smoothing the OD in 124 D. Clone

[hans-jörg]

Hi,
you certainly read that I finished my D* Clone. And for shure I´m happy with it. The only thing is how to smooth out the OD.
I know, that this Amp react different on different guitars. So mine too. But I can`t find a "sweet point".
My chain is: 220k and 250k Poti (I throw out the trim (100k) so now its better, but not enough on the back).
Anode sees 207 VDC (1,35 on cathode) on V2b and 196 (1,52) on V2a.
Tube is a JJ 12AX7.
Any Idea

regards

Hans-Jörg

[wjdunham]

There are quite a few different options and I'm sure you will get many opinions from the members here, and there is already a lot of information on the site, but here's my experience:
1) The easiest solution is to try the well documented taper on the OD channel, which is simply an RC filter after the 2nd OD stage, I've used a 100K trimmer and a .001 cap. The interesting thing is that I used to have it set to roll off quite a bit, but the more I got used to the sound of the 124 style amps, the more I opened it up. Now I don't use it at all and most people I build amps for prefer it wide open.
2) build a Dumblator Smooths out the attack as well as the top end, and you get some adjustment with the bright switches.
3) try a few different length cables in the FX loop (similar to #1 but will also affect the clean channel).
4) try some different tubes, the JJ 12AX7's are very bright - I love the way they sound but to me they are a bit more agressive than an EH say. There are members here who have a lot of experience with tube types both new and old, hopefully you'll get some ideas there...
5) I've tried a few of the different OD output resistor/drive/level pot combinations, but always come back to the #124 values. May be worth trying - I found the changes to be very subtle and changed the balance of the amp in a way I didn't like - personal preference, YMMV

Bill

[greiswig]

Hi,
you certainly read that I finished my D* Clone. And for shure I´m happy with it. The only thing is how to smooth out the OD.
I know, that this Amp react different on different guitars. So mine too. But I can`t find a "sweet point".
My chain is: 220k and 250k Poti (I throw out the trim (100k) so now its better, but not enough on the back).
Anode sees 207 VDC (1,35 on cathode) on V2b and 196 (1,52) on V2a.
Tube is a JJ 12AX7.
Any Idea

regards

Hans-Jörg

I'd like to help, but I think I need to understand what you mean by "smooth out." Do you have too much high frequency? Or is it that you can't get the tone to sound less distortion-like...i.e. with less "tooth" to it?

The other thing is I'm not sure what you've done with your trimmer. It almost seems like you are saying you replaced the 100k trimmer with a 250k pot on the back of your amp? If so, that would change the circuit quite a lot. I'd go back toward having about 320k overall in that section of the circuit. For example, on mine I also wanted the trimmer on the back, and wanted it finer-tuned. So I have a 50k trimmer there, but have 270k before that.

My build also started with a 150k resistor between V1 and V2 (after the drive pot), but I found I liked it better with 180k...to my ears that sounded smoother.

JJ tubes are not what I would call "smooth," either. They have a high-mid thing going that kind of bothers me. So you might start with the simple solution first, and try some different tubes in there. One new tube that I like better than the JJ is the Tung-Sol.

So maybe tell us more what sound you have and what sound you are after, and we can help better.

[hans-jörg]

Hi,
what I mean is the OD even in low position is to harsh to my ear, not soft.
I mean creamy not spiky. Yeah, all that what is`nt.
But this might be the JJ. I will try Tung Sol.
What I meaned with trimm/Pot: I changed from 500k Pot (during the build) to a 100k Trim. After first test I did´nt like it and put a 250k at the back (shielded cables) - was better.
Also I think my Drive Pot is 100k instaed of 250k. I mean all together there is abig different in my OD stage.
@greiswig: I can not understand hoe you tune finer with a 50k instaed of 250k. Maybe I dont understand the system quite well.
@wjdunham: you put a 0,001 cap on the trimmer? Lug 1/2 or Lug 1/3? I have 3 as ground.

Thanks for the meantime
I go on testing

Hans-Jörg

[greiswig]

Hans-Jörg,

All I meant by having the 50k trimmer (which I happened to have anyway) was that it has finer resolution than a 100k trimmer, but you have to compensate for the lower overall resistance:
220k -> 100k = 320k
270k -> 50k = 320k

With the amp not powered, if you measure from the wiper of your trimmer to ground, what resistance do you see?

