smoothing the OD in 124 D. Clone

[ampdork]

Just a small suggestion. I would consider rerouting the V1a and V2a cathodes as dumble did. I would pull the V2 leads closer to the socket and then fan out the PI leads a bit.
Not promising a certain fix but it'll be easy to do and it would behoove you to do that before any other actual circuit tweaks or alterations.

[talbany]

Hans
A couple things you may want to change..The shielded wire coming from V2b running across the PI wires and under the output trans secondary wires..

Also the shielded wire coming off the master vol going to the pre out jack looks like it runs right across the plate wire pin 3 on the output section..Is that wire also wire tied to the AC?.. I would re-route both those wires..ASAP look at 124 pics again..

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

I hope this helps..

Tony

[hans-jörg]

Thanks a lot all of you.

This are all interesting sugestions. I´ll try them all and give you a revew.

I´m close to finalize the headshell. Looks nice (very close to D. Lindleys Snake). Pics later when finished.

But now I´ll follow your tips.

Hans-Jörg

@talbany: the shielded from master is not fixed to the AC but very close - your right. I thought as its shielded thats enough protection. Looks like that its not.
Looks like I made a big mistake when I changed (by menthal error) the places of IN/OUT and AT-Out. This confuse my lead dress extremly.

[bepone]

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

hello hans jorg, i will try to help you.

i had the same problems like you, harsh und unpleasant distortion. i saw your layout and might see a problem. for me it took 4 months to solve the problem..but i did a bit of tweaking to the "dumble values" to my taste, and to smooth things out.
first you have too much "metal" resistors in your amp. for V1 it is good in some noise way.. i had also metal oxide resistors like you did. so, took them out in OD section first. my way:

1. change all OD valve (V2) resistors (ANODE ALSO!) to CARBON COMP 2W (more 2H fundament distortion because carbon comp resistors change its value with voltage across them)

2. change all cathode caps in OD tube to wima MKS (you can do it to V1 also)

3. change V2a) cathode resitor to 5K trimmer and trim cathode voltage more than 2V

4. omit V2a snubber cap and put 1nF across anode resistor

5. change V2 tube to ECC83 RFT (darker sound)
---------
hope that will help.. regards,

[bepone]

Also the shielded wire coming off the master vol going to the pre out jack looks like it runs right across the plate wire pin 3 on the output section
Tony

yes, this is also a mistake, signal wire shall not go that way ( a mess of wires with big currents near the power tubes)..

[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

hello hans jorg, i will try to help you.


i had the same problems like you, harsh und unpleasant distortion. i saw your layout and might see a problem. for me it took 4 months to solve the problem..but i did a bit of tweaking to the "dumble values" to my taste, and to smooth things out.
first you have too much "metal" resistors in your amp. for V1 it is good in some noise way.. i had also metal oxide resistors like you did. so, took them out in OD section first. my way:

1. change all OD valve (V2) resistors (ANODE ALSO!) to CARBON COMP 2W (more 2H fundament distortion because carbon comp resistors change its value with voltage across them)

2. change all cathode caps in OD tube to wima MKS (you can do it to V1 also)

3. change V2a) cathode resitor to 5K trimmer and trim cathode voltage more than 2V

4. omit V2a snubber cap and put 1nF across anode resistor

5. change V2 tube to ECC83 RFT (darker sound)
---------
hope that will help.. regards,

Hi Bepone,
thanks a lot for your tips. I was`nt in my own thread few days. So I read it now.
On Structos writing I put Smoothing caps 47p between the anode resistors of V2 and V3. And I was astonished about. Great.
For shur I changed the shielded wires wich are going and comeing to Pre/Power amp IN/OUT and to V2b. A way better, thanks.
The rest I will follow.
But I dont have CC resistors in 2 watt, only 1 watt. Does this fit too?
Usualy I put only 2 watt metal film in because of hiss with the CC R´s.

The only: Wimas would change the nice coloure of my board

The Trimmer on the cathode of V2a is interesting. For the moment I read there aproximatly 1,6 VDC. You mean over 2 V makes it darker/stronger?

Regards

Hans-Jörg

[bepone]

hello hans jorg!

great to hear that you solve your problem! i never try that method. can you tell, do you have snubber caps on OD tube IN, or you take them out?

fizz in my case had gone with 2W CC resistors, and 1nF cap over v2a) anode resistor. now when you have 47 pF across v2 anodes and if you try that take care too, maybe 1nF is too big in your case ?
/try 470 pF also/


1) CC resistors.. put 1W for grids and cathodes, but i will reccomend 2W for anodes ( smaller hiss when resistors power goes up). if you don't have 2W, put 1W to try and see the tone. if you don't like or did not see any changes, it is easy to return to MF ..

