help! my HRM overdrive sounds harsh

[dogears]

Convert back to non Bluesmaster PI for now. It will greatly smooth things. Also, following Jim's advice about raising the 100K on the treble trimmer output can help. Try 220K at first.

['67_Plexi]

Convert back to non Bluesmaster PI for now. It will greatly smooth things. Also, following Jim's advice about raising the 100K on the treble trimmer output can help. Try 220K at first.

Come on bro, thats like taking Advil to cure a cold..LOL !!

When you get a mo, re-read the original post, by the guys description something is systemically wrong. I've never gone above 100K on any amp and there should be absolutely no reason to. There is obviously a problem that needs to be dealt with, tweaks like that will mask, not cure.

The first red flag is that fact that the clean channel doesn't take OD pedals well and posesses some of the same negative characteristics of the OD channel in it's current state.
The second red flag is the excessive gain on the OD channel.

Could be many things. I just saw the amp and could instantly see the lead dress was not ideal. Thats why it was my starting place.

Sorry if my comments may appear against the grain of some folks current thinking that neat is good. You want to build great sounding amps, not perfect static displays or model amps. Leave that to the 'build by numbers' guys.

As for the questions about proper lead dress. There is a lot of theory around it, but nothing beats a blunt non-conductive utensil and one hand behind your back. You'll start to see a few cause and effect situations that you can repeat. Some cables you may think will cause issues quite often don't, yet some assumed benine ground cable routing causes havoc. Trial and error is by far the best way. You can completely revoice your amp just by how you wire it up without changing a single component.
Unfortunately it's like playing the guitar, unless you practice, you won't get better. Following the route of another amp of the same model seldom yields the same results.

Regards, Alan.

[groovtubin]

Convert back to non Bluesmaster PI for now. It will greatly smooth things. Also, following Jim's advice about raising the 100K on the treble trimmer output can help. Try 220K at first.

Come on bro, thats like taking Advil to cure a cold..LOL !!

When you get a mo, re-read the original post, by the guys description something is systemically wrong. I've never gone above 100K on any amp and there should be absolutely no reason to. There is obviously a problem that needs to be dealt with, tweaks like that will mask, not cure.

The first red flag is that fact that the clean channel doesn't take OD pedals well and posesses some of the same negative characteristics of the OD channel in it's current state.
The second red flag is the excessive gain on the OD channel.

Could be many things. I just saw the amp and could instantly see the lead dress was not ideal. Thats why it was my starting place.

Sorry if my comments may appear against the grain of some folks current thinking that neat is good. You want to build great sounding amps, not perfect static displays or model amps. Leave that to the 'build by numbers' guys.

As for the questions about proper lead dress. There is a lot of theory around it, but nothing beats a blunt non-conductive utensil and one hand behind your back. You'll start to see a few cause and effect situations that you can repeat. Some cables you may think will cause issues quite often don't, yet some assumed benine ground cable routing causes havoc. Trial and error is by far the best way. You can completely revoice your amp just by how you wire it up without changing a single component.
Unfortunately it's like playing the guitar, unless you practice, you won't get better. Following the route of another amp of the same model seldom yields the same results.

Regards, Alan.

[yeahyeah]

Ok, some new info,

The clean channel does take pedals well when the bright switch is off.

I use a seperate relay to dissengage the bright switch in OD mode. This is wired correctly and works properly.

I'm going back to the non-bluesmaster PI (using 101 values) and re-working my lead routing on the stuff going to the pots. The lead dress on the tubes looks fine right?

Not changing any other component values yet.

[greiswig]

As for the questions about proper lead dress. There is a lot of theory around it, but nothing beats a blunt non-conductive utensil and one hand behind your back. You'll start to see a few cause and effect situations that you can repeat. Some cables you may think will cause issues quite often don't, yet some assumed benine ground cable routing causes havoc. Trial and error is by far the best way. You can completely revoice your amp just by how you wire it up without changing a single component.
Unfortunately it's like playing the guitar, unless you practice, you won't get better. Following the route of another amp of the same model seldom yields the same results.

Regards, Alan.

This is bordering on thread hijacking, but I hope it will help the OP, too.

I can understand that there is likely to be some troubleshooting done after putting the amp together. But what serves as a good starting point? If you don't have sufficient slack in some critical lead, then you won't be able to move it to the "right" position after the fact. So it would be nice to know in advance what some basic layout principles might be.

