Vox high cut control in JCM800 2204 2203

[pjd3]

Hi,

Just wondering if anyone has ever installed or simply tried putting a Vox type cut control in a hard rocking Marshall in attempt to shear off some excess highs as needed. I'm curious because I will be using a single coil strat with a current amp build which is a JCM800 2204 with a handful of switchable gain mods. My speaker(s) of choice are between a Scumback BM75 or BM75-LD. I love the aggressive high mid nature of those speakers but am just a little concerned about having excess highs when in a higher gain setting and using a BM75. Had to wonder if a Vox type cut control would be the right kind of approach to gentle rolling off highs from the top down after all of the gain stages. (I take it that the Vox cut control is a gentle low pass filter).

Just as a side note, the power transformer that came with this donor combo amp is only going to be giving me a little over 400 volts of B+. I had to wonder if that will soften the highs. I haven't experimented with various B+ voltages on the same amp as of yet.

Thanks for your feedback.

[sluckey]

Easy mod. Just do it and tell us what you think.

[pjd3]

OK, will do.

It does looks as easy as using a couple of alligator cables, a cap and a pot to try it.

Phil D.

[pjd3]

OK, will do.

It does looks as easy as using a couple of alligator cables, a cap and a pot to try it.

Phil D.

[Roe]

the main issue tends to be the 1000pf bright cap. turn up the gain for a fatter sound or change the bright cap to 220pf or 2200pf

[Mant]

Did you try it?

[pjd3]

HI Mant, did not try it yet, just got back from a big vacation and still have 4 pcb's from Headfirst amplification to install. Those are a very intentional part of the plan, the Vox cut control I'm looking at as "probably a good idea". So when most of the essentials are installed I"m apt to give it a try and will get back on the results. Very often with higher gain and single coils there is this wish to just "cut a few twigs of the top" and something like a gentle low pass seems like it ought to address that issue maybe even better than a set treble control plus, being after all the preamp tube distortion.

Best,

Phil

[Gainzilla]

I thought I read somewhere that the high cut doesn't like to be in a circuit with NFB? I could be totally wrong. That said, I installed on in an old split-channel JCM800 "test bed" amp I'd been abusing, and it sounded amazing. Really allowed me to tailor the high end response. That really helped, as this was a 2x12 100w combo and the Celestion 75's that were in there seemed a bit pokey. I felt like it shaved off the jaggies and helped make it a much more modern high gain tone. Easy mod. Definitely worth trying.

[pjd3]

"Felt like it shaved off the jaggies".

Yeah, that is exactly how I would put the reason for installing one. I always put a variable NFB on my amps anyways so, that would offer an opportunity to play with balances as see if there is a range of adjustability in there.

I haven't got to that point yet - still building up the 4 mod boards I purchased from Headfirst Amplification. This amp isn't a total necessity and I have about 5 more big projects happening simultaneously but, am really desiring to having a nice little versatile Marshally distortion/gain combo.

How I understand this is that having a high freq roll off near the end will enable really trimming the "sharpies" off the top. I may expect that to attempt this early in the circuit still gives the opportunity for consecutive gain stages to generate their own higher harmonic distortion. So, a Vox cut near the end filtering some highs. Sounds worth a try to me, even it its subtle. Sometimes a little trim is all ya need!

Thanks for stopping by, and my time will come with this.

Best,

Phil D

[dorrisant]

I've installed this in lots of amps... Works great. Takes out the sharpies, preserves gain structure... Win, win.

NFB and no cut...? Look at the SSS/Wonderland models.

[rangdipkin]

Late ass reply but just gave the high cut control a try in a hot rod 2204 type build... she's a game changer alright! nice smooth gentle roll off of the shrieker frequencies. I ended up wiring in the stock presence circuit on an internal trimmer and just ballparked it around noon. I'm a convert to the vox cut!

[pjd3]

Oh no Rangdipkin, not late at all.

I started this thread when my 2204 mod build was only about 1/4 done, now its about 1/2 way done.

The high shrilly's seem to be something I constantly have to contend with and I think it can make the difference between a good tone and a nearly unusable tone. So I really like hearing folks say how its working for them. I've heard enough now where I would likely just put it in and not worry about if I "want" it or not. Hell, its such a minimal mod, may as well. And with playing a single coil Strat into a gain modded 2204, I'm sure it will justify its implementation.

Awesome, glad it made such a good useful difference to your sound. I hope it will do the same when its my turn.

Whats been taking me so long besides having way too many projects going at once is the minimal space in the little donor combo I"m using. But it was there for the taking, good transformers (apart from all the grounds in the PT being internally connected, that was weird). So, alot of the energy goes into thinking ahead of where and how to put in everything.
We will get there

Thanks!
Best,
PJD3

[rangdipkin]

It definitely gives you way more control over those spikey boys, no fighting between the presence and treble controls... I tried it with and without the standard presence circuit in place and found I preferred it with a good amount of fixed presence with a little larger cut cap. I ended up with standard presence about halfway up (a 12K fixed resistor and 100n cap strapped across the 4K7 feedback divider resistor) and a 250k log pot and a 6.8nF cap as the cut control in the presence hole. Twisted pair back to the couplers. Works like the best damn presence control I ever did see!

[pjd3]

Say, just for entertaining some future experimenting,

Would you expect to have a "2-pole" Vox cut control if you used a dual ganged pot and 2 capacitors? One gange into a cap, then into the 2nds gange into another cap all in series.

I"m just wondering if this approach would work in this instance the same way I've seen it work in others to steepen the slope of the filter.

Thanks
PJD3

[sluckey]

Say, just for entertaining some future experimenting,

Add some mushrooms, stir in some pretty colors, and close your eyes...

https://www.youtube.com/watch?v=F-kVFfK ... BlameHanzo