TMB mod - how to?

[MBD115]

I have a 40W modeling tube amp I want to do a serious mod on. Heres the dope.

The amp has 3x12ax7's and 2x6L6's.

The first 12ax7 tube with 2 gain stages is feeding an internal DSP digital modeler circuit as a preamp to it. When the signal leaves the DSP it then goes through another 12ax7 with 2 gain stages then into the PI (the third 12ax7 tube) then on to the 2x6L6 power tubes. The only tone stack is inside the digital DSP.

I want to add a tone stack (treble, bass, middle, mod). Would you put it on the first 12ax7 upsteam of the DSP, or on the second 12ax7 just after the DSP and just before the PI?

Thanks for the help.

[M Fowler]

I would put the TMB post DSP so it doesn't load the DSP down, but what equalization does the DSP have interanally?

[Jana]

+1 what Mark said.

[MBD115]

The DSP has its own tone controls (TMB) but they are not that effective on this amp. They are a digital control which only tell the DSP how to process its signal, not an analogue TMB with caps and wires and stuff. These work only in numbers and multipliers.

When I use my 7 band external EQ with this amp I generally set the bands something like this: It does from +15db to -15db on the sliders.

100hz = +5
200hz = 0
400hz = -3
800hz = -5
1.6k = +5
3.2k = +8
6.4k = +10

This doesn't completely fix the amps tone but it helps.

I'm getting ready to do a complete cap job and I though I'd try a TMB mod also. This amp needs voiced badly. (IMO of course)

[M Fowler]

Are you going to include the Belton medium decay digital reverb as well?

[MBD115]

The onboard digital reverb is pretty much usable on this amp.

I was only going to attempt to replace the caps and install my TMB and try to address the voicing of the amp in this mod-around.

I'm going to try the TMB on V1a (after the DSP). This would be the easiest place to install it anyway with the shortest cable runs also.

Thanks for the help

[M Fowler]

Are we going to see your schematic of this interesting build?

[Reeltarded]

I would wish for an insert point just before the DSP, if it were me.

[MBD115]

Thanks for the replies guys.

Ok, new question. How do you 'voice out' a nasal tone? Can the OT make an amp sound nasal?

[M Fowler]

I reread your first post abou this being a 40w modeling amp, so I answered my own questions earlier, sorry.

[MBD115]

No prob

Ok, can a crappy OT make an amp sound 'nasal'. I think the answer is yes and I'm afraid thats what I have here. An amp with a too cheap OT and no choke. The caps are those little square mini-size caps that even look cheap. I've changed out the coupling caps on V1 so far and they seem to make a difference. There is about 9 more caps in there I'd like to change out to SOZO brand, and also do another gain mod of mine on it. But I'm now afraid my TMB idea isn't going to fix this thing. I'm afraid I need a new OT and a choke mod.

What does a crappy OT sound like anyway? Nasal? Boomy, muddy bass? Simi-piercing highs? A really nasty midrange thats too strong?

You can't turn up the bass because it gets boomy and muddy sounding. If you listen real close it has no real bass tones in there.

The midrange is just about uncontrollable. I think the midrange is what is giving this amp that 'nasal' sound I keep complaining about. When I use an external EQ I haft to turn the mids way down, which seems to help but isn't a fix.

The highs are simply highs. They have no chime. They have no real tone either, they are just highs. lol


Thanks guys

[Structo]

You know it's fun to mod an amp and learn your way around by doing it but if it were me, I would save my money and either build a new amp from a kit or sell that one and build something you like.
You start adding up the parts, especially if you start buying transformers and chokes and you will have a tidy sum tied up in an amp that still doesn't do it for you.
Just my 2 cents.

[MBD115]

Tom, you're a smart man I've said those same words to myself for over a year and a half since I messed up and brought this amp home with me one day.

I have a brand new Metroamp JTM45 I finished a few months ago, a brand new Avatar 2x12 loaded with Celestion Golds. A Digitech RP1000 multi effects stomp. A Digitech JamMan Looper. A Fender Super Champ (modded). 2 Elitist Les Pauls (now discontinued). A Fender Strat fitted with EMGs. A really sweet Schecter Blackjack with SD Blackouts, and this crappy 40w (name left out) piece of junk amp that I have over $1400.00 invested in so far and I don't like it. I can't sell it for anywhere near what I've invested in it and................ actually it is kinda fun soldering, working on it, and thinking about whats its problem is.

I know, I'm wierd, but I do like working on amps as a hobby. I know I can fix this piece of junk... if I'm willing to keep at it.

Whats it worth right now. My friend sold his last week for $350. He lost almost as much as I'm facing.

Ok, what does a crappy OT sound like? Is that what I have here?

Thanks Tom and the guys. I do love this you know.

[Structo]

Good for you!
I know the feeling, I have a couple duds in the closet I need to just sell and get rid of them but, the dollar signs are still haunting me....

I don't know what a crappy OT sounds like but when you replace one with a better one you will know it.

[MBD115]

Its got 3 wires. Red, Blue, and Brown. It offers 8 ohms or 4 ohms on the back. How do you put in the choke?

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