help! my HRM overdrive sounds harsh

[yeahyeah]

cleans sound good, but the overdrive has some issues.

There are allot of high end fizzies I can't get rid of with the treble trimmer. Even when the treble trim is all the way down all I get is a mostly muddy tone with the very high fizz is still on top of it.

granted, I am playing a strat style guitar, but I know it shouldn't sound THAT bad. Even when I roll off the tone and vol on the guitar the fizz is still there.

Also I feel like the overdrive is too much... I used audio taper for the drive pot but it is very overdriven at 9 o'clock (w/ input volume at 12) and by the time I'm at 12 on the drive it's very heavy. The higher settings are unuseable.

HRM with bluesmaster PI

tube voltages:
V1
1- 190
3- 1.78
4,5- 3.3ac
6- 198
8- 1.63
9- 3.3ac

V2
1- 193
3- 1.79
4,5- 3.3ac
6- 199
8- 1.71
9- 3.3ac

V3
1- 271
3,8- 38.2
4,5- 3.3ac
6- 263
9-3.3ac

V4
2- 3.3ac
3- 416
4- 417
5- -47
6- -48
7- 3.3ac

V5
2- 3.3ac
3- 415
4- 416
5- -47
6- -48
7- 3.3ac

Dropping string voltages:
430----422----411----316----310

[groovtubin]

cleans sound good, but the overdrive has some issues.

There are allot of high end fizzies I can't get rid of with the treble trimmer. Even when the treble trim is all the way down all I get is a mostly muddy tone with the very high fizz is still on top of it.

granted, I am playing a strat style guitar, but I know it shouldn't sound THAT bad. Even when I roll off the tone and vol on the guitar the fizz is still there.

Also I feel like the overdrive is too much... I used audio taper for the drive pot but it is very overdriven at 9 o'clock (w/ input volume at 12) and by the time I'm at 12 on the drive it's very heavy. The higher settings are unuseable.

HRM with bluesmaster PI

tube voltages:
V1
1- 190
3- 1.78
4,5- 3.3ac
6- 198
8- 1.63
9- 3.3ac

V2
1- 193
3- 1.79
4,5- 3.3ac
6- 199
8- 1.71
9- 3.3ac

V3
1- 271
3,8- 38.2
4,5- 3.3ac
6- 263
9-3.3ac

V4
2- 3.3ac
3- 416
4- 417
5- -47
6- -48
7- 3.3ac

V5
2- 3.3ac
3- 415
4- 416
5- -47
6- -48
7- 3.3ac

Dropping string voltages:
430----422----411----316----310

try a 470 k right outa treble pot on HRM.. PM me, Omegaamps@wilkes.net

[dogears]

A few things...

1) 6V6 tubes are bad in these amps. Especially with the BM PI. Harsh trebly suckers... Been saying over and over....

2) What pre-od network is in there? You should not have so much gain. Double check your resistor sizes. Also make sure the clean master is in the circuit (except for the wiper) when you are in OD.

3) Shielded cable on the OD master?? If not, add 27pf caps to ground from the input and wiper both. This will simulate the shielded cable.

Set the stack to 50% on all the trimmers as a baseline. It will sound bad to set the treble tirmmer so low. It has to be up about 60%.

Build looks nice...

[yeahyeah]

I've got 6L6's in there now, biased properly. Set the OT to 16 tap since its stock D'lite iron going into an 8 ohm speaker. swapped speakers, same result. I've got a lead 80 in there now. speaker cab is single 12 oval ported back.

The pre od network is 470k in parallel with 47pf, inseries with 200k, 25k trimmer and 4.7k to ground. I just double checked with the DMM, everything looks good.

Masters are wired properly, OD master is unshielded to the relay, then shielded to the board.

I started with the HRM trimmer values set to where you suggested. Just cant dial it out with them.

The fizz sounds like it's around 6kHz.

[yeahyeah]

Any help?

I've spent the last couple days checking values and continuity with the DMM and I haven't been able to find anything wrong yet. I took my sweet time during the initial build checking everything as I went too... very stumped.

The overdrive sounds like a fuzz.

I'm thinking the problem is in the preamp somewhere because the OD is getting too much. The low gain input network checked out fine on the DMM.

What else could it be???

I don't know if this is of any use, but when I run a dirt pedal infront of the amp's clean chanel it sounds harsh too, even with the bright switch off.

[mlp-mx6]

How closely have you reviewed the PI and presence circuits? That would be where I would focus next in your situation.

Make sure you have a 25K presence pot with the 4.7K in parallel.

[yeahyeah]

How do I test to see if a cap is leaking DC?

[ayan]

How do I test to see if a cap is leaking DC?

You can improvise a very simple test: connect one side of the cap to a DC source and the other to a resistor and then gorund. Size (value and power rating) the resistor accordingly so that you don't shortcircuit the DC source and fry the resistor if the cap leaks.

So, for example, tap off the bias DC voltage (about 50 VDC or so) and connect the cap in question to it. Ground the other terminal of the cap via a 10K, 1/2W resistor. If you measure the voltage on the DC side of the cap (between that point and DC ground), you will obviously get the bias voltage reading. On the other side of the cap, you should read 0 VDC. If the cap leaks, you will get some (DC) current flow through it and the resistor, and will therefore see a voltage drop across the latter.

