Normal vs TMB Question

[BobD]

Do the Normal and TMB channels make a good 2 channel amp or are they too similar at equivalent volumes ? Will the Normal channel stay cleaner longer ?

Does anyone have clips of the TMB and Normal channel at equivalent (gigging) volumes ?

[krash]

Bob,

I originally intended to make a 2-channel amp that I could foot-switch and gig with and started out with the regular "Richie" 36W-TMB. What I found was that no, it would not really work for me for a 2-channel amp at gig volumes if I intended to use one channel for an overdrive tone and the other channel for a clean tone.

The reason I found is because a whole lot of the crunch/overdrive tone you get from the 36W (or 18W for that matter) is occurring in the phase inverter. So to get a good overdrive tone, the master vol has to be maxed or close to max and you then have to turn the channel volume up pretty high to get it to crunch, and that's very very loud. To get the other channel to the same volume level requires it to also drive the phase inverter just as hard and it crunches quite a bit. In my amp, at the volume level that I found a good lead/overdrive tone in the TMB channel, the normal channel was approaching AC/DC levels of crunch.

Eventually I had to ditch the original design and start from scratch on the OD channel in my amp. I am getting really close to having something that works just right for me... a couple of tweaks to resistor values and I think I'll be there.

I think the normal channel is loud enough to gig with and stay a little bit clean if you are not playing with a really loud band. Now everyone has a different definition of "clean". At small-club-rock-band gig levels, you are not going to get a real clean "clean" tone out of the amp unless you are playing very softly. It's a kind of clean tone that I prefer, but it's hardly clean.

[BobD]

Krash,

Thanks for the input, that's what I was looking for.

FWIW - I currently have an ef86 as the "clean" channel and it stays pretty clean at gigging volume. It has a nice light crunch to it. This is something you may want to try yourself. It's way cleaner than the TMB channel so it pairs with it nicely.

I was just curious about the normal channel, I think I'll just stick with the ef86 myself.

[Lazmo]

I too, am dead set keen on building a TMB as I love the tones, but would like it to be able to clean up at least a liitle bit on one channel.

Would a compressor on the cleanest channel help? What if you just set the compressor real mild to control any hair and then set its level pot nice and low, so the pre-amp of that channel of the amp is not cooking, but its channel volume is up. That way you could run it as loud and clean as possible but without any transients pushing it into mild O/D territory - if that makes any sense at all.

Or, is the sIII the answer with its lower gain TMB channel for a cleaner tone?

Regards Laz

[krash]

I think EF86 vs. 12AX7 doesn't make much difference in how clean it is at volume because it's all about the signal amplitude at the input of the PI. So whether you have an EF86 or 1/2 12AX7 doesn't really matter that much since the 12AX7 has enough output swing to get the PI to overdrive and so does EF86. So to get it to play cleaner at higher volume knob settings, you have to adjust the PI so that it doesn't get overdriven. The problem with that is that then that the TMB channel shares the same PI as the normal channel, and when you adust it to not overdrive with the normal channel, then you reduce the overdrive of the TMB as well.

So what I've had to do is change the gain staging in the used-to-be-TMB channel so that it can get enough distortion before the PI. Basically I think you can't rely on the PI to contribute to the distortion unless you are willing to get that overdrive from the PI on both the TMB and normal channels.

[Gauge]

can any simple mod (value swap/part swap) be done to just increase headroom on the normal channel (so that it is more of a dedicated clean to bluesy breakup channel

[krash]

Yes. Don't turn the volume knob up so high. That's about as easy a mod as you could ask for. You don't even have to open up the amp. Whatever mod you do internally will not have any remarkably different effect than just turning down the volume knob.

The fact is that when the voltage into the PI gets to a certain level, the PI is going to clip and you will have distortion from the PI. Increasing the input voltage more than that threshold will cause more distortion or saturation. You could modify the PI so that it does not clip so easily but of course it still will not improve the actual volume level of clean sound you get out of the amp. It will just make that clean sound happen with the knob on "4" instead of on "2", but it will still be just as quiet as it was before. With a multiple-gain-stage preamp you may benefit tone somewhat by moving which stage gets clipped and how but with the normal channel in a TMB, there's only 1/2 of one 12AX7 before the PI. So all of the crunch you are getting is from the PI or later.

If you want more SPL or actual volume with a clean tone, you need a bigger power amp.

[zaphod_phil]

The fact is that when the voltage into the PI gets to a certain level, the PI is going to clip and you will have distortion from the PI. Increasing the input voltage more than that threshold will cause more distortion or saturation.

