More Flipster praise (with my biasing info)

[Dave_B]

I completed the board yesterday and I've spent several hours with it already.  This thing is everything everyone says it is.  If you have a bass, IMO it should be considered a must build. 

For mine, I modified Pablo De Luca's excellent board, adding pads for resistors on either side of the bias trimmers.  This helped in biasing, but it screwed up my chances of mounting the board in the slots of a 125 enclosure.   

Regarding biasing I used 25k single-turn Bourns trimmers (not really recommended) and biased stage-by-stage as I built it.  Hopefully the table below makes sense and helps someone.

| FET	| Connected to +9v	| Bias Trimmer	| Connected to FET	|
| Q1: J201	| 33k	| 25k trimmer	| Jumper	|
| Q2: J201	| 18k	| 25k trimmer	| Jumper	|
| Q3: J201	| Jumper	| 25k trimmer	| Jumper	|
| Q4: MPF102	| 200ohm	| 25k trimmer	| 150ohm	|

As you can see, the values on Q4 are a little squirrelly.  I'm not an EE, so don't ask me to explain why the Q4 resistors actually made a difference.      If you do something similar, you will most likely have different values.  To get the values, I turned the bias pot fully clockwise, soldered a jumper across the FET-side pads, then touched different resistors on the "+9v" pads until I had about +6v on the drain.  That really helped when dialing in the trimmers, but Q4 is still touchy. 

Having said all that, if I was to do this over again, I'd use multi-turn pots as others have recommended, and leave off the FET-side pads.  Here's what that looks like. 



This lets you keep the board the same size as Pablo's original.

Thoughts, criticisms, and questions are welcome!   

[MartyMart]

Cool project isn't it ?
I remember using 2 x J201's and 2x MPF102's for this, gave a little more headroom
I think that I also used 50k trimpots, quite nice ones that were a couple of bucks a piece !
All my drains were around 6v and this sounded best ( ear adjustment !! )
It makes a superb recording front end through a suitable spkr sim

MM.

[vanessa]

I've thought about taking this project a little farther and making it somewhat on par with the Tech 21 Bass DI. Adding an parallel XLR for live DI and a unaffected buffered out for basic DI (amps or boards). Also adding some sort of cab sim. I just can't find the time at the moment...

[Dave_B]

I just noticed I should have been more clear on the diagram.  The red boxes are the extra bias resistors.  This version is the same size as Pablo's and it will fit in the slots of a 125, unlike mine. 

I'll have to try the higher bias values, Marty.  I really like it stock, but a lot of people seem to prefer it with the extra bias voltage.  I spent about an hour getting everything to 4.5 volts, so I'm a little reluctant.     I like the idea of the balanced out, too.  It would be one less box to lose track of when I cart my bass gear around.  For the time being I'm boxing this one up in a 125 stompbox with a battery and stompswitch, so I won't have room for an XLR, but I may rethink that if I find I have it turned on all the time.  Thanks for that, Vanessa.

[vanessa]

I like the idea of the balanced out, too.  It would be one less box to lose track of when I cart my bass gear around.  For the time being I'm boxing this one up in a 125 stompbox with a battery and stompswitch, so I won't have room for an XLR, but I may rethink that if I find I have it turned on all the time.  Thanks for that, Vanessa.

The Tech 21 Bass DI uses a Hammond 1590BB type enclosure. I'm positive we could squeeze a Flipster and an amp sim into a 1590BB with an XLR, an 1/4" output and 1/4" unaffected. Lend me your ears...