These are the two Valve Junior heads that you hear on Rosetta's track (Temet Nosce). I run them in stereo, each through a 2x12 closed-back cabinet with one Vintage 30 and one G12H30 (made by Avatar, who I highly recommend). On (Temet Nosce), I played my mutant '72 Telecaster through a stereo delay pedal, with each amp/cab set up and mic'ed in a different room. We just panned the tracks left/right and that was it. The outro to Monument was also recorded with these heads, but in 4 takes with my Gibson Sonex-180.The amps sound significantly better now than they did then, due to further modding. At that time, the only changed components were R1, R2, R6-9, and 10uF cathode bypass caps on the preamp triodes. That circuit was a huge improvement over the stock sound, but I think the current version is vastly superior.
The schematic below (based on stock schematics from SEWATT.com) shows all of my changes in red. You can find an excellent explanation of different components in S2 Amps' upgrade kit instructions. Whether or not you buy their kit (I did not, and doubt it is still available), the instructions are full of useful info. Loads more info can be found in the SEWATT Octal Mod file, even if you have no interest in adding another power tube. The complete repository of Valve Junior info is here.
Both amps have Hammond 125ESE output transformers. These are far larger than needed for a nominally 5-watt amp, but the greater dynamics and bass extension are worth it, particularly since I most often play a baritone-tuned telecaster (my '72 Frankencaster) through the VJs.
Not noted on the schematic is that the rectifier on the high-voltage power tap is discrete 1n4007 diodes, in the stock amp. I replaced these with UF4007 diodes and the switching noise was reduced.
For recording purposes, the black amp has a second, smaller 3-way toggle that switches R15 from 10k to 5.6k or 1.5k, for a kind of presence or power amp voicing control. Most of the time it stays on 10k, to match the white amp.
Tubes: both of these amps use a JJ ECC803S (long plate) in the preamp, and a JJ EL84 in the power amp. I specifically asked for power tubes with lower current draw for maximum clean headroom.
Final notes: these amps are LOUD -- much louder than the 5-watt rating would suggest. I can't get anywhere near breakup at "bedroom" levels. If you're interested in controllable preamp gain, I don't recommend adding a master volume. I've tried it and it sounds crappy. The best solution is to use a tube overdrive pedal in front of the amp. The closest thing I've found to adding extra gain stages is the EH LPB2ube, which works in either stereo two-stage or ganged-mono four-stage. I use it in stereo to front end both amps, with a stereo volume pedal. Getting a small amount of distortion from each tube in the overall chain adds up and sounds great.
EDIT 3/2011: I've made some more changes to these amps, detailed in a post on my work blog, Electronic States.
4 comments:
When playing "Rosetta" songs like Wake or Départe, what drive stomp box would you use if you were running these amps instead of the Marshall?
Honestly, it would be almost impossible to get the level of gain and thunderous low end on these amps that I get with my Marshall, even at very low volumes. You'd have to put a big 3-channel modeler or tube preamp unit in front of the VJ and run it with low output --- not ideal.
I don't really play Rosetta songs on anything other than the Marshall head, since it is in many ways "THE sound" that we make, at least in terms of overall texture. The Valve Juniors just aren't comparable in any way --- which is really why I have them and like them so much. The TSL is one of the most complex circuits around, the VJ is one of the simplest. In both cases, I've altered them to sound exactly how I want, but they are by no means similar. The tube OD pedal I use with the VJs gets me a very mild, singing breakup.
I despair every time I hear of someone swapping capacitors for ones of equal values. I don't know what mustard caps are but capacitance is a scientific property. It doesn't matter how many ill-informed guitarists vouch for their supernatural properties, the effect will be nil because you cannot change the laws of physics, no matter how much you pay. You would be better changing R1 to 1 meg for far better input impedance matching. The Hammond transformer has a flat response from 100 to 17khz which means that it won't be doing a great job with a baritone guitar - low E is 82 HZ so any perceived difference is probably the placebo effect as all it changes is the power output. Another uncomfortable scientific fact.
Notice I did not make any claims about the Mustard caps changing the sound. I put them in to see what would happen, and nothing verifiable did.
Also notice that R1 IS in fact changed to 1M.
The Hammond 125ESE does not need to be full range. Notice that the cathode bypass caps roll off even more bass than the output transformer. In the case of a baritone guitar, you want the lows attenuated so that the sound doesn't get "boomy" or "woofy"... most guitarists describe this low-end roll off as "tight-sounding". I sucessfully A/B'ed the VJs with the stock vs. Hammond 125ESE OTs. I don't know what the difference is between the Hammond I use and other Hammonds, just that there is a repeatably blind-verifiable difference to the stock OT. The Hammond has a low-end rolloff that is a different shape/slope than the VJ's stock OT. They have different value primaries, different inductances, FRs, etc.
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