TBMP The Tube Big Muff PI

[tubelectron]

Hi All,

This is a probably a weird thing, but some of you seemed to be interested by building a Big Muff with... tubes...

Here's the TBMP Tube Big Muff PI - it's a personal prototype design which, by experience, would be a good starting base for tweaking.

As I really don't know if I will have the time too, then here it is, in case of you may want to start some experiment about it !



A+!

[frequencycentral]

I used diodes in a similar way here: http://www.diystompboxes.com/smfforum/index.php?topic=77636.0  Really good sounds. Though I recommend a resistor (or a pot) in series or the signal loses a lot of volume. A lot of fun can be had experimenting with different cap values in the 'loop' too. Nice work!

[asatbluesboy]

Awesomeness.

[tubelectron]

I used diodes in a similar way here: http://www.diystompboxes.com/smfforum/index.php?topic=77636.0  Really good sounds. Though I recommend a resistor (or a pot) in series or the signal loses a lot of volume. A lot of fun can be had experimenting with different cap values in the 'loop' too. Nice work!

Rick, it works on 250VDC, so there is no loses of volume, you can clip the full signal - I made a

[tubelectron]

I used diodes in a similar way here: http://www.diystompboxes.com/smfforum/index.php?topic=77636.0  Really good sounds. Though I recommend a resistor (or a pot) in series or the signal loses a lot of volume. A lot of fun can be had experimenting with different cap values in the 'loop' too. Nice work!

Rick - it works on 250VDC, so you can clip the full signal with no volume loss. The coupling cap was 47n, not 22n - I made a trial some years ago, with success :



At least, the TBMP should have as sustain and saturation as the real BMP, and even more, so that's why I put 500K LOG pots to spread gain control.

The main problem, I think, will be the fight against hum and hiss, and maybe auto-oscillation. Also note that I don't tame the treble in any way, only relying on the final tone-control, so there will a need in that field, I guess.

At the first look, the device should enter in a BMP RI box quite easily on PCB, even if built in turret board version. It's probably where I will start, since I have a BMP RI box that I can rip momentarily...When time will be available for a trial on my side !

A+!

[runmikeyrun]

3 quick questions:

1.  What mods should I do for bass guitar?  The usual "increase the coupling cap values"?  There's also something we can do to monkey with the caps in series and parallel with the clipping diodes as well to adjust the clipping frequency, correct?

2.  The last discussion I read on the possibility of a TBMP stated that most of the clipping occurs in the diode sections, and not the transistors/tubes, basically inferring that there wouldn't really be a difference in the sound.  What can we do to increase the gain in the tube stages to get some grit there?  I'm thinking along the lines of the valvecaster, IIRC raising plate resistor values?

3.  What can we use for generating 250v?  I'm sure I can't find a wall wart with that voltage lol. We'll need heater voltage too... hmm... maybe a commercially available tube amp PT is the easiest way to go... should any PT schem from any tube amp work?

Thanks for drawing this up!

[Derringer]

IT AIN'T TUBE UNLESS YOU USE EB91 / 6AL5 VALVES FOR THE DIODES !!!

lol   j/k

but it would be cool to incorporate those since you're going all out anyways


BASS MOD
put a clean blend on it and you probably won't even have to worry about the other  caps


Doing this with submini tubes would be cool too (nudge nudge, wink wink Rick   )

[runmikeyrun]

BASS MOD
put a clean blend on it and you probably won't even have to worry about the other  caps

I already use a DI box in parallel with my existing distortion, silly me I forgot about that lol.

[tubelectron]

1.  What mods should I do for bass guitar?  The usual "increase the coupling cap values"?  There's also something we can do to monkey with the caps in series and parallel with the clipping diodes as well to adjust the clipping frequency, correct?

Increasing coupling caps values to, say, 0µ22 would be worth to try for bass, but with guitar, earlier experiments I made proved that 47n was the good value. Less = sound thin, more = sounds farty. 1µ is correct with the clipper : more doesn't give much better (for guitar at least, and probably for bass too). The 10p // to clipper is sensitive : 22p was early too much for guitar, the treble end was disappearing too much, but it may be less of a concern for bass. Nonetheless, it reduces hiss.

2.  The last discussion I read on the possibility of a TBMP stated that most of the clipping occurs in the diode sections, and not the transistors/tubes, basically inferring that there wouldn't really be a difference in the sound.  What can we do to increase the gain in the tube stages to get some grit there?  I'm thinking along the lines of the valvecaster, IIRC raising plate resistor values?

There will be a difference in sound, as the tubes works on high impedance. What I noticed is a smoother, much touch-responsive overdrive - but my trial was a single clipping section, not double. With double clipping section, there may be less difference as it is more saturated - but it has to be confirmed. What is sure, is that the tube in single section version doesn't clip : remove the diodes and you have a clean booster.

To increase gain, add a 22µ to 100µ / 25V across cathode resistors, but I am afraid to come to an uncontrolable circuit... The plate resistors can be increased to say 220K as is, but you wont have much increase in gain, but it will change the harmonics and attack. It's not a Valvecaster, it's REAL tube circuitry parameters...

3.  What can we use for generating 250v?  I'm sure I can't find a wall wart with that voltage lol. We'll need heater voltage too... hmm... maybe a commercially available tube amp PT is the easiest way to go... should any PT schem from any tube amp work?

