Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mason on April 02, 2021, 06:37:04 am

Title: How to lower vib/trem speed on ac30/6 build?
Post by: Mason on April 02, 2021, 06:37:04 am

Hey yall, I'd like to slow the speed of the vib/trem on my ac30 I built. I followed the layout at the bottom of this page, https://tedweber.com/6v30-c-kt/

The only deviations in my build for the vib/trem are that the 750pf cap was subbed for 680pf because that was the closest value I was able to get, and the speed pot is a 3 meg pot.

What needs to be changed to lower the speed?

Title: Re: How to lower vib/trem speed on ac30/6 build?
Post by: jlaj on April 02, 2021, 07:11:15 am

I looked at the schematic on the Weber site. If you’re looking for a really slow trem (that’s what I like) you could change capacitors C29 thru C31 from 0.01uF to 0.02 uf. That would be the extreme case, or you could start with C31 only (similar to the AB763 design) and work from there depending on your taste.

Title: Re: How to lower vib/trem speed on ac30/6 build?
Post by: Mason on April 02, 2021, 09:57:55 am

Thanks for the suggestion! I didn't have another .01uf to parallel with C31 so I clipped in a .022uf in parallel to hear how that would sound. Definitely gets me to the slower speed I want. However, when turning the speed knob up it started to lose the vib/trem effect, in a way that's different than the speed just being really fast. Like the effect goes away and doesn't return until I lower the speed knob.

So is there a limit to how high each of these caps, C29 - C31, can be before it interferes with the effect? If I like the slower speed I got is there a difference between raising two of the caps to .02uf, vs one cap to .032uf?

Title: Re: How to lower vib/trem speed on ac30/6 build?
Post by: sluckey on April 02, 2021, 10:31:52 am

Quote from: Mason on April 02, 2021, 09:57:55 am

So is there a limit to how high each of these caps, C29 - C31, can be before it interferes with the effect? If I like the slower speed I got is there a difference between raising two of the caps to .02uf, vs one cap to .032uf?

Yes, there's a limit. Replace C29 and C30 caps with .02s. Don't just parallel to make a .03 cap. This should lower the speed and still allow full range of the speed pot without dropping out on the fast end.

One way to widen your range is to use a dual ganged speed pot. I used a dual 500K in my Supro but you would need a dual 1M in your circuit. And/or you can replace C32/R65 with a red LED. This will greatly increase the gain of the oscillator which will also widen the speed range. See attached...

Title: Re: How to lower vib/trem speed on ac30/6 build?
Post by: jlaj on April 02, 2021, 12:55:16 pm

Mason, are you using a 220k resistor inline with that 3 Meg speed pot?