Recap JVC XL-Z1050 CD Player

[seppstefano]

As a followup,
thanks to the SM you uploaded, I found that I had shorted to ground the signal by replacing C385 and 386 with jumpers I thought they were coupling caps and not LPF caps...

Now, back to the JVC: from the diagram I found a pair of muting transistors for headphones output and some ELCO coupling caps (these should be bypassed with a wire )

Thank you again!

[georgehifi]

Stefano hi, I had one of the JVC-1010tN and made a considerable improvement to it by disconecting the muting and headphones, then exchange the NE5532's for AD 825' on Browndog adaptor boards, then direct couple the output (short out the coupling cap) then short out two of the three 100ohms series output resistors to make it 100ohm output impedance.
After all that is done adjust the MSB (most significant bit) on both channels, use a good sensitive scope an you won't need the the recommended amp circuit in the diagram. Then it will sing.

Cheers George

[seppstefano]

Thank you George for all these advices,
I just spent a couple of hours at listening at the results bynow with a pair of shure earphones (those once recommended by Mr. Linkwitz) and am really satisfied. The headphones sound is so good to me that I don't know if I will be able to disconnect the headphones output...

I saw three resistors just before the output (R346, 347, 348 for one channel) but aren't they marked as 51Ohm? Should I get rid of only one of it? Why are we looking for 100Ohm output impedance (my pre is an Accuphase C222).

Bear with me, George, I looked for R329 and R330 on my schematics. They are after a first op amp, spec'd as 2K. Was the same on yours? And, wouldn't you suggest to upgrade the op-amp output stage to a discrete or tubed one?

Thanks a lot for sharing and for your patience

Stefano

[georgehifi]

This is all I have hope it helps.

Cheers George

[seppstefano]

Thanks a lot George and Ahiukka,
bynow I removed all muting (yet can't hear any nasty sounds), all signal coupling caps and this evening I'm going to evaluate the sound (I still have to fix a jumper not well soldered).

BTW I found empty room for elco caps between opamps. From the somewhat hard to read schemas they seems caps supporting each opamp Vcc (so to say). I'll try to fill them even if not with 100V rated caps as I seem I can read...

Stefano

[seppstefano]

Here are a couple of shots showing the bypass work with caps and/or jumpers, all muting removal and the two rows of caps (rated 10/100 and 4,7/100).

From the schema (last pic) I haven't yet decided what to do with these missing caps (they are designed, yet are not present neither on the part list or on the board): whether solder the specified ELCOs or film caps, or both, or nothing

The sound of the unit - at least via headphones - is now very very good. Indeed I've heard lines and details never heard on well known tracks. But in general there is much more of everything... and I've collected a bunch of re-usable transistors and caps

Now, I'd like to try a FET output stage for this little wonder of dac. It seems to me it has balanced outputs

Stefano