You're right, although to split hairs, in an 18W it's actually the power stage that the distortion is mainly happening rather then the PI. So yes, you can change the EL84 grid leaks from 470k to 220k to get more clean range, but like you said, it's really no different from turning down the volume knob a little. And that's exactly what I do when I want a clean to bluesy breakup, which this amp really excels at. I've got a buddy who's into jazzy playing and he just loves the 18W for how touch-senistive it is.

[krash]

of course you're right, what was I thinking? too much time working with three-gain-stage preamp that will absolutely overdrive the PI but you don't get a whole lot of PI crunch from just one input stage.

[creeper]

Bob,
... if I intended to use one channel for an overdrive tone and the other channel for a clean tone.

.... To get the other channel to the same volume level requires it to also drive the phase inverter just as hard and it crunches quite a bit. In my amp, at the volume level that I found a good lead/overdrive tone in the TMB channel, the normal channel was approaching AC/DC levels of crunch.

I think the normal channel is loud enough to gig with and stay a little bit clean if you are not playing with a really loud band. Now everyone has a different definition of "clean". At small-club-rock-band gig levels, you are not going to get a real clean "clean" tone out of the amp unless you are playing very softly. It's a kind of clean tone that I prefer, but it's hardly clean.

Couldn't one put a master volume on only one channel, hence a "clean" and "distorted" channel?

As long as the amp didn't need to be too loud, one could lower the master volume getting earlier breakup from the "dirty" channel and matching the acceptable clean level of the other channel? (given, of course, the "clean" sound of the 36 is acceptable [ie not fender type clean, clean])

[creeper]

Bob,
... if I intended to use one channel for an overdrive tone and the other channel for a clean tone.

.... To get the other channel to the same volume level requires it to also drive the phase inverter just as hard and it crunches quite a bit. In my amp, at the volume level that I found a good lead/overdrive tone in the TMB channel, the normal channel was approaching AC/DC levels of crunch.

I think the normal channel is loud enough to gig with and stay a little bit clean if you are not playing with a really loud band. Now everyone has a different definition of "clean". At small-club-rock-band gig levels, you are not going to get a real clean "clean" tone out of the amp unless you are playing very softly. It's a kind of clean tone that I prefer, but it's hardly clean.

Couldn't one put a master volume on only one channel, hence a "clean" and "distorted" channel?

As long as the amp didn't need to be too loud, one could lower the master volume getting earlier breakup from the "dirty" channel and matching the acceptable clean level of the other channel? (given, of course, the "clean" sound of the 36 is acceptable [ie not fender type clean, clean])

[lindee]

I splitted the PI as the 18watt pre-amp schem from NIK, so the TMB + master feeds into the rightside of the PI and the TMB into the left side.

This works for me real good.

Changed the grids R's into 330k and swapped arround with the NFB resistor for the right headroom taste.

Choc

[zaphod_phil]

Say that again?

Couldn't one put a master volume on only one channel, hence a "clean" and "distorted" channel?

Not quite sure what you mean there, but the TMB channel of TMB 18Ws has a post-PI"MV". It's not quite a true Master Volume because it only affects the output of the Plexi-ish TMB channel. The TMB channel has more gain than the Normal channel. NB; There is one version of the TMB 36W where the Normal channel is actually fed into the TMB channel of the preamp - I'm not talking about that one.

As long as the amp didn't need to be too loud, one could lower the master volume getting earlier breakup from the "dirty" channel and matching the acceptable clean level of the other channel? (given, of course, the "clean" sound of the 36 is acceptable [ie not fender type clean, clean]

OK, if you use 220k grid leak resistors (instead of 470k) at the power tubes, you will get more clean range from the power amp. Then you could get cleanish tones from the Normal channel and warm Marshall crunchy preamp distortion from the TMB channel. So, yes, that would work, particularly with a 36 watter.

[creeper]

Not quite sure what you mean there, but the TMB channel of TMB 18Ws has a post-PI"MV". It's not quite a true Master Volume because it only affects the output of the Plexi-ish TMB channel.

Okay, so you could set the TMB channel "dirty" by cranking the gain and lowering the MV, then use an external A/B switch to go between it and the Noraml ("clean") channel which is not effected by the MV. Right?

btw I'm talking about the 36 version, which would have a more useable amount of clean headroom.

[zaphod_phil]

Yes, that's right. Basically, you want a 36W with Jersey_Aaron's preamp version, which has a good bit of gain in its TMB channel.