Tube boost + overdrive running off a 9 volt battery

[gluedtogether]

Cleaning up the tube boost - these were quotes from this thread

"To tame the gain I would lower R2 and R3. 220k and 100k seem pretty high for a low voltage circuit. Even in a regular high voltage amp the normal value is just 100k. So maybe cut them in half."

"if you bring down that 220k to 100k it will def lower the gain a bit.  I built mine with both plate r's at 100k. "

"but I just used a spdt, pin 3 of 12au7 going to middle lug of switch, one side of switch had pot, the other had the 12k"


I am going to get the iron ready today to try some of these. I was planning on putting a dpdt switch in for R2 to go between 220K and 100K based on the recomendations above. Then I saw the idea to put a spdt switch between the gain pot and pin three. I am starting to follow where lowering the resistance will cause the pedal to be a bit more clean. Given the two options, which one will provide a cleaner setting? I like the idea of being able to toggle between a cleaner sound and an overdrive sound.  I am not so clear on the different roles of each pin of the tube so I don't know if changing the value going to pin 3 vs pin 5 will do this. 

Thanks to all for the suggestions

[Krinor]

Okay, here's another little mod for the Valvecaster:

A usefull tonal variation can be achieved by implementing a switchable negative feedback.

Put a 22k resistor and a spdt switch between the output and the cathode of the second stage (lug 8 ).
You can also make a "bass boost" filter out of it by inserting a capacitor between there as well.
I currently have a 0.056uF cap in series with the resistor. This removes some of the mid range and helps keep things a little bit more together. It sounds nice and clean at low gain settings and it also sounds pretty good with everything maxed. More defined puch in the bottom and not so shrill. I've tried this with larger caps as well but it tends to get a bit too boomy.
All in all this is a nice little mod which will tame the gain a bit. Nothing dramatic, but it helps if you want to tune the thing for a more clean boost.

Here's an illustration:

[Chawk]

Any preferences in brand name of AU7 tube used?

Examples:
Electro-Harmonix
EH Gold
Mullard
Sovtek
Tesla
Sino-China
Odd Ball

[Krinor]

Personally I don't use EH anymore after discovering how much better almost anything else sounds. 
I currently use a brand called Tube Amp Doctor. They sound very transparent and are a bit on the treble side of the scale.
Tung Sol and JJ would be excellent choices.

[gluedtogether]

I gave that a shot. It cleaned up it pretty good. I am going to play around with that for a bit before trying any of the other gain reducers. I like the bass increase by switch, but may change the value to reduce the bass a bit

Thanks

Okay, here's another little mod for the Valvecaster:

A usefull tonal variation can be achieved by implementing a switchable negative feedback.

Put a 22k resistor and a spdt switch between the output and the cathode of the second stage (lug 8 ).
You can also make a "bass boost" filter out of it by inserting a capacitor between there as well.
I currently have a 0.056uF cap in series with the resistor. This removes some of the mid range and helps keep things a little bit more together. It sounds nice and clean at low gain settings and it also sounds pretty good with everything maxed. More defined puch in the bottom and not so shrill. I've tried this with larger caps as well but it tends to get a bit too boomy.
All in all this is a nice little mod which will tame the gain a bit. Nothing dramatic, but it helps if you want to tune the thing for a more clean boost.

[Krinor]

I gave that a shot. It cleaned up it pretty good. I am going to play around with that for a bit before trying any of the other gain reducers. I like the bass increase by switch, but may change the value to reduce the bass a bit

Thanks

You can probably go down to 0.033uF and still keep some of the bass boost effect. Or leave the capacitor out and use only the resistor as an ordinary feedback loop. You may also like other resistor values. I tried 10k too but ended up using 22k. Seems like tubes can take a real beating no matter what you throw at them. And what we are dealing with here is just some gentle cuddling anyway. 

Could someone tell me how it would affect the biasing of the second stage if I put in a 1,5k resistor to ground on the cathode (lug 8 ) ?

[Aren]

By the way - I'm not sure how many of you are into recording, but I just tried this circuit as a mixing tool, and it works fantastic.
I ran a bass track through it, and while it didn't sound that great on its own, when combined with the original clean signal it sounded great. Same deal on vocals that were too thin for my taste.

[Krinor]

By the way - I'm not sure how many of you are into recording, but I just tried this circuit as a mixing tool, and it works fantastic.
I ran a bass track through it, and while it didn't sound that great on its own, when combined with the original clean signal it sounded great. Same deal on vocals that were too thin for my taste.

Done that yes. I use it for all kinds of things. Works good with vocals. Nice to enhance things with, especially with some gain reduction as mentioned above.

[gluedtogether]

I might try leaving the cap and using the switch to just add a bit more bass, might even keep the current value. After playing with it a bit more, I think I might trying cleaning up the gain with a second footwitch with the resitor on pin 3 and see how that sounds. I think it would be nice to have the versatility to kick the gain on when needed.  This has been a good circuit to experiment on.


Thanks 



[/quote]

You can probably go down to 0.033uF and still keep some of the bass boost effect. Or leave the capacitor out and use only the resistor as an ordinary feedback loop. You may also like other resistor values. I tried 10k too but ended up using 22k. Seems like tubes can take a real beating no matter what you throw at them. And what we are dealing with here is just some gentle cuddling anyway. 

Could someone tell me how it would affect the biasing of the second stage if I put in a 1,5k resistor to ground on the cathode (lug 8 ) ?
[/quote]

[Krinor]

Without the capacitor it will just be an ordinary global negative feedback as seen in many old class A amps (Fender champs etc). Leaving it out will just flatten things out a little. But that's probably what yo were after anyway.
How about putting a 50k pot in there instead and tweaking it until you find the optimal setting ? (And then measure the resistance and report back to us of course  )

[Renegadrian]

Any preferences in brand name of AU7 tube used?

