trinityamps.com

Yes, I think these clips should be permenantly stored in the Zounds section. Though, for some reason, I keep finding I like the Normal channel clip the best...

output transformer center tap on the other side of the 1k5 resistor (2k2 in schematic BTW), in both the schematic and layout, effectively tying it to the 100ohm screen resistor at power tubes pin 9.

mentioned - I have been using everything on R5 from 1K5 to 2k5 to get the voltages right. I find I prefer to have 15 volts difference between the plates and screens - then I adjust the 125ohm grid resistor at R20 to get the voltages up where I want them (usually a 200ohm will get me to 335volts). 335 volts plate and 310 screen, with a good filament voltage seems to get the sweet EL84 sound!.

Squeal Reduction - The 100K resistor is a bleeder to reduce gain. The 500K pot also dumps some gain.

The .022uF coupling cap increases bass response. These are both good tweak points. A .0047uF yields tighter bass. This is part of a scheme to eliminate the need for negative feedback - s2

The differences from the standard TMB to get this sound are highlighted in Red on the schematic in the gallery.

The 100K bleeder on just before the gain pot reduces gain a little bit. The 2.7K cathode also drops the gain of V2. Then, there is the 500K MV rather than a 1M. This is kinder and gentler to the PI. These are all tweakable values, so there is a lot of flexibility. Want more gain? Increase the 100K resistor, decrease the 2.7K resistor, increase the MV pot.

The idea was to reduce the gain of the circuit a little bit at each stage rather than to use the big 470K grid resistor on V2 to do it all at once. This lowers the overall circuit impedance and helps make the amp behave. It also allows for a more natural sound since the signal isn't being compressed through a big resistor. Finally, eliminating that resistor makes the amp quieter in 2 ways. With the gain pot on zero, the grid on V2 is grounded. And, hiss is reduced as the signal is not in series with a huge resistor.

I also did some things to control the bass response to eliminate the -FB, which is something I try to avoid.

At least, that was the theory behind it.

If Steven is going to rework the schematic, let me nit pick. Can you move the CT of all the Trannies to the center of the windings. Or all the trannies wound like that? ha!
markd

noticed on the schematic that all resistors are 1W carbon film unless otherwise noted... Is there anything significantly different in this layout that we would need to go beyond the 1/2W resistor?

1/2 Watt are fine for most of the circuit as with the other 18 Watters. .

The 2.2K vs. 1.5K resistor is not critical. I use either or depending upon the voltages I measure in each amp. Either one will work just fine, but this is a tweakable value if you so desire.

I thought the TMB sounded a little cleaner. I also thought it was interesting the normal channel sounded thicker.

But I like the amps. It is nice to have another variation.

Yes, that's what surprised me too. The Normal channel of this amp is basically a Lite IIa. I think the 0.68uF cathode cap in the TMB preamp channel is probably loosing a little too much low end. I reckon a 2uF in that position would nicely thicken up the tone, without allowing the low end to get woofy.

Tonally, it is similar to a Plexi bright channel preamp without the high pass filter and bright cap. It can be a little light on bass at some settings, but I really don't think it is too thin. The idea was to have it sound distinguishably different from the normal channel and to cut through really well in a band environment.

Phil's suggestion is a good one, however. A 1or 2uF would bring up the bass a little without becoming overbearing.

Yes, I did notoce that. And as you know it's common to jumper the bright and dark channels together to get a more balanced tone.I would have though that with the increased gain and TMB tone controls on that channel, it would be fairly easy to tailor the sound to be distinguishably different.
Glad you like it! I just thought it was a bit of a shame for the "normal" channel to sound gutsier in your clips than the TMB channel.

Great work!

just tried those cap value changes in the first stage of the TMB. .68uf and a .0047uf. And I have to say it sounds pretty good. I don't think it's too thin. In fact, before, I had way more bass than I knew what to do with. So, I am happy with this mod. Great job guys!

BTW, I am loving these S2 transformers. Lorne

So here we have a TMB layout, the sIII that might not have all the gain but the squeal is fixed and one can mod it to their likeing.
Well done, all you guys are great. I have amps that sing, I can't thank you guys enough.

Sincerely, Al (ajkimba)

As for the design itself, I have these thoughts. It has been said that, generally speaking, the 18Watt is a one trick pony. I would tend to agree. After I got over the sheer unfettered joy of playing one (say 3 Months), I realised that for me, some more variation in tonality between channels would proablay be a good thing. The sIII provides a little different gain structure especially in the TMB channel. This, I figured, would give me the ablility to use an A/B/Y switch to get some cools tones and see a significant difference in the tone of the two channels. The Normal Channel has a wider range on the tone control and a good amount of gain with humbuckers. It is the one trick pony channel.

The TMB channel, with a bit less gain and 3 tone controls, is a natrual for great crunch tones and some less compressed more touch sensitive single note work. You have much more control over the flavour and feel with pre and post gain (vol and master) adding more options depending on pickup output playing style etc....

When I want maximum gain I just bridge channels. Maybe that should be the next clip.

Here are some tweaking notes for the sIII circuit. It can be easily modified to increase gain (as the TMB channel is not a fire breather like some of the other TMBs) and fatten up the TMB channel for those who find it a bit thin (which no one has upon hearing the circuit in person, but we each have our own personal tastes in tone, eh?).

The TMB channel was designed to be brighter than normal. As previously discussed, the Plexi has a bright channel which is too bright and a dark channel which is too dark. Most players jump them to blend the tones and arrive at something to their liking. My goal with this amp was to arrive at a happy medium between those 2 channels and to bring the gain down to for those who want the versatility of a TMB without so much gain as some of the others (although it still growls with the best of them when cranked). Of course, the TMB channel can be jumped with the normal channel for some really cool blending effects.

I consolidated the feedback on the schematic & layout and updated them to revision 1.3. They are posted at:

http://18watt.com/modules.php?set_album ... _album.php

Here's the changes:
*added s2's tweaking notes;
*moved Output Transformer Center Tap to B+; and
*moved the CT of all the Trannies to the center of the windings.
* didn't re-label VR1 to Gain or VR7 to Volume but noted that!

Thanks for all the feedback and comments. There is a review now posted on Harmony Central. This was posted for sIII number 1. You can read some real player feedback at:

http://www.harmony-central.com/Guitar/D ... ead-1.html

That amp is the purple one I put in the sIII gallery.

I also archived revision 1.2

If anyone build this &/or notices any errors, I'll be happy to update it and keep it current.

The sIII will sport a New Plexi Style Front Panel Design with 4 inputs and all contols in-line.

For the 18W community in general, this plexi panel could also be used in conjuction with the new chassis if people wanted to build the original TMB. Head chassis is more compact, with closed ends. Size is 20"W X 6.5"D X 2.5"H so it also fits standard small box plexi cabinets (16.5" cut-out) available from several suppliers.

Why is the master volume the first pot after the TMB channel inputs. It seems like it would be at the end of all the tone controls. Just curious? CSB

I agree to an extent. However, I reckon the MV or more correctly "Volume" control for the TMB channel should be the other end of the tone controls. So you would have, going right to left, Inputs - Gain - Treble - Mid - Bass- Volume. And as this reflects the order of the signal chain better, I believe it would help make for a better layout with shorter wire lengths. For a little more visual consistancy, then you would probably want to swap the positions of the Volume and Tone controls of the Normal channel as well.

Just my two cents worth...

We thought about this for a while as you can imagine. Logically it makes sense as you say, if it's the sound chain you want to represent on the panel. But we thought that when playing, it would be better to have Vol & MV beside each other. Some Marshalls do this to e.g. 2203 (Master beside pre-amp volume).

Yes is does, and so, on the sIII panel Volume is first, Master Volume is second. They are also grouped together because they control the level and the type of sound, while the three TMB controls adjust the tonal content. We didn't think that the layout of the panel necessarily had to reflect the guts of of the amp, and the hook-up inside was not a concern.

jms969 is correct. In the gallery, click on the layout a second time and you will get a large high resolution image... Then you can either download it to your computer by right clicking on it or copy and past into any progra, resize the image if you want and print away.

And it will be nice and sharp... thanks jms969

BigAl,
My impression of the sIII is that it oh-so slightly tames down the TMB channel to more managable gain levels...and gives you a bit more versatility...while bumping up the normal channel to Lite specs. If you're the kinda guy that plays with some mid-gain sounds, this might be the amp for you...

The JATMB, from what i gather...and JA (or others at Greg's last get together) should comment on this seems to really take the gain tones up a few notches to the limit of the amp, without the squealing and noise issues that seem to come with the design....The other cool thing about the JATMB, is the fact that you don't have to worry about lead dress or grounding...all that stuff is pretty much done already in the circuit trace. The JATMB is about has plug and play as it gets, without going out and actually buying an amp.

There are some goodies in the JATMB amp as well, like NFB and a boost....I'm *not* the guy to comment on it, as I've not had the pleasure of playing one yet...I'm just repeating what I hear in scuttlebut. But I'm sure JA will be glad to give you some more background.


The sIII still requires you to do all the actual work....but it takes abit of the guesswork out of the process.

One final option which might not be presented to you yet (and s2/coco is it politically incorect for me to mention this?) is to give s2's Tsunami build a look as well. It is a variation on the sIII thing....it puts the PI in the v3 spot, like the sIII....but the big difference is how each channel is voiced. The sIII took the two channels in one direction while the Tsunami did something different. I'm sure Steve would be more than happy to give you the scoop....as again, I'm not the guy to comment as I haven't been privy to the amp.

I'm actually in the same exact boat as you....after I finish my lightning...I'm going to be building some variety of 18watt...since my 18lite was gutted for another clone-project that I wont mention ( for fear of having a certain crybaby amp maker say nasty things about my mother...).

But the fact of the matter is that I will be looking at all of the various 18watt designs in the next few weeks and deciding on which one is best for my needs. I actually have a good deal of the parts for one....s2 trannies, all the caps, resistors...all I really need to do to complete a TMB is a turret board (or JA's PCB), some sockets and a chassis....

It's a tough decission, me...I wanna build em all. I might get thrown out of this house on my ass, once I reach my wife's tolerance limit...but i really want to build em all. I've got plans of building matchless clubmans, 6v6 plexis, fender builds, you name it....

But for now, making the decission on what 18 to make to tide me over until I can build another is a very hard decission.

The sIII TMB channel is similar to s2's Tsunami but with a Master Volume. The other channel on the sIII is pretty well 18W original Tremolo voiced. Different from s2's Tsunami in that way.