Tweaking an HRM. Cleaning out harshness in the highs?

[tomrasdf]

I just finished up my first d-clone! It is a bassman conversion. Original iron used. The circuit is that of a 101-non hrm, but with the hrm tonestack, if that makes any sense. I decided to keep the master volume after the OD relay, but I kept in all the HRM stuff (no snubbers, trimmers, etc). I'm thrilled with how it turned out.

It's got a lot of the main ingredients, but I'm having a really hard time tuning out a high, buzzy quality that the OD gets in certain settings. It's most noticable when it's being driven hard by the first two gain stages, as in, when the clean volume is up or the OD entrance trimmer is turned hot. It gets very sweet when the trimmer is down low, but the OD gain is very limited and the clean channel ends up being louder than the OD.

Has anyone else run into this and been able to fix it? It's frustrating because the amp is almost perfect but for this. It's not huge, but I tend to fixate on it. Where should I start? Layout? Lead-dress? I'm going to keep tweaking, but if anyone has any thoughts, I'd love to hear them. Thanks!

[mlp-mx6]

If you used the post-OD tonestack then no snubbers is correct. If you did not (and I cannot tell from your post what HRM-stuff you kept and what you did not) then you REALLY need to try some snubbers. CERAMIC ONLY, PLEASE, NO SILVER MICA - THEY SUCK FOR THIS CIRCUIT. Start with 270pF and work your way up as high as 390pF or so, to taste.

[dogears]

It is best to not combine schematics. HRM sounds best with the low gain preOD network, the .0022 OD1 coupler, no snubbers or feedback, and 1UF on OD2 cathode. You should convert the amp to exact specs. Don't accept mediocrity! LOL

[Normster]

When I first converted my Bassman to an HRM circuit, I wired the master as you did. It didn't work well at all (but I don't remember the exact symptoms). After a brief chat with dogears, I converted to seperate clean/OD masters and all was right with the world.

[tomrasdf]

Thanks for all the replies. It does have the post OD tone stack. The only area where I diverged form the ODS-101-HRM was in using a global master rather than a seperate OD and Clean master. When I get a few moments, I'll try switching to the later and see if that cleans it up.

Should I use coax on those leads (to and form the clean master) as well? In #0124, I noticed that the non-shielded wire is run to the master volume, same goes in the HRM amps? Thanks!

[tonejunkie]

I did the same thing with my HRM as Normster and after I swithed to the correct seperate masters the high end mellowed and "all was right with the world." I know this was already said but I want to feel like I contribute every once and a while.

TJ

[dogears]

Use the coax. 124 is not HRM. Forget you saw it. It is not pertainant.

Coax is used on the HRM amps on the OD master.

[tomrasdf]

Thanks again for all the responses. As soon as I get a chance to, I'll make the recommended changes and report how it works out. It might be a bit as I just graduated from college and am moving to OH tomorrow to start a new job. So, if anyone in the Cincinnati area feels like talking amps or needs a financial planner, let me know. Thanks!

[hipbluescat]

Hello

What are snubbers ?

Regards

[Darkbluemurder]

Hello

What are snubbers ?

Regards

Snubbers are caps that are wired from the plate of a preamp tube to the cathode of the same tube. They are used in the non-HRM circuits but not in HRM circuits.

[chris_sanford]

Hello

What are snubbers ?

Regards

Snubbers are caps that are wired from the plate of a preamp tube to the cathode of the same tube. They are used in the non-HRM circuits but not in HRM circuits.

While the above statement is generally true, there *are* exceptions out there. You can use them with the HRM or not. Let your ears decide.

BTW, 'snubbers' is a bit of a misnomer. These are simply high-frequency cut caps. A real 'snubber' is used to surpress transients and often consists of a *series* RC network.

chris

[tomrasdf]

Problem solved. I figured rather than trying to change the master volume to HRM style, I'l just take off the HRM tone stack and go off the non-HRM schematic for the OD section. Just finished it this afternoon and "all is right in the world." The harshness is gone and it sounds fantastic. Thanks a bunch for the help.