Phono 3 noise issues

[bob orbell]

Well this is strange, are you now taking the power to Phono from the Pre output ? if not I am baffled because the Zener will be doing nothing except getting hot . Bob

[Damien]

Hi Bob

No I’m taking the power from the phono out.

The PSU output as well as beIng noisy was also wandering up & down causing the cones to move quite dramatically.

The Zener has now stabilised the wandering supply but obviously not helped the noise.

This at least stopped me fretting about my speakers.

In terms of getting hot it’s dissipating about 1.4W & isn’t running any hotter than the resistors.

I seem to recall both Yourself & Andy have ditched the PSU in favour of a regulated design?

The scope & my speaker cones both agree this has been a huge improvement.

I would have gone with a 250V zener but we only had 220v in stock & being a bit soggy it measured out at 255V so slightly lower than intended but allowed me to test the theory without throwing money at it.

I’m not a design engineer so can’t give you a great deal more of the principals but the calculations my colleague came up with made sense to me & at the end of the day the proof of the pudding etc.

I’m currently listening to my vinyl with a smile on my face again

Happy to send you the part number & details if it’s of interest.

I’m just waiting for some new caps which should arrive tomorrow & I’ll send you some pictures & details of the mod.

Regards

Damien

[Greg.]

Originally Posted by Damien

Hi Bob

I’m just waiting for some new caps which should arrive tomorrow & I’ll send you some pictures & details of the mod.

Regards

Damien

Please publish your pics in your thread. Plenty of others are reading with interest.

[Damien]

Hi Greg

I’d be happy to, along with the calculations & a detailed explanation of the theory.

Thanks for you’re support & I do hope you are well?

Regards

Damien

[Richard]

Hi Damien,

Phono has has some problems with some equipment and has been steadily upgraded over the years. I built 2 later versions, Phono3S and Phono3 using a 3S pcb, which were run into large valve and ss amplifiers and large transmission line speakers and did not have any of the problems you are experiencing. Yours may be an earlier design or construction problem, or aging components, or your amplifier and speakers. Turntable and amplifier earthing may also be a problem.

Yours may be easily upgraded using the stability components introduced on the latest version. It will be years old now and I would suggest a complete rebuild using a 3S pcb which I think Matthew can supply. In particular, the last large smoothing capacitor should be moved from PSU into the Phono case. Note too that an LDO heater reg was introduced for PSU.

For completeness please advise which pre and power amplifier and speakers your Phono is being used with.

[bob orbell]

Richard, Damion posted pictures early in this thread, it is series II PCB, both Phono and PSU in series III cases with the small umbilical connectors, it was from Peter C in his early days and later the series III Phono still used the II PCB until stocks were used and ran alongside the IIIs, with regard to the regulator chip, I think it is the one before the LD 7084 and it does have the capacitor moved from PSU to the Phono case with 10k resistor. Bob

[Richard]

Thanks Bob, Damien's Phono3 will be early with that pcb and not have C13/14/15/16. The PSU will not have the LDO reg.

I've attached later PSU circ and Phono3S circ which includes the additional caps. C1/2/3/4/5/6 can simply be replaced by 0.1uF if no bass roll of filter is needed and C9/10 can be replaced with 200pF if you dont want to twiddle the adjustable cap for HF. C17 is the large cap moved from PSU to Phono3 case to avoid the umbilical impedance.

[bob orbell]

Richard wrote, C9/10 can be replaced with 200pF if you don't want to twiddle the adjustable cap for HF, should read, 220pF. Bob

[Richard]

Bob is correct for Phono3 without R22 but Phono3S has a different coupling. I set mine using SW on a scope and inverse RIAA filter then checked the actual value the adjustable cap was adding.

My suggestion of 200pF is the nearest common value to the result I got for anyone building Phono3S without a scope. That said, this is a very fine adjustment and setting the supplied adjustable cap halfway will be fine. I twiddled mine end to end and could see quite a large variation on the SW but could not hear it in the music. The build instructions say similar.

The version using fixed 220pF is attached for comparison.

[pre65]

After I built my Pre3, PSU3 and Phono3 I had "noise" problems with vinyl, and after a chat with Peter C I ended up visiting our esteemed Dr John, and he fitted a new regulator as the one in the kit was not an LDO type.

Cured the problem.