Mod ADK A51 internal pic ... Which capacitors shall I change?

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Disease8

Disease8

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Hi just opened up my ADK A51, it has seen a lot of use and been dropped a couple of time but I think the capsule is intact. I was planning on doing the royer mod to it, waiting for my issue of TapeOp to arrive. Any caps I can change that will make a difference as an alternative to the royer mod if I decide not to go ahead? As I have no experience I am worried getting hold of the components may be a problem, but just a couple of caps should be ok.

Which caps need changing and to what sort?
Shall I change the transformer?

Thanks for your time..
Dom
 
Here are the pictures...
 

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one more thing, the capsule looks dusty and probably needs a clean, can I get away with doing this?
 
I've cannibalized an old hi fi system and its got loads of capacitors inside that aren't ceramic.Could these be useful?
 
some of the ones that look like a lump of wax with two wires are polyester right? Is this what I want?
 
c3 c5 c10 c11 all look like crummy ceramic caps would they benefit from a change?
 
If I remember these right, there is a capacitor you're overlooking. Its on the backside of the board with the standoffs. That one really needs to be changed to a polystyrene 1000pF 50v. The other caps you mentioned are tantalium, and they can be OK. I'd put in good film caps instead. look for the same values in the 50v-63v range and hopefully you'll find ones that fit.

If you're considering do a tube mod or another rebuild to it I'd wait and do that.

Don't try to clean the capsule yourself unless you are sure of what you're doing. A dusty capsule isn't that big a threat. Its when it's covered in goop and starts sounding dull or popping that you need to worry.

A better capsule would do much more for the sound.
 
As PhilGood said, the most important one to replace is the one on the back side of the FET board leading off to the capsule. This is the coupling capacitor. This blocks the DC that powers the capsule so that the FET doesn't see it on its input.

Because this is handling the signal straight off the capsule, it is at its lowest level, and even tiny amounts of distortion are magnified through the signal path. Ideally, you'd like something that is as linear as possible, and you want it to add as little phase distortion as possible to low frequency (near-DC) signals.

Any film cap is going to be a step up from the tantalum that is probably there now. IIRC, polystyrene or polypropylene film are generally considered best. Mylar is not quite as good, but still quite usable. You do *not* want the "hi grade audio capacitors". Electrolytic caps suck in the audio path. Those might be better than the cheap 10¢ electrolytic caps from Rat Shack, but you still don't want them in your audio path if you can help it.

That said, every single cap I see in there except C1, C6, and the one next to C6 looks like dipped tantalum, and I'd replace all of them. They might be multilayer ceramic, in which case they're at least serviceable, though I'd still replace them.
 
Yeah, you could find at least good mylar capacitors in the 50-63v range that would be far superior. I saw a mod somewhere (perhaps on eBay) where they're offering an upgrade to this kind of circuit that puts in on par with a U87, although I can't verify that personally. I've seen the website where this guy "JJ Audio" does the mods. His results might be spot on, but his work looks extremely sloppy to me. Hand drawn PCB's and shoddy paint jobs and logos. Personally I wouldn't pay what he's asking until he improves his QC.

Not very professional at all.
 
Hi!

Thank you for the replies guys. I recently started to get into electronics and finding it fascinating. Going to build a very simple mic preamp from the components I got out of an old hi fi and tape deck.. There's plenty of transistors and an op amp that is the wide bandwidth low noise sort for audio. Started a thread on Prodigy Pro (if you would lend a hand).

Sorry that's off topic.

I'm getting a Behringer C1 LDC off ebay to mod first before I tamper with the £100 mic. There are lots of polyester caps from the hi fi are these any good?
Will they be any improvement over the electrolytic ones?

D..
 
Just got TapeOp royeer mod issue! Looks great! You can't buy the kit anymore can you?
 
Oh, there's all kinds of ways to get past that. I made all mine without buying the kit. I made my own PCBs and everything! There's stuff on the web, you just have to know what to look for and who to ask.;)
 
Disease8 said:
I'm getting a Behringer C1 LDC off ebay to mod first before I tamper with the £100 mic. There are lots of polyester caps from the hi fi are these any good?
Will they be any improvement over the electrolytic ones?
Click to expand...

Depends on whether they're in the audio path. Electrolytic caps used for power filtering are unlikely to have much impact on the sound. Electrolytic caps used as coupling caps (audio running through them)... bad, very bad.
 
dgatwood said:
Electrolytic caps used as coupling caps (audio running through them)... bad, very bad.
Click to expand...

They aren't that bad if they are good quality and properly biased. Capacitor distortion of this type is mostly second-order and likely way below the distortion from the FET.

Odds are pretty good your mic preamp has electros at the input anyway.
 
I don't know, I've seen some graphs with 1khz run through electros that has some pretty obvious distortion.
 
PhilGood said:
Oh, there's all kinds of ways to get past that. I made all mine without buying the kit. I made my own PCBs and everything! There's stuff on the web, you just have to know what to look for and who to ask.;)
Click to expand...

awsome!! thanks man.. I'll query you on that when I take the plunge and dissect my ADK A51 . . . Gonna have fun liking a Behinger C1 first though...
 
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