Musical Fidelity Digilog Dac

[ekidnah09]

Hello All,
I have just bought a Musical Fidelity Digilog Dac which I intend to modify. I need some help as there is a previous repair which is not as good as I would like.
Firstly does anyone have the circuit diagram/service manual?

If not would someone with one of these units be able to tell me the value of the following components: transistor TR8, resistor R46 and resistor R47 (near -15volts adjusting pot ) these have been replaced in my dac but not with the same type as the factory.

There is also a modification on the board, (near the sony receiver) R20 has 2 resistors a 15Kohm and a 4.71Kohm with a 330uF/63v capacitor from their midpoint to TR4 is this a factory modification?

I have attached some photos which may help.
Thank you in advance for any help

[Lenin21]

Yes - it seems to be a factory mod - mine has exactly the same '330uf/2 resistor' arrangement.

The values you're after are as follows:

TR8: BC414C
R46: 6.8 ohm
R47: 10k

Hope that helps.

Could you help me identify some values?

My Digilog board has several components missing, as follows:

C13
C15
C100
C23
C29
C38
C98

Reg4
Reg5
(I'm presuming these are 15v types, but better safe than sorry!)

Thanks in advance.

[Smiffy]

Be careful of the pcb tracks.They are very fragile in the digilog

Smiffy

[Lenin21]

Like so much MF gear!

Smiffy, I may be imagining this, but don't you have a schematic for the Digilog?

If memory serves, we had a discussion some years ago about my crazy idea to run the Digilog (or any TDA1541A based DAC, for that matter) at 176.4khz with the Paicfic Microsonics HDCD digital filter chip (I've got a few).

Anyhow, warning anout the PCB tracks noted (thanks) do let me know if you have those values to hand.

[ekidnah09]

Lenin21

Thanks for the information here is what I have found so far
C13 47uF/25V electrolytic
C15 47uF/25V electrolytic
C100 47uF/25V electrolytic
C23 47uF/25V electrolytic
C29 47uF/25V electrolytic
C38 47uF/25V electrolytic is this is next to C39? C38 text is not fully visible?
C98 10uF/35V electrolytic

Reg4 ua7905
Reg5 7805

I can take pictures of the markings of the regs and caps if you like. I think the 15volt rails are regulated by the transistors near the op amps (TR9, TR11 & TR7 for positive 15 and TR8, TR10 & TR12 for the negative) I will only know for certain once I trace out the circuit.

If in doubt trace the +5 and -5v rails from the DAC back to the regs

I emailed the Australian distributer for some information and got nothing back. I will have to trace out the circuit in the future as the toslink output is intermittant on warm up.

Let me know if you need any other values or photos. Oh and my board is version 4 if that helps.

Smiffy thanks for the warning.

[abraxalito]

Originally Posted by Lenin21

If memory serves, we had a discussion some years ago about my crazy idea to run the Digilog (or any TDA1541A based DAC, for that matter) at 176.4khz with the Paicfic Microsonics HDCD digital filter chip (I've got a few).

Have you actually tried that? I'm curious because I'm just starting on a reverse engineering project to work out what goes on inside an SAA7220 in an attempt to find out why NOS sounds much better. If you've found it sounds good with a PMD100/200 that'll be an interesting data point.

[Lenin21]

No, I've not actually tried it (yet).

It is still generally regarded as the finest digital filter chip ever made though....

[Smiffy]

Hi Lenin21
I'm sure I had one.I'll check in the loft.Although its not an official one.

Smiffy

[abraxalito]

Originally Posted by Lenin21

It is still generally regarded as the finest digital filter chip ever made though....

Yeah just from reading the datasheet, I get the strong impression those guys know their stuff. And they designed the Berkeley DAC too which has a fine reputation. So when I get around to building my own digital filter I'll start by modelling it on theirs...

[wakibaki]

Originally Posted by abraxalito

I'm curious because I'm just starting on a reverse engineering project to work out what goes on inside an SAA7220 in an attempt to find out why NOS sounds much better.

Not that I'm agreeing with you, but it's easy to work up a rationale for why this might be the case.

1. No-one has yet demonstrated that bit or sampling resolutions greater than 16/44k1 contribute to an improved perceived quality.

2. Post-processing from the native resolution changes the data. There's always the possibility to change it for the worse.

If I was going to upsample I'd do it in software, not hardware. Why add to the hardware design problems? It's another chip.

Upsampling to ease reconstruction is another issue.

Everybody knows that upsampling a photograph is a waste of effort. You might disguise pixellation artifacts in a large print, but only at the cost of a softened image or loss of detail. If you want improved quality, you need a bigger megapixel resolution. Below a certain size of print though, it buys you nothing.

w