Cut control taper and effectiveness

[Gaz]

Wanted to add a cut control to my new build - kind of a 100 watt Rocket - but I'm finding that the cut control only audibly effects treble at the end of its range, around 3:00.

Of course I've had this experience before with audio tapers, but man, I really can't hear a difference until way at the end of the pot's sweep. I've tried both 1MA and 250kA pots, .001, .002, and .0047uf caps, all with similar results. I've also tried adding obscene amounts of treble to see if I'd be able to hear more a difference early on, but no.

Has anyone else found the control's operation the same? I'm puzzled because I've read many reports of the controls effectiveness and usefulness.

Thanks for any thoughts.

[Cliff Schecht]

Should definitely be linear. Use linear sweep for any frequency controls. Log is for volume and gain

[Gaz]

Interesting, because it's 'always' specified as audio - i'll have to get my hand on a linear pot...

[M Fowler]

Hmm I have a 100w Rocket and my cut control is 250kA with .0047 and works very well.

[Gaz]

Do you notice much change in tone between 7:00 (zero) and 2:00 - I really don't hear any.

I tried a 500k linear pot I had on hand, and the tone change was much more consistent.

[Gaz]

BTW, it's funny about my "Rocket." I was building a 100 watt Plexi without NFB, so I could add Mr. Fischer's PPIMV that replaces the grid leaks without too much tone change.

By the time I was done tweaking, I had to reduce the first coupling cap to 500pf to tame bass, and the the bright cap to 100pf to reduce the increased treble due to lack of NFB. A few more changes, and oops! I built a big 'ol Rocket! Of course it's not cap for cap a Rocket, but hey I like to think of it as a giant Rocket

M Fowler, I'd like to see your final schem if you've got one. I'm using EL34s btw.

[oldhousescott]

Try reverse audio taper. Or wire your audio taper so cut is CCW.

[Gaz]

I'll have to try rigging the pot as reverse audio. But how would wiring the pot on hand the other way around help? Wait, let me think about that for a second....

[billyz]

It could be the brand of pot you used. Some Don't have very good tapers and behave more like a linear taper pot. I have used Audio taper for the cut control and it works very well . I used PEC pots which always seem to have a nice sweep to the taper.

[M Fowler]

I did not use a schematic or have one for the 100w rocket. Just used my usual Rocket reverb board layout that Normster gave us and added two more EL34's, larger Edcor 450mA PT and Edcor 100w rated OT at 2k1 or 3k3 I can't remember which.

The cut control works as it has with my other builds ccw is dark and cw is brighter. I usually have it a 1pm with bright switch engaged 500pf.

[Gaz]

It could be the brand of pot you used. Some Don't have very good tapers and behave more like a linear taper pot. I have used Audio taper for the cut control and it works very well . I used PEC pots which always seem to have a nice sweep to the taper.

The pot I used was a Alpha pot made for Mojotone, which is a 'clone' of the CTS pots, IIRC. It's funny that you say perhaps it's acting more like a linear, because the linear pot I tried worked so much more smoothly!

Like I said, I'm just a little puzzled because I can't find many people complaining about the sweep using a regular 'ol audio taper from brand X. The Mojo pot's taper measures about 15%, and the Regular Alpha is just about 10%, which is even worse.

I'm going to order a 250k linear pot and try that, I will also try modifying that pot to make it log and reverse log to see if either of those perform better than the two-track cheapie log pots....

[Cliff Schecht]

IIRC the cut pots in both my Rocket builds are 250kA and they feel pretty good. I use AB MIM pots because that's what I have on hand. I think because it's wired as a variable resistor the log taper acts linearly WRT frequency whereas in a true tone control the linear taper of the pot acts linear WRT log frequency.

[M Fowler]

I use the Mojotone Alpha pots that match mojo's CTS pots as well I think they are made very well.

I like their custom CTS pots too.

Mark

[Gaz]

Yeah, I like the Mojotone pots too - kind of a nice little step up from the regular Alphas.

Perhaps my amp just doesn't have enough high happening, but it's hard to believe because the roll off with a .0047 uf cap is so low. My other theory is that I just don't have any high frequency hearing left

[billyz]

It could be the brand of pot you used. Some Don't have very good tapers and behave more like a linear taper pot. I have used Audio taper for the cut control and it works very well . I used PEC pots which always seem to have a nice sweep to the taper.

The pot I used was a Alpha pot made for Mojotone, which is a 'clone' of the CTS pots, IIRC. It's funny that you say perhaps it's acting more like a linear, because the linear pot I tried worked so much more smoothly!

Like I said, I'm just a little puzzled because I can't find many people complaining about the sweep using a regular 'ol audio taper from brand X. The Mojo pot's taper measures about 15%, and the Regular Alpha is just about 10%, which is even worse.

I'm going to order a 250k linear pot and try that, I will also try modifying that pot to make it log and reverse log to see if either of those perform better than the two-track cheapie log pots....

Actually, a 10% audio pot is more of an Audio Taper than a 15% pot. So , if you liked the Alpha better , then that is why.