Tube boost + overdrive running off a 9 volt battery

[Jered]

  OK, I had a chance to try out a few more tubes in this circuit. I tried 12AV7, 12AY7, 12AD7, 12BZ7, and 6072. None of which sounded any good. 6111 sub mini's are still my fave. Need to get some 12U7's to try.
  Jered

[earthtonesaudio]

  OK, I had a chance to try out a few more tubes in this circuit. I tried 12AV7, 12AY7, 12AD7, 12BZ7, and 6072. None of which sounded any good. 6111 sub mini's are still my fave. Need to get some 12U7's to try.
  Jered

Did you try those with no other adjustments to the circuit?  Coming from a transistor background, I would think that different tubes would need to be re-biased to sound right.  Or perhaps this doesn't apply with this particular circuit 

[mojo_hand]

  OK, I had a chance to try out a few more tubes in this circuit. I tried 12AV7, 12AY7, 12AD7, 12BZ7, and 6072. None of which sounded any good. 6111 sub mini's are still my fave. Need to get some 12U7's to try.
  Jered

Did you try those with no other adjustments to the circuit?  Coming from a transistor background, I would think that different tubes would need to be re-biased to sound right.  Or perhaps this doesn't apply with this particular circuit 

The same is true of tubes, but the brute force approach is quick and easy.  I'd wager that this circuit, with some adjustments, would sound lovely with a 12AV7 and a 50 volt power supply, but then it would be a very different project.

[brett]

Hi
I think that valves with low Ri (internal resistance), and maybe low mu (the sound cows make) will work best.
The 12AU7 is the lowest of the common dual diodes (Ri about 7k, from memory), with the AT7 also fairly low (Ri about 12k ?).  Note the Ri figure is for normal operating voltages (e.g. supply at 150V) and the real internal resistance may be much higher under the conditions in these low voltage circuits.

I'm guessing that low internal resistance in the circuit (ie. at low voltage), as indicated by low Ri (on the datasheet), is the key to getting more electrons to flow at these extra-low voltages.
cheers

[Caferacernoc]

For those that have built this circuit, how well does the gain pot work? It's in a location that controls bias and feedback as well as gain so I was wondering how it "cleans up" well rolled back. Does it get gatey or weird at all? It seems a better place for it would be in between the gain stages like a regular tube pre amp.
Thanks.

[DryRoasted]

For those that have built this circuit, how well does the gain pot work? It's in a location that controls bias and feedback as well as gain so I was wondering how it "cleans up" well rolled back. Does it get gatey or weird at all? It seems a better place for it would be in between the gain stages like a regular tube pre amp.
Thanks.

The gain pot works very well in my build (using a 12AT7), at min gain I have to drop the guitars vol pot a little to get totally clean boost but the again I have fairly hot humbuckers.  Not gatey or weird at all, very smooth control.

[Krinor]

For those that have built this circuit, how well does the gain pot work? It's in a location that controls bias and feedback as well as gain so I was wondering how it "cleans up" well rolled back. Does it get gatey or weird at all? It seems a better place for it would be in between the gain stages like a regular tube pre amp.
Thanks.

I am also very satisfied with the gainpot on my build. When cranked it sounds not entirely unlike the sound of a simple class a tube amp at full tilt - even if it is maybe a bit more muddy (?)

Your question is interesting and I hope some of the tube experts will elaborate on the topic. I'd also like to add another question (since this thread is not sticktly on topic anymore anyway): Would it be possible to add a master volume onto the output of a class a amp similar to the master volume in the valve caster circuit ? Maybe we could have some of you tell us more about pot placements in valve circuits in general ?

[mojo_hand]

(The gain pot is) in a location that controls bias and feedback as well as gain.... It seems a better place for it would be in between the gain stages like a regular tube pre amp.
Thanks.

I think that the most flexible arrangement would be to have volume, bias and feedback adjustments for each gain stage, but if you made a normal pre-/amp that way you'd end up with so many controls that it would take ages just to discover all the possible settings, let alone remember which ones you liked.  So you use a lot less controls than that, and decide what sort of flexibility you're most willing to give up.

If you put the pot between stages, you have eliminated the possibility of ever changing the bias or feedback in the first stage; it will always be exactly as warm/cool, and as clean/dirty (for a given volume level) as you've made it.  All you can do is to make it quieter or louder.  Fortnately, this should also let you control clipping of the second stage, assuming you provided enough overall gain.  But you are narrowing down the possible voices of the effect to a certain range.  This isn't necessarily a bad thing.  If clean sounds like a '61 Fender Deluxe's clean, and boosted sounds like a cranked '61 Deluxe, maybe that is exactly what you want.  If nothing else, it eliminates tons of ugly sounding settings that might otherwise have been available.  But if you made it to sound like a '61 Deluxe, and the user happens to hate that tone, they're just outta luck.

