Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Willabe on June 20, 2011, 04:52:06 pm

Title: Filter Capacitance Vs. Out of Tune Low Notes?
Post by: Willabe on June 20, 2011, 04:52:06 pm

Hi All,

I guess this could also be titled;     To use more or less filtering in the power supply, for the sake of tone/feel?

I have a question as per title. I have no preconceptions or rules about it myself. I don't have any personal experience on seeing/hearing the difference when you up the filter cap values in the power supply. I can understand that one benefit is a quieter PS and another is tighter bass, but what about the tone/feel of the amp and low notes sounding out of tune?    

It seems that tubenit and Geezer seem to prefer lower values of filter caps at the OTCT and screen nodes, at least in some builds, the tweed type builds? A little more of a sound they like?

Now I've read G. Weber in a few of his books stating he prefers 110uF at the OTCT and 40uF at the screen node. He did not go into great length on the subject, just to say he does this on Champ style amps all the way to Tweed Bassman to BFFT's. Pretty much any amp gets the same values for the reason of "it keeps the low notes in tune". I do remember him saying these values do not affect sag in the amp very much at all.

Once again, he did not go into great detail on this but, somehow a one size fit's all does not make sense to me. Different amps have different demands as far as current draw so wouldn't they need different amounts of reserve in filter capacitance to keep the low notes in tune, if that's a problem?

I have not noticed this on any of my amps, but I don't turn them past 5 or 6, maybe that's why?

Have any of you had this out of tune problem on the low notes of your guitars?

Do you like more or less reserve filter capacitance in the PS as far as tone/feel?

I'm doing the last touches to the layout drawing for a scratch 5G9 Tremolux and have room for more filter caps. I'm going to try the little radial caps from nichicon, VZ(M), 105c. series, so I have room for more in reserve. Maybe I'll just put in the extra eyelets just in case.

Any and all thoughts on this will be greatly appreciated.


          Thanks    Brad      :icon_biggrin:  
    

Title: Re: Filter Capacitance Vs. Out of Tune Low Notes?
Post by: Tone Junkie on June 20, 2011, 06:06:05 pm

From reading, mind you some of it I dont understand, there is a differance. Like the guys chasing the Eddy Van Halen tones in there marshalls swear by 32uf mains 16 screens and 32,s for the pre amp, on the other side of that coin the metal guys that build slo type amps like 220uf,220uf then 20uf caps down the pre amp string they say the higher filtering helps with a good bass responce.
Now hopfully the guys that can explain why will get on here and tell us why.
Thanks Bill

Title: Re: Filter Capacitance Vs. Out of Tune Low Notes?
Post by: PRR on June 20, 2011, 11:39:43 pm

> on Champ style amps all the way to Tweed Bassman to BFFT's
> Different amps have different demands as far as current draw so wouldn't they need different...

Side-issue: Champ is single-ended. Ripple passes to output. Bassman is push-pull. Ripple tends to cancel. If BFFT is 4-bottle, ripple may cancel better.

Exact factors depend a LOT on circuit details. Fat caps is not the only way to control output buzz. However as a general thing, SE pentode is 5 or 10 times more sensitive to B+ ripple. Pairs and quads in big push-pull amps may pull 5 or 10 times more current. So "one size fits all" may not be unreasonable.

> I don't have any personal experience on seeing/hearing the difference when you up the filter cap values

Why not?? You have an amp. You have an iron. You have (or can get (http://www.hoffmanamps.com/MyStore/catalog/parts4.htm)) various caps. A "taste test" does not have to be pretty: hang or pile caps haywire, play, listen.

Title: Re: Filter Capacitance Vs. Out of Tune Low Notes?
Post by: Willabe on June 21, 2011, 02:14:11 pm

OK, thanks for the answers PRR, I'll go ahead and play around with it.


       Brad        :icon_biggrin:

Title: Re: Filter Capacitance Vs. Out of Tune Low Notes?
Post by: frank57 on June 27, 2011, 07:44:52 am

I've been trying different cap values in my Korean Hiwatt junk box and it really does make a difference.
You have to try it.In the power section raising the filter cap value from 68 to 100 uf helped some with noise but made the amp feel stiffer so I changed it back.
In the preamp raising it from 22 to 47 seems to have added bass.Perhaps too much.
Did help with hum a little.

Title: Re: Filter Capacitance Vs. Out of Tune Low Notes?
Post by: Willabe on June 29, 2011, 09:27:00 am

Thanks frank57. I think both you and PRR are right, I'll have to try it and see.


        Brad       :icon_biggrin: