JTM 45/100 - Build story

[BoogieEngineer]

The amp sounds great but it doesn't distort, very clean, even at max. i'll retest it later with a fluke later.

As I understand this is the circuit that the later superbass models are based on. So in a sense it's basically the earliest superbass which is very very clean. I use mine with a Maxon SD-9 up front and the tones are just heavenly, although recently there might be a cold joint that I haven't got time to inspect. Anyway congrats on its working fine and happy playing!

[VintageCharlie]

Mine stays clean up til about 6 with the strat, from 7 it starts to break up noticeably. With an LP mine starts to crunch a lot earlier - like on 5 or even below that. Flat out it is all classic rock tones with an lp and all Jimi with a strat. What do you mean by "clean" - that´s pretty subjective i suppose.

[Xplorer]

maxon sd9 ? i'll have to check out what it is exactly! interesting.

yeah, my amp doesn't distort like yours on your clips Karlis, it's really clean, no saturation even at 10 ! or very soft. it's as clean as the wind cries mary, even on te, jack plugged on the top left input, and presence at 6 or 7 ..
with a fuzz, it sounds really great, and i might sound better and better over time ...

with my 1969 old tele with seymour duncan antiquity humbucker and texas special loaded, it has a lot more distortion, and it's louder. this tele sounds unbelievable .... like no other i heard .. Angry Keith Richards ... only even more beautiful than his micawber.

mine also uses a 16 uf, i'll probably use a 32 uf later ( this is maybe why ?? ) , and some 470k instead of some 270k etc .

Man thanks to you all guys ! you really helped me !
Yeah i'll post clips off course ! later, not yet. and i'll wait for some other recording conditions, playing it louder ...
with a strat, with telecaster, with some univibe, tremolo, reverb after the record, fuz ... i'll see what i can do, but honestly i need some practice. Now it's ok, i can play more, but not in the desired conditions.
i'll probably get a senheiser e906 or two when i can. till hen i'll perhaps simply use my iphone to give an idea.

How long did it take for your amp to have more break up Karlis ?

If you have a hot plate put it on a whisper level and check it every now and again

i'm sorry Neil, i'm not sure to see what the hot plate is. whisper level for the audio cd or the amp volume ?

i could run the amp with the audio cd in ( not too high in input ) and have the amp plugged into the home made attenuator, just without any speaker connected to it, just big resistors to handle the volts while the amp works with an audio source ..

[VintageCharlie]

Adrien, i don't think that an amp will get more distorted after break-in. At least that is not what mine did. In regard to how early break-up starts, the amp hasn't change from day one til now, at least not noticeably. What did change was the quality of the break-up. It was a bit farty and scratchy at the beginning. I think it ghosted a bit more. As it settled in it got creamier and smoother and by now, strangely enough, i think there's a little less ghosting.
If it's really really clean, i suppose something is not right yet. It can't be just the bias if it is THAT clean - i would not be able to bias my amp to such clean headroom. How loud is it at max? Maybe you can measure the output by a amp sim VU meter (through an attenuators line out) or something in case you can't turn it up. Does it compare volume wise to your 1959 SL clone?
Maybe it's the tubes? Which ones do you use?
Anyway, congrats on finishing the amp, i'm sure you'll figure the issue out soon and will be wailing away

[BoogieEngineer]

Yea with that setting my amp breaks up quite a bit, and I use Strat's all the time. I don't know what makes the difference though. Bedding in only enhances the tones, not adding gain. Can't wait to hear clips, the amps just fantastic looking.

Anyway, Maxon SD-9 has been the choice of pedals for tone monsters like Scott Henderson and Mike Landau, you have gotta check it out. Here's the demo of the pedal: http://www.youtube.com/watch?v=qK02Ej5jZU8" onclick="window.open(this.href);return false; and http://www.youtube.com/watch?v=qK02Ej5jZU8" onclick="window.open(this.href);return false;. It adds gain and fatness to the tone without depriving you of the bass at all like other pedals I have tried. There are not many pedals that are capable of doing so.

I love single coils with Marshall a lot more than humbuckers that sound thicker in the mid but don't have as much low ends and sound as huge. I am not surprised that you loved how the Tele sounds.

[Xplorer]

yes, i went to see some sd9 clips with scott, very interesting. But i never feel like i'm missing some basse with a fuzz lol.

yeah, i prefer single coil pickups and strats, but my tele is the only guitar that i like , with a humbucker in the neck.

did you all use a 32uf on the filter board ? i used an old RS 16uf ... that's maybe why ... ?

i couldn't compare the volume of both at full level, cause i simply can't play them at 10, unattenuated, in the flat where i live !
but sure the superlead should be louder.

i compared both amps through the ame great home made attenuator and yes, the superlead gives gain and saturation, not really the jtm, unless i use a fuzz. both, with a fuzz, have a different color. both interesting.

about the tubes, yes .... i thought about it.
i'm using ome kt66 from tubetramp, shuegang from 2004, supposed to be great ( but one has 36ma and the other 29 ma , and two others 34,5 ma , i'm not sure why. )

for the preamp, i'm using a telefunken in V1, and two siemens for V2 ans V3.

i also have an amperex bugleboy and a tunsgram to try, all from tubetramp except the siemens.

any advices ?

[Xplorer]

i'll maybe try tomorrow the 240v tap, as the AC voltage coming should be a tad lower, ( i'll measure it but it should be close to 230v ) it would act as a variac, giving more break up range, saturation ...
Van halen uses a variac at 90 vac into the 120v input.

[neikeel]

Maybe you need to try some different preamp tubes, a poor one might be dragging things down.

