Authentic JTM 45/100 build diary. Clips added.

Detailed assembly steps separated into threads.

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crane
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Re: Authentic JTM 45/100 build diary

Post by crane » Sat Sep 03, 2011 11:42 am

May be some experienced builders could provide waveforms at the anode of each preamp stage with know input signal? Let's say 1V p2p 1kHz or whatever you may prefer.

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Re: Authentic JTM 45/100 build diary

Post by Roe » Sat Sep 03, 2011 12:28 pm

try to disconnect the 27k nfb
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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Sat Sep 10, 2011 9:01 am

Hey guys!

We haven't looked any further into the issues with the low headroom and ghosting that appears rather soon, but as the voltages turned out to be spot on and the amp works otherwise flawlessly i played it quite a lot in the last weeks in some spare moments. When i crank the volume to 6-8, where i feel it gives the best tones, and run it at -4 db on the attenuator, i have to say, the amp sounds phenomenal. For the strat on lower volumes i jumper the channels together to make it fatter, but on 6-8 the strat sounds great on the bright channel alone too, as the amp does the fattening-up nicely.
In this 6-8 zone the amp sounds scary close to tons of records from Cream to Hendrix and everything in between. It seems to me like it behaves like it should on these higher settings - it gets this huge, crunchy, saturated and rich, complex tone that is very smooth at the same time if you don't choke the signal too much with an attenuator and it's great at getting all the classic mid/late 60's tones. The EQ is quite responsive too (a lot more responsive than that of my former JTm-45). Everything seems to be where it should when it is approaching dimed levels. No noise either - on the highest settings the background noise of the humbuckers is louder than what the amp produces when the guitar is turned to 0.
The only thing that bothers me is the clean headroom thing - it sounds "cleanish" on a strat to up to about 3-4, but you hear first signs of break-up already at 2 on the dial (Hi treble channel), at 1.5 with the Les Paul. On the other hand, it gets really loud at 2 on the dial already and from about 4 it doesn't jump a lot in volume, but gets more and more saturated.
Ghosting on the strat is not much of an issue, the neck pickup of the les paul is a different story (initial testing of the amp was done on the les paul only due to its ability to push it harder). My strats pickups measure at about 6k and the les paul is about 8k. I haven't measured the signal strength of my les paul, but i doubt it might be overly much to cause the lower headroom.

If any of the OT taps are coloured incorrectly, is there a scenario possible where the amp sounds ike it should on higher settings, but misbehaves on lower ones? Could this still be a nfb-related issue?

How long do these amps stay clean for you, when running them on 490v taps? I mean, really clean - before you notice any audible break-up (any signs of distortion in a similar way that hi-fi guys talk about it - as a noticeable distortion of the signal)? With an LP i still have cleanish crunch at 3 on the hi bright channel and it starts to distort at 1.5 aready, maybe even earlier, but the speakers even out some of it. Though, the less i attenuate, the more the speakers make the guitar sound smoother and cleaner - like a rather increased and huge sustain, istead of (over)drive - and that is a simply fantastic tone.

I start to think it might also be tube related, but on the other hand - swapping places of the tubes didn't change much either.

Oh, and as for attenuators. I'm happy i didn't buy the very expensive Aracom, because with this amp and the hot plate i can clearly see how the speakers and they'r movement - hence loudness - is the main factor of "nailing" down many of the big tones of the greats - no matter how "transparent" an attenuator is, anything below the point where the speakers add their smoothening and punch-efect (when pushed hard) will simply give a completely different tone. In my case with the Hot Plate, it gives tone heaven at -4db, at -8db you can "imagine" how it might sound without it, sounds "almost there" and on -12db you approach a teritory, where taking the DI into a speaker sim might give better results, as the speakers start to become hi-fiish due to the decreased movement. (will try it without an attenuator as soon as i have put the other 2 speakers in my cab). So i decided to stick with my hot-plate, as it does these both things very well - kicking off as much volume as possible beore the speakers turn into a hi-fi system without noticeably colouring the tone (to about -8db) and it lets me take the DI signal into a speaker sim from the amp when it is put to Load. I can't imagine how ANY attenuator could circumvent these issues that the loss of loudness creates with the speakers. So i'm almost there - just have to figure out the possible cause for the lowered headroom. It might be psychiological or it might be what you guys call break-in, but i think that the ghosting effect has decreased quite a bit too - it is not as "effect-like" as before and gets on my nerves only with the neck pickup of the LP - bridge is fine. I kind of start to wonder if there is anything to ix at all, as it sounds glorious now, but still, the headroom thing doesn't leave me be.

