To cap or not!!!!!!

[Chris G]

Hi All,
I was wondering how many of you have gone with a small value cap between the plates in the phase inverter????

Let me know what you guy's think
Thanks
Chris

[snide]

Hi Chris,

I have tried a 47pf, 80pf and 100pf. I liked the 80 best. I now have a komet inspired high cut circuit here and it works great. It consists of a 250k pot (wired as a rheostat) in series with a .0047uF cap. If I get fatigued from the highs, I just dial some out and keep playing

Eric

[Chris G]

Hi Chris,

I have tried a 47pf, 80pf and 100pf. I liked the 80 best. I now have a komet inspired high cut circuit here and it works great. It consists of a 250k pot (wired as a rheostat) || with a .0047uF cap. If I get fatigued from the highs, I just dial some out and keep playing

Eric

Hi Eric,
Thanks for the response,I've tried small values ie 47pf-100pf and they seem to take to much of the high end away........almost sounds like a blanket over the speakers
thanks
Chris

[Jackie Treehorn]

I've got an 80pf there, too. I think much of it also depends on the choice of capacitors used in other positions. I used 716P's which don't roll off much highs. I would think an amp with Mallory 150's wouldn't require as much high frequency roll off, since the polyester caps seem to drop some highs inherently.

I've also tried bypass caps over the second and third stage plate resistors, and while there can be some "focus" gained in the mids with that approach, the least intrusive approach seemed to be the cap between the phase inverter plates. If I had to do it over again, I'd install the cut control. Overall, I can't really think of a downside to adding this cap...really improves the sound of the amp, in my opinion.

I certainly wouldn't say the cap sounds like a blanket over the speakers, though, since it really only cuts the fizz and crispiness. Chris, what speakers are you using?

[Chris G]

I've got an 80pf there, too. I think much of it also depends on the choice of capacitors used in other positions. I used 716P's which don't roll off much highs. I would think an amp with Mallory 150's wouldn't require as much high frequency roll off, since the polyester caps seem to drop some highs inherently.

I've also tried bypass caps over the second and third stage plate resistors, and while there can be some "focus" gained in the mids with that approach, the least intrusive approach seemed to be the cap between the phase inverter plates. If I had to do it over again, I'd install the cut control. Overall, I can't really think of a downside to adding this cap...really improves the sound of the amp, in my opinion.

I certainly wouldn't say the cap sounds like a blanket over the speakers, though, since it really only cuts the fizz and crispiness. Chris, what speakers are you using?

Hi JACKIE,
In looking at my post lastnight ,I was wrong in my discription of the amp....(note to self don't post while drinking!!!!! )

If I add a small value cap.....(40-500pf)There is no change whatsoever,I notice a change in hiss and noise and highend reduction begining at around 1000pf it dosen't do alot,but it does sound better..........any thoughts???? Caps are 715 (very bright!!!!)series

I run this head through a Bogner 2x12 cab w/vox blues....

Thanks
Chris

[Omar]

I put a 47pF cap across the PI plates and it seemed to tame the top end. Distorted tones were smoother (less fizz) and the high end on cleans wasn't so biting. There still is quite a bit of high end content but it is much more managable.

Just my .02

Omar

[SpinCycl]

It will always clip the high-end, but it's all a matter of setup, equipment, and personal taste as to if it is desireable or not.

For, me it's a matter of stability and preference. I didn't know what Ken Fisher meant when he spoke of the "...instability..." of an amp and that his amps are like a high-performance jet-figher. Sure, it's inherantly unstable, but it really performs well.

So, for my last, it was on the ragged edge, and in fact, over it sometimes. I used 250pF between the PI plates, and that rolled off the harsh edge at the top end. Then I used a 120pF on each plate resistor, which easily corrected the "flatness" that the 250pF caused.

I was really surprised how some very small caps at the right places can help - (or hurt) the sound.

[Chris G]

Hi Guys,
Well I setteled on a 1000pf between the plates in the phase-inverter,As I mentioned before,this was the lowest value that did anything.......just a slight reduction of high end,and about half the noise.The amp is also more stable at higher volumes.This was only done to the express,nothing is needed on the Liverpool.


I also added a cap to the treble cap....to bring it's value up to around 450pf.....I like it.....One silver mica /one ceramic,changed the bass and mid responce around in a good way!!!!!

Thanks Chris