I found my first 45/100 (with metro spec trannies) was a bit cold at first. There is (and was) much less gain than any of my Superleads. But there is also the issue of where those tones are emphasised. The Superlead will always sound louder and sharper, but it also has less lows and lower mids (due to the 0.0022uF V1 coupler and split cathode on V1). Is your SL an original metal panel with the 5000pF cap on V1? Those early metal panel can be wall paint peelers!

The type and size of bypass cap on V1 will influence how loud the amp is at lower volumes and the frequencies that are enhanced. I tried 100pF up to 5000pF on this amp and settled on 500pF although may go back to 100pF next time I have a look inside. That amp runs NOS (well they were!) GECs. I use it for bigger gigs specifically because it has more clean headroom for the funk/clean tones I need for the stuff we play. It responds well to the guitar volume controls, the coil splits on my guitar and of course a pedal or two (EP-pre, Tubescreamer, Octavefuzz for increaing levels of gain).
As you know my EL34 45/1000 uses a stock 5000pF which is perfect to give the amp some balls at lower volumes but not a 'bright cap' in the way one would expect.

What puzzles me is why your amp is clean right up to 10. Funny particularly as Karlis was worried that his amp did not have enough headroom at first not sure what came of this whether the amp improved or he found an issue to get where he is now (sounded great on the clips he posted)?

I too was disappointed with my 45/100 at first, but it did bed in. I had it set up for a couple of months in my spare room but was using my 50 watters more. First time it really rocked for me was an epiphany - plugged in my '87 LPC using bridge pick up all the way up, with both amp volumes on 8 and everything else (except bass on 3 and presence on on 10. There it was! No pedals just guitar and cord. These amps do need the presence, mids and treble to be turned up to find the gain.

Have a listen to this: [urlhttp://forum.marstran.com/viewtopic.php?f=3&t=452][/url]

Of course with vintage single coils you will always need some boost to get lots of crunch.

[VintageCharlie]

Mine still does break up with a les paul sooner than i expected - from 3 it is noticeably crunchy and even below that it is not REALLY clean. At 5 is where it gets really great crunch. The strat stays REALLY clean up to about 5, then it gets noticeable saturation and from 6-7 it starts to do the fun stuff. It behaves with a strat just as i have read from other build reports. With a les paul it crunches earlier than what others report. Don´t know why this is. I haven´t messed around with it, even the tubes, as it sounds really sweet - just like the marstran clip that Neil posted above. But i could imagine that the tubes might have to do more with the early breakup of the les paul than anything in the components or wiring.
But, yeah, clean up to 10 is strange. Have you tried a really clean boost in front of it - does it get some breakup of its own this way?

[VintageCharlie]

I just remembered one thing that did happen to my Linnemann built jTM-45 that i once owned. I had connected it the pc through a reamping device in order to use some VST effects through it and i accidentally ran an extremely high signal trhough it and switched it off immediately. After powering it on again, it still worked but it was the same as what you describe with your 45/100 - totally clean and the output level had dropped a lot. It turned out that one of the preamp tubes was toasted. IIRC it was v2. Did you try some other preamp tubes, switch them around, etc.? Maybe one is bad or weak?

[Xplorer]

Yeah, definitely something wrong, it shouldn't be that clean ...
i changed the preamp tubes, now with a telefunken in V1 ( also tried a siemens in this configuration ) , a tunsgram and an amperex in V2 , V3 ( don't remember which order, hardly visible letters on these tubes )

i should perhaps re measure the amp, right ?
i recorded a fast clip with my iphone, i'll send it when i can, you'll hear how clean it is ... at this level my metro 69 SL really has gain : angry jeff beck. and i play with presence on zero ....

i'm not disapointed with the amp, but a little, cause i'm sure that it can do MUCH better than this.

By the way, my friend offered me a Fluke 189, endly a great machine
I'll have to find a good one just to measure transistors now.

[Xplorer]

here it is a little clip from my iphone.
attenuated ( but anyway, attenuated at the same level, i have a whole different range with the SL69 ... and this looks like my SL with the volume at 3-4 ) .
volume and every controls at 10 except for the basse at 0 and presence at 4.

[Xplorer]

Things i could probably change, looking at Karlis's amp :

the RS 16uf, to an erie 32uf
the diodes, with some modern uf 50 something
the 250uf cap , to a smaller value, modern cap
the power tubes ??
the mustards : they all were measured very close to the nominal value ( so what ? )

among all this, maybe nothing, maybe a few, i really don't know.
resistors were all measured below 1% of tolerance.
RS silver micas too.
the lemco 47pf was nice too.

should i try to swap the components one by one ?

bias voltage : - 60v ac. if i go higher ( closer to zero ) , it'll increase the mv accross the 1 ohm resistors, and it's already at max.

[VintageCharlie]

Have you checked all the resistor codes - maybe there is a mix up somewhere. 470r and 470k being one of the more popular mistakes, which would lead to very low gain, from what i've read here. But i think you had 270k mixers?
Also, from what i know, none of the things that are different in my amp compared to yours would result in such dramatic clean headroom difference.
A 69 SL with the 5000pF bright cap is supposed to get in classic rock territory at 4 on the volume - so that would be totally normal in my book.
Adrien, i don´t think you should start to take the amp apart now - if the voltages checked out well, i suppose that everything's fine generally. And the amp sounds good with your fine Jimi licks. What happens if you dig in really hard on the strings? Actually, with a strat, if my amp is on 10 and i play really gently, i can get it almost clean, then get nice crunch when diging in harder.

I'm sure there is some small thing not obvious at the moment, but you'll sort it out. Just don't tear the amp apart!

[neikeel]

I'm sure there is some small thing not obvious at the moment, but you'll sort it out. Just don't tear the amp apart!

+ 10,000