Using JP2C Preamp with Simul-Class power amp?

Greetings guys! Has anyone tried using the JP2C preamp out into a Simulclass power amp? I know the JP2C is not simulclass and people argue about that feature. Would it be something noticeable to try? It's probably not a "night-and-day" difference, and a simul-class power amp isn't cheap... but it has me wondering... should I pick up a 2:90 or 295? It would effectively turn the JP2C into a DRG instead of an HRG.

I did it. Wanted to see if the preamps of the JP2C and Mark VII were on the same level or different. Did this with the FX loops.

The only issue if you slave out from the SEND jack, you bypass the GEQ circuits. I would assume the slave out would provide signal for a power amp but that would still be derived from the Class AB section so there is no way to avoid that.

I did slave the JP2C into the Mark VII so that would have the effect you seek. Mark VII is Simul-Class and its own GEQ. Much brighter sound and more power tube saturation with that. Also slaved the Mark VII in IIC mode into the JP2C to see if there was much of a difference. Well on that note, the Mark VII IIC slaved into the JP2C sounded much like the JP2C CH2 without slaving. Mark IV mode was a bit more aggressive than the CH3. Slaving from the FX Send into a return of an amp that has Simul-Class would be a true effect than using the slave out to a 2:90 as you would bypass the Class AB power section completely.

In comparison of the Mark VII to the JP2C power sections (ok the GEQ may also be a bit different). The Simul-Class power of the Mark VII is a bit more compressed, and the end effect will appear as if you have more presence in the mix. It will be brighter but still sound about the same. The JP2C power section will have a slight drop in power tube distortion and a darker warmer tone. It was quite interesting to hear each amp through an alternative power amp. If you want a JP2C DRG, Get a Mark VII, not only do you get that Simul-Class power, you also get a few more modes to choose from, in addition to a footswitch control of the FX loop. Only one GEQ so you could easily add one in the loop if you need add that feature, would not be easily switchable though.

If you opt for the 2:90, use that in parallel to the JP2C. Use a signal splitter like a Lehel P-Split to separate the signal into an isolated output to send to any mono-to-stereo effect pedal and run that into the 2:90 for a wet/dry/wet rig. You would retain the deepness of the Class AB JP2C power and add in some of the frills of the Simul-class. I have run just the one Mark VII with the JP2C. Wonder what would happen if I ran the two Mark VII with the JP2C and the P-split using a stereo FX pedal to feed the returns of the VII? Thanks for the idea, will have to try that someday if I remember do try it.

Thanks for the great explanation and write-up, Bandit! Thorough as usual! It's a combo of GAS and tone chasing that gets me... but you've reeled me in, so to speak! I do need to give a Mark VII a try some day. I put one of those Ibanez PTEQ's in the loop of my JP2C to tame some of the high-end fizz, and it's working nicely.

High end fizz? What power tubes?

The Mark VII is interesting. Similar to the JP but different. It is a bit brighter in character than the JP2C (ok I confess I am running the STR415 Sylvania 6L6GC I got through Mesa, was not easy but I managed to get a NOS quad from them).

At least you have some resolve for the fizz. One would think it could be managed with the GEQ. Have you tried swapping out the phase inverter tube?

I too find the VII to be brighter than my other Marks (V:90 and V:25). I came across a video from Mesa with Doug West going over the VII and noticed he was running Channel 3 presence at 9 o’clock. So, this convinced me it wasn’t just me that finds it bright. I did purchase some 5751 tubes I was going to roll but haven’t yet as I’ve found dialing back presence and the 6600 Hz slider to mid height or a bit below gets that sweet tone. It is a game between treble knob, presence and 6600…they do similar things but not really.

Regardless, it seems the VII is brighter than other modern Marks if all knobs are at noon and EQ off with IIc/IV and CRUNCH modes.