2) color? who will see? this is medical to take care with too fast electrolytic cap attack (if that was a problem) and some rounding too. i'm using MKT, MKP caps to bypass cathodes.

3) ECC83 tubes have much more nelinear behaviour in that region, so, when you go with more negative bias, you have more compression and sustain in your OD tone, to me it is great effect. you will see. 1.4-1.6V leads to fuzzy OD tone, it sounds (to me) not so good like "colder ECC83 bias"

regards josip

[hans-jörg]

Hello Josip,
great infos, thank you.
I will try to take the 47p across anodes out and put it parallel to V2a anode. Just to see the different - and the snubber out (its still in because I´m now at work )
But tomorrow I can give you a replay.
Thanks for the moment.

Regards
Hans-Jörg

[llemtt]

hans

your problem sounds like a ringing in your power amp which is cause number one for an unpleasant overdrive sound...

you can take out your 47p cap on V2 while leaving the 47p on V3 which is the "standard solution" and see if everything is fine

actually these problems are usually diagnosed easily by square wave testing the power amp

if V2 cap is essential to smooth your tone you have a dressing problem on V2 too, something is causing high-freq positive feedback from od out to od input

cheers
teo

[hans-jörg]

Hi teo,
because I´m a lonesome privat builder I have no diagnostic equipment (I have to write Santa Claus) so I have to find it out through the good old method - trail and error.
When I put the caps I also changed the lead dress of my shielded wires wich been to close to the output tubes Anodes. Therefore I´ll try it again whitout the cap on V2 and than parallel to V2a anode resistor.
But as I said, this amps sounds now a way better and with all your help and infos I´ll be soon on the "top" of my wishes (or so).

Regards

Hans-Jörg

[Structo]

That may help the fizzies but that is quite a departure from the Dumble topology.

1. change all OD valve (V2) resistors (ANODE ALSO!) to CARBON COMP 2W (more 2H fundament distortion because carbon comp resistors change its value with voltage across them)

The Vishay/ Dale metal films are desireable there because of the low noise and besides, that is what Dumble used.

2. change all cathode caps in OD tube to wima MKS (you can do it to V1 also)

Changing the cathode bypass caps to film caps will also change the character to something that is not Dumble.

3. change V2a) cathode resitor to 5K trimmer and trim cathode voltage more than 2V

Are you saying to elevate the cathode voltage to above 2v?
Here again, Dumble uses a 66:1 plate to cathode ratio and changing this will also alter his design.

I'm not saying your ideas are bad or wrong so much as they fall outside the ODS design.
Smoothing caps can be used appropriately in a few places but too much will destroy the grind that is part of the overdrive tone of these amps.
So don't make it too smooth or it might as well be a Boogie.

[bepone]

hello structo thanks for you comment! yes i know what dumble uses this is great forum with a lot of schematics and BOM's. but i found that CC in anodes contributes to the tone also in a good way. i leave them there.
bypass caps also.
about cathode bias, yes. i like harmonic content, compression and prolonged sustain of ECC83 in that region (more than 2V)

[Structo]

I spent most of the day yesterday experimenting with different things to hear the differences in my amp, 100w ODS.
I played with the NFB resistor value.
Also the bass pot value.
And with the Drive pot value.

In the end I ended up with 6.8K on the NFB resistor.

Bass pot I ended up leaving alone.
When I feel like experimenting some more I will try different values of the 10K tail resistor to see how that changes the response.

Lastly, I went through my small stock of preamp tubes.
Initially I had all vintage tubes in V1 through V3, Raytheon 12ax7's.

Currently I have a quad of TAD 6L6 STR's for power tubes.

You can really change some aspects of the tone with the preamp tubes.
I think that the Raytheons are higher gain than newer tubes and they were contributing to some harshness I was hearing.
I didn't want to believe that because I think using tubes from the 50's is cool....
I had some JJ's, EHX, Chinese 9th gen, GE, Raytheon, Sylvania to choose from.

But in the end I ended up with a Electro-Harmonix 12ax7 in V1 and a 9th Gen Chinese tube in V2.
I left a Raytheon long plate in V3.

The OD trimmer is set at around 27K to ground with the amp on.

This mix of tubes seems to have smoothed out the overdrive more and the cleans are a bit mellower without the crackly overtones on the top end I was hearing before.
The only thing I can think of is that the newer tubes have a lower mu than the originals and along with the high plate load resistors were causing some weird overtones or distortion.

Anyway, I'll play it like this for awhile.
Who knows next week I may not like this.

[rogb]

I spent most of the day yesterday experimenting with different things to hear the differences in my amp....

Anyway, I'll play it like this for awhile.
Who knows next week I may not like this.

Can this be made a sticky please?

[Structo]