Why am I getting oscillation?

[digi2t]

I have the Deacy circuit on the breadboard right now, and I'm contemplating building it, along with a booster, into the same enclosure. The problem is that I'm getting oscillation from the circuit when I'm powering the booster and the amp off the same power supply. To date, I've tried the Range circuit from the Skyripper, and a straight Rangemaster circuit, and both oscillate in most of the boost range when I power both off the same PSU. If I use a separate PSU for each, they work fine. I'm not sure what I'm not getting here, since all the circuits involved here are PNP, so I'm not mixing grounds. If I run the Skyripper's Range in front, with it's own PSU, no problem. Build the same circuit on the breadboard, and use the same power as the amp circuit, and it poops all over the place.

Quite honestly, I also built up the Brian May Treble Booster circuit, powering it with a separate PSU, and it sounds smashing. I know it's NPN, and I'm wondering if I build a power section using 7909/7809's, and 12vac, to power both would work. Could they cohabitate inside the same enclosure, or would the shared ground create oscillation problems?

Is it possible to have both under the same hood, or am I looking at separate builds, and power supplies?

[Gus]

Have you tried a -9VDC regulator or a RC decoupling circuit between the amp and boosters (maybe a 100 ohm, 100uf) power supply?  Sometimes all you need is a added RC filter between gain stages like you find in tube guitar amps.

You can make the Brian May Treble Booster a Si  PNP try a 2n3906 or 2n2907 or

[petey twofinger]

sorry i cant be of help .

if you could please post the findings , i have a "similar" amp i couldnt figure it out / gave up .

thanks .

[Kipper4]

My friend had this and ended up putting in a max1044 IIRC?
I can't remember the details it was a year ago.
I have the BM treble booster in the same box but I never had this problem since I put a battery snap for the treble booster on the back of the amp. The input and output of the treble boost have separate jacks with a patch cable an separate amp input with a switchable resistor for a more compressed amp sound.
Sorry this probably won't help you much Dino

[Gus]

Gain stages can couple by the power supply.   

Do you have schematic of the supply you are using

As I posted before look at guitar tube amp schematics.  The power supply often is a Cap after the diodes to the output Plate supply then a resistor and then cap for the Screen then a resistor and cap for the PI or gain stage etc.
This helps keep the stages from wiggling the other stage if the wiggle cause the circuit changes to be in phase you can get positive feedback

Something fast and simple to try is add more capacitance to the Deacy supply to lower the impedance at the supply node

Layout can also matter

[GibsonGM]

Yup....I would say with a high degree of confidence, that more decoupling is necessary.

[digi2t]

There's no "layout" per se at the moment. Just a mess on the breadboard, which I'm powering via a Morley wall wart. On it's own, the circuit is pretty quiet, considering it's on a breadboard, and I have three fluorescent light going. Powering the booster via a second wall wart, all is good as well. It's just when I try to power both via the same supply, so I would say that decoupling is probably to blame so far.

The amp pulls too much current to use a 1044, or even a 1054, in a bipolar arrangement. I tried a 1054, and the negative voltage drops to around 5.5vdc. I wouldn't even bother with a 1044.

I have however some parts left over from the PLL build (317/337 voltage regulators), so I'm going to try this arrangement, powered by a 12vac/800mA wall wart. I'll detune it to 9vdc with the trimmers, tear out the Rangemaster affair, and rebuild the BM booster for the positive side. I'll give it a go tomorrow, and report back. I'll up the caps on the amp circuit as well.

Thanks for the input guys. Have a Happy New Year's eve, and please, don't drink and solder.

[tubegeek]

Here's what Gus is suggesting. This will probably cure the problem. The component values are very flexible.

dc in ------+------+---vvv-+--> to effect #1
            |      |       |
            =      |       =
            |      |       |
            V      |       V
                   |
                   +--vvv--+--> to effect #2
                           |
                           =
                           |
                           V
All caps 22uF electrolytic, or larger or smaller
All resistors 10 ohms, or smaller or larger

[Boprikov]

It is often essential to get filtering cap(s) physically as near to the amp stages as possibly. The resistance of power supplying wires, although small, makes the difference.

[amptramp]

In addition to the filter tubegeek suggested, you may want to bring the grounds back to the power source separately to eliminate the common impedance that allows the amplifier to modulate the voltage on the previous stage's ground.  This may eliminate oscillation and replace it with hum, so doing this and using regulators as you have planned would be my best guess for the cure.