Bob Cordell's VinylTrak

[jan.didden]

Bob Cordell's Linear Audio Vol 4 article 'VinylTrak - A full-featured MM/MC phono preamp' led to a discussion that resulted in much additional material.
Bob has been so kind to place this on his website.

I'll shortly put up a link from linearaudio, but if you are interested in this stuff the additional material itself is well worth a read.

And, of course, if you want to reach out and actually touch the equipment (or Bob ) find us in the lobby at the RMAF coming weekend!

jan didden

[Bob Cordell]

Originally Posted by janneman

Bob Cordell's Linear Audio Vol 4 article 'VinylTrak - A full-featured MM/MC phono preamp' led to a discussion that resulted in much additional material.
Bob has been so kind to place this on his website.

I'll shortly put up a link from linearaudio, but if you are interested in this stuff the additional material itself is well worth a read.

And, of course, if you want to reach out and actually touch the equipment (or Bob ) find us in the lobby at the RMAF coming weekend!

jan didden

Hi Jan,

Thanks for putting this up and thanks for putting the VinylTrak preamp on display at RMAF. I'll be happy to answer any questions about the VinylTrak.

Cheers,
Bob

[Joachim Gerhard]

Thanks for posting additional material. I like the pseudo balanced trick.

[Bob Cordell]

Originally Posted by Joachim Gerhard

Thanks for posting additional material. I like the pseudo balanced trick.

You're welcome. Jan was very kind to give me as much space as he did in the LA article, but there was so much more...

The differential JFET input stages without negative feedback do indeed allow for some other approaches to input toplogy.

Cheers,
Bob

[morinix]

Interesting, A home stereo product I assume, with rack ears?

[Bob Cordell]

Originally Posted by morinix

Interesting, A home stereo product I assume, with rack ears?

Hi Robert,

Looks have never been my strong point :-). The VinylTrak preamp is currently just a one-off DIY prototype for audiophile home use. That enclosure with the rack ears was convenient and large enough to house the electronics, but not something I would use going forward. I had hoped to get a nicer front panel made by someone like FrontPanelExpress, but just didn't have the time. I'd also like to put it in a much nicer enclosure.

Cheers,
Bob

[AndrewT]

I see just two capacitors in the inverse RIAA.
2000pF & 560pF.
Both these need to be tight tolerance for good RIAA accuracy.
Is absolute 1% as important as 1% matching ratio between the two capacitors?

i.e. could the capacitors be 2% high (or 2% low), but the ratio be better than 0.5%?

I ask because I can see that 4off 1nF would get close to the desired values. It would be possible to get very close ratio matching by adding a 56pF and a 3p9F to a series pair of 1nF+1nF (for 559p9F) cf. 1nF//1nF (for 2000pF).

Once this inverse RIAA is correct then it would be possible to trim the RIAA components to give good absolute and channel matching of the pre-amp.

[Bob Cordell]

Originally Posted by AndrewT

I see just two capacitors in the inverse RIAA.
2000pF & 560pF.
Both these need to be tight tolerance for good RIAA accuracy.
Is absolute 1% as important as 1% matching ratio between the two capacitors?

i.e. could the capacitors be 2% high (or 2% low), but the ratio be better than 0.5%?

I ask because I can see that 4off 1nF would get close to the desired values. It would be possible to get very close ratio matching by adding a 56pF and a 3p9F to a series pair of 1nF+1nF (for 559p9F) cf. 1nF//1nF (for 2000pF).

Once this inverse RIAA is correct then it would be possible to trim the RIAA components to give good absolute and channel matching of the pre-amp.

Hi Andrew,

I tried to get as close as possible to the original values specified in the Lipshitz paper for his inverse RIAA network. I used 2% silvered mica capacitors and 1% metal film resistors, with no precision measurement or matching of these components. These capacitors usually come in much better than the 2% tolerance; same for the 1% resistors. To answer your question, the capacitors should be close to the right value in the absolute sense, not just in their ratio to each other.

One thing that can be very useful is to do LTspice simulations of such networks to see how much error you get, and where, with slight deviations of component values from the ideal.

Cheers,
Bob

[morinix]

Originally Posted by Bob Cordell

Hi Robert,

Looks have never been my strong point :-). The VinylTrak preamp is currently just a one-off DIY prototype for audiophile home use. That enclosure with the rack ears was convenient and large enough to house the electronics, but not something I would use going forward. I had hoped to get a nicer front panel made by someone like FrontPanelExpress, but just didn't have the time. I'd also like to put it in a much nicer enclosure.

Cheers,
Bob

Hi Bob, Fabricating chassis are a pain for electronics guys. I know this because I do both all of the time. Keith Barr (Alesis Studio Electronics) quote "The electronics are the fun part, the hardware is what is real work". Good luck at the show!

[Bob Cordell]

Originally Posted by morinix

Hi Bob, Fabricating chassis are a pain for electronics guys. I know this because I do both all of the time. Keith Barr (Alesis Studio Electronics) quote "The electronics are the fun part, the hardware is what is real work". Good luck at the show!

Very good point. This is one reason that my hat goes off to those who go ahead and make a beautiful product.

Cheers,
Bob