Tube boost + overdrive running off a 9 volt battery

[DiamondDog]

Question:

Those who are using a 78xx regulator, I'd be interested in your readings. The notes for the regulators say Vin should be 3v over your Vout. If you want 9v out, put 12v in. Is that holding true?

Build 'feelings':

Over the last week I've built and playing with two AU7 vavlecasters. The second I built is a clean boost (R2 100K, R3 47K, C1 .022uF, no tone stack) and is in the chain before the second, which is as per Dano's on-the-socket layout. Both are running at 9v at the moment.

I've left the boost on all the time, and the second is used as a switchable overdrive. I tried a Rangemaster in front of the clean boost, where it just distorted everything. However, put between the two, it pushes the 'overdrive' valvecaster pleasantly.

If you are breadboarding a twincaster, try a booster between the two "circuit-ettes". It may suit your needs- then it may not! 

I might try a vibracaster next... See you over in that thread.

[mth5044]

!!!!!!!!!!!!! You have one of the morley oilcan do-dads! Oh man. Plus plenty of other stuff. Luckly its all jambled around in a workspace, so if someone breaks into your house, they wont realize theres thousands of dollars crammed in there. Geez man you should move that stuff to a volt or something.

[Franky]

Yeehaa! A friend of mine gave me a whole bunch of tubes, mostly 12AU7, he found an incredible stock (about 200 tubes) in his garage, some of them might be dead but I found some good references (Telefunken)..

There are also a lot of PCF, ECF, PCL tubes, I don't know if these are usable for low (or high) voltage amplifier circuits, but that is so good, I'm ready to build a bunch of tube pedals.. 

[tranceracer]

Yeehaa! A friend of mine gave me a whole bunch of tubes, mostly 12AU7, he found an incredible stock (about 200 tubes) in his garage, some of them might be dead but I found some good references (Telefunken)..

There are also a lot of PCF, ECF, PCL tubes, I don't know if these are usable for low (or high) voltage amplifier circuits, but that is so good, I'm ready to build a bunch of tube pedals.. 

Awesome!  Looking forward to seeing some builds soon!   

[Smiler]

Hi all,

I just finished building a Twincaster with switchable second tube stage.
My problem is that the pedal is VERY quiet. Even with only one tube stage the output signal is MUCH lower than the input signal. I've checked the circuit a few times. When I turn up the Gain the signal gets distorted , but the output signal is always very low.
I tried running it at 9 and 12 Volts. No change. Any ideas?

Thanks

[SirElwood]

Any ideas?

Post your voltages.

[Smiler]

Voltages with pedal running at 12V

PIN1 9,14
PIN2 -0,44
PIN3 0,006V
PIN4 0,00V
pIN5 12,33V
PIN6 10,07V
PIN7 -0,38V
PIN8 0V
PIN9 6,1V

Or should I better post voltages at 9V ?

[frequencycentral]

Here's mine (again):

Pin 1: 3.02v
Pin 2: -0.518v
Pin 3: 0.00v
Pin 4: 0.00v
Pin 5: 11.97v
Pin 6: 8.21v
Pin 7: -1.285v
Pin 8: 0.00v
Pin 9: 5.91v

Your pin 1 voltage is way too high - are you sure you have the corect value resistor?

[frequencycentral]

Pin 6 is also a little off. Thats both your plate voltages off.

[Smiler]

Hm, checked R1. Its 999 Ohm.

[frequencycentral]

Hm, checked R1. Its 999 Ohm.

Yeah, that's a 1K resistor you have there, not a 1M. Like having a volume control at the front end turned almost all the way down.

[Smiler]

Sorry its 999 K ... I used the right one but my post was wrong

[frequencycentral]

Check the value of the resistors at pins 1 and 6 too.

[Smiler]

R2 220K
R3 100K

Seems to be ok.
How muck boost of your input signal do you have? Maybe I expect too much?
When Gain is a litle above 3/4 then the output level is equal to the input level (but overdriven as it should be)

[frequencycentral]

It should have plenty of gain and boost. Set the gain to maximum and the volume to unity with the bypassed signal - measure the ohmage of readings between the volume control lugs. I'll compare yours to mine. Probably best to debug the two valvecaster circuits seperately

[Smiler]

Ok, I think I found out the problem. I debugged both stages separately. Both work fine. The tone stack I added was the problem. Without it all voltages seem to be normal and the pedal has enough boost ;-)
Maybe I find another tonestack which works.

[Renegadrian]

Smiler, glad you finally got that one working...So is my layout verified??
Impressions on that one or sound samples??

[kurtlives]

Ok, I think I found out the problem. I debugged both stages separately. Both work fine. The tone stack I added was the problem. Without it all voltages seem to be normal and the pedal has enough boost ;-)
Maybe I find another tonestack which works.

Tonestacks seriously suck gain. If you want one you'll need a recovery or boost stage.

[frequencycentral]

Ok, I think I found out the problem. I debugged both stages separately. Both work fine. The tone stack I added was the problem. Without it all voltages seem to be normal and the pedal has enough boost ;-)
Maybe I find another tonestack which works.

You can increase the volume of a Valvecaster by changing R3 to 220K or higher, if you do this for both stages it might be enough to compensate for the tonestack volume loss.

EDIT: You should get even more volume by increasing R2 as well, 470K maybe.

[Smiler]

@Renegadrian:

Not 100% Yet ;-) I completely rebuilded the whole pedal to find this error. Tested the first and then the second stage. After adding the tone stack the pedal becomes very quiet and all voltages become strange. Don't know why. I'm testing at the moment, but your Twincaster board-layout (Twincaster rev 0_11.jpg) looks good. My first build was an enhanched version of your layout (with switchable second tube stage and tone stack). My current build has no board. The tons of wires make it more difficult to debug By the way: Why do you use electrolytics for C3 ?

@kurtlives & frequency central:

I've heard that it sucks gain. Anyway I'm confused about the voltages when using the tone stack. PIN2 has about 4V without and about 9V with tone stack. Will try using 220K for R3 tomorrow.