Nice phono stage with subsonic filter?

[pre65]

Originally Posted by Greg.

In my experience, the WD Phono 3's (and the earlier Phono 2) performance is a considerable improvement over the EAR834P, and I mean considerable

Can only agree.

I went from an 834P to a Phono 3s, job done.

[Richard]

As Bob says there was an IEC change to the RIAA for a few years which did include a roll off at about -3dB at 20Hz but it wasn't widely adopted.

We don't know which RIAA Croft use so why not drop Glen Croft an email ask his advice and maybe have him do it for you, glenn@croftacoustics.co.uk

[Infinitely Baffled]

Thanks for all the replies, fellows. The Phono 3S is clearly something a bit special - certainly well thought of round here!

I have in fact been in touch with Glenn Croft over the past few days, and he has been his usual helpful self. However, his default position is that he doesn't put subsonic filters into his pre-amps as a matter of course, because they sound better without. Which is a fair enough point of view. However, he has said that "There may be more scope to tweak the low frequency response on the Epoch than the current amps - depending on the circuitry fitted to yours [there were several different circuits]", which suggests that his pre-amps of the generation of mine may have been RIAA but sans IEC. He needs me to send a photograph of its innards to him so he can determine what he circuit he used in it. I'll do that shortly - I have had a bit of an accident last week so my mobility is restricted at the moment. So there could be a happy ending to this, if Glenn is willing to mod my amp, I can have the one-box solution I prefer, AND get to keep using the Croft-designed phono circuit I like so much.

Thanks very much for all your help and suggestions, though. By the way, no-one has ventured to say what they do about this problem. I can't be the only one, surely? Regards. Infinitely Baffled.

[Richard]

Originally Posted by Infinitely Baffled

By the way, no-one has ventured to say what they do about this problem. I can't be the only one, surely? Regards. Infinitely Baffled.

I'm not sure what you're expecting. Have you established the problem? It sounds like warp so compare cone movement to record rotation. Warp or rumble, same solution; fix the mechanical problem (inc change of cart or arm if needed) or filter the low frequencies. I suggested contacting Glen and you say you've already done it. What more

[Greg.]

As my WAD Phono 2 has a subsonic filter, I don't suffer from speaker cone flap. Off course, it can also be caused by circuit instability. I remember a member here (who has not posted for several years) bringing his Phono/Pre 2 around and on switch on, my speaker cones started flapping. Switched off and refused to use his kit in my system. Whether or not he got it sorted, I have no idea.

[Infinitely Baffled]

Quote:
Originally Posted by Infinitely Baffled:
"By the way, no-one has ventured to say what they do about this problem. I can't be the only one, surely? Regards. Infinitely Baffled."
Originally posted by Richard: "I'm not sure what you're expecting. Have you established the problem? It sounds like warp so compare cone movement to record rotation. Warp or rumble, same solution; fix the mechanical problem (inc change of cart or arm if needed) or filter the low frequencies. I suggested contacting Glen and you say you've already done it. What more"

It was simply an open invitation to forum members to say if they had experienced this problem, and say what they had done to eliminate it. I was starting to wonder if it was only me. Don't feel your contributions were not taken on board.
Regards. IB.

[Infinitely Baffled]

Originally Posted by Greg.

As my WAD Phono 2 has a subsonic filter, I don't suffer from speaker cone flap. Off course, it can also be caused by circuit instability. I remember a member here (who has not posted for several years) bringing his Phono/Pre 2 around and on switch on, my speaker cones started flapping. Switched off and refused to use his kit in my system. Whether or not he got it sorted, I have no idea.

Interesting - so the WAD Phono 2 has a built-in subsonic filter, does it? Is it permanently in circuit, or is it switchable like the 3S?
IB

[Richard]

You could fit input coupling caps to the RCAs of Kit6550; 0.22uF into the 100K input shunt resistance would give a -3dB roll off at 7Hz. (Check your inputs are 100K if not or if a vol pot is fitted let us know.) This was done as standard on the first WAD power amps and other valve amps to stop OPTX saturation at LF.

Make them up in a box between 2 pairs of RCA sockets if you don't want to disturb the amp, or detach the input signal wires inside the amp and re-make the connections with caps. Polypropylene or polyester film cap 63V+ rating would be fine, cheapies to try it maybe, then good quality audio caps if it helps the problem.

[bob orbell]

After reading a lot about Decca cartridges on Google, and their problems in the bass department, warped records etc, it seams to me that your problem is with the Decca, some say that a damping paddle fitted to the arm helps, of course, you cant fit such to a uni pivot, I don't think, correct me if I am wrong, you obviously like the Decca, but in this instance, it may be the cause of your problem, can you try another cartridge?, just to eliminate the Decca from the equation. BOB

[Infinitely Baffled]

Well, many thanks to all - I have learned a lot through this exchange. Testing and tweaking is now completed. There's really not a lot I can do, I cannot swap out the arm, but I have tried a different cartridge - a Music Maker with a more compliant suspension system. The arm/cartridge resonance points (as measured using a set-up disc) shifted slightly but the cone flap was still there when playing the "rogue" LPs. Conclusion: subsonic hash is just there on the record and despite the purists who say the problem is mechanical and needs to be eliminated at source, I don't believe you can. The choice is either don't play the record, don't worry about the overworked amp and speaker cones, or filter the rubbish out. I am going to opt for the last one. Many thanks to Richard for suggesting some simple passive filtering on the RCA inputs of the power amp. As you guessed, I would be happier implementing this as an off-board box rather than trying to attach yet more components to the inside end of the RCA sockets. I seem to remember from the build that the inboard end of those sockets are already loaded up like christmas trees with various resistors and capacitors. However, emboldened by your advice, I am going to try for some filtering steeper and higher up the frequency range. I have found this online: http://sound.westhost.com/project99.htm
This simple pcb-based project can be configured to produce an ultimate 18 db or 36db roll-off below 20 Hz. I have ordered the board (plus the one for the power supply it requires). I plan to implement it as a standalone box which can be inserted into the system just upstream of the power amplifier when I am listening to records, and taken out of circuit when I am listening to other sources. I'll report back to this forum when it's done and let you know how it works. Meanwhile thanks to all for the help and suggestions. Regards. IB.