Capacitor Choice In Tube Microphone Construction

wiggum665@hotma · 1st April 2008, 08:51 PM

Hey Everyone. Have some quick questions, as I'm planning out the bill of materials for a Gyraf G-7 out of a MXL 960 . I'm used to Guitar Amp construction, so the component choices for capacitors are a little different, mostly just Sozo mustard cap replicas, silver mica for the smaller values, and Sprague TVA's for electrolytic. Occasionally I will see bypass caps across electrolytic, but not always.

My question is, what kinds of caps does everyone like to use in their microphones?

Francis Vaughan · 2nd April 2008, 04:16 PM

Not having built up a mic, but a general observation. HiFi capacitor selection is pretty much the vogue. But the big constraint is space.

So, small values, best first: polystyrene, silver mica, NPO aka COG ceramic.
Medium values. Polypropylene film foil, polypropylene metalised film, then polyester.
Big values. Electrolytics. Blackgate if you can find any. Then Silmic, Cerafine, Nichion Muse, typically go for low ESR, better brands.

The Sozos are basically polyester film foil with a lot of hand rolled mojo. The polypropylene orange drops (715P and 716P series I think) would be good.

You can spend any amount of money on capacitors. Really. But using good dielectrics is 99% of the issue. Looney stuff like copper foil in paper and vegetable oil is not going to do anyone any good. Let alone the silver foil caps.

tINY · 2nd April 2008, 08:21 PM

Generally speaking, Polypropylene caps are the best practical choice if they will fit.

For DC blocking, Low ESR electrolytics are the way to go when you need big values.

-tINY

craigmorris74 · 3rd April 2008, 02:23 AM

Haven't built this yet, but read most of the threads on it. There are two caps that need to be polystyrene. The others can be polyester. Look at the schematic and parts list on the Gyraf site, and you'll find this info.

gyraf · 3rd April 2008, 10:11 AM

Yes. The critical caps - associated with the very-high impedance section - need to be polystyrene/styroflex types to achieve stability in hostile environments. Other than that, the signal pass capacitor between the tube plate and the output transformer is the only real contributor to capacitor "sound" in the G7. Personally, I like simple Wima polyester here - but differences are very small indeed.

Jakob E. (Gyraf Audio)

Gilad · 8th April 2008, 08:27 PM

hi, i am about to have a go in building the Gyraf G7 mic, and there seems to be a difference of some capacitor values between the schematics and the layout prints. there is a 220u/25v Capacitor on the on the layout diagram, which seems to replace thee 100u/35v Cap, in parallel to the 1uf on the Schematics. -any ideas what would be better?
Also, the 2u2/250v Cap connected to grnd (through the 100k and 10k Resistors at the 160v feed) seems to be gone in the print, while appears in the Schematics. is it not important for keeping the voltage feed clean?
if anyone has some light to shed, i will be very pleased -.

thanks for your help,
-Gilad.

gyraf · 9th April 2008, 05:40 AM

All this is explained and discussed at the P-P nerd-forum found at Prodigy Professional :: Index

Jakob E.

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1st April 2008, 08:51 PM	#1
wiggum665@hotma Gear Head Join Date: Aug 2006 Posts: 35	Capacitor Choice In Tube Microphone Construction Hey Everyone. Have some quick questions, as I'm planning out the bill of materials for a Gyraf G-7 out of a MXL 960 . I'm used to Guitar Amp construction, so the component choices for capacitors are a little different, mostly just Sozo mustard cap replicas, silver mica for the smaller values, and Sprague TVA's for electrolytic. Occasionally I will see bypass caps across electrolytic, but not always. My question is, what kinds of caps does everyone like to use in their microphones? __________________ There are two kinds of people in this world, those who like Kid A, and those who like Pablo Honey. Although they might not get along, they can both agree that OK Computer was pure genius - Musings about Radiohead

2nd April 2008, 04:16 PM	#2
Francis Vaughan Lives for gear Join Date: Jan 2008 Posts: 537	Not having built up a mic, but a general observation. HiFi capacitor selection is pretty much the vogue. But the big constraint is space. So, small values, best first: polystyrene, silver mica, NPO aka COG ceramic. Medium values. Polypropylene film foil, polypropylene metalised film, then polyester. Big values. Electrolytics. Blackgate if you can find any. Then Silmic, Cerafine, Nichion Muse, typically go for low ESR, better brands. The Sozos are basically polyester film foil with a lot of hand rolled mojo. The polypropylene orange drops (715P and 716P series I think) would be good. You can spend any amount of money on capacitors. Really. But using good dielectrics is 99% of the issue. Looney stuff like copper foil in paper and vegetable oil is not going to do anyone any good. Let alone the silver foil caps. __________________ The night is coming, and its filled with dark surprise.

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2nd April 2008, 08:21 PM	#3
tINY Lives for gear Join Date: Jul 2004 Location: Orygun Posts: 6,017	Generally speaking, Polypropylene caps are the best practical choice if they will fit. For DC blocking, Low ESR electrolytics are the way to go when you need big values. -tINY

3rd April 2008, 02:23 AM	#4
craigmorris74 Gear maniac Join Date: Jul 2005 Posts: 206	Haven't built this yet, but read most of the threads on it. There are two caps that need to be polystyrene. The others can be polyester. Look at the schematic and parts list on the Gyraf site, and you'll find this info.

3rd April 2008, 10:11 AM	#5
gyraf Gear addict Join Date: Jun 2002 Location: Denmark Posts: 487	Yes. The critical caps - associated with the very-high impedance section - need to be polystyrene/styroflex types to achieve stability in hostile environments. Other than that, the signal pass capacitor between the tube plate and the output transformer is the only real contributor to capacitor "sound" in the G7. Personally, I like simple Wima polyester here - but differences are very small indeed. Jakob E. (Gyraf Audio)

8th April 2008, 08:27 PM	#6
Gilad Gear interested Join Date: Apr 2008 Posts: 1	hi, i am about to have a go in building the Gyraf G7 mic, and there seems to be a difference of some capacitor values between the schematics and the layout prints. there is a 220u/25v Capacitor on the on the layout diagram, which seems to replace thee 100u/35v Cap, in parallel to the 1uf on the Schematics. -any ideas what would be better? Also, the 2u2/250v Cap connected to grnd (through the 100k and 10k Resistors at the 160v feed) seems to be gone in the print, while appears in the Schematics. is it not important for keeping the voltage feed clean? if anyone has some light to shed, i will be very pleased -. thanks for your help, -Gilad.

9th April 2008, 05:40 AM	#7
gyraf Gear addict Join Date: Jun 2002 Location: Denmark Posts: 487	All this is explained and discussed at the P-P nerd-forum found at Prodigy Professional :: Index Jakob E.