Electrictabs' JCM800 Emulator - first impression review

[Bucksears]

WOW. That's the first thing that I thought messing around with a few gain settings and playing some rhythms/leads. It sounds just like (as best as I can remember) the JCM800 1x12 combo I played about 7yrs ago.
It's a little bright (like I remember the JCM800 being), but has a wonderful variety of gain happening. Bluesy clip up through classic rock, and on up to some early EVH-esque sounds.
Like the MiniTubes I built a year ago, the EQ doesn't do a whole lot. It doesn't dial back or boost any of the frequencies very much. I may sub in a lower value pot for the treble, unless anyone else has other suggestions (short of popping in my EQ pedal).

It's a keeper. It sounded like blatty/farty crap prior to adjusting the trimmers to 4.5v on the drains, but after that, it turned into a Marshall. I'm seriously amazed at how these emulators get 1) a tube-y distortion sound and 2) they actually sound like the amp they're emulating.
And this thing is dead quiet too; makes my DS-1 sound like a rainstorm.

I'm going to try and post some soundclips tonight. Oh, this was using my PCB layout I posted a while back, so I can officially say it works!!
- Buck

[vanhansen]

YEAH!!!! I'm glad to hear that, Bucksears.  This is awesome.  Funny how electriclabs and I were making schematics of this at the same time, although mine is slightly different.  Can't wait for the clips.  

[Bob N]

I JUST finished mine a couple of minutes ago and agree wholeheartedly with Buck. This thing ROCKS and has a nice wide variety of sounds. Biasing this one is a bit of a b*tch, but once it is biased in properly, definately a keeper. And talk about GAIN, geez, there's just so damn much of it. I can't run the Main Vol on the box any higher than at about 2 without feedback within 6-7 feet of the 15 watt Krate POS. All in all, another fine job by Electrictabs and Buck!!! My appreciation guys, in a HUGE way. And Vanhansen, thanks again for the direction on how I could understand all of this a bit better. I think I got a pretty good grasp on it now! Much Appreciated!!!

One other thing I learned... I try to always use Wall Warts with effects to save on batteries. Well, a 9v wall wart puts out ~14.5v and I could not get the damn thing biased until I figured that out. The voltage on the back half of the box stayed around 7v at the Drain. Once I figured this out, I grabbed my trusty adjustable voltage wall wart and found that a 6v setting puts out about 9.5v. I then was able to get it biased properly... Something I'll need to keep in mind for further projects. For some reason, I didn't have this problem with the DR Boogey though. I STILL have yet to get that box back from the guitarist I lent it to though. He doesn't want to give it up! I might have to go repossess it shortly to figure out why that one biased properly and this one didn't...

[vanhansen]

Hey BobN.  Glad to hear you like it too.  Yet another happy builder.  

It took alot of studying and asking questions where I got lost but the ROG guys and several others have been very helpful.  Just sharing the wealth.

If either you or Buck get any sound clips done, I'll gladly host them on my site since I made a project page for this.

[Bob N]

Trust me when I say, you don't want a clip of me playing the guitar. I think Lance is coming out this weekend (Lead Singer and Guitartist from O.D.M. www.musicodm.com). Maybe I'll hook him into CuBase if we can get our business done that we need to accomplish... He's a million % better than I could ever be. I'm just the tech! LOL

[Bucksears]

Bob,
What value resistor did you use in the tone stack for the 33k? Did you leave it as-is or did you lower/up it at all? I found that the 33k (or higher) made the tonestack more active, but at the cost of an 'open' feel to the distoriton.
Originally, I had an 820ohm (accidentally) and got an unbelievable sound out of it, but almost ZERO tone control, and it was bright, to boot.
I've got a 10k in there right now and, if I drop the treble to 0, I can use the mid pot to adjust the treble.
- Buck

[Bob N]

Buck,

I left it as is with the 33k resistor. I wanted a working model before mucking around with it. I do need to get the tone stack more active, but don't want to give up the openness. I want this circuit with the DR on an A/B switch, so the tone stacks on each need to have pretty decent control for shaping.

I think I'm going to let Lance play it and let me know what he feels with it before I do anything.

Bob

[Dman]

Please excuse the ignorance (I'm a bass guitarist), but is this thing a kit, and where can I get it? Curiousity is killing this cat...

I tried E searching for it but came up empty.

TIA

[PaulC]

I've found with building preamp based pedals in the past is preamp tone stacks don't work well into another preamp with a tone stack that's pretty much the same thing.  They sound great into flat pwr amps, but not into amps where it's tone stack is sort of doubling up on the pedals stack - unless you set the amp controls to work with the pedal, and then you might not have a great bypassed tone. A Bax tone circuit at the end of the pedal can help alot.

One thing I was working on 4 or 5 years ago was a sort of backwards tone stack that would be used to flatten out an amp like a black face so a preamp based pedal would work better.  If you set the controls just like what the black face was set at it would cancel it out leaving things pretty flat, and then the preamp pedals would rock.  I had alot of headroom issues with it and shelved it for later, and never got back to it.  I think it would be just the thing to add to these types of pedals  when it's debugged, or a better way to do it than the way I was doing it!    I always wanted to work it out where this thing would kind of re-eq a black face into a type of marshall pwr amp/cab sound so the pedals would work better.

Later, PaulC

[transient]

is this thing a kit, and where can I get it?

No, it's not a kit. You can find the schematics at vanhansen's home page.

.
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[Dman]

Thanks again, I'll check it out...

[Bob N]

This is just a follow up post. I mentioned earlier that I was going to let Lance from O.D.M. play the pedal for a while and get his impression before I did anything with the tonestack or any modifications. After playing it for a couple of weeks now he has told me NOT to change a thing with the circuit. He absolutely LOVES it just the way it is. He's using it for a solo channel and it gives him the boost he needs to cut through with great character.

There is one modification I need to do however to the way I have the power supply wired up. He uses a power brick on his effects board that outputs an advertized 9v (14.5v actual or something like that). He would rather be able to use that supply rather than my supplied wall-wart (6v advertized, 9.1v actual). So I just need to be able to regulate the power supply a bit which is completely independant of the circuit.

He told me to convey a major thumbs up to the design. He also says that this is one of the most powerful pedals he has ever played. So guys, major props for a job very well done!!!!