Peavey Chassis Build up and running, edit... CLIP ADDED

[Bob-I]

Everything works, but I'm not at all happy with the sound. The clean side is nice, smooth and round, but the OD side is harsh and brittle with no bloom or sustain. It's better in PAB mode, and dogears claims that this is how HRM amps should be run, but still it's not a Dumble sound.

Here's a link to the layout... if you download it it's decent resolution.

Voltages are :EDIT:

V1a 195
V1b 202
V2a 201
V2b 202

EDIT:
PI plate 300 and 289
tail 58
output tubes 475 screens 470 (UL)
bias is imbalanced, 48ma one side 33ma the other.

http://www.patmedia.net/bob-ingram/Dclone%20Board3.jpg

I'm open for suggestions

EDIT:

OOps Turns out I can't even read resistors without the color code. I put in a 91 OHM resistor on one side of the PI plate load instead of a 91K. Sounds far better now but still not exactly what I expect from a Dumble.

Dogears... if you read this... sorry I didn't get back to you.. we had car issues today. Talk to you tomorrow.

EDIT:

I swapped the cathode resistor, all voltages are in spec now and the overall tone is excellent. I made a few adjustments to the HRM and both channels now sound great. The OD side even sounds ok without the PAB mode engaged, a little crunch as opposed to a nice singing OD.

Overall, this has been a fun project, now it's time to build a cabinet for it. I think I'll build a head cabinet for flexibility.

http://www.patmedia.net/bob-ingram/DClo ... on_HRM.mp3

[Normster]

Bob, if your amp is wired exactly as the layout shows, your V1 cathode resistors are reversed. The 3.3k should go to V1a. (Of course I haven't looked at a '97 ODS circuit so maybe that's the way it's supposed to be?)

[dogears]

Call me for HRM settings. OD only sounds good in PAB mode as you found out. But, did you adjust the stack while in PAB mode? I can help.

Did you disconnect the bass pot wiper in boost mode? Maybe the ultralinear is a factor? I remove it on all amps I tweak. It is a real wildcard here. Also, your preamp voltages are really abnormal. The triodes should be closer. Maybe you have some lame tubes.

Oh... What speaker? The HRM does not sound good with certain drivers that have a midscoop.

[dogears]

Good catch. Not supposed to be...

Bob, if your amp is wired exactly as the layout shows, your V1 cathode resistors are reversed. The 3.3k should go to V1a. (Of course I haven't looked at a '97 ODS circuit so maybe that's the way it's supposed to be?)

[Bob-I]

Bob, if your amp is wired exactly as the layout shows, your V1 cathode resistors are reversed. The 3.3k should go to V1a. (Of course I haven't looked at a '97 ODS circuit so maybe that's the way it's supposed to be?)

Actually the layout is wrong... damnit I thought you were onto something. The 97 schematic is totally inaccurate. It shows 3.3k on both. The s3988009.127 schem is better but still not perfect.

I have 220K/3.3k and 150K/2.2K on V1 and 180K/2.7K and 120K/2.2K on V2.

Yes I lifted the bass pot wiper in PAB. Also I think I'm going to remove the jazz/rock switch, it's just too thin in jazz position. I adjusted the HRM several times, in PAB and out. The bass pot is almost a switch but the mid and treble are very effective.

I suspect that the voltages are the cause of the harshness more than anything else. I'll have to figure out why they're so odd. components all measure correctly but the odd thing is the imbalance between V2a and V2b.

hmmm.......

[llemtt]

..but the odd thing is the imbalance between V2a and V2b.

hmmm.......

Bob

I think it's caused by the 2.2k cathode res, try to use the standard 1.8k and see if the voltage on V2b lowers (as it's supposed to do).

teo

[dogears]

Whoa!! How did I miss that! Must have a 1.8 on there. Good spot....

Also, put the HRM bass trim up about 40%. In PAB mode that works. Disregard tone in non-PAB mode. Mine doesn't sound right unless the bass trimmer is up a bit. That is why there is that low gain bass attenuating network!

[dogears]

Hey Bob,

Let us know how she sounds with the changes! Nice chattin' with you.