Bandit, I'm running Yellow Mesa-branded TADs on your recommendation. I couldn't get a hold of any Greens, so settled on a quad of yellows. I'm also using SOVTEK LPS in the phase inverter. All the other preamp tubes are ANOS RCAs.

bandit2013 said:

I did slave the JP2C into the Mark VII so that would have the effect you seek. Mark VII is Simul-Class and its own GEQ. Much brighter sound and more power tube saturation with that. Also slaved the Mark VII in IIC mode into the JP2C to see if there was much of a difference. Well on that note, the Mark VII IIC slaved into the JP2C sounded much like the JP2C CH2 without slaving. Mark IV mode was a bit more aggressive than the CH3. Slaving from the FX Send into a return of an amp that has Simul-Class would be a true effect than using the slave out to a 2:90 as you would bypass the Class AB power section completely.

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FWIW I did something similar... my IIC+ is non-simuclass and used the V:90 90W power section setting. It was pretty amazing and had the same take "brighter and just more alive"

Us nerds like to explore all possibilities. Heck I even slaved the Mark V90 into a Roadster wondering what that would sound like through a 100W power section. Bummer it was still an ice pick. At least I know where the root issue is. Still pondering what is up with that amp and would like to fix it. Perhaps I should email Mesa and see if they can offer a solution. Come to think of it, I do not believe I tried to slave into the Mark V90. I should give that a try. Also slaved the TC50 into the JP2C. Then the JP2C into the TC100 (curious what it would sort of sound like if it had a bias switch and ability to run EL34 tubes.)

It's nice to have a second power amp for the ability to run a stereo FX loop. It's like drugs... since I started using stereo delay and chorus, I can't get my fix off of mono versions anymore. I just can't imagine going back to mono now.
But I'm running my Mark V into a 2x12 as the dry center channel, and splitting the FX send to run thru stereo FX which return to a stereo solid-state power amp and 2x12. So, I wish I had one of those Mesa stereo tube power amps. I'd buy one right now if I didn't still have the Mark V and a new computer/interface on my credit card balance...

bandit2013 said:

The only issue if you slave out from the SEND jack, you bypass the GEQ circuits.

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On which amp(s)? On the Mark V I have, the FX send is post-EQ and post-reverb. I run a w/d/w rig with it, FX send -> parametric EQ, signal split -> Mk V return for dry and to a stereo FX chain that returns to an old Line 6 Flextone III XL with stereo FX loop and 2x12. The GEQ and reverb is present in both power amps' returns.
I wish the reverb was post-FX return, but the GEQ pre-FX send is right where it should be.

That is with the JP2C, the two GEQ circuits are after the FX loop. Same with the Mark VII. Mark III, Mark IIC, Mark IV also have the GEQ after the FX loop. The Mark V90, Mark V:25 and Mark V:30 place the GEQ in front of the FX loop since that is what is used to derive the send signal. the only tube buffering is the recovery stage with the V.

Darkstar2 said:

Bandit, I'm running Yellow Mesa-branded TADs on your recommendation. I couldn't get a hold of any Greens, so settled on a quad of yellows. I'm also using SOVTEK LPS in the phase inverter. All the other preamp tubes are ANOS RCAs.

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I see. I will have to check If I have yellows in the STR448. I think I do as I wanted to blend them with the STR445 in the Mark VII. Will have to try them in the JP2C. I know the reds were just lame. No power tube distortion. Grey coded tubes were good. That is what the JP2C shipped with in the STR440 tube. That I stuck with. Grey has more early distortion characteristic. I tried the STR443 as replacements for the STR440, ok not fizzy but not all that great either.

