Meridian 508-20

[Richard984]

Can anybody point me to a good resource(s) for modifications to this player?
I do not think (for now at any rate) that I am interested in upgrading to 24bit.
Thanks.

[buchignani]

Similarly, I'm losing my battle with my urge to open up my Meridian 508-24 and start upgrading it. Anyone out there have a schematic of this player?

Norman

[Mikelo]

What laser does the Meridian 508 use? The
206 used cdm4/21 and 4/19 and the 506
used a cdm12.

Thanks.
Michael

[EUVL]

I just opened mine this morning, and decided to do nothing other than 4 constant current diodes from pin 6 to pin 4 on the 4 opamps (NE5534).

It is already a very good player as it is. The most obvious mod is to change the clock. But look at the layout -- practically no space to put a clock and a separate power supply.

Then I thought about a JFET analog stage -- again no space to do anything exotic like separate transformers or batteries. The output stage is already discrete (2x MPSA52s).

Then maybe one could change the opamps. Some people might find NE5534s awdful. So maybe an OPA627 or OPA132 or AD797 according to taste. I'd rather just bias them class A, which I did. Takes any remaining harschness away, but no hugh difference (was already very good).

Maybe an external DAC is easier to do, but then it is not Meridian anymore.


Patrick

[Mikelo]

Is the transport a CDM12?

[Lourens]

Quote from Bob Stuart (designer): "We were using the Philips CDM12.4, now we're using the CDM12.5"

From this Stereophile 508.24 review

ATB
Lourens

[EUVL]

Well I could not resist the temptation and changed the 4 NE5534's to OPA627s, again with 2mA bias from output to V-.

Highly recommended.
The difference is NOT subtle. And I am not changing back.
(Always a matter of taste of course.)


Patrick

[buchignani]

Dear Patrick,

A couple of questions:

What are these OpAmps doing?

Was opening up the Meridian straightforward?

Any other possible modifications that came to mind? Caps? Diodes?

Did you perhaps secure a schematic? I haven't been able to find one anywhere.

Thanks,

Norman

[David Nessim]

To whoever asked,
All the mentioned players use Philips transports, cdm-7 to CDM-12, swingarm for the laser. The obvious easy upgrade is to replace the opamps, but the AD 797 mentioned will suffer from current noise if source resistance is over 1-2 K Ohms. It is best with very low source resistance. So I would opt for the much cheaper OPA-134, 2134 etc.

David

[EUVL]

Like the NE5534, the AD797 is a bipolar device, which accounts for the very low noise figures. Like the NE5534, it suffers from a higher current noise compared to any FET based opamps. I do not therefore see it as disadvantageous as a one-to-one replacement for the original opamps. It is much more prone to instability, but that is also well known fact.

As you can see in post #7, I did not opt for AD797, but OPA627 (just spontaneous choice, have not and do not intend to try all opamps in the world). Whether OPA134 is good enough or better than OPA627 is a matter of subjective judgement. There are no dual opamps that I can see in the analogue section, so OPA2134 is NOT applicable in the Meridian 508-20.

You should be prepared to adjust closed loop bandwidth if you choose to change op-amp from the original NE5534s.

And I have not changed anything else. If I were to change anything, then probably next would be the regulators (LM317 and 337 on the stock PCB). There is no limit as to what you can change -- clocks, caps, power supplies, digital chips , ...... ) Lack of space is a big issue as far as I am concerned.

And I have no schematics. If anyone has one, I would appreciate a copy as well. Makes life a lot easier.


Patrick