Advice on recapping a Digital recorder?

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Hi All
Newbie here. This looks like the place to ask for advice/help on re-capping and generally upgrading my Fostex D1624 digital multitrack recorder.

After reading several threads here over the past few days, I'm hoping you guys wouldn't mind offering your suggestions on a specific application? I assume what I have here is basically a AD-DA DAC X 8 which I have seen extensive excellent comments on!

I am not totally pleased with the sound of this unit but its functionality fits my setup perfectly and audio-wise I don't think there's anything better out there worth investing in. Soooo upgrading is my option.

In addition to upgrading the Op Amps (LM6172, ADA4627-1 X 2 with Brown Dog adapters (see input section of pic) and LM4562 are on my short list), I'd like to put the best possible caps in for the best possible sound.

In the pic, I've put black dots on the caps I want to change (Ch 1 is basically what is identified). I've also attached .pdf's of the circuit sections in question.

As you can see from the attached pic, my choices are REALLY going to be limited by space on the board. I do have vertical space if that helps?

Could you all please comment on the following?

1) Good idea to remove mute transistors?

2) Is there a better analog input cap you can recommend vs. those tiny 10uF/16V SMDs?. I'll only be using the unbalanced input in the future and would feel comfortable soldering a full sized cap in there).

3)What would you recommend arofor the 100/16 analog output caps?
The only cap that I found to fit here are the Panasonic FM 100/25s?

I think I'll skip bypass caps on ins and outs as that seems to be hit or miss?

4) What would you recommend for the three 10/16 caps around the Digital In Converters?
Sounds like Rubycon ZA/ZL are the way to go?

5) What about the two 10/16 and one 47/16 caps around the D-A stage?
Sounds like Rubycon ZA/ZL are the way to go?

I have a bunch of Nichicon Muse ES bipolars if you think they would work anywhere (reading this forum seems to indicate that bipolars are only for crossovers)?

Is there anything else you see that can be improved?

Next I am going to research clocks and I'm thinking about an external power supply (Acopian or so).

Thanks in advance and I really appreciate the help!

Fleximan 5


  • D1624 Mother Board.jpg
    D1624 Mother Board.jpg
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  • D1624 Ins and Outs and Converter circuit diagrams Mother Board.pdf
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I'm sure you'll get suggestions for Elna Silmic caps as I'm told they sound better. I repair broadcast gear and I'm more interested in only doing it once so I tend towards Panasonic FM and FC series caps for through hole and FK/FC/FP for surface mount. Do they sound inferior? Don't know but I get no complaints even from the audio guys. I think they're just happy to have things working correctly.

You have the skill and tools to do the job without lifting pads? I use a Metcal iron with a 700 degree tip. Pad damage is very rare. The STTC-126 tip is really good for both through hole and SMD.

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Thanks for the tips!
Yes, I only want to do this once but also get it sounding as good as I possibly can. I've got no probs with surface mount stuff.
I've built great sounding acoustic spaces and want to try and capture that as audiophile-esque as possible.
I've written an albums worth of stuff for a sound track and need to get to it!
I did read some posts about the Silmics not lasting so long and also posts stating that they were just fine.
I am new at this. Have you any reason why they would use a small SMD cap at input but use a larger through hole at output?
If you all out there have preferences for different caps in different locations, please explain. I am really enjoying learning about this stuff.
Thanks Again
Hi All
Thought it might help if I blew up the .pdfs of the circuits?
Hope this helps.
All the Best


  • Analog IN.pdf
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  • Analog OUT.pdf
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  • AD-DA First Stage.pdf
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  • AD-DA 2nd Stage.pdf
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  • AD-DA VBIAS.pdf
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Bipolar Al electros have less measureable audio distortion - Bateman's Capacitor Sound series recommends using higher V rated bipolar Al electros in signal path where film won't fit

also "supersizing" - larger C value to put RC constant way below audio helps distortion too

but physical oversize caps can pick up more emi
Thanks JCX
According to Bateman, all electrolytics are CRAP!
Too bad lead length inductance is such an issue....
However, that article was written in 2002. Have there been no significant improvements in electros since then?
Someone on SOS forum had said electros have made great strides and you don't even need to bypass them any more..
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Volumetric efficiency... that's why the newer Panasonic FM 100/25 has the same size as the stock Nippon Chemi-Con SME rated at 100/16.

Can you give an example/link of a brand of solid polymer electrolyte bipolar?

At this point...I am going with the Panasonic FM on the Analog Outs (only thing that fits and probably better than stock) and the Nichicon Muse ES bipolars on the AD-DA sections. I'll use Panasonic FMs wherever else I decide to "upgrade".

I also get now that the SMD caps for the analog inputs are no big deal due to the low voltages going through them and they are actually good for the fact that there must be minimal RFI and inductance due to the lack of leads. Leaving those alone.

I found another good article that makes reference to Bateman here:
Capacitor Characteristics
As I've been reading another question has popped up.
Seems like lowest ESR caps are what you want around digital due to the need for high instantaneous currents.
Could somebody please look at the AD-DA pdfs in post #4 and tell me what they do / which ones should use the low ESR caps.....I assume that's what Rubycon ZL/ZA were mentioned for?

AD-DA First Stage

AD-DA 2nd Stage

AD-DA V Bias

Thanks Again guys. This is really appreciated as I am a muscian and a metallurgist but NO EE.
All the Best
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