Another matter on triaxis. Maybe a mod???

[fatboy135]

Hey dear boogie fellowship. I had an idea on this morning.
Everybody knows that there is an IC on triaxis a tl072 that flows all the signal of the amp into it. No be afraid it will not due a lack on our tube taste, but if we saturate this IC this will appear a great problem, a square waveform and the classical odd harms that are so nasty on our amps.
So to saturate an OP. AMP we must to get an amplification louder that voltage supply or by trying to increase the current that is able to give us that operational. So we could mod the voltage supply, but this could be a bit bored for us, so I think that we can add a IC socket under our IC3 and trying to get another better operational for this issue.
The operational has the goal of mix the signal with the dinamic voice circuit. It is a first stage classical follower and a second stage inverted operational, so the gain is 1 and the first thing to know is the voltage that feeds that operational, I think that it is maybe +/-15 v so we must to find an equivalent or sustitute operational for the tl072 that could improve our TA.
I was thinking for a rail to rail operational, any suggestion ????

 

[psycle_1]

You should be able to swap the TL072 for a Burr Brown OPA2604 without any problems. These op amps are known for a tube-like full sound in the hi-fi world. I wish I still had my Triaxis so I could try this!! Let me know if you decide to do it and the outcome.

 

[fatboy135]

yes I will do it :wink:

 

[ylo]

This is the reason I sold my Triaxis. Ch 1 (Clean) was distorting in a nasty way. I believe that the op-amp that drives the "dynamic voice" / graphic EQ thingy was the culprit, from looking at the schematic.

After I sold my Triaxis, I found a posting that said to swap the 12AX7 driver tube out and put in a lower gain 12AU7. I don't remember which one this is (V3, V4?). I could look it up. Anyway, this lowers the signal to the opamp and solves the clipping problem, supposedly.

Sheesh. Now I wish I had kept my Triaxis !!

 

[ylo]

Oh, by the way, I don't think swapping the TL072 out for a Burr Brown will help. I think that the problem is that tube drives the output of the opamp right up to the supply rails, + / - 15 volts. You would have to increase the supply voltages to the opamp to + 18 volts and - 18 volts as well to get a little more headroom, assuming it can handle that.

Anyway, easier to try a 12AU7 first.

 

[fatboy135]

easier to try a 12AU7 first.

False. I think that you are referring to 5751 tubes, swapping 12au7 into 12ax7 socket only because they are similar is not a good argument.
The only swap that I´m agree is the 5751, download the datasheets and compare the 12ax7 with the 5751 and the 12au7 with the 12ax7.
So I think that I at last decided for the burr brown opa2134 I think that it seems to be a great value. Any opinions about that op amp???

 

[ylo]

Hello Fatboy135
If we are talking about the same opamp . . . The cure I saw on the web claimed that putting a 12AU7 instead of the normal 12AX7 before the opamp in the dynamic voice section eliminates clipping. The 12AU7 has lower gain than 12AX7, 20 as opposed to 100. Your idea of trying a 5751 is a good one too, but maybe not enough. The 5751 has a gain of 70.

Note that I am not talking about V1, the first tube in the preamp, which has a big role in determining the gain of the amp and the sound of the guitar. I am talking about the tube used to drive the dynamic voice section, which comes after all of the distortion / gain stages.

The TriAxis also has opamps in the recording output. You can reduce clipping at high volumes in the rec outs by changing two resistors (one for L and one for R outputs) to reduce the gain slightly. This fix is approved by Mesa.

I'm not arguing that the Burr Brown opamp is not a better opamp. It's just that you cannot expect any opamp to swing past its positive and negative supply voltages, which I suspect is the problem in this case.

 

[phantomlord2oo]

holy crap!!! finally a solution to my biggest triaxis problem!

my cleans are always clipping (and if i turn it down i get the volume that i need). so does anyone know which tube socket should be swapped out for the 12au7?

also, does it matter that i don't use the dynamic voice? i use a separate rack eq.

thanks a bunch guys!

+Mike+

 

[ylo]

PhantomLord

Check out http://www.tubefreak.com/triaxis.htm

Looks like it is V3.

 

[ylo]

If I am understanding the schematic correctly, the signal goes through the opamp regardless of the DV setting.

 

[fatboy135]

The TriAxis also has opamps in the recording output. You can reduce clipping at high volumes in the rec outs by changing two resistors (one for L and one for R outputs) to reduce the gain slightly. This fix is approved by Mesa.

