more than 18 months since the last update but of course COVID messes with everyone's lives. For a long time I have been meaning to get around to solving a problem that could threaten the viability of larger tube mixers. In a nutshell I discovered that the SMPSU I was using for the heaters of the Mark 3 (which could require up to 20 amps at 12V) was giving me problem with noise measurements. To cut a long story short, the 100Hz component in the noise spectrum was much larger than I thought it should be. With just a couple or three boards plugged in it was reasonably OK but not brilliant, However,as soon as a plugged in more boards the 100Hz component went up in direct proportion and with 8 boards plugged in it dominated the noise spectrum.

Now, the SMPS I was using I thought was made by Meanwell - although their name was not on the side, the part number looked like one of theirs. This week I finally got round to replacing it with a genuine Meanwell, an RPS-400-12-C which will output over 30 amps with cooling an 20 amps without. I am happy to report that I tested it this evening with 5 boards the 100Hz component is below -80dBu with the mic pre gain set to 60dB so it is a good 10dB below the theoretical noise floor. And to my surprise, as a plugged in more boards, the 100Hz component actually reduced even further. At 40dB mic pre gain it is below -100dBu. So now with the mic input shorted, REW reports the 60dB gain output noise as -70.4dBu rms from 22Hz to 22KHz. That is the lowest noise I have ever measured on one of my tube mic pres. OK the input is shorted but it is now low enough I feel confident enough to make up an XLR with a 150 ohm termination in it.

Edit: I just discovered the SMPS I was using, an S-180-12 is made by Geeetech and is intended for powering a 3D printer so I guess output ripple is not really an important parameter for that application. S-180-12 12V 15A DC power supply for I3 PRO B Printer [700-001-0761] - $20.00 : geeetech 3d printers onlinestore, one-stop shop for 3d printers,3d printer accessories,3d printer parts

Moral of the story: make sure you use a reputable SMPS.

Cheers

Ian

 

[ruffrecords]

BTW, I have now measured the EIN with a 150 ohm source - it measures -126dBu which I think is pretty good for a tube mic pre.

Cheers

Ian

 

[Tubetec]

Hi Ian ,
Impressive results ,
Did you use any additional filtering after the PSU ? although we have seen that causing issues .
Would be interesting to note the differences in components between a good low noise unit and the typical fuzz box switcher , You typically do see a common mode Inductor or two and a (10-47uf)capacitor at the output of half way decent audio smps .
Is there any trace of smps switching frequency in the REW spectrum or is the frequency beyond the 80 or so khz we can see at 192khz sample rate ?

Ive replaced a few meanwell units mostly internally in Roland and Korg Yamaha keyboards , layout , build quality and components are first class , you typically see a metal screeing cage or foil screening in this application too , its always quality 105C Nippon caps , no Chinese junk . Do the Meanwell include a surge limiter to prevent the typical spark when a SMPS is energised by mains ? I wouldnt think that violent switching transient would be doing my heaters any good , Do you provide a standby on the HT on your mixer supplies ?


Im not sure what the PSRR of your topology is but supposing we required a quieter supply is there a good passive way of filtering an Smps , I know Squarewave( Bo) strongly recomends the capacitance multiplier , but for the sake of maybe 30-40 db getting away with a passive network lends simplicity .

 

[ruffrecords]

Hi Ian ,
Impressive results ,
Did you use any additional filtering after the PSU ? although we have seen that causing issues .

When I first determined it was the heater PSU causing the problem, the first thing I did was add some external filtering. However, all the standard advice for external SMPS filtering refers to the high frequency content and not twice the mains frequency which is what was causing the problem.

Would be interesting to note the differences in components between a good low noise unit and the typical fuzz box switcher , You typically do see a common mode Inductor or two and a (10-47uf)capacitor at the output of half way decent audio smps .

The one I replaced is probably 10 years old. The Meanwell one is literally half its volume so technology has obviously moved on in that time. I will take the lid off the old one and look at the components it uses.

Is there any trace of smps switching frequency in the REW spectrum or is the frequency beyond the 80 or so khz we can see at 192khz sample rate ?

I have only looked in the audio band so far but I suspect the Meanwell switching frequency is well beyond 200KHz

Ive replaced a few meanwell units mostly internally in Roland and Korg Yamaha keyboards , layout , build quality and components are first class , you typically see a metal screeing cage or foil screening in this application too , its always quality 105C Nippon caps , no Chinese junk . Do the Meanwell include a surge limiter to prevent the typical spark when a SMPS is energised by mains ? I wouldnt think that violent switching transient would be doing my heaters any good ,

I have never had any problem with switch on surges in heater supplies, quite the opposite. Most times you need to make sure the SPMS is adequately over rated for the heater current to be able to avoid the PSU going into foldback current limiting and never light the tubes at all.

Do you provide a standby on the HT on your mixer supplies ?

No, I do not.

Im not sure what the PSRR of your topology is but supposing we required a quieter supply is there a good passive way of filtering an Smps , I know Squarewave( Bo) strongly recomends the capacitance multiplier , but for the sake of maybe 30-40 db getting away with a passive network lends simplicity .

The PSRR of most class a tube circuits is very poor by op amp standards. The raw PSRR of the SRPP output stage I use in my designs is a mere 6dB. Negative feedback improves this by about 20dB but even that it is pretty poor which is why you need very well smoothed HT. If you want the HT ripple at the output to be better than -90dBU then the actual T ripple need to be less than -74dBu which is about 150 microvolts. My linear HT supplies use three RC stages which typically achieve more than 90dB of tipple reduction. Nobody makes 250V or 300V SMPS but Meanwell does make a constant current LED driver that outputs 300V at up to 500mA before the current limit sets in and reduces the voltage. So the current plan is to follow this with some combination of capacitor multiplier and linear regulator to achieve the same level of ripple/noise.

Cheers

Ian

 

[Tubetec]

Thanks Ian ,

 

[ruffrecords]

I took the lids off the old and new supplies. The old is on the left and the new Meanwell is on the right. The old one uses caps by Dongbaohe (never heard of them). The Meanwell uses Rubicon mostly.

Cheers

Ian

 

[rjuly]

I was mulling over the possibilities for EMI shielding with the type of channel modules Ian is developing and I found this mu foil online:

https://hollandshielding.com/Mu-copper-foil
comes in some different styles including tinned for easy soldering and as thick as .18mm.

- Richard

 

[ruffrecords]

Interesting in that they never actually say what mu-copper foil is made of. If it is just copper then it is no better than an aluminium box. I don't know if the mu in the name is meant to imply it has some magnetic shielding properties as well but if it did you would think they would be a little more explicit about it.

Cheers

Ian

 

[PermO]

From what I understand, a mu-metal can not be bend or otherwise deformed after the proces that makes it a mu-metal, it will loose some of it's sheilding quality.

So it should never be a foil but rather solid.