audio-talk

Thanks for the comments. I 'spose the umbilical thing is usually one of necessity. Things are too heavy so need splitting (this case) or too noisy to be close to audio bit say phono which is the case with mine (plus it's too big for one box) If I can do the connection internally, then I don't need a...

Nice design, whats the software ? Have you considered having switches offboard ? Reduces complexity, avoids nasty mainses near the audio and easier to reach for if something is wrong. With an obvious indicator to show power is applied. It's Sketchup 3D modelling software. Free. Use it for audio but...

Been puttng some thoughts together about the destination for this thing so I can plan where to go next and also to get some design input from my better half in order to make the thing safe and domestically acceptable. To give her something to design around, I have to have something visual. Idea is t...

I got my head in a mess about grounding until I read that Karna article. He talks about the Morrison book but there's one key line... "Don't think of ground, think of return current paths". That turned my thinking around, about lots of things. Yes and something I need to think about as we...

Your layout isn't too far removed from Lynn Olson's Karna. It takes a bit of looking to work it out. Try that for starters but don't earth points A or B coz they aren't earth or 0V.

Cheers,
Stephen

I imagine it might seem I'm coming late to the party but I have been following from the start. I asked about the 2nd stage bias coz I only looked at 2 x 220 for the driver and 1 x 220 for the input. Guilty of not doing calcs as Mark pointed out, so it wasn't really much lower current given the volta...

Sorry Steve, but I got another question. Didn't notice before but you have the grid resistor for the 13E1 after the 10k. Is that right? If so why? If not, I'm assuming you have a 10k grid stopper and that makes a bit more sense.

Great set of scope pics! You must be pleased.

Cheers,
Stephen

Cressy Snr wrote: ↑Fri Jan 04, 2019 4:42 pm I like the sound with it like that.

Thanks.
Excellent. The 5687 is a great sounding valve.
Look forward to hearing it at Owston if you and it are going.

Cheers,
Stephen

Probably not the time for a question like this but I'll ask anyway. Prolly covered previously tho I don't remember. Why is the driver biased with less current than the input?

Well one point was that you can put a higher-quality cap in here because it's only something like 20uF rather than 100uF or more in the power supply ; so you can get a bit less cap-induced distortion for bigger signal levels. But having that link there then allows you to use some series resistance ...

It's meant to keep the plate to cathode path a tight local loop. Effectively it's the difference/imbalance signal only so to my mind, minimal. If this was single ended, then I get it and can see it making a big difference. It could be called ultrapath, Western Electric bypass or some other similar t...

Interestingly, the same cap (b+ to cathode) had no effect on the 71A and increased buzz on the 26. I don't yet pretend to really understand this. I went back to one of the articles I found really inspirational... Lynn Olson's Karna. http://www.nutshellhifi.com/triode2.html There's a lot in there I ...

Ah yes, I remember that circuit - nearly 15 years ago I suspect. So the DC conditions for the 8020's must be set by the choke DCR's ? These days I'd be very sceptical of that circuit, too many transformers in which low-level signals can get lost. Yes, DCR sets bias.From what I've read, it can drift...

Nick wrote: ↑Sat Dec 29, 2018 2:11 pm

He floats the grid center tap on a choke to ground too.

Ok, any link I would be interested in seeing.

http://izzy-wizzy.com/audio/phono/Diffphono.gif


It's from a while ago I think.

Cheers,
Stephen

Yes I think I've mixed up my logic somewhere. Long tail with high impedance may be needed where the anode load is resistive, but I've kept that logic after moving to interstage coupling. Lots of re reading to do. Partially true but there are a bunch of designs out there with high Z tail, ccs, and t...