Experimenting with caps

[pro_crip]

I was curious, when one is experimenting with cap sizes and assuming I stay within voltage ratings and outside the power supply, can I damage the the circuit by going too high or too low? I know there'll be audible diffs, I just don't want to fry an amp. Thanks

rich

[Grainger49]

In some instances the cap value can change.  For instance PJ said there would be no problem with upgrading the FP III output caps, 2.0uF, with "better" 0.47uF caps.  In most all cases the voltage rating should stay the same as you indicated.  I don't know of an instance where the Bottlehead selected cap has a voltage rating higher than needed.  That eats up cost and space, but it might be done somewhere.

Decreasing the value of signal path caps will raise the point where the RC roll off starts in the bass range. PJ aims for a pretty low f_o, the 3dB down point of that roll off.  Increasing the value will lower the f_o, but you will waste cash.  You might want to get an even better cap instead.

In Bottlehead equipment you can't damage the circuit changing signal path caps.  Don't mess with the RIAA EQ caps in a phono preamp.

[pro_crip]

Thanks grainger, just the info I needed and pretty much expected. Just needed some reassurance from those that knows. A round of Woodford Reserve on me

Rich

[Paul Birkeland]

Hello Rich, I would say you're OK as long as you stay within half an order of magnitude in either direction.  If you really want to try, for instance, a 100uf cap at the output of the Foreplay, a small circuit change would be in order.

[Tickwomp]

Expermenting can get expensive fast.  I'm very interested in this topic, because the extended Foreplay has the 3.0uF Auricaps for coupling caps.  I founds some V-Cap CuTF in .47uF that I would love to try, but at that price, I need to know I'm not rolling off any base. 

Can anyone post the math that is necessary to "show" how it all works.  FWIW, my extended Foreplay is only connected to my 300B Paramounts using 24" Silver Interconnects.

Thanks,

Ken

[Grainger49]

Ken,

Edited, I shouldn't leave misinformation out here.

Let's see.  If you are talking about the FP III final output cap, the formula is 1/2*Pi*R*C.  The formula gives the 3dB down point.  Pi is the constant, R is the input resistance of the power amp following the FP III and C is the capacitance.  Remember that 1uF is 0.000001, or 0.47uF is 0.00000047.  For the Paramount I calculate F_o, 3dB down point, of 1.3599 Hz.  The response will be essentially flat a decade above that at 13.599 Hz.

[JC]

Isn't micro 6 places to the right of the decimal?  As in 1 microFarad = .000001 Farads?

[Grainger49]

Yes, that makes the f_o, 3dB down point at 1.3599 Hz and the response essentially flat at 13.599 Hz. Still very low frequencies.

Edited the above post.

I shouldn't post after working in the yard for 2 hours.  It is near 100 here today.

[Maxwell_E]

Hot weather can have an effect on the maths, indeed.

[JC]

Particularly comical when doing it on a cocktail napkin, I might add!

[Grainger49]

A cocktail might have helped.

[Jim R.]

Even though the F0 looks good in the edited calculation, you can still hear some cap effects up to 10x that frequency, so take it all with a grain of salt -- it may be fine, or your upper bass;/lower mids may sound a little off.

Also, the cap following a tube rectifier often can't be changed beyond the max for the tube type -- for example, 55-60 uF for a 5AR4.  I realize this doesn't apply to any BH gear, but it's a useful thing to know.

-- Jim

[Paul Birkeland]

Expermenting can get expensive fast.  I'm very interested in this topic, because the extended Foreplay has the 3.0uF Auricaps for coupling caps.  I founds some V-Cap CuTF in .47uF that I would love to try, but at that price, I need to know I'm not rolling off any base.

Go with the OIMP's if possible.  I say this because most of the teflon V-caps are made for high voltages, and the Foreplay III does not demand this.  Teflon capacitors are huge almost no matter what you do, but having a higher rated voltage really makes them giant!  In the Foreplay III, this might present you with some mounting issues.  

Even in the standard teflon lineup, there are some larger values with lower rated voltages that should work well.  0.47uf at the output of a Foreplay going into a Paramount isn't a huge issue, but if you plug your preamp in to any old solid state amp, you will likely lose significant amounts of bass.  

[corndog71]

I've used the oimp vcaps in my foreplay II and thought they sounded better than Solens.  After a long time and even changing different tube types I feel they're not so great.  I would recommend Erse or Sonicap.  There are lots of others I haven't tried so there are plenty of other options.  I've read some good things about Clarity caps and will be checking those out soon.

[ssssly]

Which caps are you speaking of for the V-caps? Power supply or signal?

Have never used them myself but have only heard good things about them.

Have pretty much gone to all motor runs with a few Obbligato PSU caps for power supplies (have a Solen in the PSU of my SEX). And in my FPII my favorite signal caps are Jupiter wax caps.

Had been debating picking up some V-caps to try out but have been holding off because of the price. What don't you like about them?