[Bob-I]

..but the odd thing is the imbalance between V2a and V2b.

hmmm.......

Bob

I think it's caused by the 2.2k cathode res, try to use the standard 1.8k and see if the voltage on V2b lowers (as it's supposed to do).

teo

Damn... how'd I do that?

Yes, I fixed it and the voltages are right in line now. Unfortunately I have to wait until this afternoon to test it.

[dogears]

Bump to top! Dogears just wants to gloat about his advice being right yet again..... LOL!!!!

[dogears]

Several small additional suggestions....

I like the .001uf on the bass pot.

Bright cap may be much more useable at around 120pf

Clean master bright cap may be better at 22pf or so.

Your caps are 33uf. You may want to try 22uf. For example, Suhr is using 10uf in the OD100 classic! (he told me) I'd at least try it

Also, try raising up the mains from 2X100 to 2X220 You will hear a difference. Maybe you will like more?

Is there a PI trimmer? If not raise the resistors to 110k and 120k or thereabouts. Or better yet, add a 20k or 25k trimmer. I find best tone with maybe 10k seperating the plates and not 20k.

Lastly, monkey around with the 180k OD2 grid. Try putting a 1M or 2M across it to see if you like the sound of a slightly smaller resistor. It may add some "sing" on top. Something like a 160k to 170k resistor does make a noticeable difference due to the miller effect.

[Bob-I]

Bump to top! Dogears just wants to gloat about his advice being right yet again..... LOL!!!!

Damn straight!! Once I fixed my bonehead screwups it just sounds great, plain and simple.

So the difference between this and my non-HRM amp....

I find the HRM to have much more shimmer on the top end.

The non-HRM is more midrangy and fat where the HRM is more cutting.

The non-HRM is jucy and huge

Both have similar charactor in the texture and grain.

Of course we have to qualify that they have different iron, different tone stacks, different power supply's (the HRM has a bridge rectifier) and the HRM is UL where the non-HRM is not.

[Bob-I]

Several small additional suggestions....

I like the .001uf on the bass pot.

I've clipped one on, subtle change.

Bright cap may be much more useable at around 120pf

Yep, already done.

Clean master bright cap may be better at 22pf or so.

Ok, I'll try that one. I'll just clip another 47pF across it.

Your caps are 33uf. You may want to try 22uf. For example, Suhr is using 10uf in the OD100 classic! (he told me) I'd at least try it

I have some 22uF coming from Mouser, I'm way ahead of you.

Also, try raising up the mains from 2X100 to 2X220 You will hear a difference. Maybe you will like more?

I clipped some 100uF across the 100uF already in there. The jury's still out.

Is there a PI trimmer? If not raise the resistors to 110k and 120k or thereabouts. Or better yet, add a 20k or 25k trimmer. I find best tone with maybe 10k seperating the plates and not 20k.

No trimmer but I've already changed to 100k and 110k and I agree, 10k seperation is about right. I haven't tried 110k and 120k yet, I'll let you know.

Lastly, monkey around with the 180k OD2 grid. Try putting a 1M or 2M across it to see if you like the sound of a slightly smaller resistor. It may add some "sing" on top. Something like a 160k to 170k resistor does make a noticeable difference due to the miller effect.

I'll give it a try.

Here's a few pics for those interested.

[img:640:309]http://www.patmedia.net/bob-ingram/DClone/Pic1.jpg[/img]
[img:640:303]http://www.patmedia.net/bob-ingram/DClone/Pic2.jpg[/img]

[Bob-I]

Report..

47pF clean master bright cap is ok. I ran 2 in series for drop it to 23pF and it's reduces the effect until it's almost not heard. I like the shimmer of the 47pF.

The .001uF across the bass cap is a subtle but nice change. I'm leaving it.

The mid boost is a .005uF across the 330pF treble cap. EXCELLENT. I like this boost with the OD side, without the PAB. I like the overal tonality better and there's more flexability in the OD tone because the tone controls still work. It shifts the treble control dramatically down to the mids with a very smooth grind.

[Allynmey]

Hi Bob, are you going to revise the layout above? Maybe you can post it on the "other" site. I think I have to add a dumble to the list.

Allyn


Dogears, do you want to head up a project?