For starters, does the layout at http://www.brownnote.net/shared/images/ ... %20Mod.bmp take into account "proper" lead dress? Or is it just drawn in a way that lets you see what connects to what, but doesn't really show how to correctly route the leads?

[yeahyeah]

Just look at the pics of dumble's amps.

TONE REPORT:

OK, so I switched back to the standard PI and it did make a big improvement as far as smoothness goes. The high end fizz is still there although not as bad as before.

Also, I'm not sure if I mentioned this before- the overdrive does not sound weak or thin. The EQ sounds "right" but there is just a bit of fizz rideing on top of it.

I messed with the lead routing every way I could and I could not get rid of it. And in all the Dumble pics I've seen his routing to the pots is cable tied together too.

I think that the OD isn't getting too much as I had thought in my first post. When playing single notes it sounds pretty clean. The fizz makes it sound nastier than it really is.

[dogears]

Change the OD master to all shielded. Not only does that eliminate lead dress issues, it introduce some more highe end smoothing die to capacitance. Dumble always used 2 pieces of shielded on the OD master.

['67_Plexi]

Change the OD master to all shielded. Not only does that eliminate lead dress issues, it introduce some more highe end smoothing die to capacitance. Dumble always used 2 pieces of shielded on the OD master.

+1

['67_Plexi]

Just look at the pics of dumble's amps.

TONE REPORT:

OK, so I switched back to the standard PI and it did make a big improvement as far as smoothness goes. The high end fizz is still there although not as bad as before.

Also, I'm not sure if I mentioned this before- the overdrive does not sound weak or thin. The EQ sounds "right" but there is just a bit of fizz rideing on top of it.

I messed with the lead routing every way I could and I could not get rid of it. And in all the Dumble pics I've seen his routing to the pots is cable tied together too.

I think that the OD isn't getting too much as I had thought in my first post. When playing single notes it sounds pretty clean. The fizz makes it sound nastier than it really is.

What speakers are you using ?

[yeahyeah]

Lead 80 in an oval back cab.

['67_Plexi]

Lead 80 in an oval back cab.

It's not that then....those speakers sound pretty good with a HRM circuit.

[jelle]

Hmmm, sometimes a OT just sounds strange or fizzy.... I have had that once before. OT did not sound great in one amp and in another amp it did the same thing.

If you play loud through the clean channel, do you still have the fizz?

[ayan]

Ok, some new info,

The clean channel does take pedals well when the bright switch is off.

I use a seperate relay to dissengage the bright switch in OD mode. This is wired correctly and works properly.

I'm going back to the non-bluesmaster PI (using 101 values) and re-working my lead routing on the stuff going to the pots. The lead dress on the tubes looks fine right?

Not changing any other component values yet.

I guess if you toy with building amps long enough you will at some point come across a puzzling build, and this may be your turn. What I suggest you do is try to isolate the area where the oscillation (what I suspect your problem is) generates. How to do that? Well, proceed from back to front starting at the phase inverter.

1. See if a cap across the plates of the PI will kill the fizz, and go pretty much as high as you have to to find out if you can do so -- it'd be great if you had a scope, which I presume is not the case... otherwise, scope the muha' and see the fizz. If so, you will then know the oscillation is already present at that point. Do the same for each previous stage and located the two points between which the problem develops. Once you know that, look at lead dress, solder joints, components, etc.

If you can't kill the fizz with any of those suggestions, find the smallest cap across a plate load resistor (i.e., from output of the stage where the oscillation appears to ground) that will kill the fizz. Does the cap kill much else? If not, you're done; if it does... you have to keep trying to buck it by other means.

2. If you can't kill the fizz at the PI level no matter how large the cap, it may be because it is introduced by oscialltions introduced at the power tubes. If so, you can hang (like Fender silverface amps) caps to ground from the control grids of the power tubes and see if you find the culprit(s). If so, you can once again look at lead dress or at increasing the value of the grid stopper resistors, or resorting to hanging to ground the smallest cap that will kill the oscillation without ruining your tone

Hope this helps,

Gil

[yeahyeah]

I changed to shielded wire to the OD master- no difference, the fizz is still there.

Oh yeah, I also cranked the clean channel with the master set at a low volume and it does the same thing.

I hate oscillation. The last amp I worked on had oscillation problems and it sounded sorta like this. Unfourtunately I don't have a scope. here we go again.

[heisthl]

OT wires too close to anything?