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Re: Authentic JTM 45/100 build diary

Post by Xplorer » Sat Sep 10, 2011 10:46 am

Karlis, please, can you post some clips ? so it would be easier to appreciate your amp tone, and what's you're asking about the break in, and ghosting.

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Re: Authentic JTM 45/100 build diary

Post by shakti » Sat Sep 10, 2011 10:48 am

Good to hear! Just curious about the noise level in yours, as my build is just about identical: if you turn down all controls (to cancel out as much hiss as possible), then bring the high treble level to 10, do you get any noticeable hum through the speakers? And if you turn the bass up, does it increase?
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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Sat Sep 10, 2011 11:03 am

I will make a clip as soon as i have a bit more time, as it takes quite a bit of time to find a good spot for the mic, etc.
Thorleif, i will check what you are asking - if i got you correctly, then you suggest to turn ALL controls to 0 and then turn up the hi bright channel to 10?
With the normal channel on 8, treble and presence on about 8 or so i think i could not notice any noise at all. I will check with the method that you suggested.

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Re: Authentic JTM 45/100 build diary

Post by shakti » Sat Sep 10, 2011 11:36 am

Yes, turn everything to 0 - amp should be dead silent at that setting. Then crank *only* the high treble channel to 10 - is there any hum? And then turn up the bass to around 3 - does the hum increase?
JTM45 RS OT, 1973 18W, JTM45/100, JTM50, JMP50 1986, JMP100 "West Coast", AC15, AC30, BF Super Reverb, Boogie Mk 1, Hiwatt CP103, DR103

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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Sat Sep 10, 2011 1:07 pm

ok, everything to 0, nothing plugged in, unatuanated into 100db sensitivity G12h 75hz speakers (pre rola cones). Can't hear anything from 1m distance (sticking ear right next to a cone reveals barely audible transformer hum or what ever that is called - sounds like "electricity" :D ). Hi bright channel on 6, still can't hear a thing from 1m, but slight hiss is audible from very close up to the cone. I hear a VERY slight hiss from 1m at about 7 and upwards - sounds like a quiet wind is blowing, it maxes out at 9 and stays the same up until max (10). So at 10 i have a very slight hiss that is quite a bit quieter than my pc next to it (and the pc has an antec case with double walls and noise isolation stuff and what not (sorry don't have a db meter), but it is barely audible.
When i start to add bass, the hiss i had before doesn't increase - it just gets "more body" :D , but i simply get a similary low vol bassier version of the same thing - the "bassy noise" seems quieter than the higher hiss and it seems to max out at about 4-5, stays vaguely the same up until 10.
When i dial in my preferred settings for rather bright type of tone - P: 7-8 B: 0-2 M: 7-8 T: 7-8 Vol I: 6-8 Vol II: 0 - i get the background noise level of old vinyl played back on moderate volume levels. On this setting, when i turn Vol I (bright volume) to zero, the hiss appears at about 1 and increases very little up to about 7, then up to 8 it increases a bit faster and makes a relatively big jump in volume when going from 8-10. With these settings on 10 the background noise is about the same volume as when you would hush somebody loudly, say in a library, just with the "sh" sound, which is a good comparison because it is very limited how loudly you can pronounce the "sh" alone. When it's on 8, i'd say these are "loud whisper volumes" - you can easily say "sh" louder. When i imagine how many decibels would come out of that thing, i can't think of a way how this might be audible on a record, when the mic is adjusted not to clip, even when the amp is on 10, where the hiss is naturally the loudest.
I will compare it to my 18w animal at some point, but it's a completely different design and different output levels, so not a very useful comparison.
When i plug in a humbucker guitar and turn its volume full up, the noise from the buckers is bigger than what came from the amp previously, so i'd say that i can't see how this might be improved upon.

Are you after an amp that is "totally" silent or do you have bigger noise levels with yours? Is the noise louder than the bucker background noise?

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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Sat Sep 10, 2011 1:23 pm

btw., while playing around with this, i noticed that my presence pot is kind of "hissy" - i hear a hissy noise when i turn it. It doesn't sound like a a "scratchy pot" though. Is it supposed to do that or is it just a bad pot or maybe a different issue - something related to the possible nfb issues the amp might have?