Believe me that was my first mod and it isn´t enough
dear friend you can´t change tubes as potatoes, you must to download the datasheet of a 12au7 and a 12ax7 and compare them, there are several issues that I could write down an entire book " Why I couldn´t change tubes as girlfriends :wink: ???'
Believe me I was working on several tubing desing, mods and that kind of matters since 4 years ago, there is not as easy as change a tube, you must to redesign all the polarizate circuit on DC and you must to adjust the new values on some caps ( for ac signals ) you need to have about a dozen of equations, paper, pencil, and a casio to do some number and then you can change the tubes and the appropiate other components

If I am understanding the schematic correctly, the signal goes through the opamp regardless of the DV setting

Yes my friend, all the signal goes by that ******* op.amp

my cleans are always clipping (and if i turn it down i get the volume that i need). so does anyone know which tube socket should be swapped out for the 12au7?

also, does it matter that i don't use the dynamic voice? i use a separate rack eq.

No man, no 12au7, only 5751 is possible because is the brother in law of the 12ax7 no mods or design is needed
Phantom that issue is not only on clean channels, it also affects on all the channels, as ylo said to you, but in clean channels the clipping op.amps shouts so hard, in lead channels you couldn´t appreciate the real tube saturation from the op.amp clipping, you must to hear both on a stand alone mode to then be able to differenciate them
Even if you abuse or not from the dinamic voice the signal will be still passing through that op.amp

 

[phantomlord2oo]

Ok thanks for the help guys! A question:
I'm using all stock mesa tubes right now. They're about 2 years old. I play heavy metal (think Metallica's Black Album) and I like playing crystal clean too. Can one of you guys recommend tubes for me for V1-V5? I have my Korg DTR-2000 tuner comeing out of one of the recording out jacks and a Rocktron Hush Super C in the fx loop in case those two things matter. I mainly use the LD2 Yellow for all distorted playing and RHY Green for cleans. I'm still working on a LD1 preset (looking for a soft overdriven tone). Thanks for any help!

+Mike+

 

[ylo]

I would try the new Tung Sol re-issue in V1, or the 12AX7LPS. These generally get good reviews. For the other tube slots, I don't think you will notice much difference, but the new Mullard re-issue is worth a try. This has a slightly darker sound that works good for distortion modes, according to some reviews. I'm have not tried the new JJs, but some people like them

There is no problem using a 12AU7. 12AT7, 12AY7 or 5751 in V3 -- this won't hurt anything, in spite of somewhat different operating characteristics of these tubes compared to 12AX7. Each of these will either sound better or it won't.

If you try any of these tubes or a Burr Brown opamp, let us your results.

 

[fatboy135]

There is no problem using a 12AU7. 12AT7, 12AY7 or 5751 in V3 -- this won't hurt anything, in spite of somewhat different operating characteristics of these tubes compared to 12AX7. Each of these will either sound better or it won't.

there is not a damage issue but there is a not properly operation of the tube, you can change a 12ax7 by a 12at7 and you will can even think that it sounds better, but trust in me the 12at7 is not working properly is if you are driven your car all times on the 4th gear, please change to the 5 gear and get your cruisser speed
Phantom you can read a bit more about tubes on triaxis in some posts of mine for example testing some tubes on triaxis...

 

[fatboy135]

holy crap!!! finally a solution to my biggest triaxis problem!

my cleans are always clipping

I solve your trouble, dude
A couple of days before my fx loop doesn´t work, so this afternoon I had 3 hours free to repair my TA.
I think that if i open the TA to repair the fx loop why not to test the op amps, so after reparaing the fx loop I installed an IC socket for the IC3 ( the op amp that is through by the signal chain ) and dude believe it, I achieve more dinamic range.
I tested the TA with the signals and features that appears on the service manual of the triaxis and compare the photos of the service manual with my oscilloscope and the 10 first presets were so close to the service manual, except the preset 4, and 5 that are the clean channels. On the manual the oscilloscope photos became with the classical summit waverform cut, due the op amp saturation, well with the burr brown installed there wasn´t any saturation, even I could increase a the master until the saturation becomes into the osciloscope.
Another preset was the 9, that corresponds to a very compressed ld2 yellow, well on the TA service manual it appears very compresed but in my osciloscope with the burr brown appears with more dinamic range.
Well the conclusion is that it seems to be a good chance to replace the IC3, now the trouble is which IC is best for triaxis???
I leave on the burr brown opa2134, but I also buy the analog devices op275, the mc33078, and the jrc 4558, so I will compare the datasheets and of course the osciloscopes waveforms to get the best op amp with the TA.

 

[Timbre Wolf]

Another preset was the 9, that corresponds to a very compressed ld2 yellow, well on the TA service manual it appears very compresed but in my osciloscope with the burr brown appears with more dinamic range.
Well the conclusion is that it seems to be a good chance to replace the IC3

This is good news, as the Triaxis can truly benefit from some more dynamic range.