In the worst case scenario, if the cap was completely DC conductive, you would read 50VDC across it and 5mA of current through it and the resistor. The resistor would be dissipating 1/4W (50x50/10,000) of power.

Gil

[yeahyeah]

OK, the preamp checked out fine, I went through every inch of it checking each component and connection.

really strange.

The amp sounds like it's working properly exept for this nasty fizz on the top. Which obviously ruins it.

['67_Plexi]

Sounds like the issue is systemic. Voltages look fine.
You may think this sounds bizarre, but your lead dress around your pots and input stage is very pretty, but is akin to lining up all the tuners on your guitar in one direction. Great to look at, but thats about it. Also check the speaker secondaries or feedback wiring is completely clear of the preamp stages, especially under the board. In these designs, perfect neat wiring nearly always accounts for bad lead dress. It may sound like an oxymoron, but from a electro-magnetic perspective it's certainly not. Check out examples of actual Dumbles amps to verify this. His wiring wasn't a bit messy in places because he was lazy. His sporadic use of cable ties in certain areas also wasn't because he forgot to go to Home Depot (who by the way sell some awesome small safety ties that I've not seen anywhere else).
Lead dress issues can appear with many symptoms from strange artifacts to high noise to phase cancellation effects to frequency response issues to lack of harmonics to an overabundence of nasty harmonics to out and out deafening squeals.....you get the picture. In this design check especially the feeds to the masters.

As a a side note, have you measured your pot values ? Alphas can be up to 20% away from their stamped value and in some positions that can sund real bad. I usually throw around 10% of all the pots I buy away because they are too far out of spec. Some values are worse than others.

Hope you figure it out.

Kind Regards, Alan.

[greiswig]

SNIP
You may think this sounds bizarre, but your lead dress around your pots and input stage is very pretty, but is akin to lining up all the tuners on your guitar in one direction. Great to look at, but thats about it. Also check the speaker secondaries or feedback wiring is completely clear of the preamp stages, especially under the board. In these designs, perfect neat wiring nearly always accounts for bad lead dress. It may sound like an oxymoron, but from a electro-magnetic perspective it's certainly not. Check out examples of actual Dumbles amps to verify this. His wiring wasn't a bit messy in places because he was lazy. SNIP

This is a very interesting paragraph to me. Other than trial and error, how does one go about deciding what to route next to what, and otherwise what accounts for GOOD lead dress? Is there a tutorial somewhere that takes these sonic changes into account? Is the D'Lite layout already taking lead dress and routing into account?

Thanks!

[drz400]

SNIP
You may think this sounds bizarre, but your lead dress around your pots and input stage is very pretty, but is akin to lining up all the tuners on your guitar in one direction. Great to look at, but thats about it. Also check the speaker secondaries or feedback wiring is completely clear of the preamp stages, especially under the board. In these designs, perfect neat wiring nearly always accounts for bad lead dress. It may sound like an oxymoron, but from a electro-magnetic perspective it's certainly not. Check out examples of actual Dumbles amps to verify this. His wiring wasn't a bit messy in places because he was lazy. SNIP

This is a very interesting paragraph to me. Other than trial and error, how does one go about deciding what to route next to what, and otherwise what accounts for GOOD lead dress? Is there a tutorial somewhere that takes these sonic changes into account? Is the D'Lite layout already taking lead dress and routing into account?

Thanks!

If something is really wrong you should be able to see it on a scope.
That would remove a whole lot of this guess work

[stelligan]

Might I ask about the white wiring looped around the impedance selector? I am sure there is probably a purpose, but I had not done this to my builds and was curious about it's function.

Thanks in advance.

[brownnote]

...bridging the contacts of the rotary selector to provide some redundancy to the connection.

[greiswig]

SNIP
You may think this sounds bizarre, but your lead dress around your pots and input stage is very pretty, but is akin to lining up all the tuners on your guitar in one direction. Great to look at, but thats about it. Also check the speaker secondaries or feedback wiring is completely clear of the preamp stages, especially under the board. In these designs, perfect neat wiring nearly always accounts for bad lead dress. It may sound like an oxymoron, but from a electro-magnetic perspective it's certainly not. Check out examples of actual Dumbles amps to verify this. His wiring wasn't a bit messy in places because he was lazy. SNIP

This is a very interesting paragraph to me. Other than trial and error, how does one go about deciding what to route next to what, and otherwise what accounts for GOOD lead dress? Is there a tutorial somewhere that takes these sonic changes into account? Is the D'Lite layout already taking lead dress and routing into account?

Thanks!

If something is really wrong you should be able to see it on a scope.
That would remove a whole lot of this guess work

True, assuming that you have a scope and know what to look for. But it would be nice to have some rules of thumb before you get to the point of having to use a scope, rules that explain some general principles of lead dress like "although it may look clean, always offset signal wires from the chassis by 3/8" or so...otherwise capacitance will make your Tele sound like a cucumber."