Meridian 508-20

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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
 
OpAmp functions?

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
 
CDM-7

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
 
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
 
Opa727

Two months on, and I finally got round to trying something else.

OPA627 was fine, but at +/- 5V rail it was not getting properly fed. Also the high slew rate led to a touch too much brightness. One could increase a slew rate limiting PS cap at the opamp inputs (I used 2.2n instead of 1n as original). But still not elegant.

Just tried OPA727. Love it. For this application definitely the better choice (+/- 6V supply, output almost rail to rail, just as low noise, half the slew rate of 627). Only complaint is that it comes in MSOP only (note -- NOT SOP). Could not find any adaptor board on the market, so etched my own. A pain to solder at pin pitch of 0.6mm !!!


Patrick
 
Discrete I/V conversion

Hi Patrik,

This is an old thread, I know…

I just placed 4x Burson's Discrate OpAmp (single) in my AVM DAC1.2 (DAC + PreAmp) directly behind the DAC chips. Best solution for this I/V problem, at least in my configuration.

They are simply superior to NE5534, OPA604, LME 49710 or even OPA627BP - none of the which came even close to the Burson's all round sound reproduction.

By changing the DACs from PCM63 to PCM63-K, it seems that the Burson’s are even better then I would have thought...

By the way, in the PreAmp Section I am using 8x OPA627BP.

The positive character of the AVM is not damaged by doing all this; neither have I thought something dreadful would have happened to a Meridian by such a tuning.

Meanwhile, you might have build a discrete I/V conversion unit for your Meridian (I can't tell). If not - this is indeed the right way to go.

IY
 
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