Catalinbread Sabbra Cadabra

[Alex]

Layout updated (with extra 1M resistor to ground, Presence 1&2 connected and 4n7 cap at the input instead of 47n) and verified by Travis.

[Travis]

Wow! Another fantastic looking layout. Thanks albru, you're the man!

I wonder how easily these JFETs will bias up? I don't have the MPF4393 but I'm looking for some

[Frank_NH]

Yes excellent job with the layout.

Try 2n5457s in this...I think they'll work.  No need to bias the  JFETs in the usual way as this is a mu amp configuration, but probably having matching pairs would be good (i.e. Matching Vp and Idss).

[rocket88]

One word....awesome.......just awesome.

[Travis]

Unfortunately all I've really got right now are J201

I've been wanting to stock up on 5457 but they're expensive! So far I've only found the MPF4393 on eBay at a pretty high price

Still gonna start building this!

[adapt]

really cool. i made one too and it came out bigger than this. i concede!

[Travis]

I've populated the board, but unfortunately won't have time to test this probably until tomorrow.



I saw that there were some corrections made to the schematic on fsb. There needs to be a 1M resistor to ground at the point where the 33k and 100n meet between the treble booster and first jfet. You can see I added this as a standing resistor. Also presence 1 and 2 should be connected (or just connect vol 3 to presence 2)

[Frank_NH]

Arrghh!   This always happens to me.    I finished my build last night (I used Mirsol's since he had posted it at the main site) and a correction is posted!  Well, I suppose someone needs to confirm these circuits...

Actually, this is good as my build worked but it sounded bad, and definitely something was wrong.  I used 2N5457s for the JFETs.  In any case, I'll fix up my build and see if it works better.

[Travis]

Luckily I actually just had enough time to wire it up to my test rig..

It works! I'm getting some oscillation, but that may be due to using a high gain BC550C for the treble booster and maybe the J201s.

Other than that, it pretty much sounds how I would expect. There's a lot of gain available..

After you add the 1M resistor and fix the presence control I'm 90% sure you can call this verified

[Frank_NH]

Hey Travis,

Yes - mine works too, after making the mods (which were pretty simple using Mirosol's old layout)!

I ended up using J202s for the JFETs and a 2N2222 for the BJT.  It sounds pretty good.  The Range works quite well, going from low gain trebly to higher gain bassy as it's turned up.  The gain is pretty large and it can get wooly, but it doesn't seem to get blatty or gated.  The presence also works nicely as a tone control (gradually rolling off treble as you turn it CCW).  So all in all, a big thumbs up!  

Only one issue cropped up while testing and that's some noise (hum) in the circuit.  It can be reduced by putting a buffered pedal in front (I used a Klon).  I'm sure it would also be reduced if it were boxed in a metal enclosure, but still it's annoying and other circuits haven't been as noisy.  It's possible there is cold solder joint somewhere, or perhaps a minor solder bridge so I'll check for those.

[Alex]

Thanks guys.
I've updated the layout.

[Frank_NH]

I really like your layout Albru80.  I hope I can sort out my noise issue, but if not, I may try rebuilding it using yours.  It may be just a bad soldering joint somewhere.

[Travis]

Thankyou for the layout! The layout was very nice.. Actually a pretty quick build.

If anyone else is struggling to find a deal on the MPF4393, check eBay for the PN4393. I just got 50 for $13 shipped which seems pretty good

[Travis]

Oops, I just noticed one more issue. I think the 47n cap at the input should be 4n7

[Alex]

Stupid mistake. Thanks Travis. I've updated the layout.

[motterpaul]

PN4393 - much cheaper....

actually, most of these are selling at about the same price as the MPF4393 (a little cheaper) but here is one very decent source.  Are they the same or close? I do not know personally.

http://www.ebay.com/itm/50PCS-PN4393-Encapsulation-TO-92-SINGLE-N-CHANNEL-JFET-SWITCH-/131218121239?pt=LH_DefaultDomain_0&hash=item1e8d35a217

[motterpaul]

According to this datasheet, the PN4393 appears to be a suitable alternate for MPF4393

http://www.datasheets360.com/part/detail/mpf4393/3848263618536507948

I'm just trying to help here by doing some research, but would appreciate it if more experienced people weighed in.

[Beaker]

Not used these before in this build, so not 100% sure, but they are as far as I know, identical.

The only difference is that the MPF are made by Motorola, and the PN by Texas Instruments.

Just buy a bunch and try them.

p.s. Our Bulgarian friend has them in Motorola metal can version.

[motterpaul]

Thanks - I do have 50 on order. The same shop also had the BC184 so I also got 10 of those.

Edit: if I was in Europe I would buy the others, but I imagine shipping from Eu to US would not be easy.

[Beaker]

Lots of the guys in the States buy stuff from Bulgaria. His postage is fast and reasonably priced, and he is a great guy, so don't be worried about giving him a try - he sells fantastic stuff.