Hey Kevin. Thanks! Unfortunately the C2 I was talking about is on the signal board, not the PS board. I have the two 47uF/350v caps on the PS board (C2 and C4). That board also has a C5 which is the 4700uF16v cap for the filament supply (somehow I got that as a 1000uF but will fix that). I am going to experiment with chokes in place of the resistor (R1) between the two 47uF filter caps. So for all that I'm OK. But the signal board shows a single C2 cap right at the input (see attached image, to the right). If that is redundant to the C2 on the PS board, I can leave it out (should work fine with out it other than any filtering/decoupling it would provide).
Attachments
BTW, here's the PS board with the C2 and C4 filter caps in place already, on either side of R1 and to the left of the L7806 regulator with heat sink. Below that is the 1000uF I have in C5 which I need to replace with an appropriate 4700uF cap. I hope this illustrates my question.
Attachments
One last question (for you or others who have built it). In the schematic I don't see a POT on the input. I see a 100R at the grid (what I THINK might be a "grid stopper") and a 1M which seems to be a "grid leak" resistor. I see no indication of a POT, but I admit I may have missed something in the discussion leading up to this point (on or off of this thread). In any case I'll use a 50k as you suggest above. I think I have something decent to use. I think I'm getting closer.
The pot is on the front panel and is not part of the board. Some interpretation of design requirements is required. The 100R is indeed a grid stopper and the 1M resistor is there to keep the grid circuit from going open circuit in the event of an intermittent pot wiper or in the event that a stepped attenuator is used with break before make contacts which would make a very bad pop sans that resistor.
On the line stage board. Note that C2 is not redundant and should not be left out, it provides local decoupling on the board which becomes more critical as you plan to mount the supply outboard and connect with some length of wiring. You don't really want to see what sort of oscillations you might get from the CCS without it due to wiring inductance.
C2 Lead spacing 5mm diameter up to 12.5mm
On the line stage board. Note that C2 is not redundant and should not be left out, it provides local decoupling on the board which becomes more critical as you plan to mount the supply outboard and connect with some length of wiring. You don't really want to see what sort of oscillations you might get from the CCS without it due to wiring inductance.
C2 Lead spacing 5mm diameter up to 12.5mm
Last edited:
For now I'm using the 10M45S/DN2540 combination for the tube loads from post #20. I have a number of the 10M45S on hand, and use the others (DN2540) more often in other projects, so used up the 10M45S in the top spot and using the DN2540 in the lower spot. Don't know if that matters, but the last post I saw above seemed to indicate it shouldn't matter.
Ah, right. I think I recall the issue with break before make, and will consider that I may need to think some details through for myself (e.g. the 50k pot). I wasn't expecting it on the board, but I also wasn't sure if I should see it on the schematic. I think I'm in reasonable shape now.
The input and output circuits are entirely at the discretion of the builder. Mine has 2 sets of unbalanced RCA inputs and a single pair of balanced XLR inputs. Outputs are balanced over both XLR and RCA jacks (in parallel).
There is muting and polarity inversion switches on the output - none of this is detailed in schematics or elsewhere because the few builders were mostly knowledgeable enough to handle this without my help. (Assuming anyone other than you actually attempted to build one - honestly I have no idea at this point who has the 3 remaining boards)
FWIW I went with an all solid state analog source interface to the RME ADC I am currently using.
There is muting and polarity inversion switches on the output - none of this is detailed in schematics or elsewhere because the few builders were mostly knowledgeable enough to handle this without my help. (Assuming anyone other than you actually attempted to build one - honestly I have no idea at this point who has the 3 remaining boards)
FWIW I went with an all solid state analog source interface to the RME ADC I am currently using.
Last edited:
In a commercial design there absolutely should be a schematic that shows how everything is connected together, and some of my older published designs have that level of detail. Mostly they don't since I/O is at the discretion of the DIY builder IMO. This was as much about learning what could be accomplished on a limited budget, and on reflection I grossly undersold the design and the intent. Well it was in that time frame and I was playing. It is also the only tube design I have worked on since 2018 until quite recently. Out of the last 30 or so projects only 1 has been tubed, and only one other was of immediate interest to anyone else, and that one now seems to be dying on the vine like the last phono stage design I did.
Note that R1 on the PSU is definitely cold soldered, neither lead looks good. Might want to check the others.
I don't have any schematic showing J14 and C2, and my BOM from you doesn't have anything for this C2 (at least that I've seen). As for R1, the back side is nice and shiny on both joints, and on the front no solder is visible (even with magnification I don't see any).
Did either of you experiment with the parafeed output low side returned to the tube cathode rather than ground? This is a curiosity question. I built a parafeed 6V6 amp recently and returned the OPT low side to the output tube cathode. I didn't experiment with a ground connection so can't offer a comparison. Just wanted to ask the question. I've seen parafeed amps with both types of connection. Seems to me as though the output audio current loop is shorter with the cathode return vs. grounded.
Thanks,
John
Thanks,
John
Kevin, I meant to add my thanks for providing the info about C2 and it's too late to edit now. I appreciate it!
The classic definition of a cold solder joint, you do know that the solder is supposed to flow through the entire joint from bottom to top or vice-versa? So half soldered.
Please email me a copy of the documentation I sent you since something is wrong. This is the problem with waiting almost 3 years to put something together.. J4 is solder pads.
The cathode bias is generated by 3 leds, and the AC impedance at the cathode is relatively low so it was not considered.
This is what the built up board should look like.
PSU rework for graetz bridge (for power transformer without center tap)
PSU rework for graetz bridge (for power transformer without center tap)
I did not know that it had to flow through. Hadn't really thought about it. I'd always just looked for good shiny joints well flowed around the lead and pad. I'll look back through the boards. I'll try to email you the materials I have. I think I have them from a few versions.