Examples:
Electro-Harmonix
...

Well, I have an EH in and my Valvy doesn't sound as expected, I know everyrthing's ok so I am surely going to try another brand to make it sound better, maybe jj or anything I could find on evilBay...For this little esperience of mine, EH are a no-no, also I read bad comments elsewhere on the forum, so...

[Zben3129]

[opinion/]

Those comments you read are correct, in my mind.

I've got 2 EH 12au7, and they sound sterile, crappy, plain old bad. In fact every EH tube I have tried sounds like this, unfortunately.

I've still got some baldwin's, and just got a bunch of conn's, and they both sound WAY better. I believe they are RCA made, judging by looks?

[/opinion]

Zach

[Krinor]

For an excellent range of tubes try these guys:

http://www.tubedepot.com/index.html

[LMJS]

Tube Depot are great!  No "hidden" fees for orders, you get what you pay for with no additional charges other than the usual shipping.
I can think of at least one tube store that could learn from them.

[Renegadrian]

Adding resistance to the plate resistors(R1 and R2) will increase gain. Adding resisitance to VR1, in series with the gain pot, will decrease gain.

As I am on the "MORE GAIN" party, I think I'll do a vero version socketing the above mentioned R1 and R2 trying some increased values, also swapping some gain pots, like 100k, 250k, 500k...
It should "gain" some gain that way, am I right?!

[Caferacernoc]

Adding resistance to the plate resistors(R1 and R2) will increase gain. Adding resisitance to VR1, in series with the gain pot, will decrease gain.

As I am on the "MORE GAIN" party, I think I'll do a vero version socketing the above mentioned R1 and R2 trying some increased values, also swapping some gain pots, like 100k, 250k, 500k...
It should "gain" some gain that way, am I right?!

Yup. The ultimate tweaker box would probably be to replace the plate resistors with 250k pots. Then put a 1k resistor on the collectors to ground. Bypass each collector resistor with a 5uf capacitor. Put the 50k "gain" pot in series with the bypass capacitor. And dial it in!

[Caferacernoc]

Adding resistance to the plate resistors(R1 and R2) will increase gain. Adding resisitance to VR1, in series with the gain pot, will decrease gain.

As I am on the "MORE GAIN" party, I think I'll do a vero version socketing the above mentioned R1 and R2 trying some increased values, also swapping some gain pots, like 100k, 250k, 500k...
It should "gain" some gain that way, am I right?!

Yup. The ultimate tweaker box would probably be to replace the plate resistors with 250k pots. Then put a 1k resistor on the collectors to ground. Bypass each collector resistor with a 5uf capacitor. Put the 50k "gain" pot in series with the bypass capacitor. And dial it in!

Let me revise that slightly:

Replace the plate resistors with 250k pots. Then put a 10k resistor on the collectors to ground. Bypass each collector resistor with a 1uf capacitor. Put a 5k "gain" pot in series with the bypass capacitor. And dial it in!

[earthtonesaudio]

Adding resistance to the plate resistors(R1 and R2) will increase gain. Adding resisitance to VR1, in series with the gain pot, will decrease gain.

As I am on the "MORE GAIN" party, I think I'll do a vero version socketing the above mentioned R1 and R2 trying some increased values, also swapping some gain pots, like 100k, 250k, 500k...
It should "gain" some gain that way, am I right?!

Yup. The ultimate tweaker box would probably be to replace the plate resistors with 250k pots. Then put a 1k resistor on the collectors to ground. Bypass each collector resistor with a 5uf capacitor. Put the 50k "gain" pot in series with the bypass capacitor. And dial it in!

Let me revise that slightly:

Replace the plate resistors with 250k pots. Then put a 10k resistor on the collectors to ground. Bypass each collector resistor with a 1uf capacitor. Put a 5k "gain" pot in series with the bypass capacitor. And dial it in!

When you say "collector," you're really talking about "cathode," right?  (or kathode if you prefer)

[Renegadrian]

First observations from the valvecaster test rig:

Using a 12AX7 at 12V and no tone stack, everything else stock - a bit "wooly" for my liking not alot of note defination, a bit boomy (this is coming from a confirmed metal head).  Change the input cap (C1) to 22nF and its a whole new game.  Lots of ACDC-esque tone, lovely response and works well with humbuckers (no idea about single coil).

So you say it works well with a 12AX7 too? Did you try to increase R1 and R2 values, as well as the GAIN pot value???
We already said it is "gainier" with increased values of the above...

[Caferacernoc]

Adding resistance to the plate resistors(R1 and R2) will increase gain. Adding resisitance to VR1, in series with the gain pot, will decrease gain.

As I am on the "MORE GAIN" party, I think I'll do a vero version socketing the above mentioned R1 and R2 trying some increased values, also swapping some gain pots, like 100k, 250k, 500k...
It should "gain" some gain that way, am I right?!

Yup. The ultimate tweaker box would probably be to replace the plate resistors with 250k pots. Then put a 1k resistor on the collectors to ground. Bypass each collector resistor with a 5uf capacitor. Put the 50k "gain" pot in series with the bypass capacitor. And dial it in!

Let me revise that slightly:

Replace the plate resistors with 250k pots. Then put a 10k resistor on the collectors to ground. Bypass each collector resistor with a 1uf capacitor. Put a 5k "gain" pot in series with the bypass capacitor. And dial it in!

When you say "collector," you're really talking about "cathode," right?  (or kathode if you prefer)

Yes. I goofed up my tube with my transistor lingo!