WDPHONO3 3.18uS

[Richard]

Originally Posted by pre65

From a kit builders perspective Richards solution would seem better as very few of us have the skill, or equipment to adjust the pot properly.

If I remember from my Phono 3s build instructions, the advice was to set the pot in the central position.

That's right and it would make nominally 180pF + 25pF = 205pF which falls between what I checked as 190pF for ECC83 and 220pF for 5751. Leaving it there gives a slight dullness to ECC83 and a slight lift against the RIAA to 5751. Hence, as John says, you'll get folk reporting different sound with different valves. You get this anyway of course across brands but here there is a definite reason which checks empirically and by calculation and is due to the output impedances of the 2 types. Even specifying just ECC83 there is little point having the trimmer if a user doesn't have a sig gen, inverse RIAA filter and scope etc to set it optimally. This is further complicated by those nominally 0-50pF trimmers checking in at around 0-70pF or greater, so even the mid point really is guesswork unless it's checked with a meter before installation. Overall I'd build with fixed caps.

Whether to have the 3.18 is easy. Firstly, the cutter will have been rolled off, if only by non deliberate means or to a non-standard, so it does make sense to have at least some correction in the replay. Secondly, Phono3 will not check poorly against a test RIAA signal of either 3.18 or non 3.18 shape as it rolls off anyway and shows a steady decline after 20KHz with both. Having the 3.18 does help flatten the response around 10KHz upwards and maintains the response a little further after 20KHz. I don't doubt Noel for one minute with other phono stages but would urge you to make your own checks first Dave before dumping 3.18 on this amp. It's also very interesting to check a few older phonos and see how tailored they were. Lest it be thought by anyone reading that this all sounds a bit hit and miss I can assue them that Phono3 really is very good indeed.

[Richard]

Dave, if you do keep the trimmer be careful which type and watch the voltage. I thought I'd upgrade the supplied ceramic type (piezo sound worries ) and, seeing that the pcb was already set out for larger film types, upgraded to polyprop film. One channel went noisy after a few weeks and I realised they see a higher voltage than film trimmers are rated for so mine's back on ceramic.

[Clive]

If keeping the trimmer then builders could use a freeware oscilloscope to set the trimmer, the one I use has a signal generator too.

[BOONDI]

Originally Posted by Richard

That's right and it would make nominally 180pF + 25pF = 205pF which falls between what I checked as 190pF for ECC83 and 220pF for 5751. Leaving it there gives a slight dullness to ECC83 and a slight lift against the RIAA to 5751. Hence, as John says, you'll get folk reporting different sound with different valves. You get this anyway of course across brands but here there is a definite reason which checks empirically and by calculation and is due to the output impedances of the 2 types. Even specifying just ECC83 there is little point having the trimmer if a user doesn't have a sig gen, inverse RIAA filter and scope etc to set it optimally. This is further complicated by those nominally 0-50pF trimmers checking in at around 0-70pF or greater, so even the mid point really is guesswork unless it's checked with a meter before installation. Overall I'd build with fixed caps.

Whether to have the 3.18 is easy. Firstly, the cutter will have been rolled off, if only by non deliberate means or to a non-standard, so it does make sense to have at least some correction in the replay. Secondly, Phono3 will not check poorly against a test RIAA signal of either 3.18 or non 3.18 shape as it rolls off anyway and shows a steady decline after 20KHz with both. Having the 3.18 does help flatten the response around 10KHz upwards and maintains the response a little further after 20KHz. I don't doubt Noel for one minute with other phono stages but would urge you to make your own checks first Dave before dumping 3.18 on this amp. It's also very interesting to check a few older phonos and see how tailored they were. Lest it be thought by anyone reading that this all sounds a bit hit and miss I can assue them that Phono3 really is very good indeed.

Simple solution guys

Keep the 3.18us but put in a hardwired cap and get shot of the trimmer Dave......

Excellent observation Mr Richard good sir...

By observation and logic indeed...

Touche !

[John Caswell]

Hi Dave et al
Step-up transformer ratios for the latest cubic tx as opposed to the older cylindrical tx , completely bare no terminations whatsoever, thus:-

1Khz tone from low impedance source - Levell TG152DM/AWA G233 > TX primary > Tx secondary > AWA F242A automatic distortion analyser. Input level measured on a Levell TM3B, output levels measured on the AWA F242A
These are purely voltage readings so......

Tx set to 20:1 ratio - 5mV in = 100mV out so 20:1 ratio is correct
Tx set to 10:1 ratio - 5mV in = 52mV out so 10:1 ratio is correct. (10.4:1 to be pedantic, Yeah Right!)

John

[BOONDI]

Originally Posted by John Caswell

Hi Dave et al
Step-up transformer ratios for the latest cubic tx as opposed to the older cylindrical tx , completely bare no terminations whatsoever, thus:-

1Khz tone from low impedance source - Levell TG152DM/AWA G233 > TX primary > Tx secondary > AWA F242A automatic distortion analyser. Input level measured on a Levell TM3B, output levels measured on the AWA F242A
These are purely voltage readings so......

Tx set to 20:1 ratio - 5mV in = 100mV out so 20:1 ratio is correct
Tx set to 10:1 ratio - 5mV in = 52mV out so 10:1 ratio is correct. (10.4:1 to be pedantic, Yeah Right!)

John

Thats right on the money spec wise guys......

I take it that only the wires were involved and that there are no resistor loads anywhere?
Is this assumption correct guys...

[Dave Cawley]

OK, I thought I must be doing something wrong! The HP-8903B audio analyser has a 100K input impedance and was loading the output! Even the HP-400F at 1M was loading it too. The HP-3400A true RMS voltmeter with 10M impedance gives a ratio 21.5. And hence unloaded 102 ohms which is close to my 100R favourite MC impedance load!

Thanks

Dave

[John Caswell]

Hi all,
Sorry forgot to add that the Levell TM3B is v high impedance so tried it in place of the AWA F242A - Negligible change in level.
Babylon5, yes it was purely bare wires in and bare wires out no load resistors or anything. However as I was measuring both the input and the output levels as voltages, then it would not really have mattered 'cos although the secondary load resistor would have been a reflected load of, say, 100R the input level would have dropped 'cos the generator has an output impedance but I then turned the output of the generator up to 5mV.

John

[BOONDI]

So the only question that remains then is this...

Do the new Tx sound better than the old design????

[John Caswell]

I would doubt it very much.

John