If you leave the pot where it is, you CAN change bias and negative feedback along with volume, but you can only change all three at once.  It gives one a wider range of tones to pick from, but it may be that you don't care for most of those tones, and can't arrive at some you'd prefer.  Maybe it now ranges from clean Deluxe, to cranked Marshall 18, to distortion monster created by the gods of metal, and you can no longer get to the cranked Deluxe sound at all.

So it just depends on what you're after.  Every guitarist's ideal setup would probably be a little different.

[brett]

Hi

If you put the pot between stages, you have eliminated the possibility of ever changing the bias or feedback in the first stage; it will always be exactly as warm/cool, and as clean/dirty (for a given volume level) as you've made it.

I'd suggest that you haven't really eliminated the opportunity for a bias change.  It just requires one resistor to be changed, or a trimpot to be adjusted.  And amps have the bias set, so unless there's a problem with every tube amp out there, there's not much of a problem with setting the bias to a "sweet" value and leaving it there.

A small value cathode resistor (1k) seems to work for 12AU7s, so a small resistor (470 ohms) and a trimpot of 1k would seem ideal.  Large cathode resistance (e.g. 10k) is only likely to give low gain, and eliminate much of the "overdrive" effect.  Personally, I would also keep any pot between stages 1 and 2 cranked, so it might as well be wired direct.

Again, this works well, IMO :


Just my 2c.
cheers

[mojo_hand]

Hi

If you put the pot between stages, you have eliminated the possibility of ever changing the bias or feedback in the first stage; it will always be exactly as warm/cool, and as clean/dirty (for a given volume level) as you've made it.

I'd suggest that you haven't really eliminated the opportunity for a bias change.

Sorry, I guess I was unclear.

You've made it impossible for a normal user, who only opens cases when they need to change batteries.  If you're the guy holding the soldering iron, anything's possible.

[snoof]

you could also parallel a cap (.68 - 25uf) with R3 and use a switch to cut it in/out for more gain.

[andrew_k]

To anyone who's built this circuit -- stick a boost in front!

I added a mosfet boost circuit before the start of the tube boost and the result is a much more pleasing breakup than the gain pot provides. It also seems to make the tube boost more humbucker friendly. Cranking both the boost and the gain gives a fat saturated tone that I totally dig. Adding the boost was enough for me to decide that this circuit deserves an enclosure and a spot on my pedalboard 

[tranceracer]

To anyone who's built this circuit -- stick a boost in front!

I added a mosfet boost circuit before the start of the tube boost and the result is a much more pleasing breakup than the gain pot provides. It also seems to make the tube boost more humbucker friendly. Cranking both the boost and the gain gives a fat saturated tone that I totally dig. Adding the boost was enough for me to decide that this circuit deserves an enclosure and a spot on my pedalboard 

Out of curiosity what boost did you use?  Maybe a sound sample if you have time?

Thanks!

[andrew_k]

The boost I used is a SHO, because I had one in my pile of circuits and the only other boost I had floating around was an EH LPB that I don't like.

I'll look into a sample; unfortunately I'm having some massive issues with pro tools and OS X and pretty much can't use pro tools at all at the moment. ARRRGH.

[tranceracer]

Cool Andrew_K!  Are you planning to box the booster in the same chassis and have a separate switch for the boost ckt?

Sorry to hear about your recording setup woes... hope you get it fixed soon!

[brett]

Hi
Any booster with about 10dB of gain will be fine.  The Stratoblaster booster, which gives pleasant boost of up to about 15dB, is nice.
cheers

[andrew_k]

Are you planning to box the booster in the same chassis and have a separate switch for the boost ckt?

Same box, but no separate switch. It'll just be a pre-gain control or similar. With the tube laying flat between the 3PDT and the pots, it all fits nicely in a hammond BB.

[Renegadrian]

Hey, I noticed that in the layout it wasn't stated that C3 is electrolytic, as far as I remember it is an electrolytic in the schematic..Should it be a big trouble to put an unpolarized cap or it has to be polarized??? 

[mojo_hand]

Unpolarized is fine.

I don't think you'll find many situations where a polarized cap is required.  They're cheaper, and that can matter, but unpolarized will usually work in their place.

[Renegadrian]

'k, thx!!!