JFET - MOSFET High Gain Preamp?

[WGTP]

The speaker sim appears to use N and P channel Jfets???

[J0K3RX]

as a note:

i was reading that the B1 should be used through a send return, correct?...so it uses the power amp only i guess, and not the amps pre-amp/eq!...

makes sense to me..  i only use a clean channel of my marshall anyway...but i'd be interested to try that!...just for kicks..

have you tred yours that way?

Yeah, I have tried it straight into the fx return on a 5150 combo and I also have an old B.K. Butler - MosValve poweramp. Sounds killer on both. I have also tried it through the input of a small practice amp and sound pretty good but not as good as straight into a power amp... I think they say not to use it into the input jack of an amp because you would be coloring the true tone from the preamp pedal.. For best results should be used as a preamp rather than a distortion pedal... I run it mostly direct using cab impulses, to me that sounds the best! You know the Spitfire sounds killer as a preamp as well!? The new Legend 2 pedals have 3 outputs "CAB SIM-PREAMP-DRIVE" so, you can run them into the front of your amp using the Drive output.

May have something to do with the final stage which was left off the schematic that I posted earlier. This is the full schematic of the B1 minus the cab sim..


Not sure why it was left off of the final schematic but I am sure it would work also.

[J0K3RX]

The speaker sim appears to use N and P channel Jfets???

That's what I am thinking... On all of the AMT Legend schematics they have all three listed as 2SK208R's which I believe can be substituted with J201's. I think one or more may not be 2SK208R's?

This is the cab sim from the P1 schematic.. they are all the same on all of the Legend pedals.

[J0K3RX]

ok here is a real crap sound clip of the B1... A little too much lows, maybe a going in the red/clipping a little and my playing is........CRAP!!! I just sat down and played the first thing that came outa my fingers, sorry   But you can get an idea of the tone. I am still messing with the tone stack, not completely happy with it but I love the pedal!!!

http://dl.dropbox.com/u/11178619/B1%20TEST22.mp3

[fretzburner]

Jok3rx the first schematic posted have different values(resistors/caps) compared to the final schematic.Should it make big difference in sound?

[J0K3RX]

Jok3rx the first schematic posted have different values(resistors/caps) compared to the final schematic.Should it make big difference in sound?

Well those are not my schematics.. Another guy in another forum posted them and they were a progression of what he thought sounded best to his ears. Actually, the first schematic was the latest one, the other was the direct exact schematic from the traced out B1 pedal so it would be the most accurate but since the J201's are being used in place of the 2SK208R's it won't really work right.  I have have tried them all and they really don't sound any different as far as I can tell. The main thing is the trim pot for the 12k resistors coming of the drain of the JFET's. Since the AMT pedals use different JFET's the J201's are the closest match but not quite the same spec so the resistors (trim pots) have to be set by measuring the voltages or by ear like I did. After you get it set the way you like it you can measure the resistance of the pot and replace it with a regular 1/4w resistor. So to answer your question, no they really sound pretty much the same but like I said you have to use trim pots for the drain resistor... hope that makes sense?

You might want to try deadastronaut's layout... it looks good to me!

[fretzburner]

Thanks Jok3rx your answer is very helpful and Deadastronaut's layout is already in my DIY creator planning to add that last transistor after the volume control.Don't really know exactly what this last stage for,just want to try.Maybe for direct to PA or the other way direct to amp front end?

[fretzburner]

Deadastronaut's layout correction 47nf to MID should be after 24k from Q4 not from Q4.

[deadastronaut]

oops!.

[zambo]

JOKERX I love that clip. pedal sounds good. playing sounds good too. Been trying to understand solid state stuff more these days. May have to build this! Thanks for sharing!

[J0K3RX]

Here's a layout I did... let me know if you see anything wrong with it? I am not good at making board layouts so let me have it!
There are some extra pads for whatever reasons... some extra pads for optional diode configuration and a secondary output that bypasses the last stage like in the other schematic where the last stage is missing. Extra pads under the trim pots for different kinds of trim pots etc...



Here is the board transfer.
http://dl.dropbox.com/u/11178619/B1%20Transfer.png

I went by this schematic
http://dl.dropbox.com/u/11178619/AMT%20B1%20Schematic.png

[fretzburner]

Jok3rx, R3 is supposed to be 330ohms as per final schematic.

[J0K3RX]

Jok3rx, R3 is supposed to be 330ohms as per final schematic.

Ah, good one! That's what copy and paste gets me...  

Changed it, thanks!

[J0K3RX]

Here's the new layout. Looks pretty much like the last layout but I have made numerous corrections and is now verified!

I will upload the new board transfer if anybody wants it.

Sounds amazingly good!

http://dl.dropbox.com/u/11178619/B1%20v2.PNG

DON'T USE THE OLD LAYOUT.

[deadastronaut]

@jim, cool, sounds well mean.. ., can you do a clip standard tuning though!...just want to get an idea of the riffin in standard E...cheers bud!.

hows ya tonestack coming on that?

you need to add pads for r13/r14/switch..

have you dabbled with the cab sim yet?....that looks interesting, especially the 'T' wah type section, i'd be interested to see what a 10k/20k pot on that instead of the 6.2k would do...hmmmm...
may need trimmers on that too..



@fretzburner:  isn't that last fet for lifting the level back up after  the tone stack / buffer  ?....thats what i thought...i could be wrong though, as i am often..

[J0K3RX]

Created new post called "AMT B1 - S1 clone"