VHT D-50 Mod Journey

[bwest]

Revised stock amp with some corrected values and the tonestack corrected / the switch in the 'rock' setting. Note that where I took one of the 183 "D" values as a guess I wrote that in the component name:

Ltspice attached. Pictures also attached:

https://ampgarage.com/forum/download/fi ... w&id=64444

https://ampgarage.com/forum/download/fi ... w&id=64443

https://ampgarage.com/forum/download/fi ... w&id=64442

[bwest]

Also forgot to mention as part of mod 1.1 I added a 2meg resistor across the first power supply cap for the preamp (the one for the screens, not the V1 tube). This is to bleed out all the DC after the amp is unplugged in case I get stupid/forgetful - cheap insurance policy and it only dissipates 0.1w continuous in normal operation

[bwest]

Ok so looking to tweak the OD section - here is the signal post 1B with no bright cap, then post the 50n leaving 1B, then post 10n going into the OD trim - shaving some bass but only 3-4 db down at 80hz. You can see some HF shaping happening also (reminder no bright cap engaged).

https://ampgarage.com/forum/download/fi ... w&id=64445

[bwest]

Here's another interesting one - mod 1.1 post OD post OD level pot vs v1B - you can see some bass and treble are rolled off through the circuit (purple is post OD, green is pre-OD):

https://ampgarage.com/forum/download/fi ... w&id=64446

[bwest]

Tried a potential "Mod2.0" mod - not sure if I like it or not. Basically I took V2B and biased it warm with an 820 ohm resistor. I also wanted to drop some bass so I was going to go to a 1u cap, but I didn't have one, so I just used the 820 as I figured there isn't much feedback there anyhow.

Its interesting - really changes the character of the amp. Makes it much more dry and hard rock/metal, but if you turn the trim pot up (input to v2a) and the drive pot down (input to v2b) you can get more of that wetter looser bassier "d" sound. I will say the jam I just had on it was the most fun I've had with the amp so far, but I think it is telling that I wound up playing some metallica and 80s rock riffs...so that's where it is right now

Other thing I might try at some point is making V2B a cathode follower, but then really we are in the soldano/marshall master volume amp territory and I want to stay more in "d" topology ideally to play with that

[bepone]

you can go other way... not 820r, but in V2b put 4k7, 5k6 etc, soldano route.. imo better drive

[bepone]

too much of the highs lost because you have master set on 10% (900k series resistor!), at least put there 20-30pF in bypass.

[Reeltarded]

Tried a potential "Mod2.0" mod - not sure if I like it or not. Basically I took V2B and biased it warm with an 820 ohm resistor. I also wanted to drop some bass so I was going to go to a 1u cap, but I didn't have one, so I just used the 820 as I figured there isn't much feedback there anyhow.

Its interesting - really changes the character of the amp. Makes it much more dry and hard rock/metal, but if you turn the trim pot up (input to v2a) and the drive pot down (input to v2b) you can get more of that wetter looser bassier "d" sound. I will say the jam I just had on it was the most fun I've had with the amp so far, but I think it is telling that I wound up playing some metallica and 80s rock riffs...so that's where it is right now

Other thing I might try at some point is making V2B a cathode follower, but then really we are in the soldano/marshall master volume amp territory and I want to stay more in "d" topology ideally to play with that

I like it. You have just approached the Ripper. Bypass that with .68.

By the way. I looked 100 times. I can't find the gain VHT lost in the clean channel.

[bwest]

Aha! Yes the ripper mod is almost exactly what I was modelling as a very compressed soft clipping combo gain/cat follower stage. Should sound great. Also funny enough there is tone shaping post distortion - I'm aligned with the thinking of the ripper mod.

In regards to this comment: "By the way. I looked 100 times. I can't find the gain VHT lost in the clean channel." - could you clarify what you mean? That you would expect the clean channel to break up more than it does?

[Reeltarded]

YES

[talbany]

Aha! Yes the ripper mod is almost exactly what I was modelling as a very compressed soft clipping combo gain/cat follower stage. Should sound great. Also funny enough there is tone shaping post distortion - I'm aligned with the thinking of the ripper mod.

In regards to this comment: "By the way. I looked 100 times. I can't find the gain VHT lost in the clean channel." - could you clarify what you mean? That you would expect the clean channel to break up more than it does?

Does anyone here know what the Ripper is? Has a schematic, layout or an accurate drawing of it's topology?
If so Love to check that out
Thanks
Tony

[Reeltarded]

hold on let me get a proper emoticon

32C49348-FF96-46AC-8A9D-6436E08C2009.jpeg

As far as a real Ripper circuit: nobody got time for that

[bwest]

Not sure I can quote cross threads but I was referring to this schematic from 10thTx as the "ripper" which shows a partially bypassed 820r/100K stage DC coupled into a 82K cat follower stage.

So, you're talking about something maybe similar to this?

With respect, 10thtx

I was playing with something similar where I put some resistance on the anode to drop the voltage a bit and prevent burning up preamp tubes. It seemed to compress more gradually - really that is my back pocket fallback plan - the other benefit is I'd have a spare pot I could use for tone shaping, so that's cool. But I was worried it would sound too much like a marshall or soldano so I'm trying to avoid that for now, but its the fallback plan.

Sidebar I used to buy that the unbypassed cold biased stage in the Soldano and JCM800 were "cold clippers" and would lead to very asymmetric waveforms, but now I more buy the stance they are just very low gain stages - I think the 39K soldano stage is only like a 2x gain. Why that matters is I don't have room for a "cold clipper" stage, but I don't really think it matters. Anyhow I'll throw it in spice and show you guys what comes out, but I think it is going to be a pretty linear low gain stage that clips super hard because of all the feedback.

[bwest]

YES

@Reel I'm guessing you own a D50? If so some ideas:
- Replace v1 with a tested high amplification factor 12ax7 (I don't have the means to test tubes, but my understanding is they are all over the place)
- Delete the v1b negative feedback - that's good for a few more DB
- Tweak the tone stack to be lower loss (it is a very lossy beast)
- Run a boost in front? (yeah cheating but I'm putting in all the ideas. The real thing had that FET stage, which you can buy as a VHT pedal, so there's that maybe)
- Reduce negative feedback in the power amp to make it easier to overdrive - can put that on a switch

[bwest]

One more idea - you could bias V1b hot or cold so it is out of center - will break up easier