Oh, and one time i noticed that, when playing the amp at about 8 and hitting some chords hard, when standing close to the amp, i get a high-pitched noise right after the attack (if i keep the notes short). If i understand it correctly, that's some kind of oscillation or a microphonic tube? But it goes away as sson as i'm not standing right next to the amp - is this normal too? Haven't put the shields on the preamp tubes - maybe they pic something up therefore?

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Re: Authentic JTM 45/100 build diary

Post by shakti » Sat Sep 10, 2011 1:26 pm

No, sounds like mine is similar to yours. The hum I am getting is not something I need to worry about at playing levels, so it's really more an obsession with getting it as quiet as possible. At 1m distance I'd be hard pressed to hear any hiss until I'm above 6 on the volume (with treble and mids cranked, and presence at 5). I think I just have to live with the tiny bit of hum above 8 on the volume, as it's probably a transformer coupling kind of thing. It's definitely not a ground hum, and it's not audible at playing levels and some distance from the cab.
JTM45 RS OT, 1973 18W, JTM45/100, JTM50, JMP50 1986, JMP100 "West Coast", AC15, AC30, BF Super Reverb, Boogie Mk 1, Hiwatt CP103, DR103

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Re: Authentic JTM 45/100 build diary

Post by shakti » Sat Sep 10, 2011 1:27 pm

VintageCharlie wrote:btw., while playing around with this, i noticed that my presence pot is kind of "hissy" - i hear a hissy noise when i turn it. It doesn't sound like a a "scratchy pot" though. Is it supposed to do that or is it just a bad pot or maybe a different issue - something related to the possible nfb issues the amp might have?
No, this is completely normal.
JTM45 RS OT, 1973 18W, JTM45/100, JTM50, JMP50 1986, JMP100 "West Coast", AC15, AC30, BF Super Reverb, Boogie Mk 1, Hiwatt CP103, DR103

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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Fri Oct 07, 2011 5:55 am

Hi guys!

By now i have played around with the amp extensively and i have to say that i love it! The ghosting is obvious only with the neck pup of the LP once the amp is quite heavily in overdrive. Otherwise it's practically non existent. This was the first amp for me that has any ghosting, hence i suppose i was very "sensitive" about it at first.
The amp has a very complex and smooth overdrive and it gets a fantastic punchy/squashy/compressed attack when dimed.
With a strat i get a really nice kind of clean tone at 6 - it still seems kind of clean, but gets already round and warm, punchy, saturated, with slight overdrive - that's my favorite strat tone i have heard. then from 6 upwards with a strat it gets lots of the Hendrix goodness going on. For a strat the ability to jump the channels is also great as you can let it be bright and bitey or you can fill it up as much as you want, without changing youre favorite controls. I'd say this is it as far as the strat goes - the later amps probably get too much unnecessary brightness and stifness.

For the Les Paul i go into lo bright input for cleans, set it at about 5 on the vol. and i get a similar thing going on as with the strat - punchy, saturated "clean" that holds together nicely. And then any gradation of volume over 5 in lo or hi input gets me in various stages of classic rock. From 8 and upwards it gets a really nice compression and i love that dimed sound with the LP bridge.

EQ is surprisingly responsive. Much more so than on my former JTM-45. Diming presence and treble gets you almost into later marhsall territory. For clean and cleanish sounds you can get also very bright tones - if you want it will be a very bright amp, so don't get scared away with the coments on this model that it is just a bass-heavy "vintage-sounding" (=muddy) beast. It can get extremely fenderish if you want - clean, articulate and bright (and at that it won't get peircing).

I keep my bass at 0 or max at 1, at least when i'm in overdrive territory. The amp has plenty bass on this setting. If i wish more boidy to the sound with a strat, i just add in the normal channel. In overdrive, increasing bass also increases the "grain" of the distortion, it becomes less smooth and at some point kind of farty - not what i'm after. But, from what i've read, seems like most people rtun their JTM's with bass at 0 or max 2.

Soon my other 2 speakers should be here - then i can complete the proper 4x12 and test it without the hot plate.

The last thing that i was concerned with was the rather low headroom with a les paul, but after talking to other 45/100 users it seems like it is pretty much normal that you can easily overdrive it at 3. I get some slight breakup at about 1.5-2 on hi bright vol. That might be tube related i suppose, or it has to do with the pot travel maybe. Either way, for the nice saturated semi-clean one would have to use the lo bright input anyway with a lp, so also this is not an issue.

