walco sustainer

[ben]

Hi,
I've found this in the anonymous database
http://experimentalistsanonymous.com/diy/

What is the 3SK30 (b) ?
Is that this stuff :
http://pdf1.alldatasheet.com/datasheet- ... SK300.html

What does this effect kind of compression ?
Thanks
Have a nice day

[expanoncolin]

That is a funky variety of MOSFET- a dual gate mosfet.  They have higher gain with lower noise.  I would experiment with a variety of them, some more common part values are BF981, BF961 or 3SK88.  This circuit is a compressor/sustainer with a RIDICULOUS amount of sustain.

-Colin

[ben]

If it's ridiculous no need for a try...i'l looking for a lot of sustain !!!

[expanoncolin]

If it's ridiculous no need for a try...i'l looking for a lot of sustain !!!

By ridiculous amount of sustain I mean a LOT of sustain-this thing sustains a TON.

-Colin

[ben]

It's a false friend for frenchies !!
Where could i find those BF981, BF961 or 3SK88 ?

[expanoncolin]

I searched hard, the closest thing I could find readily available is
http://www.mouser.com/index.cfm?handler ... mber=78022

I didn't realize they were so hard to find... you may want to consider that a dual gate mosfet is just two in series, like this:



and then just use two mosfets, which are easy to find.

-Colin

[ben]

What kind of mosfet you think is good to do such a thing ??
Why does this thing gave a lot of sustain
What is an equivalent of the 2SC871 in the same schematic
Scuse me for the tons of questions...It's so simple...
Do you have one ? If so could you make a sample ??
You really have intereste me into it !!!

I hope i'm not too booring and i thank you in advance !  

[expanoncolin]

In a case where it is so hard to find datasheets for all these parts, experiment!

You could try replacing the 2SC871 and 2SC644 with 2n2222 or 2n3904, or other general purpose NPN devices.

You could try using common MOSFET's such as the BS170.

This device has so much sustain because the dual gate mosfet configuration can provide a lot of gain.  It is commonly used in radio for automatic gain control, here is a well-applied use of it for guitar!  You don't see dual gate mosfets much anywhere anymore.  I do not have one, sorry.

-Colin

[sir h c]

As Colin says just stick two in series.  The dual gate works as a cascode configuration but with only one package so that you do not have as many parasitics at the drain node of the bottom device.  For RF this is important as parasitics here will slow you down a lot, but for audio, not as important.  Odd configuration, in effect they are shutting off the bottom device unless these are depletion mode transistors, weird.  I have one of these things and they are a lot of fun.  You can still find them on the 'bay for dirt cheap.

[sidandnancy]

These have been built using run of the mill fets like a J201. That grounded leg of the 3SK is the one connected to the case. My guess is that it is shielding for this NOISY little circuit.

Here's the layout of the original:

http://users.rio.com/senorris/junk/wsusmk.gif

The 2 3M3s are parrallel, so can be replaced with one 1M5 (close enough).

[ben]

Do you mean i can substitute the first tranny with 2 j201 ?

[sidandnancy]

Do you mean i can substitute the first tranny with 2 j201 ?

Try one J201.

[ben]

hi

So i've try at last to do this stuff. There is quite a lot of sustain but also a lot off noises too as i see in lots off posts on diy stompbox forum. I use a 2n5457 as the 3SK30 and try also with a j201 (2n5457 is better...) and i use 2n5088 as the 2 2sc871 and try 2n5089 and 2n5088 as the 2sc644.

The effect is good but i can't use it there is too much noise coming with. I use metal film resistors 1%. What could i do to tame this damn white noise back ground sound. I wanted to use it with an overdrive after but the noise is too much !!!!

thanx for ideas

[expanoncolin]

Well,  it's going to amplify your signal more and more the quieter and quieter it gets...  so when you aren't playing, when it's just noise being input, it will amplify the most.  The way to solve this is to wire up an envelope follower of your guitar signal, and send it to a comparator, that decides when there is basically no input (do this with a trimpot, to get the most sustain).  When the comparator flops into no input state, have it control SOMETHING that shunts the signal to ground, or just reduces the gain a lot in general.

-Colin

[ben]

I was thinking about a thing like that but do you have schem of this ?