Here's the solution I use, which is simple, reliable and plentifully satisfactory with one 12AX7 :



A+!

[tubelectron]

IT AIN'T TUBE UNLESS YOU USE EB91 / 6AL5 VALVES FOR THE DIODES !!!

lol   j/k

but it would be cool to incorporate those since you're going all out anyways

IMHO, to be honest, it is quite useless to try to build a TBMP ... But it's probably an interesting challenge  And it may sound interesting 

A+!

[defaced]

This is a cool concept.  Definitely one I've thought about since I build high gain tube amps, but haven't gotten around to working on yet.  

There will be a difference in sound, as the tubes works on high impedance. What I noticed is a smoother, much touch-responsive overdrive - but my trial was a single clipping section, not double. With double clipping section, there may be less difference as it is more saturated - but it has to be confirmed. What is sure, is that the tube in single section version doesn't clip : remove the diodes and you have a clean booster.

How much of this have you built?  Have you just built a single clipping stage or have you cascaded two stages together?  I would think that with the first two stages cascaded (no diodes) you would get clipping.    

To increase gain, add a 22µ to 100µ / 25V across cathode resistors, but I am afraid to come to an uncontrolable circuit...

I definitely wouldn't go that high in a 3 cascaded gain stage type circuit. Similar circuits (JCM 800, SLO, Dual Recto, VHT Deliverance, etc) use in the 470n to 1u range early and up to 10u (partially bypassed) late in the preamp.  Obviously experiment, but with increased cathode capacitance comes increased gain AND more bass, which typical wisdom says you don't want in these types of circuits (actually you want to cut it early and add it in later).  Also most of these circuits use 0.022u coupling caps in the preamp more/less exclusively for the aforementioned bass attenuation.  

2.  The last discussion I read on the possibility of a TBMP stated that most of the clipping occurs in the diode sections, and not the transistors/tubes, basically inferring that there wouldn't really be a difference in the sound.  What can we do to increase the gain in the tube stages to get some grit there?  I'm thinking along the lines of the valvecaster, IIRC raising plate resistor values?

In the full circuit, with the diodes removed, the tubes will be distorting.  There can be *no* interstage attenuation between stages 1 and 2 and there's barely any interstage attenuation between stages 2 and 3.  Since the diodes are set up as a local negative feedback, I'm not sure what effect they'll have on the typical tube behavior, but without them, the stage 2 will probably be clipping, stage 3 will be clipping, stage 4 is up in the air because I don't know how much attenuation the tone stack will provide.

Oh, when we get a final circuit, I'd be willing to do a turret layout for it.  I kinda enjoy doing them. This the Soldano Avenger (the OD channel of the SLO) preamp circuit; prototype in the back, finished board in the front.

[runmikeyrun]

In the full circuit, with the diodes removed, the tubes will be distorting.  There can be *no* interstage attenuation between stages 1 and 2 and there's barely any interstage attenuation between stages 2 and 3.  Since the diodes are set up as a local negative feedback, I'm not sure what effect they'll have on the typical tube behavior, but without them, the stage 2 will probably be clipping, stage 3 will be clipping, stage 4 is up in the air because I don't know how much attenuation the tone stack will provide.

I plan on possibly removing the tone stack if there's not enough grind... so stage 4 would def clip then!  I like the sound of my transistor BMP with the tone stack cut out.

I thought about cathode bypass caps a while after I posted that... it's a definite option to try

[defaced]

There can be *no* interstage attenuation between stages 1 and 2 and there's barely any interstage attenuation between stages 2 and 3.

Correction.  There's also no attenuation between 2 and 3.  I was looking at the resistors wrong. 

[tubelectron]

How much of this have you built?  Have you just built a single clipping stage or have you cascaded two stages together?  I would think that with the first two stages cascaded (no diodes) you would get clipping.   

It was only a single section. I mean : no preamp before, no preamp after, only a half 12AX7 with the clipping on FB. It works well - think about the distortion range and tone similar to a Grey DOD 250, but smoother since that the tube doesn't clip itself. Another one of my release based on that :

I definitely wouldn't go that high in a 3 cascaded gain stage type circuit.

relying on what I obtained with a single section as described above, I would not even use de-coupling caps across the cathodes... To be tested, but it may be different for bass.

In the full circuit, with the diodes removed, the tubes will be distorting

Exactly. With exception of the 1st stage, of course. But the sound may not be very nice and require tweaking !

Since the diodes are set up as a local negative feedback, I'm not sure what effect they'll have on the typical tube behavior

The diodes act like on an OP Amp FB, but due to the high output impedance of the tube, the entry in clipping is smoother, less blunt, so is the de-clipping, vanishing with the sound.
The inter-stages resistors are only intended to avoid oscillation at max. gain, they do not act like on Boogies (where you found at least 220K or more). If you remove the clippers, you will certainly need higher interstage resistors, or a multi-section gain pot.

A+!

[defaced]

Gotcha.  Thanks for the clarification.  If someone want to come stain my deck railing I can fab this up this weekend 

[rankot]

Looking for a schematic for this one...

[stringsthings]

 

[tonight, we ride]

This one sort of went off the rails, but this thread has some info:

https://www.diystompboxes.com/smfforum/index.php?topic=110776.0