Time for a a guest appearance. Sebastian sent me some interesting layouts that might interest some of you. Here is what Sebastiam says about it.
The best-sounding amp I ever played through was a friend's Miles Platting 100W head (made by Wilsic Sound during the 1970s in Doncaster, England), which was basically a Bassman preamp going into a Marshall power section. So I did a JFET translation of the preamp and grabbed the "power section" of the model feT and voilà, a Miles Platting-in-a-box.
I'm going to hold out for the JHS version.
ReplyDeleteDang, I better start producing a bunch of these that I can trade for gold bullion after Josh compares it to, I dunno, a ZVex Box of Rock or whatever.
DeleteIn all seriousness, this looks pretty impressive Sebastian.
DeleteThank you kindly, Tom! Honestly, with all I've learned from here, the least I can do is offer an idea in return. Now, let's just hope the thing works! (Hoping to get my prototype off the breadboard and onto vero this week...)
Deletewhoa - this just shot to the top of my to-do list!!!!
ReplyDeletecan you make the shematic of the anasound brand pedals?
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteThat 470pf (C8) looks so wrong in my eyes...
ReplyDelete+ C8 is not found anywhere in the original schematic... So what's up with that? Why is it there?
My logic tells me that this section will have the sound of tin can, with no frequencies below treble. IOW: I would not expect any Mids or Bass to pass trough from such a configuration.
Are you certain that you would want to do such an extreme HighPass, or am I missing out on something here?
Or: is the input impedance so far off that you need such a tiny cap to filter out rumble/excess lows?
Which schematics are you looking at? I was working from the ones with the John Hornby Skewes Co. stamp on them, and they all have a 470p coupling cap between the preamp & the phase inverter.
DeleteIt *does* seem like an absurdly small cap value, I agree, but it works - the sound is still full, with plenty of bass on tap. You can find the same value coupling cap at the same place in the signal chain in old Fender amps, too, like the blonde Bassman, and they certainly aren't lacking low-end. I'm not expert enough to explain *why* it works, but trust that it does.
Thanks for the explanation!
DeleteYour wording confused me...
The Text Above it states: "I grabbed the "power section" of the model feT", and that kind of implies that the model feT schematic would be the place to look as a reference. So that is the schematic I looked at for comparison (when seeing the tiny coupling cap).
Thanks for sharing, caring and helping to explain my confusion!
Cheers!
VERIFIED! Haven't checked the voltages on the JFETs yet, so I'll report back with that later. For now, I can say this does indeed remind me of the actual amp: super interactive tone controls, Fendery cleans, and, oddly, Hiwatt-like breakup - snarly & stiff, not compressed & hairy. "Touch sensitive," as the cork-sniffers say.
ReplyDeleteIt takes a bit of dialing in, but there are great tones with either humbuckers or single-coils. Even bass works, with the gain low and the bass cranked. Generally, this will really butter your biscuit if you're into post-punk or Chicago noise rock tones.
Thanks Sebastian!
DeleteReally appreciate you contribution in here.
Tagged.
Hi Sebastian, I was looking to build something different so I gave this one a try. I finished yesterday at night but I have not been able to make it work... here are my voltages (IC2 looks odd) maybe you can help me:
DeleteIC1(MAX1044)
1. 8.7v
2. 4.36v
3. 0
4. 4.36v
5. 8.69v
6. 4.27v
7. 6.52v
8. 8.77v
IC2 (TL072)
1. 0
2. 0
3. 0
4. -8.68v
5. 0
6. 0
7. 0
8. 8.68v
(2n5088 and j112's)
Q1:
E 8.09v
B 8.59v
C 12.8v
Q2:
E 8.1v
B 8.54v
C 12.56v
Q3:
G 0.01v
S 0.67v
D 8.9v
Q4:
G 0.01v
S 2.53v
D 8.46v
Ok... I tried a third TL072 and voilaaa! Now it works!
DeleteThe j112 lacked character, I replaced them with j113 and the 2n5088 with some bc108 and now I really like it, very touch responsive... Big A chord and instant Pete Toushend tone 🤘
Deletehttps://www.youtube.com/watch?v=BxDfElk3IsU
Great demo, Felipe! So glad that you got the circuit working. And thanks for the tip about the BC108 transistors; I've got a few on hand, so I'll try them out too.
DeleteYou just ticked a lotta boxes. The trimmers are 100k? Also, did you use BF245A's? I'm not familiar with them.
ReplyDeleteTrimmers are 100k, but 50k might help zero in on the "sweet spot" better - worth a try!
DeleteBF245As are just the DSG-pinout N-channel JFETs I could find the cheapest in eBay, instead of desperately hunting down J201s that weren't fake. They have yet to fail me in any circuit, so worth a gander. But for now, try whatever you have on hand!
Any difference between a BF245A and a BF245B?
DeleteBF245Bs have a considerably higher drain current rating, so they'll bias differently and not have as much gain (although, of course, that varies wildly from any one JFET to another). Should work with the trimmers, though.
DeleteSebastian RULEZ! Very cool idea, excited to build.
ReplyDeleteJust built this thing. What voltages do we want on the jfets? Also, which leg do you measure on?
ReplyDeleteYou'll want to measure the voltage on the drain legs of the two JFETs (in this case, the legs on S6 and L7). The voltages on mine measured 8.57V for Q3 and 8.41V for Q4, but I'd say use those as starting points and adjust according to what sounds good for you.
ReplyDeleteI have built this circuit 3 times and can not get it to work right. I can't figure out what I'm doing wrong.
ReplyDeleteSorry to hear that! In what way is it not working? Are you using DSG pinout JFETs? Even with the correct pinout, I've also found this circuit to be pretty fickle about which JFETs will work: sometimes they do, sometimes they don't, sometimes they will but only after some wild re-tweaking of the drain voltages.
DeleteThanks for responding. I made sure to have the correct jfets but to no avail. I checked through the circuit multiple times. I think the tweaking of the drain voltages might be where I'm dieing.
Delete