Help with Music Hall CD25.2 Mods (pics included)

[Ampersand]

Hello all,

I'm in the process of performing an underwoodhifi mod the affordable way, by doing it myself. I've gone over the list of mods that underwood performs and selected the specific ones I would like. Here is a list of those specific mods:


Here's Level 1 Mod

* We install two BlackGate output coupling capacitors
* 4 x 1% polystyrene film and foil capacitors are added in the analog filter
stage
* 6 x Riken Ohm ½ and one watt signal path 1% gold-plated leads carbon
comp resistors are added in the signal path
* 4 x IR Hexfred ultra-fast soft recovery diodes are installed in the power
supply

Here's Level 2 Mod

* We install 8 x BlackGate capacitors. These are two output coupling caps
plus six additional 10uf/16V and 220uf/ 16V BlackGate standard-grade
capacitors in the power supply and around the Dac.
* 2 x Rel-Cap Teflon TFT film and foil bypass coupling caps for the main B-G
output caps.
* 4 x Telefunken SF4007 utra-fast soft-recovery diodes in other sonically
critical power supply positions


I've marked the circuit board picture with 'colored' arrows corresponding to what I believe is being replaced. Here's what i think:



Green Arrows = these are the diodes, both HEXFRED and SF4007
Red Arrow = Rel-Cap teflon (I'll be using Multicap PPFX-S here instead)
Orange/Yellow Circle = I think this is the 1% Polystrene film and foil caps
Blue Arrow = these are the Riken resistors, I see 2 definitely in signal path,
not sure about the other 4 locations.
Grey Arrow = I think these are the output coupling caps, but I see 4 and
not 2, maybe I'm mixing these up?

I'm looking for any feedback on the accuracy of my guesses. And also, any further suggestions for replacement parts.

As for the blackgates, I was thinking of using the FK series instead of the Std. Is this just overkill?

 

[Pars]

Quote:

Originally Posted by Ampersand /img/forum/go_quote.gif Hello all, I'm in the process of performing an underwoodhifi mod the affordable way, by doing it myself. I've gone over the list of mods that underwood performs and selected the specific ones I would like. Here is a list of those specific mods: Here's Level 1 Mod * We install two BlackGate output coupling capacitors * 4 x 1% polystyrene film and foil capacitors are added in the analog filter stage * 6 x Riken Ohm ½ and one watt signal path 1% gold-plated leads carbon comp resistors are added in the signal path * 4 x IR Hexfred ultra-fast soft recovery diodes are installed in the power supply Here's Level 2 Mod * We install 8 x BlackGate capacitors. These are two output coupling caps plus six additional 10uf/16V and 220uf/ 16V BlackGate standard-grade capacitors in the power supply and around the Dac. * 2 x Rel-Cap Teflon TFT film and foil bypass coupling caps for the main B-G output caps. * 4 x Telefunken SF4007 utra-fast soft-recovery diodes in other sonically critical power supply positions I've marked the circuit board picture with 'colored' arrows corresponding to what I believe is being replaced. Here's what i think: Green Arrows = these are the diodes, both HEXFRED and SF4007

Not sure. What is on the heatsinks (TO-220 package)? Are those regulators (LM317, etc.) or the main PSU rectifier diodes? If these are the main rectifier diodes, then that is where the hexfreds should go (those are usually TO220 pkg.)
Quote:

Originally Posted by Ampersand /img/forum/go_quote.gif Red Arrow = Rel-Cap teflon (I'll be using Multicap PPFX-S here instead)

Does the stock have film bypass on the output electrolytics?
Quote:

Originally Posted by Ampersand /img/forum/go_quote.gif Orange/Yellow Circle = I think this is the 1% Polystrene film and foil caps

Hard to say on this one. Those and the ones to the right of the DIP-8 pkgs. look more like decoupling caps. I would think filter components would be to the right of this, but could be wrong.
Quote:

Originally Posted by Ampersand /img/forum/go_quote.gif Blue Arrow = these are the Riken resistors, I see 2 definitely in signal path, not sure about the other 4 locations.

Probably. The other 4 should be over by the opamps to the left.
Quote:

Originally Posted by Ampersand /img/forum/go_quote.gif Grey Arrow = I think these are the output coupling caps, but I see 4 and not 2, maybe I'm mixing these up?

Those look a little big. Ohm them out to the output jacks.

Quote:

Originally Posted by Ampersand /img/forum/go_quote.gif I'm looking for any feedback on the accuracy of my guesses. And also, any further suggestions for replacement parts. As for the blackgates, I was thinking of using the FK series instead of the Std. Is this just overkill?

FK for the coupling caps, STD for the PSU ones.

 

[Ampersand]

Thanks for the reply Pars. I've followed a few traces under the circuit board, and the rectifier diodes are definitely the ones I have marked. I'm guessing those are regulators that are attached to the heatsinks. It's hard to read numbers as they are squeezed in so tightly.

I assumed the Orange/Yellow Circle was the 1% Polystrene film and foil caps based on this picture of a modded unit. While blurry, you can see that they are replaced by something aftermarket.



Also, I noticed something strange while poking around. The white film capacitors near the output jacks are labeled as 1uF. However, the board position states '104' which I believe translates to 0.1uF. I'd like to replace this part with 0.1uF as it would be significantly cheaper. However, I'm not sure why there is a discrepancy? If I remember correctly, this film cap is part of a high pass filter and I shouldn't change the value, but then why is there this discrepancy between board and part????

Thanks guys.
Mike

 

[Pars]

First thing I would do if I were you is get my hands on a service manual including schematic.

It wouldn't be unusual for changes to have been made in production... they aren't going to respin the board for a label (silkscreen) change.

Was the pic you posted a stock unit or a modded one?

 

[Ampersand]

The picture in my 1st post is of my stock unit (although I've swapped opamps). The 2nd post is of a modded unit done by underwoodhifi (and reviewed by 6moons). I'd love to get my hands on the schematics, but a search reveals many people have tried unsuccessfully, even when contacting Roy Hall of Music Hall.

 

[Pars]

Well, that sucks. I only see 1 link in the 1st post


http://img59.imageshack.us/img59/785...yer3cr7.th.jpg

 

[Ampersand]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif Well, that sucks. I only see 1 link in the 1st post http://img59.imageshack.us/img59/785...yer3cr7.th.jpg

I think there's some confusion here. The link in my 1st post shows my unmodded unit.

My second post has a picture of a modded unit (not mine).


edit: I've gone back and removed the link to help clear up the confusion.

 

[Pars]

That's post 3? I don't see anything there in post 3 (link or pic). I'll look at home later.

 

[Ampersand]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif That's post 3? I don't see anything there in post 3 (link or pic). I'll look at home later.

Okay, thanks. This is getting weird. I've only posted 2 pictures. I see both. Am I the only one?

Maybe this thread has picture-snatching gnomes..

 

[dcheming]

Quote:

Originally Posted by Ampersand /img/forum/go_quote.gif I'd love to get my hands on the schematics, but a search reveals many people have tried unsuccessfully, even when contacting Roy Hall of Music Hall.

YGPM

 

[magliner0316]

I'm currently doing some mod on my CD25.2 too.. is there any way I can get the schematics too?

:O