New Amp! Sounds great but a little dark.

[jackaroo]

I just picked up a JTM-45 clone. The amp sounds great, but it's a little dark. I have the treble pretty well maxxed and the presence up almost all the way too. The bass is at 2 or 4- the amp sounds just a little dark even at what seems like extreme settings.... I'm looking for suggestions on how to brighten it up via the circuit and tubes.

For example: If I'm playing a strat on the back pu with the tone full up - I can't get is to sound harsh...not that i want that, but it's usually pretty easy.

Speakers...right now I'm using a pair of greenbacks- they sound fine with everything else I own. I have a scumnico and a scumback I'm installing in another cab this wek so perhaps that will fix this.

Ideally I'd like to tighten up/ reduce the low end a bit, add some sparkle to the amp, and a little more gain.

Any tube or circuit changes or recommendations as far as, caps/resitors etc? I'm clueless about these things, but I'd go off the advice of forum members to get this thing right.

I'm sure gutshots would help...but alas they've been taken down from the FS post.

[Jade]

Hey Jack,

The JTM 45 shouldnt be a Dark sounding amp in stock form, so I'd be suspicious of some non stock cap values in the build. What brand of Clone is it?

If it turns out that it's built per the stock marshall specs, and you still want a little more top end, I'd suggest you raise the value of the "slope resistor". Off the top of my head, I think the stock value is somewhere in the 33K range. You could try bumping it up to somewhere between 56K, and 100K. This should shift your tonal response more to the High end side.

Hope that helps some

Jade
www.TwisterAmps.com (http://www.TwisterAmps.com)

[jackaroo]

Thanks!

I had heard that it's a bassy circuit...it's based on the Bassman after all.


The cleans are OK -though still incapable of shrill tones. It's more that when the OD sets in the bass get a little too Wooly and the highs seem to roll off.

It's a Metro amp kit- so they're heralded for their accuracy, but I didn't build it. I'm looking to contact the builder and get some gut shots so other guys can troubleshoot it. I think it's pretty damn close to right on... I like the direction you're talking about so thanks again.

Anyone else know Marshalls?

[doc]

You could try a speaker with a bit more high end - maybe an Emi Wizard? As that's a more efficient speaker you'll also get more volume.

[doc]

BTW, I enjoyed your playing on that Tonefest video a couple of years back.

[trisonic]

Well, I would never call a JTM45 "sparkly" neither would I call it "harsh" with a Strat. So my views on JTM45's line up with your experience so far.......but then I haven't heard yours. You need a tech who understands JTM45's inside out, you may want to give Hogy a call tomorrow....
Best, Pete.

[samtheman]

No bright cap??

[57special]

I find that all the clone JTM45 's have blurry bass and mids compared to the real thing. Part of the problem is KT66's. Getting some old Genelux KT66's, even pulls, will give you a purer tone on the bottom and mids. This will give you the impression that the amp is a bit brighter. Try some brighter NOS tubes for the preamp, also, such as Telefunkens. I like Mullards for the extra gain. I actually found that my Metro JTM45 wasn't all that dark, even stock, though i did find the normal channel to be dull by itself. I also found the Metro to be gainier than an original. I did try some plexi values and found that it just made the amp fizzy sounding.
I've heard good thing about the Sozo premium caps. If yours doesn't already have them you might swap out the caps in there for some of them, or go for some old Mustards, which sound better, IMO, than the standard Sozos.
Finally, i've found the Bonnie Blue pedal to be an excellent match for Marshalls. It can give you just a tad more gain, especially on the top end. It isn't harsh, very nice, musical sound.
Or just spend another 6 grand and get the real thing.:dude
Just like a good vintage guitar, they don't go down in value (except recently, but they will come up again just like a pre CBS strat or 50's LP).

