Hello fellow solder-slingers. Having retired at last, I thought it was time I tackled some of those projects I had waiting and the VDV Trans-30 amp was one I have wanted to build for years. I was impressed by the design which works to minimise the influence of the output transformer, improving the fidelity of the amplifier. I have trawled the threads but found no mention of this amp so started a new thread. Apologies in advance if I should have looked harder (my wife always says I seek not to find).
I decided to build my own aluminium chassis with individual side, top and bottom panels so that if the amp was a disaster, the top panel could be scrapped and most of the remainder reused for a new project. At one point I thought this approach had been well justified... I also decided to build 2 separate monoblocks for reduced crosstalk and the avoidance of needing a forklift to move it.
When I first started planning this project the UK was still in the EU, so I sourced the toroidal mains (TSTA 0220/001) and output (TTG-EL34PP) transformers from Toroidy in Poland and avoided paying VAT and duty 🙂
The VDV circuit comprises identical solid state drive/control modules for each of the push-pull EL34 O/P valves plus single bias set and phase splitter sections. A PCB was designed on KiCad that accommodated all these functions so that two PCBs were used per monoblock with the bias and phase splitter omitted from one of them. A power supply PCB was designed for the opamp, bias and HT supplies. I used a gyrator with an 04N80C3 for HT smoothing. Plenty of sand here! Stop reading now if you feel offended. 1k grid stoppers were mounted direct to the EL34 sockets and a small tagstrip carried the HT distribution, screen grid and cathode resistors, and the screen grid current balance preset. The PSU board was equipped with connectors to enable individual supplies to be unplugged and tested. Just one amp was built initially 😉
One cockup was spotted before testing - the footprint KiCad gave me for the MJE350 bias control transistor for some reason had its collector and emitter pads swapped, so this was fixed by bending the transistor's leads (see pics). The bias supply measured low, which was traced to me putting in a 12V zener instead of a 100V. This was caught on the bounce and the amp was powered up into a dummy load, monitoring the O/P on a scope. All seemed OK until it burst into oscillation and one of the EL34s started blushing furiously. My problem was that the O/P valve red plated as soon as the amp warmed up which made live measurements impossible. With many other things to do, I put the amp away in disgust. At least I had built it such that I could easily recycle the chassis!
I returned to it with renewed determination several months later. I reasoned that the red plating should be due to some failure of the grid bias circuit. Since it was the same EL34 that was affected every time, I tested the BSP35s responsible for pulling the grid down on its corresponding board and found the culprit. Having replaced the defective sand, I decided to critically review the bias circuit before powering up again. That was when I found I had altogether omitted the 10uF damping capacitors on the autobias circuit 😵 The sharp-eyed amongst you may have spotted the tacked-on caps on the driver boards...
The amp was powered up again, monitoring the volts across both cathode resistors and the O/P on a scope. Both resistors measured 0.6V, so 60mA quiescent bias current per EL34. No sign of oscillation so test signals were applied - all good.
Time for a listening test. I tried it with a Quad 12L2 and an Acoustic Energy AE1 speaker. It sounded highly detailed and musical, especially with the AE1 although it lacked the power to drive this speaker to high volume.
Having made one, its stereo partner was very much quicker and easier and I could then listen in stereo. The sound is impressive. I found myself hearing details that I have only heard before on good headphones (Sennheiser HD800 and Stax SR404 electrostatics).
Has anyone else built this amp or any other of Menno's Trans designs? It would be fascinating to compare experiences.
Tim
I decided to build my own aluminium chassis with individual side, top and bottom panels so that if the amp was a disaster, the top panel could be scrapped and most of the remainder reused for a new project. At one point I thought this approach had been well justified... I also decided to build 2 separate monoblocks for reduced crosstalk and the avoidance of needing a forklift to move it.
