Master Brightness Caps in Non-HRM Amps

[ayan]

Many of you have known me long enough and realize that I've changed my mind about a few things regarding ODS style amps over the last 14 years or so.

Earlier this year, I tried to use my amps without anything in the loop to see how I liked it , since I'm getting tired of having to schlep around too many things for gigs. To accommodate that, I got rid of the Master volume brightness cap, which in my case was 30pF. [ Results of not using the loop sent me down a rabbit hole and I ended up buying a delay pedal and an Xotic BB Preamp to go with my home brew Blue Magic for overdrive. I like all of that and it works, but it is off topic here ] At the end of that experimentation period, I decided I'd rather fine tune my amps for use with the loop again.

I started playing with different cap values in my "124 ish" amp, which is my main gigging amp, and ended up with a 47pF cap which makes the clean channel very, very nice. With the stock D-lator clone in the loop and no master brightness cap in the amp, my amp's clean sound was dull in comparison. I messed with presence settings, bright switches on the D-lator clone, etc., but nothing worked out well in a consistent way. Of course, adding the 47pF cap made the overdrive channel harsh so I dialed back down the HF trim from 1 Meg to 270K to ground or so. I'm very satisfied with this and believe it is the best combination of clean and overdrive tones I've been able to get from this amp.

Next, I plan to tweak the 102 clone (this one's a straight copy), and I can see where a 68pF cap (instead of the 30pF cap I have there now) will bring some nice shimmer to the clean channel with the high plate circuit. I am prepared to dial down the HF as well, if needed.

As for what to do if I were to use the amp without anything in the loop, if turning down the treble control doesn't get rid of the excessive brightness, I guess I will make a little patch cord to plug into the back of the amp and use either a cap to ground or a series resistor to tame the high end.

Cheers,

Gil

[talbany]

Gil are you using the newer Xicons RN 65's on the plates of your 102..If so I sometimes find these to be a bit bright and harsh sounding at times (in OD) a bit too articulate for an OD plate resistor.. The newer KOA's don't seem to be as bright/brash on the top end.. I left the Xicons a while back for this reason..

Hope this helps!!

Tony

[Structo]

Yes, I have chased my tail on those type of problems on my amp as well.

For me, I have a 120pf bright cap on the preamp volume pot which is controlled by a relay.
It inserts the cap when in clean mode, but when I switch to OD, it takes it out of the circuit.
It's come to be called, bright on clean.
So you have three settings, down is bright off, middle is bright on both clean and OD and up is bright on clean only.

I use your idea of the High Frequency taper control on the OD channel to trim the fizz or HF artifacts.

I think I have a 15pf or 30pf on the Master pot.

I typically run the preamp volume at around 1:00 and the Master volume at 1:00-2:00.

I control the overall volume with the Output pot on the Dumbleator.

As a caveat, I don't gig with this amp so the whole tone package may not suit live play, but it sounds pretty good in my music room.

[bluesfendermanblues]

gil, sooner or later you're gonna put a build-in loop in those amps.

Doing that eliminates the need for a master vol bright cap, altogether. you sub the master vol for a fixed resistor pair and the return vol of the loop, becomes your master vol instead. Works like a charm.

And if you put in a 25k pot in the loop you get parallel functionality as well, and you can put your new rev and delay pedals in the (parallel) loop. Try it. It'll solve your tone issues.

[stelligan]

I am following your pursuits here. My challenges with the amps I have built are ongoing, but different. I seem to be an HRM guy. I don't like LNFB on V1 and like my clean tone without a d-lator. I can't live without the d-lator on the HRM OD. I need to modify them like the amps Henry at RedPlate has built for me. Internal d-lators that can be defeated. Best solution for me would be a step beyond that. My ideal: one button footswitch. Off = clean tone with no loop. On = loop, OD and Boost. Total drag is gain matching and the right effects device to take the heat of preamp out on clean tone without pegging(and have analog dry path). Smaller value bright caps are always better for my tastes.

As far as a loop cable - I have toyed with the idea of buying one of these: http://www.neutrik.com/en/audio/plugs-a ... 2rx-timbre
I just can't bring myself to spend the coin.
Also waiting on a 25K pot to implement BFMB's solution.
Forge on.....

[ayan]

Gil are you using the newer Xicons RN 65's on the plates of your 102..If so I sometimes find these to be a bit bright and harsh sounding at times (in OD) a bit too articulate for an OD plate resistor.. The newer KOA's don't seem to be as bright/brash on the top end.. I left the Xicons a while back for this reason..

I think I use Vishay/Dale in all my amps.... are those Xicon? If so, I didn't know that.

