Hi everyone o/
So, last year i got this amp:
It's a 100w 2x10 brazilian V8080 copy, that consists of a valvestate preamp going into a gallien krueger 400RB bass power amp =o
Works and sounds great after i done some stuff to it, but now i want to try this out:
original schematic for reference: https://www.thetubestore.com/lib/th...Valvestate80-80W-8080-8100-8412-Schematic.pdf
The idea here is to take more advantage of this single tube by turning it into its own gain stage with its own gain control and later add that to the front panel. But as you can see in the schematic i posted, i'm planning to use a tl081 buffer to replace the cathode follower and i'm not sure if this opamp will have enough headroom(+-15v) to handle the signal coming out of that second tube half, but i don't know what else could be done.
I'm basing this redesign off of a JCM800's input stage, and if this works i'm planning to add a switch to disengage the bright caps, and another one to bypass the "boost" section and go directly into the tube grid across a 68k resistor.
Any inputs? Suggestions? What do you guys think?
So, last year i got this amp:
It's a 100w 2x10 brazilian V8080 copy, that consists of a valvestate preamp going into a gallien krueger 400RB bass power amp =o
Works and sounds great after i done some stuff to it, but now i want to try this out:
original schematic for reference: https://www.thetubestore.com/lib/th...Valvestate80-80W-8080-8100-8412-Schematic.pdf
The idea here is to take more advantage of this single tube by turning it into its own gain stage with its own gain control and later add that to the front panel. But as you can see in the schematic i posted, i'm planning to use a tl081 buffer to replace the cathode follower and i'm not sure if this opamp will have enough headroom(+-15v) to handle the signal coming out of that second tube half, but i don't know what else could be done.
I'm basing this redesign off of a JCM800's input stage, and if this works i'm planning to add a switch to disengage the bright caps, and another one to bypass the "boost" section and go directly into the tube grid across a 68k resistor.
Any inputs? Suggestions? What do you guys think?
Don't use the IC, just use a Mosfet source follower. You are not asking for gain so the IC is not needed.
Mosfet source follower guitar - Google Search
Mosfet source follower guitar - Google Search
All right, after some digging and drawing i came up with this:
Do you think C7 is needed in this case?
Not as long as the tonestack caps have the voltage rating. Usually you also use a zener diode from the gate to the source just in case
Tonestack caps are rated ~100v
upd: added 12v Zener, i think it's ready now 😎
here's the kicad project files: View attachment v8080 mod.zip
If you spot anything that might not work please let me know o/
upd: added 12v Zener, i think it's ready now 😎
here's the kicad project files: View attachment v8080 mod.zip
If you spot anything that might not work please let me know o/
No idea what the files are. But otherwise I would try it. Actually might, I had an idea for a one tube preamp, will have to look it up again.
Good news
It works! 😀
However, the gain is so absurd that if you do as much as touch the gain pot it goes squealing really loud, but if you make REALLY fine adjustments you can get a pretty usable setting
Its also really trebly, will have to adjust that later too
Here's how the circuit is right now:
I think i could up that 470k(R4) to 2.2M and that would maybe get the signal to usable levels.
I could also try to attenuate the signal coming from the boost section somehow
All n' all, i'd say it has potential 😀
ideas?
It works! 😀
However, the gain is so absurd that if you do as much as touch the gain pot it goes squealing really loud, but if you make REALLY fine adjustments you can get a pretty usable setting
Its also really trebly, will have to adjust that later too
Here's how the circuit is right now:
I think i could up that 470k(R4) to 2.2M and that would maybe get the signal to usable levels.
I could also try to attenuate the signal coming from the boost section somehow
All n' all, i'd say it has potential 😀
ideas?
Put a 100k (pulled the value out pf my...) or apropriate value across the pot instead. Is it an ausio taper pot?
Across 2 legs of the pot in parallel with the cap? its a B pot =/ only type i got 😕
could try this:
could try this:
Last edited:
Did not even notice the resistor and capacitor. Funny how the mind is selective. Yes, you also should have an audio pot.
Yep, maybe i should disconnect it
i dont think it is needed anymore
What would adding this resistor across the pot do?
I think that the problem is that v1a ins't clipping the signal coming into it, its just making it louder, and that would be causing the high pitched squealing(oscillation) because its hitting v1b too hard
So i think i should try to attenuate both the signal in and the one that comes out of v1A, that and disconnect the positive feedback
?
Of course. The stock amp HAD enough gain. Your conversion adds about 50:1 of gain (and an inversion), which makes WAY too much gain.
You don't make "a gainy amp" by shoveling gain into it. More like making bread: knead and thump it, then let it rise, repeat. Alternate gain and loss.
EXACTLY. I knew that going in. However, i'm not trying to get more gain, but different gain. Makes sense?
So instead of a SS preamp going into a clean tube volume boost/buffer, i'm trying to make this whole thing behave like a boost pedal going into a tube preamp 😉
I did some changes to my schematic:
removed some caps
added some resistors
changed some values
what do you think?
You have a 1M resistor in series with a 500k pot. One third of the signal is dropped across the 500k pot and 2/3 is dropped across the 1M resistor (except highs). So with 100V out you have 33V across the pot.
If you have a 100k resistor in parallel with a 500k pot the effective resistance is 83k. So you get 100V x (83k/ 1000k + 83k) = 9.3V You have less than a third of the voltage across the pot. The capacitor high frequency bypass response changes but I thought it a quick way to drop some signal to see how you like it.
Well gentlemen, after much tinkering, i found that the following circuit worked the best:
Its makes for very loud sparkly cleans, but starts getting fuzzy after you start adding gain. Sounds kinda like one those old Fender Champ amps.
And if i tried bypassing the boost section and going directly into the tube i could have a very good pedal platform, but that's not what i want haha
If you want a classic sounding clean amp, this mod will give you that easily with minor adjustments
i'll be reverting the changes to my amp o/
A big thank you to Printer2 for the help
Its makes for very loud sparkly cleans, but starts getting fuzzy after you start adding gain. Sounds kinda like one those old Fender Champ amps.
And if i tried bypassing the boost section and going directly into the tube i could have a very good pedal platform, but that's not what i want haha
If you want a classic sounding clean amp, this mod will give you that easily with minor adjustments
i'll be reverting the changes to my amp o/
A big thank you to Printer2 for the help
UPDATE
Just wanted to update this topic cus' i finally got this working. Here's the schematics and a sample(od1, no pedals of any sort, no post FX or EQ, recorded directly with IRs in FL studio, D std):
View attachment Valvestate Vulcano GAIN mod + TS mod.pdf
I also modded the clean channel:
View attachment Valvestate Vulcano CLEAN TS mod.pdf
Sample:
View attachment sample OD1 no OD Dstd.mp4
I can post more info/pictures/samples if anybody's interested.
o/
Just wanted to update this topic cus' i finally got this working. Here's the schematics and a sample(od1, no pedals of any sort, no post FX or EQ, recorded directly with IRs in FL studio, D std):
View attachment Valvestate Vulcano GAIN mod + TS mod.pdf
I also modded the clean channel:
View attachment Valvestate Vulcano CLEAN TS mod.pdf
Sample:
View attachment sample OD1 no OD Dstd.mp4
I can post more info/pictures/samples if anybody's interested.
o/