When I first started planning this project the UK was still in the EU, so I sourced the toroidal mains (TSTA 0220/001) and output (TTG-EL34PP) transformers from Toroidy in Poland and avoided paying VAT and duty 🙂
The VDV circuit comprises identical solid state drive/control modules for each of the push-pull EL34 O/P valves plus single bias set and phase splitter sections. A PCB was designed on KiCad that accommodated all these functions so that two PCBs were used per monoblock with the bias and phase splitter omitted from one of them. A power supply PCB was designed for the opamp, bias and HT supplies. I used a gyrator with an 04N80C3 for HT smoothing. Plenty of sand here! Stop reading now if you feel offended. 1k grid stoppers were mounted direct to the EL34 sockets and a small tagstrip carried the HT distribution, screen grid and cathode resistors, and the screen grid current balance preset. The PSU board was equipped with connectors to enable individual supplies to be unplugged and tested. Just one amp was built initially 😉
One cockup was spotted before testing - the footprint KiCad gave me for the MJE350 bias control transistor for some reason had its collector and emitter pads swapped, so this was fixed by bending the transistor's leads (see pics). The bias supply measured low, which was traced to me putting in a 12V zener instead of a 100V. This was caught on the bounce and the amp was powered up into a dummy load, monitoring the O/P on a scope. All seemed OK until it burst into oscillation and one of the EL34s started blushing furiously. My problem was that the O/P valve red plated as soon as the amp warmed up which made live measurements impossible. With many other things to do, I put the amp away in disgust. At least I had built it such that I could easily recycle the chassis!
I returned to it with renewed determination several months later. I reasoned that the red plating should be due to some failure of the grid bias circuit. Since it was the same EL34 that was affected every time, I tested the BSP35s responsible for pulling the grid down on its corresponding board and found the culprit. Having replaced the defective sand, I decided to critically review the bias circuit before powering up again. That was when I found I had altogether omitted the 10uF damping capacitors on the autobias circuit 😵 The sharp-eyed amongst you may have spotted the tacked-on caps on the driver boards...
The amp was powered up again, monitoring the volts across both cathode resistors and the O/P on a scope. Both resistors measured 0.6V, so 60mA quiescent bias current per EL34. No sign of oscillation so test signals were applied - all good.
Time for a listening test. I tried it with a Quad 12L2 and an Acoustic Energy AE1 speaker. It sounded highly detailed and musical, especially with the AE1 although it lacked the power to drive this speaker to high volume.
Having made one, its stereo partner was very much quicker and easier and I could then listen in stereo. The sound is impressive. I found myself hearing details that I have only heard before on good headphones (Sennheiser HD800 and Stax SR404 electrostatics).
Has anyone else built this amp or any other of Menno's Trans designs? It would be fascinating to compare experiences.
Tim
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Did you mean Toroidy TTG-EL24PP? I assume you meant TTG-EL84PP. I would also be interested to know more about VDV Trans Amps.
That was a typo Francois, apologies, I meant TTG-EL34PP (ra-a 6.6k, 50VA). The Trans-30 was published by Menno Van der Veen in 2015. He has published several more valve based transconductance designs in AudioXpress, for example the single ended SE10 and SE18 and the larger PP80 push pull.
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I am very happy to share, but can anyone advise if there are copyright issues here?
Congratulations.
The amp might run for years without further trouble.
You said: 60mA cathode current in the EL34.
How many volts Plate to Cathode?
How many volts Screen to Cathode?
Perhaps it is time to estimate plate dissipation and screen dissipation.
If anything fails now or later, then . . .
A lack of a schematic causes blindfolded archers to miss hitting the bulls eye.
"All circuits are equally reliable, some circuits are more equal than others"
"The reliability of a circuit is inversely proportional to the number of parts in the circuit"
"All generalizations have exceptions"
Have fun listening!
The amp might run for years without further trouble.
You said: 60mA cathode current in the EL34.
How many volts Plate to Cathode?
How many volts Screen to Cathode?
Perhaps it is time to estimate plate dissipation and screen dissipation.
If anything fails now or later, then . . .
A lack of a schematic causes blindfolded archers to miss hitting the bulls eye.