But it almost does sound like what you're saying is that you have too much treble on the overdrive. If so, you may want to build a Dumbleator and include it as part of your setup, or see https://tubeamparchive.com/viewtopic.ph ... eble+bleed for information on a way to roll off some of the treble.

[talbany]

Hans
This comes up quite a bit here harshness..So you know a harsh sounding amp can be due to many possible reasons.. Lead dress for example , resistor types or a not so happy cap or combination of caps a poor solder connection to name a few..These are sometimes difficult to find..
Since most of the harsh frequencys are really noticed in the upper mids 1K-5K range where our ears are most sensitive the knee jerk reaction is to start tweaking parts that shape frequency responce like pot values or coupling caps, snubbers,this IMO alters those sensitive frequency's making the harshness less noticable but doesn't IMO always cure the cause..This can drive one mad!!..
Sometimes a fresh amp off the bench can have a kind of grit to it that will eventually work it's self out after a break in period..Some amps will have a certain level of harshness to it no matter what you do or how well you built it will always have..It takes years to develop a good enough ear to determine where the harshness is coming from..This IMO makes it difficult to recommend what might be making your amp sound harsh without actually hearing it..I know this doesn't help you much..
I start with preamp tubes..Perhaps some nice NOS..I then move to lead dress and double check all my connections.. I rarely change cap values and pot values (unless they are bad) or do any voicing with an amp that is harsh sounding

Good Luck!!

Tony

[David Root]

A NOS GE long plate might help. Not too expensive.

[dogears]

Don't use a 100K trimmer for the post OD bleed. Use a 1M trimmer. Or at most a 500K trimmer. 100K is engaged in a big way even when all the way off. 500K would be much more adjustable to taste.

Big ups on the tube recommendation. A nice Holland made 12Ax7 or a RCA long black plate woudl really improve things, IMO.

[johan]

When you talk about tubes, GEs or RCAs Long Plate, you mean V1 or V2 or both?

[hans-jörg]

Hi all,
thank you a lot for all this interesting recommandations. I wiil folloe them.
The harshness what I see is only at OD. So I saw that I used on Drive a 100k Pot - will be changed, second: the Bleed Pot will be 500k to 1M. I have to see whats at home. And a good information for me - I´ve some NOS tubes (in my other Amps reachable) so i´ll try the too.
I´sure, at the end of this chain this wonderfull Amp will sound as I expected.
Thanx for your help - I will inform you

Greetings and nice weekend

Hans-Jörg

Edit: D´Lator is on the list - for shure

[wjdunham]

Scott, you're right (as always) - I have a 500K in there on the treble bleed, just measured it, my eyes are really starting to get bad It's set at about 300K to ground.


Bill

[David Root]

V2 is where the OD is generated, but V1, if too bright, can accentuate the situation in V2.

If you have any NOS 12AX7s try them in both, and the PI too. Sylvanias tend to be a bit bright though. Amperex are nice in #124, and anything else, for that matter. Also you don't want anything with too much mids in V2.

FWIW, my #124 currently has Amperex 7025 in V1, RCA long black plate 12AX7 in V2 and a Telefunken long smooth plate 12AX7 in V3.

Remember, #124 circuit (1984-88) was not designed for any current production 12AX7. The Sovtek LPS is probably your best bet in current production. Be careful with this tube in the PI, it does not like high cathode voltage. Or at least the early ones don't, may be better now.

If tubes don't do it, start looking at lead dress. I had to do a bit of that too. If yours looks exactly like the pics of the original, you are OK on that. If not, move it around!

[hans-jörg]

Hi,
I´ll try as soon as poosible with your recommendet tubes.
For now all Pots and R´s are right to original schematic. But until now no chance for testing.
Leaddress is also as close to original layout and pics.

https://tubeamparchive.com/download/file.php?id=16366


Tank you

Hans-Jörg

[llemtt]

lots of times harshness in the OD mode it's caused by the power amp more than anything else!

just take your preamp output and feed another power amp: is it getting better or worse?

my .02
cheers

[dogears]

Interesting.... I always found 270K to 350K to be a sweet spot. I like the 1M as it basically takes it out of circuit if you crank it off. 500K is still very noticeable compared to no trimmer.

Great ears think alike!

Scott, you're right (as always) - I have a 500K in there on the treble bleed, just measured it, my eyes are really starting to get bad It's set at about 300K to ground.


Bill