Hybrid Build Issue *Fixed*

[Aaron]

Here is a new build that I'm working on. I had an issue with the output wiring that I posted in tech page, but the issue I'm having now is probably more specific.
I am getting strong ghost notes, to the point it sounds like I'm playing through an octave pedal. The sound is like the bass start in Jeremy by Pearl Jam.

The tone controls work, switching works, overdrive works, everything works as it should, just has a low octave note with it.

Maybe the layout it picking up something?

The build is basically SSS pre - Deluxe OD - Odyssey PI.

The voltages are pretty much the same as my Odyssey Guitar build, but when I test the 1M resistors on the P.I it makes a loud thump when the meter touches. The volume also drops right down as well. I have already swapped valves, makes no change.

Any ideas?

Thanks,
Aaron

[Bob-I]

I don't know if its related to your problem, but the last filter cap isn't soldered to ground.

Edit sorry it's the hot that's not soldered.

[Aaron]

Hi Bob,

I accidently added one too many capacitors so I didn't connect it.

Will post the schematic showing voltages when I get home from work.

Aaron

[Aaron]

Here is the schematic with voltages.

I haven't done the neon globe test on the output tranny cause I have to order one, plus it passed the basic testing that was in the link. But if it I'm getting a sound,would that mean there is no shorts.
Or is the sound I'm getting the sound of a dying one?

Thanks,

Aaron

EDIT:- Revised schematic down a few

[vibratoking]

Low octave means frequency cut in half. I know that's obvious, but think about what could be half wave rectifying your signal. Chopping off top or bottom, either fully or partially, will give you that low octave sound. Wrong value plate or cathode resistor? Ground missing on some stage?

Do you have a scope?

[Aaron]

Ground missing on some stage?

Went through again checked all grounds, everything connected was good, until one last ground. THE BIAS SUPPLY WASN'T GROUNDED

Connected the wire, fired her back up. No sound but if you turned right up, very distorted and would cut in and out very quick.

Checked the bias, cause it was set to -40ish, since connecting the earth at the filter cap it had jumped to -90.

Re-bias and turned back on, no sound. Plugged in guitar to hear what was going on............

WORKS PERFECT

Amp is so quiet, no background noise at all.
Clean sound is exactly what I've been looking for. The tone controls are a lot more responsive. I would suggest anyone that has built the John Mayer Two Rock to change to this pre, especially the feedback circuit.

Overdrive still to be tweaked. I guess cause the pre is so much cleaner than an ODS it will need to be driven a bit harder. I don't want as much gain as an ODS, I am aiming for more of a Tubescreamer "drive at 12'oclock" sound.

Thanks Vibra!!!!!!!

[lovetone]

Nice build, very neat !!

What chassis did you build it in?

[Aaron]

One of the Asian chassis of eBay a few years ago.

[M Fowler]

Aaron great job in finding the problem and nice build.

[67plexi]

Aaron, How do you like the 12AU7/12BH7 PI / Driver combo ?

Look's Great, Steve.

[Aaron]

Aaron, How do you like the 12AU7/12BH7 PI / Driver combo ?

Look's Great, Steve.

Thanks Steve.
I really like the sound of the 12AU7-12BH7 combo. To me, the clean sound is almost like a valve version of a JC120. I have swapped a 12AX7 for the 12AU7, a bit more volume and grit but I might try a 5751 in there today.

The bias supply voltage straight out of the tranny was 100V. I was thinking of using a voltage doubler circuit and trying the SSS style PI, but will have to wait until I get back from holidays.
Anyone one else compared the two?

Aaron

[Aaron]

Amp is finished (for now).......

Iron is out of a gutted '73 Marshall. So I have the option of either EL34, 6550 or 6L6.

Still deciding either a mid switch or deep switch, but sounds so damn nice I'm not in a rush to decide. Also, no foot switched PAB yet. I might use it a few times and see how I go.

I spent a night tweeking the overdrive and came up with this. The biggest difference is I'm using the trimmer as the volume for the overdrive. With drive on 3 and volume on 2 it sounds like a cranked up tweed which is what I was after.

Now for a FET circuit.........

[groovtubin]

Amp is finished (for now).......

Iron is out of a gutted '73 Marshall. So I have the option of either EL34, 6550 or 6L6.

Still deciding either a mid switch or deep switch, but sounds so damn nice I'm not in a rush to decide. Also, no foot switched PAB yet. I might use it a few times and see how I go.

I spent a night tweeking the overdrive and came up with this. The biggest difference is I'm using the trimmer as the volume for the overdrive. With drive on 3 and volume on 2 it sounds like a cranked up tweed which is what I was after.

Now for a FET circuit.........

Inquiring minds want CLIPS!!!!!!

[Aaron]

Amp is finished (for now).......

Iron is out of a gutted '73 Marshall. So I have the option of either EL34, 6550 or 6L6.

Still deciding either a mid switch or deep switch, but sounds so damn nice I'm not in a rush to decide. Also, no foot switched PAB yet. I might use it a few times and see how I go.

I spent a night tweeking the overdrive and came up with this. The biggest difference is I'm using the trimmer as the volume for the overdrive. With drive on 3 and volume on 2 it sounds like a cranked up tweed which is what I was after.

Now for a FET circuit.........

Inquiring minds want CLIPS!!!!!!

Oh mannnnnn!!!! Then you'll hear my playing

[10thTx]

Any chance you'd be willing to post the ExpressSCH version of the schematic, please?

With respect, 10thtx