"All circuits are equally reliable, some circuits are more equal than others"
"The reliability of a circuit is inversely proportional to the number of parts in the circuit"
"All generalizations have exceptions"
Have fun listening!
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6A3sUMMER, the schematic is in the public domain - in the book 'Trans Tube Amplifiers' by Menno van der Veen
https://linearaudio.nl/trans-tube-amplifiers
This book describes Menno's development of his transconductance concept, culminating in this amp. As an author myself, I respect Menno's copyright which I believe I would be breaching by publishing his circuit here.
Thank you for your concern over the health of my O/P valves. They run at 80% of maximum dissipation - hot by any reckoning but acceptable to me in terms of performance and longevity.
I'm having a great time listening 😎
Tim
https://linearaudio.nl/trans-tube-amplifiers
This book describes Menno's development of his transconductance concept, culminating in this amp. As an author myself, I respect Menno's copyright which I believe I would be breaching by publishing his circuit here.
Thank you for your concern over the health of my O/P valves. They run at 80% of maximum dissipation - hot by any reckoning but acceptable to me in terms of performance and longevity.
I'm having a great time listening 😎
Tim
I suppose you have the May 2023 issue of Audio Express to refer to? with "The Vanderveen Trans - 80" DIY article? There is also "Trans -10 Secrets" in the January 2021 issue and I believe follow-up articles in the three immediate issues after that one. It looks like an interesting approach to negative feedback, but the one reviewer who focused on the sound (I forget what magazine) thought it sounded kinda dry and far too much like a solid state amp. I am surprised more folks haven't tried Vanderveen's design approach (or maybe they did)?
Would it be possible for someone who has one of those magazines to describe what 'the transconductance concept' looks like in practice? It is a new term to me, and I do not have access to the resources above.
Found this on the web:
https://audioxpress.com/article/you-can-diy-vanderveen-trans-se10-secrets
This is an all-valve 10W SE amp but it describes Menno vdV's trans concept nicely.
Tim
https://audioxpress.com/article/you-can-diy-vanderveen-trans-se10-secrets
This is an all-valve 10W SE amp but it describes Menno vdV's trans concept nicely.
Tim
Now I do. Monno posted it on his website.
https://www.mennovanderveen.nl/index.php/nl/research-development#sixmoon
Yes, I subscribe to AudioXpress. I might have built Trans-80s instead but by the time it appeared had already committed to building Trans-30s. I think I have all the parts to build an SE-10 which being single ended would make an interesting comparison. I wouldn't describe the sound of my Trans-30s as dry, they do retain some tube warmth in comparison with a Quad 303 or 405. They do sound more 'clinical' (if that's the right word) than a pair of Quad iis.
Anyone else heard a Trans amp?
I tried the concept, yes, actually still working on them. Here at DIYaudio a lot of discussions and projects were done based on this concept of negative feedback. Occasionally reference is made to the article by Broskie, where he explains the concept calling it "partial feedback" and saying there are other names as well, Menno calls it trans now.
https://www.tubecad.com/march2001/
So many times that the description sounds as if Menno did something new, and when one looks into it further, it is known stuff that is maybe new only to him. WRT the Trans-80, I find it overly complex. I know an input transformer can be expensive, but that would allow for the desired SE and balanced input and provide the phase inversion right away. And if one wants to use ICs to obtain a balanced drive signal, get the DRV134, no need to adjust Lissajous figures...
https://www.tubecad.com/march2001/
So many times that the description sounds as if Menno did something new, and when one looks into it further, it is known stuff that is maybe new only to him. WRT the Trans-80, I find it overly complex. I know an input transformer can be expensive, but that would allow for the desired SE and balanced input and provide the phase inversion right away. And if one wants to use ICs to obtain a balanced drive signal, get the DRV134, no need to adjust Lissajous figures...
Just finished restoring a pair of Quad ESL 57s. They sound sublime on the Transamp. Even my wife, who normally couldn't care less as long as she can recognise the tune was captivated by the combination 😍
The detail is fantastic, yet more being heard that was never noticed before.
The detail is fantastic, yet more being heard that was never noticed before.