[deuginthesky]

Hi everyone,


I am thinking to tweak a Sony CD payer, among other mods (caps, OP amps, bypass...) I would like to try better transistors. The original parts are:

-"3901 5H" tripods (seem to be 2sc3901 "PNP / NPN EPITAXIAL PLANAR SILICON TRANSISTORS").

-"A144 ESF" small size tripods, I ignore what they are

-"C144" small size tripods, I ignore what they are.

-"B1041 RF" (TO-92L format tripod) which seems to be 2SB1041 "1.2W PACKAGE POWER TAPED TRANSISTOR DESIGNED FOR USE WITH AN AUTOMATIC PLACEMENT MECHINE"

-NEC "C3514" (TO-220 format), which seems to be "2SC3514"

-"D 1944", seems to be 2SD1944 made by ROHM.

-"A1048", seems to be 2SA1048.


Which parts would improve quality ?


Thanks in advance.

 

[deuginthesky]

Can somebody give me a hand ?

Are there some transistors replacement databases on the web ?

 

[cotdt]

i think it would be better to replace the analog stage completely.

 

[deuginthesky]

Too expensive mod compared to the DAC performance, unless there are some great and cheap good analog stages.

 

[Pars]

Take a look on DIY audio and look for Jocko's simple I/V and variants (rbroer posted a couple based on this). Supposed to be really good and cheap... four transistors (2SA970 / 2SC2240) and a few other parts per channel. Also, the Pass D1 stage is another one to look at.

To your original question: are these transistors all used for I/V functions? What DAC is in here? Current or voltage output? I would definitely recommend getting a schematic if possible before just shotgunning parts out.

 

[deuginthesky]

DAC is a Sony CXD8567AM (can not find the datasheet).
I will post some pictures of the board.

Thanks for the help.

 

[deuginthesky]

Here are some pics of the board.

Unfortunately, I can not find the schema.

 

[cetoole]

I really would suggest leaving the transistors alone, especially since you dont have any idea what they do in this circuit. Also, I really cant see that sony used them for the I/V or buffer stage; this is probably handled by the opamps I see in your pictures. I would guess at least some of them are for output muting. It would be much more worthwhile to replace the whole output stage, preferably with a discrete solution. If you are looking for easy and inexpensive, Jocko Homo's easy to build I/V stage is probably the way to go. There are improved variations on this, as it was really just posted to get people thinking, but this is probably the simplest it will get while still offering good performance. Some of the variations get quite complex; the one I am working on for my DAC projects currently uses something like 62 parts per single ended channel, so would be in the range of 250 parts for differential stereo. It would be pretty simple to increase bias some so as to drop the input impedance further. As Pars suggested, Nelson Pass's D1 I/V stage is also pretty simple and good.

 

[deuginthesky]

Thanks for the tips

 

[deuginthesky]

Is there somewhere where we can buy PCBs of discrete analog stages ?

I mean PCB with seperate parts to solder, or PCB only.

 

[cetoole]

No discrete I/V PCBs I know of for sale. For the discrete I/V I am working on, it is meant to be part of a larger integrated DAC, so I have no plans to offer PCBs for sale. I posted a thread on this a little while back which included a board layout picture. This isnt for the schematic I am currently working on, but should be pretty good. There may be others like this posted on DIYAudio, but I am not positive. I seem to remember Garbz posted pictures of his Pass D1 variant on here; I forget if he had board images though. If you can etch your own board, or use protoboard, you could build some of the stages pretty easily.

 

[deuginthesky]

Quote:

Originally Posted by cetoole /img/forum/go_quote.gif No discrete I/V PCBs I know of for sale. For the discrete I/V I am working on, it is meant to be part of a larger integrated DAC, so I have no plans to offer PCBs for sale. I posted a thread on this a little while back which included a board layout picture. This isnt for the schematic I am currently working on, but should be pretty good. There may be others like this posted on DIYAudio, but I am not positive. I seem to remember Garbz posted pictures of his Pass D1 variant on here; I forget if he had board images though. If you can etch your own board, or use protoboard, you could build some of the stages pretty easily.

I am not able to design an analog output by myself, I am only able to proceed with basic mods (solder/desolder op amp both DIP or SOIC), choose good combinaisons of film caps, change RCAs...).

As I have many CD-players, I would like to find a discret I/V able to go on almost any player.

 

[Pars]

Well, there's always the LC Audio Zapfilter (http://www.partsconnexion.com/catalog/digital.html). 15% off sale until the end of the month also.

The only PCBs I know of are for the Pass D1 (or a somewhat copy of it):

http://www.diyaudio.com/forums/showt...962&highlight=

I know that Promethius still has some of these available (at least as of January). The PCB set is 18 Euro, and he can supply parts as well.

and this one. Colin (cetoole) looked the design over and saw some things he didn't like. Even so, this would still be better than an opamp stage for I/V:

http://www.diyaudio.com/forums/showt...hreadid=101874

Note that both of these require power supplies in the +/-30Vdc range to feed them.

 

[ECM]

I agree with cetoole. Leave the transistors alone. The ones closest to the opamps look like they are the muting transistors. You should be able to easily trace the output RCA back to the opamp. You'll see the signal from the opamp output will go thru a cap and a resistor or two followed by the muting transistors.

I performed a similar mod on a Sony DVD player. After bypassing the electrolytics in the power supply and adding damping to the chassis I tackled the analog stage. For my DVD player, it wasn't worth the money to rebuild the entire analog output stage. What I did was to change out the opamp and replaced it with an OPA2227. I class-a biased it with two jfets. Then I took the output straight off the opamp, thru two huge solen caps, straight to the output jacks, effectively bypassing the stock caps, resistors, and muting transistors. Sometimes I can hear noise when the player is searching for a track, but the increase in sound quality is worth it.

take a look here: http://www.head-fi.org/forums/showthread.php?t=119323

ECM

 

[deuginthesky]

I will perform the same kinds of mods if I can not find any discrete "ready to solder" I/V stage (zapfilter is too expensive to me).

I have soldered 2 OPA2277P for the analog stage instead of the JRC4580D, OPA2134PA instead of the OP amp at the right on the 1st picture, same OPA2134PA between red and black cap on the second picture, and OPA2228P between the main cap and the big transistors (I think the op amp is used as a voltage regulator).

I will replace carbon resistors by standard 1% metal (except the 620ohm which will be 5% metal) and use some big MKP + polystyrene caps soldered on gold plated new RCAs.


Hope will raise sound quality.