MV on AC30 TB w/ Cut?

As I always say - I am an idiot.

This Vox TopBoost circuit's Cut control is tripping me out... I'm a little shakey on how to install a Master Volume control with the damn Cut control all up on the PI.

Any tips/hints/help?



Here's the circuit I'm using:

http://www.el34world.com/Hoffman/images/AC30.gif



At first blush I was thinking the 1M off of the PI's pin2 (right after the Normal/Bright channel's summing resistors and 0.047uF cap) could be swapped for a 1M MV pot... IDK, I am a moron :(

While I prefer the Fischer style MV with a typical long tail PI when going thru octals, I personally feel like Matchless built a better mousetrap (for AC30'ish amps) with their crossfade MV across the bias feed.

Here's Nik's layout:

http://www.ceriatone.com/images/layoutPic/matchlessLayout/DC30Ceriatone_100508.jpg

The Lightning uses a crossfade that you can't switch out, but it doesn't have a cut control, either.

Both the Lightning and DC30 use a simple 1 meg audio taper pot - nice and simple. And if the pot goes up, it won't kill your output section like other PPIMV's will.

Give it a shot - you can drop it in, test it, and pull it out in about an hour if you don't like it.

While I prefer the Fischer style MV with a typical long tail PI when going thru octals, I personally feel like Matchless built a better mousetrap (for AC30'ish amps) with their crossfade MV across the bias feed.

Here's Nik's layout:

http://www.ceriatone.com/images/layoutPic/matchlessLayout/DC30Ceriatone_100508.jpg

The Lightning uses a crossfade that you can't switch out, but it doesn't have a cut control, either.

Both the Lightning and DC30 use a simple 1 meg audio taper pot - nice and simple. And if the pot goes up, it won't kill your output section like other PPIMV's will.

Give it a shot - you can drop it in, test it, and pull it out in about an hour if you don't like it.



Ah, there we go!

OK, I have problems finding 1M push/pulls that I like. The DPDT lugs are a bit sketchy. I don't want a switchable one anyway :)

I'll be finishing this build just in time for my 2x12" Celestion Blue cab to arrive!!

Thanks 11 Gauge! I can always count on you to help me with my amp-retardation :)

JC, the master 11ga. suggested works well on cathode biased EL 84 amps, use the cut control too.

Almost done.

The half power switch will have ot wait, I'm out of a variety of cathode resistors (5-10 watt flavors)...

Johnny, I answered the same question on the 18 watt forum. For those of you who are watching this and don't belong over there, here's what I said:

Johnny, to add a crossline master volume, just run a jumper wire from each lug on the cut control pot that has a wire connected to it to the same lug on an additional pot, but don't put a cap on that one. The pot can be 500K audio or maybe 250K audio, doesn't make much difference. Electronically, you're just mixing the left and right signals out of the phase inverter together, and the phase cancellation lowers the volume as you mix more and more of it. The cut control is the same, but the cap on the cut control pot makes the volume reduction occur only in the high end above the cutoff frequency of the cap.

Slight hijack -- if an amp already has a treble control, what is the appeal of the Vox-style "Cut" control? I mean, it's a neat solution, but it seems redundant to me.

- Scott

Slight hijack -- if an amp already has a treble control, what is the appeal of the Vox-style "Cut" control? I mean, it's a neat solution, but it seems redundant to me.

- Scott

It's not quite the same, you can shape the preamp tone stack, and seperately shape the post phase inverter signal tone.

Cut is cutting treble after the PI. honestly, it's not too huge a difference. Treble cut is treble cut - it's just a slightly different dynamic.

The bonehead I am, this MV also works on a PPIMV level (similar to the Cut control) - I'm stuck in non-caffeinated today...

I have NO cathode resistors of the value that I'd like (one 62 ohms, the other 68 ohms). I'd even settle for two 50uF's. In half power the resistors will run in parallel for closer to 130 ohms. Full power 62 ohms. though I really want to hear full power with 50 ohms to see what a AC30 "usually" sounds like (I know it's not that big of a difference between 62 and 50 ohms hehehe).

Looks like it's time to go to my local electronics store.