Building Mark Levinson 38 preamp chassis from scratch

[Elso Kwak]

Regulators

I also replaced original regulators, 78xx type, for low dropout type (from National), used in 38 to 380 upgrade.

Hi Peter,
What type of regulators from National did you use ?
Ever tried LT1963(A)' s?
The cheap stinking normal 78xx types in this multi-Dollar preamp
keep surprising me. 😉

 

[carlosfm]

Please don't use the OPA627 or the OPA2132/4 there.
It will not sound good.
PSU bypassing on the op-amps is .

 

[Elso Kwak]

Power Supply Bypassing

Please don't use the OPA627 or the OPA2132/4 there.
It will not sound good.
PSU bypassing on the op-amps is .

Hi Carlos,
Power supply bypassing on op-amps is extremely important. Why do you think it is """" in this preamp?

 

[carlosfm]

Re: Power Supply Bypassing

Hi Carlos,
Power supply bypassing on op-amps is extremely important. Why do you think it is """" in this preamp?

These op-amps need capacitance on the PSU pins, and a small bypass.
I repeat: as near as possible to the PSU pins.
They will sound bad otherwise, and what I see here doesn't inspire any confidence to use these op-amps, I know they will not sound good, anywhere near of what they can deliver.

Read this page:
http://www.diyaudio.com/forums/show...928&perpage=10&highlight=bypass&pagenumber=34

and also post #341 here:
http://www.diyaudio.com/forums/show...928&perpage=10&highlight=bypass&pagenumber=35

 

[Sunsun22]

The newer 380S is using OPA627 replacing LT1217 and a AD823 replacing one of the OPA2604 (with changes on the R value). It should not sound bad if ML is choosing them.

 

[carlosfm]

The newer 380S is using OPA627 replacing LT1217...

😀
I like it.

But don't try them with adapters on your pre, they don't like it.
Or make some adapters with bypassing, and a wire for ground.

 

[Peter Daniel]

Here's the pic of how I mounted the rectifiers. As I've been using those MUR860 a lot, I tried them here as well and they sound very good.

As to the caps after regulators, I found that 1000/50V BG N sound the best. I tried some Panasonic for audio (6,800u), Technics for Audio (3,300) as well as Nichicon Pure Gold (4,700u) and I noticed that the absolute capacitance is not that much improtant for the sound, but the type of caps used.

BG N sounded best, followed by BG STD, then Technics, Panasonic and Nichicons were the last I would use from the whole bunch.

 

[Peter Daniel]

Re: Regulators

Hi Peter,
What type of regulators from National did you use ?
Ever tried LT1963(A)' s?
The cheap stinking normal 78xx types in this multi-Dollar preamp
keep surprising me. 😉

I'm using LM2937 and LM2990. This is part of 38 to 380 upgrade, and they indeed sound much better than 78xx.

I never tried LT1963, yet.

 

[Sunsun22]

Hi Peter, the pic is missing.

BTW, what is the diode that you are using now? I am still missing how does the Vishey look like. Can you also post a pic of it?

Sunny

 

[Peter Daniel]

Here you go; http://www.diyaudio.com/forums/attachment.php?s=&postid=390344

Those are the diodes I'm using now: MUR860

 

[Peter Daniel]

Here's Vishay/ROE caps pic: http://www.diyaudio.com/forums/attachment.php?s=&postid=427336

You might also check this site and download high res images (5Meg) http://www.marklevinson.com/image_library/index.asp?categoryID=7&productID=9

 

[Sunsun22]

Thanks Carlos, does it mean I need to put two caps between 4 and ground as well as 7 and ground?

Sunny

 

[Sunsun22]

Hey Peter, you are pretty fast.

The high res photo is not available from ML website anymore. I can see the changes of caps in the Lo res pic.

I see you are having some marks on the Vishey caps. Are they polar caps? Where can I buy them from US?

Do you mind telling me the diode that you are using too?

Sunny

 

[Sunsun22]

Peter, the diode I'm talking about is the 16 diodes such as the one installed as CR4404. Or the diodes that you are talking about is the AC rectifiers MU860?

Sunny

 

[carlosfm]

Thanks Carlos, does it mean I need to put two caps between 4 and ground as well as 7 and ground?

Sunny

Yes.😉
And also a 0.1~0.22uf poly between + and -.
Of course, you need to put them under the circuit, as the circuit doesn't have place for them.🙄

Sharing electrolythic caps between several op-amps it not the way to do it, if you want to get the best out of the best op-amps.

When everything's ok, start testing better op-amps.😎
My god, is this a Mark-Levinson?😱
Well... do it, let it playin' for some days, the caps need to -in, and listen carefully.
Then, pick the op-amp that you sounds better to you on that circuit.

 

[Peter Daniel]

High res pics work on ML site, you just have to us "save target as" command and download them first.

The rect. diodes I'm using are MUR860.

 

[Sunsun22]

Carlos, noted with thanks. What brand of caps you would suggest?

 

[carlosfm]

No need for fancy or expensive caps here.
The secret is how and where you use them.
Use good ones, but no need for BGs.

 

[BrianGT]

Interesting. Did you add all the sockets, or were they already on the pcb?

I ordered a ML38 board yesterday, and will see what this thing is about.

--
Brian

 

[Peter Daniel]

Whenever I experiment with bypass caps, I usually install those sockets, so I can try different caps without soldering.

The black stripe means outer foil (I measured them). The caps usually sound better when outer foil is connected to the ground.