audio-talk

In the meantime, here is the newest version of the audio circuit:

I've fitted a dual 220uF, BG as the bypass cap(s) for the output stages and removed the bypasses from the input stage, which has reduced the gain, but the amp is so sensitive it's no great loss. It's the best I can do at the moment. Not tried it on music yet. That'll have to wait until later tonight...

Power supply now:

A layer of hash has been removed as it was last time. I have to ask. Did the layer of hash come back when you put the electrolytics back in last time? Yes, it was just a slight bit of fuzz around the treble. It's not a night and day difference with the motor runs in place but it's there nonetheless...

You knew I wouldn’t be able to resist didn’t you! :lol: :lol: :lol: :thumbright: And could you hear any difference? I'm guessing not as you didn't comment? Yep, there was a difference. I knew there would be as I'd commented before when I took the electrolytics out of the PSU. A layer of hash has be...

… I don't think I'd be able to resist trying the 80uF after the stacked lytics, to see if it sounds better than the electrolytics as the last cap in the audio circuit. :D You knew I wouldn’t be able to resist didn’t you! :lol: :lol: Enter 2 30uF 440VAC motor run caps in parallel, giving 60uF, which...

… the fading away thumping noise on switch off suggests low frequency oscillation. But not sure how. Could have been the PSU doing weird things, and amplified by the o/p stages. Just guessing. Aye it’s been a saga but I’m enjoying the fault finding and the general argy-bargy involved in wrestling r...

…I don't think I'd be able to resist trying the 80uF after the stacked lytics, to see if it sounds better than the electrolytics as the last cap in the audio circuit. :D Or I could just bung another blue LCR motor run in as the final cap and remove the electros altogether. Look…you’ve set me off ag...

Was getting more weirdness yesterday: a series of soft thumps at warmup and again on power-down. The thumps faded out as the HT drained away. I've finished up simplifying the power supply to a single channel but with an extra choke. Changed the rectifier to a GZ34 to keep the same voltages as before...

Hope everything works out Phil.

Thanks for that Paul. I’ve started to realise that inadequately rated components and choke-input supplies don’t mix. It seems self-evident from the wobbler throwing telly, that the iron I have is not up to the job. A cap-input supply is perfectly adequate for my needs. The amp sounds great with the ...

So here are the mods: RC filters after the first cap now have 270R resistors as opposed to the previous 470R, which have been shifted onto the cathodes of the EL34s. EL34CinputPSU.png Because of the higher HT voltage, the OPT is now on the 5K tap, cathode resistor on the output valve has been change...

I don't know what the hell has been going on with this amp, but it was putting out some kind of electromagnetic pulse every time it was powered down. It has been doing this ever since I built it with the choke input supply. It got that bad on two occasions, that on power down, accompanied by a crack...

There's a lot more room in the chassis than in the Mk1 version of the amp, so, copying Paul, I purged the power supply of electrolytic caps by installing a nice pair of LCR motor run caps in place of the electrolytics that decoupled the input stages. Didn't think it would make a lot of difference, b...

It’s back in the system after the cosmetic facelift and power supply upgrade.
Sounds great with the LCRCRC supply. Glad I searched out the 450V transformer, despite the head scratching over the primary phasing.