Can a GGG Phase 90 be safely run on 12v (or 18v)?

[kerryandray]

Hi all.  I've been searching the internets for a clear answer but can't find one.

I have successfully built a GGG Phase 90 before as a stand alone stomp box pedal and love it.  Currently I'm building a travel guitar with an Danelectro Honeytone amp circuit on perfboard, a speaker, a boss sd-1 circuit from GGG and the Phase 90 I'm asking about all built into the body of the guitar.

I know the boss sd1 and the honeytone can handle and possibly benefit from higher voltages (i.e. run at up to 18v rather than the standard 9v power).  Amd I'd like to experiment with that.  But can the phase 90 handle the same voltages?

In practice, i don't think I'd go above 15v because some of the electrolytic capacitors on the boss and honeytone are rated at 16v.  As to the phase 90, i didn't find any components rated less than 18v.  The ICs were all rated above that and there are no electrolytic capacitors.

But i did find this one reference to a p90 getting fried on just 12v.

https://www.ultimate-guitar.com/forum/showthread.php?t=1090670

The user "handlerb" says: "The phase 90 uses a negative 9V adapter, make sure that is what you have. Those pedals are very easy to fry by giving them too much voltage. It's possible that just once you (or the a$$hole you bought it from) accidentally plugged in a 12v adapter. Most likely it cannot be repaired for less than another pedal."

What do you all think given the GGG P90 circuit?

Thanks in advance for any help/advice/opinions you can offer!

Ray

[antonis]

12V instead of 9V would only hurt 9V rated capacitors..
(I don't presume there is such a voltage rating cap inside Phase 90..)
Lowest voltage commercially available electolytic caps are at 16V..

33% raise of voltage shouldn't also make any harm neither on resistors nor on ICs..
Not even on 5V1 voltage stabilizer Zener diode..

P.S.
Altering output mixer pnp quiescent point & "useless" (in the mean of 5.1V Vref retention) raising op-amps supply is another (off-topic) matter..   

[Mark Hammer]

Not what I'd choose to do, but let's at least optimize the situation.

12V may improve performance of the amplifier.  Personally, I don't expect it would improve anything on the SD-1.  The headroom of the circuit is capped by the diodes in the feedback path, not by the supply voltage.  Similarly, I don't see much advantage to increasing the supply voltage to the P90 portion, apart from having only one onboard supply voltage shared by everything.

Note that a change in the P90 supply voltage will likely involve different biasing.  In particular, I think you will likely need to replace the 1M current-limiting resistor coming off the bias trimmer with a second trimmer.

[kerryandray]

Similarly, I don't see much advantage to increasing the supply voltage to the P90 portion, apart from having only one onboard supply voltage shared by everything.

This is exactly my reason for asking.  To see if i can have one voltage feeding everything.  I've already gone WAY overboard on this project, LOL.  I'm not going to build a multi-voltage power supply. 

I'm just seeing if I can safely plug a 12v supply to the entire system via the DC power jack.  If it's seemingly safe, I'll try it. If it doesn't sound good, I'm not going to do anything to improve it.  I'll just use the normal 9v.  The guitar body also holds a 6 AA battery compartment to get 9v without wall power, BTW.  So it's designed for 9v.  The higher voltage idea is an afterthought to be sure.

But the consensus is that 12v should be fine...and that guy i linked to talking about it being really easy to kill a p90 with 12v is likely not correct?

[iainpunk]

LM7809

use that on a tiny perf/vero to regulate it down to 9V in a really small form factor,

[Mark Hammer]

But the consensus is that 12v should be fine...and that guy i linked to talking about it being really easy to kill a p90 with 12v is likely not correct?

Yep.  But since a different supply voltage could easily make the bias setting "wrong" and result in no audible sweep, I can see why someone might think that 12V "killed" the JFETs. 

So, in sum, things should be fine using 12V supply, and adjusting the bias for the FETs appropriately.  Remember that the FETs will sweep, based on the sum of what's coming from the LFO and the bias subcircuit.  So you may need to up the value of the 3M9 resistor on the output of the LFO a wee bit as well.

[Slowpoke101]

Some genuine MXR phase 90 units used a 10 or 11V zener diode for polarity protection. These units can be harmed by 12V - it isn't much fun cleaning up the mess but they can be repaired - usually (heat damaged PCBs are not fun to repair ). But since you are using your own GGG build it is unlikely that you used a zener as polarity protection anyway.

Use 12V and see if the phasing effect works and if it doesn't work they way you want it, follow Mark's suggestions regard the biasing and sweep levels....Or (as has been suggested ) install a 78L09 voltage regulator and forget about it.

[Mark Hammer]

Ian's suggestion is a sound one.  I guess it's your decision as to whether regulating 12V down 9 is more of a hassle or less of one than using 12V and futzing around with the biasing and sweep-limiting.  Six of one, half dozen of the other.

[kerryandray]

Thanks all!  I'll give it a go and see if 12v input makes any positive difference.  If not I'll just use 9v.  Just want to get this project done.

I'll spend some time playing with voltages on a different day/project.  I'll definitely be referring to the tips here to inform that experimentation. 

Again...thanks all for your responses!

[Rob Strand]

When operated at higher than 9V both the swing and average DC level at the output of the LFO going to increase.
The DC shift can be compensated for by rebiasing the JFETs.   The LFO swing should be noticeable.     If you have used low Vgs_off JFETs that means, which seem to be more like what is available these days, the combination of the low Vgs_off and the larger LFO swing will push it further from the original.   You can compensate for the LFO swing to some degree by increasing the 3M9 resistor.   Yet another thing is the duty cycle of the LFO is like to change.

You might like the change in sound but you can do similar mods on a 9V unit as well by tweaking the LFO.

All things that change the sound but by small amounts.