Getting a smoother OD

[philbard]

Phil
Thats cool and I get it and commend you for taking on the build..4th Generation amps can be a real challenge just due to it's (simple) design and cascading OD gain stages.I struggled with those same issues for many years.IMO there are some amps where all these things I mention are not as critical and are a little more forgiving,unfortunately the ODS's devil is in these details and is never just 1 thing but combination of several.
I don't want to be the old guy on a forum that is demeaning other peoples builds if they are not up to my standards, however knowing what you are going through and being there myself for so long am just trying to relay my experience with these amps..
BTW. I've upgraded many a OTS's with the problems you mention so I get it..

Good Luck!

Tony

No worries, Tony, I don't take it as criticism. I've become accomplished in a number of things during the years of my career work and also know that you can't educate someone who is new on the scene to highly technical issues in just a few paragraphs. I'm impressed that there are so many helpful folks here and will bide my time on the learning curve.

[JD0x0]

On mine, I felt like increasing the V2b snubber to ~500pF and increasing the coupling cap from .005uF to .0082uF was a big improvement. Increasing the snubber on the last OD stage ensures that the harsher upper harmonics being produced by the clipping are smoothed out. The coupling cap change was more because I felt like it was dropping off a very noticeable amount of bass compared to the cleans.

[philbard]

On mine, I felt like increasing the V2b snubber to ~500pF and increasing the coupling cap from .005uF to .0082uF was a big improvement. Increasing the snubber on the last OD stage ensures that the harsher upper harmonics being produced by the clipping are smoothed out. The coupling cap change was more because I felt like it was dropping off a very noticeable amount of bass compared to the cleans.

Interesting idea. I too feel its losing some bottom in the OD channel. Both of these seem like easy mods to make as well and I just happen to have some 470pf's handy. Thx

[ijedouglas]

I would try stay with the Dumble "formula" as much as possible. Try changing out component types before altering values on the amp (grids a definite). Upping the value of the snubbers may mask the issue and you may end up losing something else in the amp.
Here is a pretty cool thread that details resistor changes and their effects: https://ampgarage.com/forum/viewtopic.php?f=4&t=32580

[philbard]

Here is a video clip of the amp in both clean and OD channels with 2 different guitars, one semi-hollow and one solid (slightly darker).

I recently found that by turning volume up past noon and trimming the master I got quite a bit of improvement in the OD tones, not so harsh but still on the trebly side. Let me know if you agree or not, interested in all of your impressions.

https://youtu.be/ne_CF878tB4

[philbard]

I would try stay with the Dumble "formula" as much as possible. Try changing out component types before altering values on the amp (grids a definite). Upping the value of the snubbers may mask the issue and you may end up losing something else in the amp.
Here is a pretty cool thread that details resistor changes and their effects: https://ampgarage.com/forum/viewtopic.php?f=4&t=32580

Thanks, Ian. More good advice it appears, I think I'll hold off on altering the component values until I've had a chance to swap some of them.

[scotto]

Just to follow up on the OT, Heyboer doesn't have the OT-4400 in stock right now as they are backed up several months due to Covid. They do have OT -4000 in stock which is same construction with slightly lower primary impedance. It's $125. I spoke to Arlyn there who is very helpful. I asked about whether the 4400 was available to those of us other than Brandon and didn't get clarity. My impression was that it might be but Charlie could be right on this. Another slightly cheaper but very good option is the one in this link. http://www.hi-endstore.com/TranFender.html not sure who makes it (Hammond?) But it sounds great in my Red Plate Black Loop. Output impedances don't include 16 ohm but that's never been an issue for me.

[philbard]

Just to follow up on the OT, Heyboer doesn't have the OT-4400 in stock right now as they are backed up several months due to Covid. They do have OT -4000 in stock which is same construction with slightly lower primary impedance. It's $125. I spoke to Arlyn there who is very helpful. I asked about whether the 4400 was available to those of us other than Brandon and didn't get clarity. My impression was that it might be but Charlie could be right on this. Another slightly cheaper but very good option is the one in this link. http://www.hi-endstore.com/TranFender.html not sure who makes it (Hammond?) But it sounds great in my Red Plate Black Loop. Output impedances don't include 16 ohm but that's never been an issue for me.

I went ahead and ordered a 774 from MojoTone, replacement for Fender Bassman, on the recommendations previously made here. Will wait to see how that works. Its hard for me at this point as I'm in the early stage of tweaking, but I'm ordering up some other replacement components and hope to gain a better understanding of what makes a difference. Thanks!

[scotto]

Cool, that should be fine Phil. Enjoy the tweaking!
Scott

[drew]

I went ahead and ordered a 774 from MojoTone, replacement for Fender Bassman, on the recommendations previously made here. Will wait to see how that works. Its hard for me at this point as I'm in the early stage of tweaking, but I'm ordering up some other replacement components and hope to gain a better understanding of what makes a difference. Thanks!

I'm going to call this right now; having a spare OT is going to be the "camel's nose in the tent" impetus toward construction of Amp #2.

[pdf64]

My ‘go to’ for smooth preamp overdrive is to leave the cathodes of its clipping stages unbypassed. If that loses too much gain then at least have low value resistor, eg 470ohms, in series with the bypass cap.
The overdriven waveform becomes more rounded, the harsh, high order harmonics necessary for a sharply clipped waveform are never generated in the first place, so no need for stinkin’ snubber caps to clean up after the fact.

[philbard]

I went ahead and ordered a 774 from MojoTone, replacement for Fender Bassman, on the recommendations previously made here. Will wait to see how that works. Its hard for me at this point as I'm in the early stage of tweaking, but I'm ordering up some other replacement components and hope to gain a better understanding of what makes a difference. Thanks!

I'm going to call this right now; having a spare OT is going to be the "camel's nose in the tent" impetus toward construction of Amp #2.

Just yesterday realized this is the wrong number for the tranny I need, its actually the 775, replacement for Showman/Twin Reverb. I called MojoTone and changed my order. Sorry about the misquote...

[martin manning]

Just yesterday realized this is the wrong number for the tranny I need, its actually the 775, replacement for Showman/Twin Reverb. I called MojoTone and changed my order. Sorry about the misquote...

Just to be sure... your amp is a 100W, correct?

[philbard]

Just yesterday realized this is the wrong number for the tranny I need, its actually the 775, replacement for Showman/Twin Reverb. I called MojoTone and changed my order. Sorry about the misquote...

Just to be sure... your amp is a 100W, correct?

No, its 50w. Is that transformer incompatible?

[philbard]

Just yesterday realized this is the wrong number for the tranny I need, its actually the 775, replacement for Showman/Twin Reverb. I called MojoTone and changed my order. Sorry about the misquote...

Just to be sure... your amp is a 100W, correct?

No, its 50w. Is that transformer incompatible?

After going back over the posts, I see that for 100w its 775 and for 50w its 774, and that you were the one who gave that correction. Missed it yesterday and it looks like I need to stay with the 774 after all. Back to MojoTone...