[bigeasy]

Hi,
Earl here from Schreyer Audio. I do a JTM45 like amp called the EDS45. I don't know anything about the metro kit (btw are you running KT66's)?, but I would say in general the JTM45 can be a bit of a bassy (meaty I like to call it) amp. It is typical to cut the bass down to 3, and increase the treble and midrange to 6-7. If you're boosting the presence and treble that high with a strat, , then yes it seems like you're over compensating for something. A strat is usually fine through the normal channel, and then on a les paul, I usually switch to the bright channel.
But as others have said, what will make a big difference is the speakers (also closed back vs. open back, closed being more muffled). I use the weber blue dogs (ceramic or AlNiCO), and I find this is a good match to give the amp a little more edge. (Even the ceramics in a closed back bite very well with my EDS45.)
Listen to the clips on my site as a reference.
http://www.schreyeraudio.com/EDS45.html
This is through black face 2x12 type closed back cab loaded with 2x12 weber ceramic blue dogs. The stat is through the normal channel, and the les paul is through the bright channel.

All the tones are at 50%.

[jackaroo]

I've got the Scumnico (75Hz) and a Scumback (55Hz) being put into a Vertical 2x12 cab from mojo- it's closed back though. The comments I'm making are from listening to an open back horizontal (even in the beam) with 2 greenback speakers.

Tubes and perhaps raising a value or two coupled with the speakers should get me there...I hope.

Earl thanks for your reply- The amps you made/make for Marc Ford look pretty sweet. Yes KT66s-

Here's some pics of the circuit/guts of the thing for those who can make heads or tales of this stuff!

http://img.photobucket.com/albums/v234/jack_devine/jtm45forsale12.jpg

http://img.photobucket.com/albums/v234/jack_devine/jtm45forsale10.jpg

http://img.photobucket.com/albums/v234/jack_devine/jtm45forsale09.jpg

http://img.photobucket.com/albums/v234/jack_devine/jtm45forsale08.jpg

http://img.photobucket.com/albums/v234/jack_devine/jtm45forsale07.jpg


Pete- I'm not saying I want to make a harsh sound- Im saying there isn't enough room in the circuit to get that much high end...even out of the bridge position of a strat.

What I'm most concerned about is the low end just being a little too non-desript and going too low. I'd love to roll of the lows and add some highs via circuit tweaks...I think the slope resistor does that no? I don't want to use an EQ to voice the amp.

57- Perhaps some new tubes are in order- though the thought of plunking down $400 for a pair of old Genelux 66 in pretty painful.


Doc thanks for the compliments!

[WaltC]

I just finished building my latest Marshall-style amp based on the JTM/JMP circuit and the stock normal channel on it is certainly "darker" than the bright channel and doesn't work as well w/ humbuckers but is OK sounding w/ single coils. The "normal" normal channel on those type of marshalls uses a 330uF cathode bypass cap on the first preamp stage and contributes greatly to the dark and boomy character of the channel, I drop the bypass cap to 100uF or 50uF and this helps significantly to reduce the flabbiness and brighten up the channel.

The bright channel however is really bright verging on icepick built to the original Marshall specs , and I usually remove the 250pf cap on the vol. pot or make it switchable and that tames it down very well and leaves you with a great sounding and flexible channel.

Your amp looks like it is a two channel amp and that it's built with the stock values, so I'd expect your normal channel to be dark and the bright channel to give you all the high end you could ever want <G>.

[doc]

Thats a sweet looking build.
I think you just find that style amp a bit bassy for your taste - I think you've got a good example based on the build quality. I'd probably have a tech tweak it - probably raise the value of a few coupling caps and stiffen up the power supply a bit and that should do it. I suspect you're more of a "plexi" guy than a "JTM" guy.

[trisonic]

Pete- I'm not saying I want to make a harsh sound- Im saying there isn't enough room in the circuit to get that much high end...even out of the bridge position of a strat.

What I'm most concerned about is the low end just being a little too non-desript and going too low. I'd love to roll of the lows and add some highs via circuit tweaks...I think the slope resistor does that no? I don't want to use an EQ to voice the amp.


