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CDP 3.5 op amps Richard H

B

bmudge

Member
Richard
I saw your post in faq regarding changing the op amps in the CDP. I wonder if you have a picture showing the inside and the position of the opamps. I can solder and have changed caps in my 32.5 sucessfully, but am not an electronics person and have difficulty sorting the parts. But if the effect is like you say I would like to try doing this.
Bob
 
Wasn't me that did it - it was a cull from the old PFM forum. If you look at the bottom of the FAQ article, you'll see the source is ced, who's a member here. Hopefully he will chip in (so to speak).

R
 
I have some reasonable pictures of the innards of a CD3.5 attached to my little article on installing superreg boards.

The 6 opamps are located close to the rear panel, four grouped to form the first 6poles of the lowpass filter, and two (last pole+output driver) located close to the output socket.

M.
 
Sorry Richard, I'll get to understand this forum someday.
Martin,
I appreciate the picture, I can work from that just fine ( I hope ). The article states the ad8610s need some kind of adapter, I assume the ad825s don't, I wonder if using the ones with the adapter would be better than using the ad825s without.
Iwonder if anyone could comment on this.
 
Whether an adaptor is required depends on the packaging of the opamps you want to use; check the datasheet/your supplier before you order. Naims OPA604s are in DIP format - the classic eight legged chip. Newer opamp designs are mostly in the physically much smaller SO-8 or SOIC packages. These are both designed for surface mounting, and the smaller package physically enables better performance, because the leadout s from the 'die' are shorter, reducing errors of various sorts.

Bottom line - pick your favourite opamp, and make it fit. You'll certainly need an adaptor for AD8610 or AD825s and the like -and steady hands for the soldering, and a couple of spares to practice on. The improved chip performance absolutely swamps any potential side effects of the adaptor in an application like this.

For a drop-in replacement that requires no adaptor do not overlook the OPA627. It's what I installed and they really are superb in this role.

Have fun!
M.
 
Hi Martin

The superreg boards seem to be very close to the CD tray. Is there another position where you can place the superreg boards?

There seems to be a piece of copper underneath the boards, did you put it down yourself?

Regards
Hon
 
Hello Martin,
I appreciate the info, especially the different formats, I will investigate the opa627, is there any particular make I should be looking for?.
 
Hon - there isn't much free space inside the CD3.5 case for the boards at all; but equally important is to have them close to the required connections, and to a mounting point. The copper is the top of the mount described in the article, which uses an existing screw inside the case to fix the whole new regulator section in place.

Bmudge - the OPA627 is BurrBrown part.

M.
 
Martin,

Did you replacxe all the chips, or just the O/P pair?

Cheers, Rusty (who's mate has a 3.5...)
 
Just the output pair - it was a quick investigatory hack, and I had only 2 OPA627s to hand ;-). If I were doing the lot, I'd look at using AD8610 or 8065s and Browndog adaptors, or 6no OPA627s if expense were no object! Frankly though, I'm really very happy with things as they stand.

The superregs have now been in place over a year, and were only ever an easily-reversible stepping stone. The greater plan - which has fallen by the wayside - was to get an olive flatcap, kit it out with superregs then use is to case an experimental CD output stage+ headphone amp/preamp section. That way I could develop any number of DIY amp stages on a modular board and retain the 3.5 unmolested as a reference.

As it is, the modded 3.5/ nait2/impulse horns are so beguiliing I am just listening to music instead; I think that's a good thing, actually.

M.
 
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