Phono 3 noise issues

[bikerhifinut]

Yes its me back from the dead!
Sorry for being quiet guys, lifes been a bit strange last 3 months but looking up again now the quacks got a grip of my soaring BP!

Ok Bob knows exactly where I am coming from here, I think he followed my experience with the PSU.
I had a really bad issue with LF instability, this was a sub1Hz oscillation that was making the speaker cones flap.
I tried all the tricks, but in the end the only thing that worked was using an aftermarket regulated HT kit which killed all the instability dead.
It's likely that the PCB on the PSU3 may not have been constructed well, this was an allegedly pro built job that had some glaring earthing faults. Nuff said.

As to the background noise, it's a noisy amp, and there's not a lot you can do about it as its valve noise for the most part (Hiss and odd rustles). I found it was very sensitive to Valves that weren't quite up to snuff.
So the best thing to do is to accept the background hiss as once the stylus is in the groove then record surface noise will be louder for the most part.

These days I have been using a home brew Silicon based RIAA preamp that I sweated over last year and the final iteration has been remarkably good. And totally hum and almost hiss free.

There, I am outed and no doubt will end up in the stocks for my heinous sins!

Andy, hoping to get back in the garage and bash some metal soon.

[bob orbell]

Nice to hear from you Andy, so, I take it you are on blood pressure reducing tablet for life now, if that is the case then join the club. A very noisy phono amp !!, well I cant agree with that comment, mine is almost as quiet as a solid state unit, and the regulated supply has improved it again, any way, feel free to join in on Damion's problems, I know only too well motorboating can be a sod to get rid of, now could be the time for Matthew to give us a regulated HV PSU, hello, are you still with us Matthew . Bob

[Damien]

Hi guys.

Many thanks for your support & input, it’s greatly appreciated.

Having had chance to get a scope on it the PSU is terribly noisy.

I work in an electronics company & my colleague who used to design audio kit for a hobby has been a great help.

His first comment when he looked at the schematic concerned the earthing design which I guess is where you are coming from Andy.

I suspect the main smoothing caps have gone leaky & have a couple of 350V variants which will do for checking on no load.

I’ll let you know how it goes & will swap the other electrolytic caps in the PSU while I’m at it.

It’s been an interesting learning curve as have never worked with valve stages before but always like to try & optimise things.

I’d be very interested to find out more about the regulated kit for the PSU as whilst I understand the point about noisy valves it’s clear on this one that most of the noise is getting through from the PSU & then being amplified.

At present I’ve gone back to the solid state stage I built about 15 years ago to my colleagues design which sounds fantastic but doesn’t glow in the dark

I’ll update you on progress tomorrow.

I’m on the same tablets. I think it’s years of chasing audio nirvana!

[bikerhifinut]

Correct me if I am wrong Damien.
You are using PSU2?
In which case the PSU3 is slightly different, I believe, in quite a few ways.
As it happens I have an unused spare PSU3 PCB lying round somewhere and if you're going to rebuild the thing, then this might be useful to you.
Let me know and for the price of a stamp its yours.

There are differences in stuff like the regulator for the heaters where PSU3 uses a 3 Amp LDO regulator rather than a 7805 with a couple of silicon diodes hung off the bottom leg.
And no zener diode regulator for the preamp HT if i remember right, again its not needed.
I think its got a better earthing scheme too.
Now the main thing as I found out, was to ensure the 100R earth lift resistor was in place and actually in circuit. This was the main glaring error on my PSU as bought and the Phono 3 hummed like an old AC/DC mains radio.
It's still sensitive to placement in regards to hum pick up from mains transformers etc.

A.

[Damien]

Hi Andy

That would be great if you don’t mind.

I’d be happy to stretch to more than a stamp.

I’ve tidied it up & touched all the joints up but there’s no substitute for starting from a clean sheet.

The earth lift resistor was the main suspect until yesterday ( I couldn’t see what was under the insulting tape) but re worked & no improvement.

I didn’t realise prior to Bobs help that there were different versions as I acquired this second hand but I believe from his advice that it’s a PSU 2 in a PSU 3 case?

I have posted a couple of pictures earlier if that helps.

Damien

P.S also biker hifi nut & better not mention the streamer DAC combo I’ve just put together or I’ll probably get struck off 😜

[bob orbell]

Andy is correct, the PSU III board is better and uses a better LT regulator ( LM1084 ) and package or discrete diodes for LT, but the rest is the same circuit. For full regulation kits, look at John Broskis' Glass Ware Audio Design, PS-1 kit. Bob

[Damien]

Thanks Bob

I’ll have a look at that.

Damien

[Damien]

Hi

Just a quick update to let you know I've fixed the problem of the cones flapping about by fitting a 220V 3W Zener in the position left empty at C4.

New capacitors didn't solve the noise problem but 5 minutes after testing it the postman arrived with a pair of ECC803 S valves & it's now super quiet .

I can now hear mains hum if I wind the amp up which was being masked by the rest of the noise previously.

I will see if I can cure that & let you know but it's tiny compared the the original problem.

In the meantime I'm off to listen to some vinyl

Regards

Damien

[Greg.]

Sounds like a result well done. Enjoy your tunes

[Damien]

Thanks to everyone for the advice & support.

I’ll keep you updated with eliminating the mains hum.

Regards

Damien