Yes, I have chased my tail on those type of problems on my amp as well.

For me, I have a 120pf bright cap on the preamp volume pot which is controlled by a relay.

Yes, I have thought about trying that because I think it could be a good thing. But, knowing myself, it would still annoy the heck out of me to know the amp wasn't "naturally balanced," if that makes any sense. Taking, for example, RF's clean sound it's always very chimey... He could use the neck pickup on his Tele (which one would expect to be on the dark side) and it chimed like crazy. I wanted something like that, especially since I have been incorporating the Strat quite a bit and I like positions 2 and 4, which tend to sound muffled.

Cheers,

Gil

[ayan]

Only thing is shoehorning the extra tube and guts in an already-built pair of amps.

Gil

gil, sooner or later you're gonna put a build-in loop in those amps.

Doing that eliminates the need for a master vol bright cap, altogether. you sub the master vol for a fixed resistor pair and the return vol of the loop, becomes your master vol instead. Works like a charm.

And if you put in a 25k pot in the loop you get parallel functionality as well, and you can put your new rev and delay pedals in the (parallel) loop. Try it. It'll solve your tone issues.

[Structo]

I agree about Robben Ford's tone.

But, he sounds about the same whatever he plays through.

On his tele, reportedly it has pretty hot/ overwound pickups.

The dual humbucker guitar I play mostly has Dimarzio 36th Anniversary PAF's in it and I like the neck for clean and the bridge for OD.

Seems like there is always a trade off.

[aflynt]

My #102 clones both tend to want to sound brighter on the OD side than the clean side. I've done a few things that don't really change the circuit too much but seem to help mitigate the issue.

* I keep the 68pF on the master and add about 120pF to ground on the loop return. For my amp with the outboard D'Lator I just use a cable that measures about 120pF and for the amp with the built-in D-Lator I use a 120pF SM cap.

* I always run the amp master high (like about 60/40 value-wise). It's high enough that the amp really breathes and compresses, but you can still hear the bright cap add a bit of shimmer.

* I use a brighter sounding tube in V1 (JJ ECC83) and a darker sounding tube in V2 (JJ ECC803).

Between all that the OD and clean generally balance out in a way that I'm comfortable with.

-Aaron

[ayan]

Well, I agree that's the sound he goes for, but he is human. With his amp settings (i.e., treble low and bass high) and with stuff in the loop, I am sure his tone through a Tele's neck pickup would not have that amount of chime if the amp didn't have the infamous 68pF cap on the master volume. That's what I was trying to convey.

Gil

I agree about Robben Ford's tone.

But, he sounds about the same whatever he plays through.

On his tele, reportedly it has pretty hot/ overwound pickups.

The dual humbucker guitar I play mostly has Dimarzio 36th Anniversary PAF's in it and I like the neck for clean and the bridge for OD.

Seems like there is always a trade off.

[Structo]

OK, understood.

Aaron, I may have to revisit my amp with those suggestions.
I recall doing something similar in my 6L6 D'lite.

[JazzGuitarGimp]

How about adding another 12AX7, and making the clean channel a separate entity? Then you can voice each channel to what you want to hear.

[Structo]

That is an idea as well, but most of us are limited by the chassis available for the Dumble builds.

I like the idea of the HRM amp, but with the tone controls on the front panel.

Sure you can order a one off custom made but with my luck all the holes would be in the wrong place.

[Guitarman18]

I, like most of us, have spent hours messing around with 102 and I've come to the conclusion that there is a lot of mileage in component composition (as opposed to just value). My first attempt at 102 ( https://tubeamparchive.com/viewtopic.ph ... hlight=hrm )was unsurprisingly bright but also brittle sounding, which is the unpleasant thing for me. Changing component value often kills the amp IMO, particularly 68pF bright cap.
It's pretty well documented that HAD is pretty consistent in his choice of signal caps, so I went to work on the resistors.
There have been a lot of comments over the years that HAD used whatever he had to hand, but I really believe that he probably didn't do anything unintentionally.
Changing brands of plate, cathode, grid resistors has had a dramatic effect on the quality of the tone (as opposed to character). Also NFB resistor composition.
Looking at pictures of amps like Bradons Bludodrive tells me that he is following this philosophy quite closely. Even resistors that don't seem to be in the signal path have made a significant change in my amps.

I know most of you know all this, but for anyone who hasn't tried it, I really think it gets you another step closer.

Cheers,

Paul.

[Structo]

Hi Paul,

What resistors do you like for preamp plates?
Cathodes?
Presence?

Thanks!