Yeah, I get what you're saying, Jack - my point was with the originals I don't recall a Strat being harsh at any setting, I'd be more concerned about the low end but it is difficult to assess without hearing you play it. I think our friend in BR said that Clapton, for example, on Beano was using EL34's and ceramic magnet speakers - i.e. the earlier ones used KT66 and and the Silver/Blue Alnico Celestions.

Best, Pete.

[brad347]

what ECC83 do you have in there? Certain ones (like JJ brand) are darker than others. The JJ 12AX7/ECC83 is VERY dark.

[Jade]

Thats a sweet looking build.
I think you just find that style amp a bit bassy for your taste - I think you've got a good example based on the build quality. I'd probably have a tech tweak it - probably raise the value of a few coupling caps and stiffen up the power supply a bit and that should do it. I suspect you're more of a "plexi" guy than a "JTM" guy.

Doc,

Just an FYI, Raising the value of coupling caps will increase the bass response.

Jade

[jackaroo]

Jade...

Nice Spicoli quote there.

[Jade]

Jack, That's a really nice looking build.

There is always more than one way to skin a cat... especially when it comes to tube amp mods. Increasing the value of the slope resistor like I mentioned before is a quick easy thing that you could try. The slope resistor is the one in the picture that is turned sideways on the board, and is located right near the V2 socket. The higher you raise that value, the more trebly the amp will get. I wouldnt go much higher than 100K. If I had to start somewhere, I'd try 68K, and see if you like more or less.

Good Luck, and Nice amp!
Jade

[Jade]

Jade...

Nice Spicoli quote there.

LOL... Thanks. You're the first person to say they caught that.:dude

[jackaroo]

I just read on Germino's site that they use a 56K on the Classic or Club 40 both are JTM style heads.

I might start there.

Are brands or slope resistor? Or is it a generic little part?


I hope I can find one.


Thanks for the comments on the amp build quality. It looks nice but I wouldn't know except that it looks neat.

[Jade]

Jack,

No, you don't need any special boutique resistor. Standard 1/2 watt radioshack resistor will work just fine in that position. You can get a whole bag of assorted values for just a few bucks.

Cheers,
Jade

[mwm523]

Hey Jack, got your email. Glad to hear this amp ended up in your hands!

As the builder, I can say that the amp was built to George at MetroAmp's stock specs. If you find it a bit dark, there are several ways to brighten it up a bit, some of which have already been mentioned here.

The easiest way to add some sparkle would probably be to increase the bright cap on the Volume 1 pot. I think I had a 100pf or 120pf cap there. You might want to try increasing this to 250pf or 500pf to add some brightness. The higher the value, the more brightness you'll have. Of course if you're running it with the volume dimed, it will not have much of an effect. You'll get the most mileage from this at volumes of 8 or less.

Also, as someone else mentioned, the V1 cathode capacitor (parallel with the 820 ohm resistor all the way at the left end of the board) is a very high value at 330uf. This is the stock JTM45 value and lets a lot of bass frequency through. Many people go as low a 1uf - 5uf here to tighten up the bass response.

Also, as someone else mentioned, you might want to try some different preamp tubes. a nice NOS Bugle Boy or Brimar in V1 would probably add some brightness, and NOS pres in general would be a big step up over the JJs that come with the kit.

Another option for increasing brightness (or actually reducing bass) would be to change the phase inverter coupling caps from .1uf to a lower value, such as .047uf or .022uf. These are the two Sozos on either side of the PPIMV wiring.

In the end, the JTM45 is really a bass circuit, and is not overly bright. You could perform some other mods as well to increase brightness, such as splitting the V1 cathode or changing the tone stack from 56k/250pf to 33k/500pf, but you'd be moving the amp further away from the JTM45 circuit, closer to a JMP50 type.

Good luck with it!

[jackaroo]

That's what I'm talking about.


Now I just have to figure out where to get the right combo of parts and get someone to do the work.


Ugh!


J