audio-talk

Nick has suggested some LC filtering after the reg to see if things quieten down, this is a useful trick, why didn't I think of that! I was contemplating using my LCLCLC smoothed supply for the other phono for the pentodes. Nick's idea seems much simpler! I'll try this tonight on the pentodes and go...

I wish my hum chasing efforts were as sucessful as yours. The hum on the phono must now be coming from the PSU, though theory says its should be chuff all. Huh, what did theory ever tell us. The hum is getting into into the pentodes, and going through all the gain stages and by the time it leaves th...

Oh go on.......I have a schematics for a 15 amp one somewhere, only 3 LM317s

cheers,

-- Andrew

Bad day or rather two or three bad days. The old scope I use has given up the ghost, I just as I was getting somewhere :cry: 100Meg time base delay dual channel irreplaceable. And during my initial experiments a couple of weeks ago I must have taken out either the voltage reference for voltage buffe...

Well me too, that's why I wanted to take a more orthodox approach. In fact, someone questioned T about this on the thread where he detailed the mk2 and in the end all agreed it was probably OK if you used a step up TX that can isolate - not everyone wants or has one of those. The bit I had missed wa...

Hi Nick,

T's mk2 is attached.

cheers,

-- Andrew

Well, it makes sound, but I wouldn't call it working. I didn't copy T's circuit, because I didn't undestand it, I just used a normal pentode arrangement, after all, thought I, my load is 2.5 times higher, so I thought I could get away with it. Perhaps I should have, copied his design...but there you...

So I went back and looked at both of T's LCRs and now the reason for the slight unorthodox biasing arrangements on the input pentodes on both versions becomes clear. Sometimes you have to build it to understand it.

-- Andrew

Ok, it works......but bad news and good news..... The bad news is it hums like a good 'un well much much more than my other phono(s)......the good news is that it seems to be confined to one channel only, and when I pull the phono plug on that channel out just a bit (signal connected but not ground)...

Hi Nick, Yes the extra triode does give more gain, a bit more, I can see that but what confuses me is that I can't get it to give anywhere the same level of gain as a bypassed cathode, assuming the same load, (or diodes in this case) on the straight forward pentode stage. Now, it does indeed look mo...

I copied your circuit deleted the upper triode and set the B+ to 250v, output taken from the usual spot. Changed the load to 5k6 for both circuits. Right dead quick shufty, what am I doing wrong? I can't see the extra gain compared to the straight D3A with diodes in the cathode. I seem to get twice ...

Hi Nick, Did you get chance compare the gain at both loads and against a standard bypassed cathode, or even fixed grid bias? 5k6 would be about right for Simon's phono. So many questions, would you be OK with sharing the sim? Might be easier. It also occured to me that if Simon prefers fixed grid bi...

Here ya go, courtesy of SB, I beleive.

Nope its not working tried it as a .inc, as a .txt and a .gif. I can mail it if you prefer.

cheers,

-- Andrew

OK, next step accomplished, new 9v tx from Rapid powers the two regulated DC supplies fine, one for the Aikido and the other for the input pentodes. The Aikido needed one of those tv40 heatsinks before I was completely happy, with a 12v supply there was too much work for the regulator but the Aikido...

Hi Nick, Have you tried this in Spice, seems a good way to explore its workings, it won't tell us the whole story but....then suppose it depends on how long it will take someone to knock this up on a bench, less time if you have a bench HT supply. I have a D3a pentode model, if its any help? cheers,...