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Walt

Thanks, David. I'm confused about the recommended capacitance. Does he mean before or after the Maida board? It seems to say that you don't need a cap after the board but maybe I am misunderstanding. I have 5AR4 > 47uF > 30H > 47uF > 30H > 47uF > Maida board > plate resistors. Should I add a cap after the board? Should I reduce the 47uF caps? I feel like it's not set up right to do it's job.

At the moment I have 370vdc at the input of the board and 330 vdc at the output. So the board is dropping 40 vdc. That's enough headroom for the board, yes?

Diodes are a possibility. Right now my preferred output caps, the Fostex, are limited to 250vdc. I hesitate to hit them with higher voltage at turn-on. Will the board absorb the excess voltage? Would I need a delay circuit for the B+?

I found a thread on the original design and implemetation of the Maida board and am reading through it now to better understand how it works:

https://www.diyaudio.com/community/thre ... or.209067/

Okay, glad I read the original thread. My grounding scheme was wrong, I had it looped, not isolating the input ground from the output ground. So power supply +/- to the input, output +/- to the circuit. Also added 10uF to the ouput of the board. Effectively ripple was being passed along to the common groiund. Dead quiet now with only one choke. Now I'll see how little filtering I can get away with.

I also learned that the board has a soft start up so I'll play around with solid-state rectification. It would be nice to remove the tube recvtifier coloration.

The best cap for Ck might be no cap at all…. It’s a line stage, you probably don’t need the gain….

Roscoe

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I can explain it to you, but I can’t understand it for you.

That's possible, I can certainly try it.

Lots of progress otherwise. With the board properly implemented, I now have

300-0-300 Antek > UF4007 > 100uF > Maida > 10uF

Dead quiet. And I like not fussing with the tube rectifier--it really colors the sound in a way that makes it sort "confusing" as to which type and brand to employ. Swapping 6V6's gives you plenty of options for "tuning."

The toroid PT definitely affects the Maida board, I have it shifted off the breadboard for now and all is well. I'm thinking of a separate supply with raw DC and filament supply, and put the Maida board on the signal chassis.

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Walt

Grover,

Sorry I was out of contact today...was rehearsing all day for a memorial concert this evening. Glad you got everything sorted out on the grounding, I was worried about that. And that the regulator is working as it should.

Antek now sells inexpensive extruded steel toroid covers that should provide some magnetic shielding, not as robust as much more expensive 12GA steel ones they sell, but should help a bit for the sensitivity you are having with the transformer. Worth trying it if you want to retain a compact arrangement, otherwise getting the transformer away is preferable.

Walt, I am not sold on having so much gain in a linestage. I think that it really depends on the overall gain structure of your system and of course the input sensitivity of your amps. I find with Williamson UL PP amps and 90dB speakers one can just get by with a passive with a 2VRMS source, but a small about of gain may help. For me, the best sound is direct from my DAC (Chord DAVE using the digital volume control as a preamp), which can put out 3VRMS in SE mode at full output. Anything else in the way compromises transparency. It makes little sense to attenuate the source by several dB and then add an additional gainstage with the resultant coloration. My Eico HF-60 "clone" amps with a EF86 pentode input tube is so sensitive, I cannot tolerate any additional gain. I have recently been using a 10dB attenuator at the amp input just to get it into the same level as my Williamson amp. Now, my GM70 SET amps probable could use a little help, though the low-ish bias voltage of the triode strapped E280F/7722 input/driver tube I use limits the voltage swing in the negative direction. But I *think* in the case of the PASS (Colburn) circuit, it is more the case of eliminating some of the negative feedback used when you increase the gain as you did. I think you mentioned that in my thread on the Colburn BA2018 linestage.


David

David

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Walt

Speaking of cathode bypass caps, has anyone tried polymer types? I just got some for a power supply application. They are rated for 4 volts and 560 uF, in a package 5/16 inch tall and same in diameter. Seems perfect for a 12AX7. The impressive thing, and is why I got them, is the fantastic ripple-current rating of 6 A. I know that you are not putting 6A through a 12AX7, but to have that rating they have extraordinarily low ESR and ESL. Higher-voltage types are available that could be used for the likes of a 6V6.