Do you still have the stock Mesa 12AX7 tubes? I did not mind the JP2C with those. Not sure how the RCAs would compare. I used to use the Sovtek LPS with other amps but never tried it in the JP. I had issues with the Russian tubes in the JP2C for some reason. Never figured out what tube position resulted in the motor boating issue. Mullards, Tung Sol, EHx, did not matter if long plate or medium plate, got this ramping up motor boating oscillation that would occur instantly after taking the amp out of standby. Nothing plugged into the amp except for the speaker cab. The tubes do have some use on them but test fine. No issues with those in the Mark V90 but that amp is not the same thing as the JP2C. Never tried any alternate tubes with the Mark VII assuming that would have the same effect.

bandit2013 said:

That is with the JP2C, the two GEQ circuits are after the FX loop. Same with the Mark VII. Mark III, Mark IIC, Mark IV also have the GEQ after the FX loop. The Mark V90, Mark V:25 and Mark V:30 place the GEQ in front of the FX loop since that is what is used to derive the send signal. the only tube buffering is the recovery stage with the V.

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Wow, good to know. That's another huge deal breaker for the VII I've been wanting, the lack of master volume being the other. EQ after the FX return is a terrible spot for EQ, and makes it unusable in a w/d/w rig (the other power amps will be receiving an un-EQ'd signal)... That EQ is an essential part of the sound from these preamps. You'd have to buy one of their 5 band slider pedals to put in front of the other power amp returns to get the same sound in all channels. As if $3500 wasn't enough already, you gotta buy even more things to use it properly outside of a mono 1-amp config.

I run mine in stereo. I have two of them. I tried doing the w/d/w rig once, was not for me as it was more difficult to get the center amp on the same level as the other two. Not using a 2:90 or anything like that. It was two RA100s and a Marshall Silver Jubliee. That actually worked out. Tried it with two BADS and a MWDR, not what I expected. I get your point though. That would mean the JP2C, Mark IV, Mark IIC, and Mark III are out of the question. They have the GEQ post FX loop. That is the traditional location for it. The Mark V is different.

bandit2013 said:

I see. I will have to check If I have yellows in the STR448. I think I do as I wanted to blend them with the STR445 in the Mark VII. Will have to try them in the JP2C. I know the reds were just lame. No power tube distortion. Grey coded tubes were good. That is what the JP2C shipped with in the STR440 tube. That I stuck with. Grey has more early distortion characteristic. I tried the STR443 as replacements for the STR440, ok not fizzy but not all that great either.

Do you still have the stock Mesa 12AX7 tubes? I did not mind the JP2C with those. Not sure how the RCAs would compare. I used to use the Sovtek LPS with other amps but never tried it in the JP. I had issues with the Russian tubes in the JP2C for some reason. Never figured out what tube position resulted in the motor boating issue. Mullards, Tung Sol, EHx, did not matter if long plate or medium plate, got this ramping up motor boating oscillation that would occur instantly after taking the amp out of standby. Nothing plugged into the amp except for the speaker cab. The tubes do have some use on them but test fine. No issues with those in the Mark V90 but that amp is not the same thing as the JP2C. Never tried any alternate tubes with the Mark VII assuming that would have the same effect.

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I had a quad of the STR448 yellows. I do not have them in green though. Popped out the STR415 and struggled to get those oversized tubes in the amp. Forgot how much longer they were. PSVANE needs to learn how to make the tubes shorter. Some of those workers came over from the Shuguang plant when they were forced to close up.

Anyhow. I anticipated a lame and fizzy sound from the JP2C. Note the preamp was loaded with JJ E83CC tubes (the frame grid version of the Mesa branded JJ ECC83s tube, has less noise floor). Talk about low end. That was interesting. Amp had plenty of grind too it as well. a bit brighter than the STR415 tubes. First time for me to run the STR448 yellows in the JP2C. Not bad, not fizzy. Even tried the shred mode on CH2 and CH3. Just makes it brighter and less low end and adds in some noise. Moving plenty of air through a Mesa Vertical 212 cab. Ran the channel volumes at noon. I may keep them in the amp for a while as they were difficult to get into the amp, they are as difficult to get them out. The pins on the STR415 are on the thin side. Will hold off on getting them back into the JP2C for a while.