compensation cap recommendation? is conventional Ceramic NP0?

jcx

Member
2003-02-17 7:38 pm
..
I would use NP0/C0G but you do have to check ceramic for the specific type

multilayer ceramic have very low inductance, you lose some advantage if you use through hole parts though

film types can have different constructions that may give resonances in the MHz depending on foil edge termination style
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
There is nothing inferior about Wima or Kemet products unless you believe low cost and wide availability are minuses.

If you will feel better by spending more on obsolete dielectrics, try polystyrene film/foil: FSC 160V 100PF 2.5% - LCR COMPONENTS - Film Capacitor, FSC Series, 100 pF, ± 2.5%, PS (Polystyrene), 160 V | Newark element14
or silvered mica: CD15FD101J03: 100pf Dipped Silver Mica Capacitor: Jameco Valuepro

Personally, I would never use low voltage polyester (MKT or greencaps) for compensation caps. Mica and polystyrene types may also not be technically as good as PP film types but some find the small distortion increases useful. Just keep voltage ratings as high as possible within sensible size limitations and performance will be acceptable. In any case, typical VAS compensation caps will need to be rated ≥ the rail-rail voltage supply of a conventional audio amp.
 
There is nothing inferior about Wima or Kemet products unless you believe low cost and wide availability are minuses.

If you will feel better by spending more on obsolete dielectrics, try polystyrene film/foil: FSC 160V 100PF 2.5% - LCR COMPONENTS - Film Capacitor, FSC Series, 100 pF, ± 2.5%, PS (Polystyrene), 160 V | Newark element14
or silvered mica: CD15FD101J03: 100pf Dipped Silver Mica Capacitor: Jameco Valuepro

Personally, I would never use low voltage polyester (MKT or greencaps) for compensation caps. Mica and polystyrene types may also not be technically as good as PP film types but some find the small distortion increases useful. Just keep voltage ratings as high as possible within sensible size limitations and performance will be acceptable. In any case, typical VAS compensation caps will need to be rated ≥ the rail-rail voltage supply of a conventional audio amp.

I have used polystyrene capacitors for comp but the sound became more unforgiving. It was not hyper detail but it was showing the mistakes of the mix engineer. I would prefer the polypropylene may be in that location or need to try MLCC Radial C0G type cap.
 

jcx

Member
2003-02-17 7:38 pm
..
its entirely practical to have 30-40 dB excess loop gain @ 20 kHz with dominant pole compensation
any "error" of the compensation cap is reduced just like any other measured by the feedback loop - by that 30-40 dB @20 kHz, and by proportionately more at more musically significant lower frequencies

if concerned then use "2 pole" compensation for another order of magnitude of 20 kHz gain and compounded by the reduction of signal across the cap at the VAS input over audio range

of course these factors presume a genuine high loop gain design
 

Jay

Banned
2003-02-11 9:02 am
Jakarta
I have used polystyrene capacitors for comp but the sound became more unforgiving. It was not hyper detail but it was showing the mistakes of the mix engineer. I would prefer the polypropylene may be in that location or need to try MLCC Radial C0G type cap.

I don't use polystyrene for Miller compensation. I think it is "distortion", not being "unforgiving".

Problem with polystyrene is I think not every manufacturer follows the coding standard. If "220J" were thought of as 220pF while actually it is 22pF, of course the effect is unexpectedly negative.

Also, if voltage rating is important (as suggested by Ian), not all specify this voltage rating on the body :(
 
I don't use polystyrene for Miller compensation. I think it is "distortion", not being "unforgiving".

Problem with polystyrene is I think not every manufacturer follows the coding standard. If "220J" were thought of as 220pF while actually it is 22pF, of course the effect is unexpectedly negative.

Also, if voltage rating is important (as suggested by Ian), not all specify this voltage rating on the body :(

I think I need to build the cap by myself with copper foils in 5 square cm with 100gsm paper in between.
 

Jay

Banned
2003-02-11 9:02 am
Jakarta
I think I need to build the cap by myself with copper foils in 5 square cm with 100gsm paper in between.

Can such thing reach a hundred pF? Another interesting experiment is using variable capacitors found in many RF circuit. This will make it easy to dial the perfect capacitance (using CRO). I think Hugh Dean had mentioned about variable capacitor but I have never seen this RF variable capacitor implemented in DIY amps so I'm reluctant to try.
 
I have a question that most of the comp caps are available in 100VDC range so how much ACV can be applied on the cap? 1.414 times multiplied?

Most Vas compensation capacitors see the total supply voltage, so if you have 50V rail, a total of 100V. I would not use a 100Vdc capacitor on 100V.

The advantage of these NPO and COG ceramics is that you can get 250V to 1kV ratings in a 1206 package. This will have much better behaviour at MHz frequencies than many boutique parts and that is what matters for compensation
 

Bonsai

Member
Paid Member
2003-07-25 10:44 pm
Europe
www.hifisonix.com
NPO and COG are indeed very good - stable over time, temperature and humidity and especially so against voltage. Film are good, but at high voltage swings, they do have voltage dependent non- linearity issues - see self for example (poly prop, polystyrene and poly carbonates are discussed in 'Small Signsl Design').

I've used Mica 500V types with good results, but some people don't like them - I found nothing objectionable.