no FETs

[lightningfingers]

is there a modded orange squeezer i can build that doesnt have any FETs in it?
i just cant get them out here

[gez]

ESR (in 'the frozen north') sell four different N-channel FETs, BF244C, BF245B, 2N3819 & 2N5245.

If you compare data sheets I'm sure at least ONE will be suitable in that circuit.

www.esr.co.uk

Cricklewood Electronics probably sell the exact FETs used in the Squeezer, but you'll pay through the nose for them and, if they don't have them, they might try and palm you off with unsuitable replacements (the sales staff haven't got a bloody clue!)

[lightningfingers]

(the sales staff haven't got a bloody clue!)

i know ive had experience with them before.....and how convenient that they dont refund!

thanks for the help

[TheBigMan]

i just bought a bunch of mpf102s on ebay.  Before that I was going to order from smallbear for some parts I can't get in the UK (Fife to be precise).  I haven't found a source for germanium diodes in the UK either, but smallbear are great to deal with and very reasonable for international shipping.

[Mark Hammer]

Consider using an LED/LDR combo instead of FETs, if possible.  You may have to up the gain of the op-amp a bit, but it should work.

The entire subcircuit involving the FETs simply creates an attenuator on the input of the opamp.  The 82k resistor forms one leg of this imaginary input-volume pot, and the pair of fets and associated components forms the other leg.  

Run an LDR from the junction of the 82k resitor and .047uf cap to ground (replacing  the 2 FETs, 2 caps, 2 resistors and trimpot that normally go there).  Replace the 470k resistor from diode/cap/resistor junction in the envelope follower with a 1k resistor and an LED, and that should be enough to do it.

The existing circuit uses component values that will produce a certain amount of input attenuation for a certain input level.  As such, depending on the LDR you end up using, you may have to a) reduce the 82k resistor a bit, or b) run a 500k-1meg resistor in parallel with the LDR, or c) stick a variable resistance in series with the LDR.

What you want to end up with is enough of a change in resistance to ground that there is audible gain reduction (produced by attenuating the input signal) without the attenuation effectively turning the input signal off.  So, for example, if your LED and LDR choice illuminated the LDR enough to drop the resistance to ground down to, say 5k or less, that would likely produce too much attenuation, so you'd want to stick some additional resistance in series.  If the amount of resistance change was great, but still not enough to produce usable attenuation (e.g., an LDR that went from 10meg to 200k), you'd want to stick some resistance in parallel to produce a more effective range.  With a 680k resistor in parallel with our hypothetical LDR, the resistance change would now go from about 637k to  about 155k.  In conjunction with the 82k resistor, this would produce modest attenuation possibilities.

[Ge_Whiz]

ESR used to stock OA47/OA90/OA91/OA95 Ge diodes. Otherwise, you can get them from CPC http://www.cpc.co.uk or try ringing Birketts of Lincoln http://www.zyra.org.uk/birkett.htm and ask them. A couple of years ago they were selling CG84/CG85 types at 100 for £1. They will work fine.

Heck, in an emergency you can still get OA90/91 and 2N3819 devices from Maplin...

[lightningfingers]

Consider using an LED/LDR combo instead of FETs,

how exactly would i do that?
im guessing it wouldnt be a straight sub

[Peter Snowberg]

See the recent "LA-2A as a pedal" thread for Johan's design on Charlie's site.

Take care,
-Peter

[bwanasonic]

I've dealt with Olaf at Banzai Effects a number of times from here in the states, so I imagine the UK would not present  a problem. He has Ge diodes and transistors among other things.

http://www.banzaieffects.com/europe/partshop.htm

Kerry M

[TheBigMan]

Maplin stock some n-FETs.  2N3819 and BF245C in TO92 cases.  Haven't checked the datasheets but one of them will probably do.

[lightningfingers]

mmkay, almost got it, just one more thing

Replace the 470k resistor from diode/cap/resistor junction in the envelope follower with a 1k resistor and an LED, and that should be enough to do it.

does the 1k got to the +ve end of the LED or the -ve, and where does the end not connected to the 1k go?

[lightningfingers]

oh and another thing, will a regular 741-type (or a better single opamp) work instead of a half a 4558?

[smoguzbenjamin]

Sure, the 4558 is basically two 741s in a DIP. But I say use the dual opamp, then you can try out different opamps in the socket etc. You can do that with a signle opamp too though. Hmmmm there must be a reason for using a dual instead of a single opamp... :? I donno.

[gez]

Hmmmm there must be a reason for using a dual instead of a single opamp... :? I donno.

Layout? :wink:

[lightningfingers]

or maybe Mr Armstrong used all his single opamps :wink:

[TheBigMan]

Buffer the non-effected stage through the second half?