How does the SYRUPP work? It seems too simple!

[Caferacernoc]

I know this is old business for a lot of vets here but........

Tim's SYRUPP:

http://folkurban.com/Site/SyRuPP-711.html

This circuit just seems to be missing parts compared to every other jfet mu amp I've looked at. How does it compare to the more complex mini-booster?
Thanks.

[Caferacernoc]

I guess the Duende jfet is similar in having a low parts count:

http://folkurban.com/Site/DuendeJFET-699.html

Wow that's minimal!

[squidsquad]

It's a fun little build.   Dialing in the trimmer to bias both JFETs & BAM....a big loud boost appears.
Someone else could explain how it works...all I know is it was fun & easy...so I made two of em...hehe.

[Caferacernoc]

Have you run one into the other? It would be the simplest cascaded mini-booster ever!

[squidsquad]

I didn't....because I've found you usually need add extra parts....like high pass filtering to the control bottom end from getting too muddy, and low pass for preventing hiss from being over-amplified.  But have fun...try anyway...experiment...learn!

[Caferacernoc]

I plan to experiment. I realize it's a building block. I'm just amazed that there are essentially no parts on the "upper" jfet. Unlike a regular mini-booster that has like two 10k resistors, a capaciter, and another resistor connected to it's gate.
And thanks!

[earthtonesaudio]

I plan to experiment. I realize it's a building block. I'm just amazed that there are essentially no parts on the "upper" jfet. Unlike a regular mini-booster that has like two 10k resistors, a capaciter, and another resistor connected to it's gate.
And thanks!

Building blocks, indeed! 

In terms of getting a deeper understanding of the circuit:

The "top" fet, plus the series resistance set by the 100K trimpot, act as a very simple current regulator.  This decreases drain current to the "bottom" fet, which has the effect of increasing the gain of the bottom fet.  The top fet/current regulator isn't that sensitive to the resistance between the gate and source, so the trimpot is mostly to set the bias on the bottom fet, and it's just convenient to use one part there instead of two.

Jack Orman's minibooster: http://www.muzique.com/amz/mini.htm#history
This one has the top fet acting like a source follower for the bottom fet.  Hence the 1M voltage-divider bias.

Also of note is the fact that Tim's circuit uses the input level control (2M pot) as voltage divider bias to the bottom fet, so there is also less of a need for pull-down resistors to ground to eliminate switching pops, and Jack's design incorporates RF filtering, 1M pulldown on the input, and I'm not sure what the voltage divider and cap on the top fet are used for, but it sounds good so I just leave it alone.

What's really interesting is, if you read the pdf of the vacuum tube circuit patent, it is almost identical to the Syrupp, except replace the tubes with fets.  Neat!


Hope this helps break this thing into nice bite-sized fragments.  Good luck!
-Alex

[Caferacernoc]

"Hope this helps break this thing into nice bite-sized fragments.  Good luck!
-Alex"

Very much. Thank you Alex. I'm a single ended guy and I don't know anything about "push/pull" circuits. The Syrupp is push/pull, right? ;-)

[JDoyle]

Well it's a lot simpler than a minibooster because it ISN'T a minibooster.

The top JFET, as has been mentioned acts as a constant current source which to the bottom JFET resembles a high resistance. Remember that if you attach the gate to the source and the drain to a positive voltage, then the Idss value of the particular JFET is constantly able to pass through the drain source channel. But the amount of current passing through the top JFET depends on two things: the voltage between the gate and the source, and the voltage between the drain and the source. So the trim sets the relative Vgs and the signal swing changes the Vds causing the 'constant' current to actually fluctuate with the input signal.

The output is taken from the source of the top FET allowing for a lower output imedence then would be seen at the drain of the bottom JFET.

[earthtonesaudio]

Well it's a lot simpler than a minibooster because it ISN'T a minibooster.

The top JFET, as has been mentioned acts as a constant current source which to the bottom JFET resembles a high resistance. Remember that if you attach the gate to the source and the drain to a positive voltage, then the Idss value of the particular JFET is constantly able to pass through the drain source channel. But the amount of current passing through the top JFET depends on two things: the voltage between the gate and the source, and the voltage between the drain and the source. So the trim sets the relative Vgs and the signal swing changes the Vds causing the 'constant' current to actually fluctuate with the input signal.

The output is taken from the source of the top FET allowing for a lower output imedence then would be seen at the drain of the bottom JFET.

This helped me a lot!  I'm somewhat new to effects building myself, but I learn faster when I try to help explain it to someone.  I'm just glad there are people on here like JDoyle to help keep all the facts straight.  Thanks!