AMT Electronics - SS-20  [schematic]

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bluestomp
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Post by bluestomp »

This pedal use one 12AX7 tube and about 3 JFET which have 300VDC like describe in this link http://dallashodgson.info/reviews/AMTSS ... iagram.gif

any one can give suggestion what type of JFET they used?

thanks
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AMT Electronics - SS-20 block diagram
AMT Electronics - SS-20 block diagram

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Tomby
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Post by Tomby »

If this may help....
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800-DSC_0144.JPG
800-DSC_0145.JPG
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Ihunda
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Post by Ihunda »

Bumping an old thread, any news on what type of FET's are being used?
I am have one and it sounds very good and is very dynamic, my only concern is the tone stack, I usually keep it all the way up and use my own circuit for tones.
I can take a look inside if other people are still interested!

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HomerChel
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Post by HomerChel »

This is not just jfet. This is some circuit, named "jfet-tk". I will try to draw the input stage today.
Sorry for my English.

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Post by Ice-9 »

Ihunda wrote:Bumping an old thread, any news on what type of FET's are being used?
I am have one and it sounds very good and is very dynamic, my only concern is the tone stack, I usually keep it all the way up and use my own circuit for tones.
I can take a look inside if other people are still interested!
More than likely 2sk208 (JR) in the same topology they use in there othere valve emulating pedals (jfet + shottky diode) See the AMT S1 legend thread for examples of how the schematics go.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by HomerChel »

I do not know what these parts. I think 1st is diode.
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First Stage AMT ss-20
First Stage AMT ss-20
Sorry for my English.

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Post by bajaman »

looks like the Peavey transtube input :wink:
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Post by Ice-9 »

bajaman wrote:looks like the Peavey transtube input :wink:
Which i believe is patented ?
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by Ice-9 »

KMG wrote:Nothing close to Peavey patent
http://milas.spb.ru/~kmg/files/literature/US5647004.pdf
Thanks for that info, I already drew out the little circuit snippet and could see it was different anyway. I have / had a few AMT pedals and think the stuff there doing is great. Would love to see a bit more of the SS-20 ans I would expect it to follow more or less in line with the Legend series topology but with the obvious addition of the valve bits.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

No silicon heaven ? preposterous ! Where would all the calculators go ?

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Post by oneleg »

The ic mark "EY1 0619" is what?

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Post by GAMMOTH »

Hi,

I would really enjoy more if this pedal had a "post-boost" option rather than two dirty channels. Does anyone see possible to turn the crunch channel as the LEAD channel and the actual lead switch and pot be used to turn on a boost for solos?

I believe that this would require to actually merge a booster plate like the MXR Microamp there...

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Post by cris_muschilensis »

sorry to necrobump this post but i have a doubt. I bought the "V2.0" of the SS20 and also the SS30 "Bulava" as a backup. Turns out V2 and Bulava has a control output and find this interesting but, counterintuitive. It shouldn´t be control in? so you can control it from outside like a remote switch? I dont understant how it works, manual isn't very clear and it's been a long while since i've made mods or build pedals. If isn't the way i would like it to work, how could i mod it to make it "control in"? I just purchased a Boss MS-3 and would be awesome to be able to control the AMT through the Boss.

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Post by Manfred »

I came across this old post and I was interested in this circuit.
I redrew the circuit, replacing the component representation of the semiconductors with the circuit symbols.
I did a simulation with a similar Schottky diode, the MPSA18 BJT and various replacements for the MMBF5459 JFET.
Depending on the type of JFET used, the result was a stage gain in the range of about 60-70.
AMT JFET-TK.jpg
AMT JFET-TK.jpg (22.86 KiB) Viewed 3993 times
Last edited by Manfred on 24 Jan 2022, 22:07, edited 1 time in total.

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Post by bmxguitarsbmx »

Nice Manfred!
That looks like a cascode. The resistor from the gate of the BJT to the Source of the Jfet could probably be used to adjust the bias. Additionally, the 51k is also interesting that it would put a signal on the base of the transistor in phase with the normal operation of the cascode. Something to ponder there.

R5 put to 1M to make it a little easier to drive.

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Post by Manfred »

R5 put to 1M to make it a little easier to drive.
Thanks for the hint.
That was my fault I transferred the value wrong in the schematic, 1Megohm is the correct value.
I have fixed the circuit above.

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Post by J0K3RX »

Maybe these will come in handy..?
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SS20_2B_assy_mod18_01_13.pdf
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Post by Manfred »

J0K3RX wrote: 25 Jan 2022, 20:32 Maybe these will come in handy..?
Thank you very useful for me.

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Post by bmxguitarsbmx »

AMT does a lot of interesting things. I like that 3 jFet amplifier/buffer with the constant current source output circuit using the 2sk208's.

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