Topic: Opinions on coupling caps/DC-blocking caps?

[groovon]

A question for DIYers or small manufacturers of battery boxes: What sort of coupling caps are you using in your battery boxes, phantom supplies, and mic preamps (or have observed that others use)?

At 10uF and up, polypropylene or film-type caps would seem to be ruled out as being too physically large to suit small box designs.

I've used NP electrolytics bypassed with small metal film caps, and they sounded fine. I recently made a tiny phantom box using large tantalums as DC blockers. Tantalums of course are in disrepute as poor signal-coupling caps, due to their non-linearity - though some reputable manufacturers in the past had no qualms using them (Revox recorders, and Naim hi-fi preamps come to mind).

I'd be very interested in your opinions. Thanks!

Dave

[kirk97132]

^^^ dead link

[groovon]

@mshilarious - Also the comprehensive 'capacitor listening' tests in two articles by Walt Jung in The Audio Amateur in the late 1970s (part 1 here):

http://waltjung.org/PDFs/Picking_Capacitors_1.pdf (interesting comments here specifically on distortion in tantalums [edit] - and ways by which it can be reduced.)

It's always surprised me, after all this, that some real classic hi-fi designs used tantalum caps all over the place, yet received wide acclaim as having pristine sound.
No doubt, in the case of Revox, any possible capacitor-related ills were masked by normal tape distortion... In any case, the end result, tantalum caps and all, was still 'hi-fi'.

cheers

[kirk97132]

Whoops, let's try this one:

http://www.scribd.com/doc/2610442/Capacitor-Sound

[groovon]

I don't think anybody would select tants anymore unless size is absolutely critical--tantalum has gotten very expensive; prices on those caps have doubled in the past year or so.  I use lots of them as filter caps in my small designs    I have one microphone where I use them as coupling caps, but in that case capsule distortion is much higher anyway.  No one has ever complained.

As for a battery box, a nonpolar electro is less than half of the price of the tant.  Kind of a no-brainer there.

And the price of solder!  Aaagh!  The pound I just bought had nearly doubled since January!  So I checked the price of tin, it went up some but not that much . . . 

Actually, size was critical (I used too small a box!), and yeah they were kind of a lot, but the local place didn't have the right NPs anyway. I've just ordered some 33uF NPs from Mouser to replace them (if they'll fit).
BTW, I get my solder from the 'solder guy' at my regular ham swapmeet, Alpha metals 63/37 for $9/lb. PM me if you want the contact, and I'll get it for you next time I go.)

cheers

[Walstib62]

anyone have a schemo for a good batt. box?

[groovon]

What mics are you powering?

Post #7 on this page (link below) shows a simple 9V battery box circuit that should work for most electrets, I believe:


http://taperssection.com/index.php?topic=132627.0

(BTW, the poster of the circuit mistakenly calls it a phantom supply, but it's not - it's just a 9V battery supply.)


I'd get a second opinion though, based on your specific requirements.

[guysonic]

Using Tantalums as DC blocking low distortion audio signal coupling can work just fine if using a large enough capacitance value so 'as loaded' low frequency -3 dB (high pass filter cutoff frequency) is (ideally) ~<10x below the lowest audio frequency of interest.  Use 10x+ cap rated DC voltage to expected audio P-P voltage.  And >2X voltage rating of expected cap applied DC bias voltage.   Also, best to place as low an impedance load at the 'output' of the capacitor to minimized cap DF factor, do this while keeping -3 dB HiPass filter cutoff well below the audio low frequency of interest as suggested.

These are just general rules-of-thumb allowing Tant Caps very good audio performance at least in my experience.  Also, these 'rules-of-thumb' seem to hold true considering the two articles detailing this subject showing where distortion is not an issue, and under what conditions Tantalum capacitors start to show excessive audio distortion characteristics. 

In other words, don't rule out Tantalums for quality audio coupling especially when tight on board space, it's how you're using them that makes all the difference!

[Walstib62]

What mics are you powering?

Post #7 on this page (link below) shows a simple 9V battery box circuit that should work for most electrets, I believe:


http://taperssection.com/index.php?topic=132627.0

(BTW, the poster of the circuit mistakenly calls it a phantom supply, but it's not - it's just a 9V battery supply.)
Audix "miniature" caps. 1290 specifically, which use 9 volts.


I'd get a second opinion though, based on your specific requirements.

[groovon]

What mics are you powering?

Post #7 on this page (link below) shows a simple 9V battery box circuit that should work for most electrets, I believe:

http://taperssection.com/index.php?topic=132627.0

(BTW, the poster of the circuit mistakenly calls it a phantom supply, but it's not - it's just a 9V battery supply.)

I'd get a second opinion though, based on your specific requirements.

(Just cleaned it up a bit for you:  8>)

Walstib62 says:

Audix "miniature" caps. 1290 specifically, which use 9 volts.