I know you disagree with my method, but I've radically increased the dynamic range of my Triaxis by using a 12AT7 in V1, 5751 in V3, and 12BZ7 in V5. These changes work, and the Triaxis does not malfunction. I don't mind "changing tubes as potatoes" (whatever that means)

but trust in me the 12at7 is not working properly is if you are driven your car all times on the 4th gear

I guess I like 4th gear better!! Again, ...whatever!! :roll:

There is no problem using a 12AU7. 12AT7, 12AY7 or 5751 in V3 -- this won't hurt anything, in spite of somewhat different operating characteristics of these tubes compared to 12AX7. Each of these will either sound better or it won't.

I agree completely. And I'm coming from having years of experience doing just that, with bold results. I'll add some overlooked, longer-bottle preamp tubes: 12BH7, 12BZ7, and E180CC. [Who's Quijote, now, Roberto? :wink: ]

The cure I saw on the web claimed that putting a 12AU7 instead of the normal 12AX7 before the opamp in the dynamic voice section eliminates clipping. The 12AU7 has lower gain than 12AX7, 20 as opposed to 100. Your idea of trying a 5751 is a good one too, but maybe not enough. The 5751 has a gain of 70.

I have found that using a 5751 in V3 does lower the gain enough to significantly increase dynamics and clarity. The 12AU7 drops the gain too much, in my experience, making for too stiff a feel for my taste.

The TriAxis also has opamps in the recording output. You can reduce clipping at high volumes in the rec outs by changing two resistors (one for L and one for R outputs) to reduce the gain slightly. This fix is approved by Mesa.

You can also simply be mindful of your output levels, lowering them to adjust for this.

:arrow: This is a great thread. Fatboy, don't think I'm at odds with you - I'm truly intrigued by the opamp mod, and would like to hear an update on how you like it after having used it for a while.

- T

 

[fatboy135]

you know that the only tube replace that I´m agree for a 12ax7 is the 5751 the rest models could works, cound sounds diferent but it will not working properly 100%, if you realy want to use a 12at7 on the v1 I´m totally agree with you, it could be perfect, you experiment with them and you like it, but I will say you something if you like now how the TA sounds with the 12at7 if you calculate the correctly work point for the 12at7 reducing the resistors on anode and cathode you will be the happiest man in the world.
I´m not against using 12at7, I´m against using a 12at7 for a 12ax7. If you like the 12at7 so go on and change your work point and do the things entirely well.
You want a 12at7, ok put one on, and finished your idea with a correct bias point on your TA.
I recomend totally to you, put the 12at7, calculate the new resistor values with the new tube and enjoy that good idea.
You could not do the things at leave them at the middle, so put the 12at7 and replace the resistors and you will notice that the 12at7 will be the tube of your life

 

[fatboy135]

oops I forget to chat about the op amp, well I had been playing the TA all the morning along and definetely it is cleaner than with the tl072

 

[Timbre Wolf]

Ok thanks for the help guys! A question:
I'm using all stock mesa tubes right now. They're about 2 years old. I play heavy metal (think Metallica's Black Album) and I like playing crystal clean too. Can one of you guys recommend tubes for me for V1-V5? I have my Korg DTR-2000 tuner comeing out of one of the recording out jacks and a Rocktron Hush Super C in the fx loop in case those two things matter. I mainly use the LD2 Yellow for all distorted playing and RHY Green for cleans. I'm still working on a LD1 preset (looking for a soft overdriven tone). Thanks for any help!

+Mike+

Mike, this can be a deep (and expensive) question. Are you sure you're ready for that? :lol:

First, check out this thread and this more-recent thread. In your case, I would not recommend a 12AT7 for V1, though you may want to explore that later, if your cleans are not clean enough yet. You may want to try a (not JJ) Tesla E83CC in V1 instead, for cleaner high gain. There are other clean/clear 12AX7 I could recommend for V1 (NOS TungSol12AX7, long-plate GE 12AX7, long-plate Mullard 12AX7, etc.), though, depending on what flavor of tone you desire. Humbucker vs. single-coil makes a difference as well (let me guess, humbuckers?)

I would try the new Tung Sol re-issue in V1, or the 12AX7LPS. These generally get good reviews. For the other tube slots, I don't think you will notice much difference

I agree about your new-production tube choices, particularly the new Russian Tung Sol (not a reissue: there's no connection to the original, and it looks nothing like the original) which has very good clarity (for new-production) and a thick, liquid character.

I strongly disagree, Ylo, about the impact of using fine tubes in V2-V5. It has been my experience that each position reveals the character of a new tube. The more you optimize your Triaxis, with tubes of your choice, the greater an impact each new tube substitution has.

- T

 

[ylo]

Hello Timbre Wolf

You Wrote ". . . I strongly disagree, Ylo, about the impact of using fine tubes in V2-V5."

OK, well, I mostly used my Triaxis for clean sounds, so that kind of shows my bias at the time. Many of the MK II etc. distorted / overdrive modes using the other gain stages after V1 all sounded about the same to me. In any case, I will defer to your judgement on V2 - V5, since I have not experimented much with changing tube brands in those slots in the Triaxis.