Altogether i'm very pleased with the amp. I find it very musical and versatile. I have done some test clips with a cab sim, but i will probably post something only when i have figured out a good way to mike it properly and that turns out to be much harder than i ythought, especially once you're in overdrive territory. (i got an sm57 and either i don't know how to handle it properly or it's just not a good chocie for this amp - i like the tones from the cab sim better than from my sm57 attempts).

I will also post some more pics of the finished amp once i have a bit of time for that and will try to get up some proper clips too.

Thanks to everyone involved in this project. Thank you very much for all your advice and kind help! THere are too many of you by now to mention, but you will know who i mean.

Next up, at some point, will be a 10 000 series or 12 000 series thing, switcheable to either of those, depending on which will be the "platform".

Kind regards,

VintageCharlie

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Re: Authentic JTM 45/100 build diary

Post by emmjaydubya » Sun Oct 09, 2011 11:08 pm

Been following your thread from the beginning and I have to say it's a work of art. I'm beginning a 12,000 soon but some day hope to do one of these for sure, and this is one of the threads I will use as a reference! Can't wait to hear some clips and congrats, AWESOME AMP!

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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Mon Oct 10, 2011 1:18 pm

Thanks! The compliment goes to the guy who built it - Crane. On my part - i just did my homework in regard to the vintage-correct parts (for the most part). Yup, clips will follow as soon as i have figured out how to get useable tones out of my sm57 on the cab (for now in initial attempts a cab sim sounded better). Will try to play around with the mic some more this weekend. I see many on this forum have done great clips with the mic, so it's just a user-problem obviously.

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Re: Authentic JTM 45/100 build diary

Post by VintageCharlie » Sat Nov 26, 2011 5:22 am

Hey guys!

As quite a few of you have been asking me for clips, i finally got around to record some snippets of my crappy playing. Before i continue, i apologize to Angus, Jimmy and Eric for raping a number of their songs! :dlr:
The reason why i hesitated to put something out there is because i haven't had lots of time practicing lately - should have done that instead of searching for NOS parts :D So i don't really do the amp justice (yet), but i hope you can get the picture even through my sloppy hands.

This was recorded with an Epiphone Les Paul (, almost antique strings, all controls to 10) with what i believe to be Gibson classic 57 humbuckers - straight into the amp.
Amp settings: Hi bright volume: 10; Normal volume: 0; Presence: 5; Bass: 0; Mids: 5; Treble: 5. Basically the EQ is flat, except the bass.
As i still get not very good results at trying to capture the tone of this beast with my sm57, i recorded this as follows. Amp set to 8ohms, goes into 8ohm hot plate set to "load" - no sound coming from the real cab, then the line out signal of the hot plate goes into my E-mu sound card. Recorded in Cubase, no post EQ done here. What i added is an Impulse Response cab sim from Redwirez (3 mics - a 121 and a m160 at 0.5 inches from the cone edge and an U67 12 inches away from the cone edge; all mixd in at equal amounts, which lets a lot of frequencies through, as i wanted that as many nuances and harmonics are audible as possible through a sim). Then i added room reverb and that's it.

What i love about the amps tone (even when cranked to 10), is that i don't hear not a single frequency that would jump out as unpleasant - no fizz - it all blends together very nicely - very rich harmonics, but not too mushy and a lot of detail comes through even at dimed levels. My 18w had/has one such frequency that just jumps out and since that i have gotten very touchy about it - no idea which range it is, but it sounds like oil cooking on a frying pan. I hear it in this amp too, but in this case it simply sounds musical and it sits nicely along with the other frequencies.

The clip is rather long. At the end i'm trying to demonstrate the responsiveness and dynamics of the amp - even at 10 you can get clean/semi clean with very light touch and go to over-the-edge-mean just by digging into the strings.

I also did 2 clips to demonstrate the ghosting, which is my only complain with this amp and which i hope to solve during the winter holidays - hope it is a filter cap, as that would be an easy fix. First clip is recorded with volume at 10 and the other is set at about 3.5. Also i was wondering if the amount oif breakup that i get with les paul get at 3.5 is typical, or if it breaks up rather early?

So here are the clips:

http://soundcloud.com/vintagecharlie/jt ... i-les-paul" onclick="window.open(this.href);return false;

Ghosting "demo" with both tracks in one playlist:

http://soundcloud.com/vintagecharlie/sets/ghosting" onclick="window.open(this.href);return false;

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