WDPHONO3 3.18uS

[Richard]

A reference level check might be at 1KHz but surely any meaningful testing would be with the intended loads and voltage across the audio bandwidth using an RIAA signal to see how it would handle a cartridge output signal.

[Guy Pettigrew]

Back to the 3.18uS correction, if I may.

A friend of mine has the same sort of set up which Clive referred to in an earlier post; "If keeping the trimmer then builders could use a freeware oscilloscope to set the trimmer, the one I use has a signal generator too."

At my friend's suggestion I fitted a variable cap--my phono 3 had a fixed 220pf cap--and then we used his freeware and a reverse RIAA filter.

Before taking the amp to him I'd had great fun listening with various random positionings of the trimmer cap. There was no doubt even small movements made an audible change. Deciding on the right position, though, was near enough impossible. What seemed fine for one LP didn't seem
quite right for another!

Having been able to set the trimmer cap exactly, though, has been a real benefit. The top end is cleaner, and imaging is much better.

So, I'd say the 3.18uS correction is valuable, and particularly so when it can be adjusted using a 'scope. If builders don't have a scope, then it can be done acceptably by ear.

Guy

Just a suggestion - keep the trimmer and then some kind person who knows what to do could add something to the FAQ section with instructions on using a freeware oscilloscope and signal generator to set it properly.

I have no idea if this is a large or small task though

Phil

[Clive]

Originally Posted by PhilN

Just a suggestion - keep the trimmer and then some kind person who knows what to do could add something to the FAQ section with instructions on using a freeware oscilloscope and signal generator to set it properly.

I have no idea if this is a large or small task though

Phil

and if an inverse RIAA is needed then maybe WD could send one out in exchange for a deposit, the customer returns the inverse RIAA when the set up is done. Or maybe an inverse RIAA circuit could be a small project for WD to produce as a kit?

[Phil Y]

This is all getting very complicated for most people I suspect. I would suggest, as the kit is supplied with ECC83s, supply the kit with a fixed cap that gives best (near enough)results with that valve. The PCB could keep the holes for a variable cap and the instructions could refer buyers to the FAQ on the forum for the ones who are interested/skilled enough to start changing valves types or tweaking things to the max.
This would strike me as the best compromise that should keep everybody happy.

Regards Phil.

[Clive]

I agree that having fixed and variable options is a good way. I don't agree though that what I suggested is complicated. I downloaded a scope the other day so I could check the azimuth setting of my cartridge using the HFN test record. It was really easy. What I'm suggesting for the phono stage is no harder, indeed it may be possible to use a tone from a test record as the signal generator, removing the need for reverse RIAA.

These kits are not bargain basement priced, I think most owners would feel greater pride of ownership and achievement if they knew they had set up the circuit accurately. By using a software scope they would learn a little too, though it's not really any harder than using a DMM, which I would hope they would have the skill to use....if not they shouldn't be building a kit.

[colin.hepburn]

Originally Posted by Clive

I agree that having fixed and variable options is a good way. I don't agree though that what I suggested is complicated. I downloaded a scope the other day so I could check the azimuth setting of my cartridge using the HFN test record. It was really easy. What I'm suggesting for the phono stage is no harder, indeed it may be possible to use a tone from a test record as the signal generator, removing the need for reverse RIAA.

These kits are not bargain basement priced, I think most owners would feel greater pride of ownership and achievement if they knew they had set up the circuit accurately. By using a software scope they would learn a little too, though it's not really any harder than using a DMM, which I would hope they would have the skill to use....if not they shouldn't be building a kit.

Hi Clive
I think if this software is a good idea it may help to start a new thread on where to download and how to use it and what other items are required to use this software as it sounds very usefully for other project as well as the new WD phono

[Clive]

Originally Posted by colin.hepburn

Hi Clive
I think if this software is a good idea it may help to start a new thread on where to download and how to use it and what other items are required to use this software as it sounds very usefully for other project as well as the new WD phono

OK, done.

http://www.world-designs.co.uk/forum...ead.php?t=6027

[Phil Y]

Originally Posted by Clive

I don't agree though that what I suggested is complicated.

Hello Clive.
If I may explain my thinking a little. It all depends what your skill level is. I was thinking of people taking their first step into kit building and/or valves. If the standard kit involves the use of a scope, sig gen, reverse RIAA filters etc (real or virtual) I can see some being put off and as a result either not bothering or buying a kit from another company that does not require all this extra (and mysterious) complication which would be a real shame. We all started somewhere.

On the other hand, for the more experienced builder, buying the extra bits, reading and digesting information on the forum and then doing whatever is required to get everything "just so" is no problem. I believe many of us started by building a "standard" kit, then with the confidence that gave, got more adventurous.

It is just a matter of presentation really.

Regards, Phil.

[Dave Cawley]

Here is the reverse RIAA network I use. http://www.hagtech.com/pdf/riaa.pdf

I do have an accurately defined 50 ohm source though.

In reality, setting the trimmer to half way is OK.

Regards

Dave