freestompboxes.org

even though i put this up in the Honey Bee thread, i had to post it again in the amp section because it's so freakin cool. so far i've tried out the dual gang gain control on the input, and it sounds fantastic. super smooth. lots of other fun stuff to try in here as well!

and here the preamp-schematic from the actual version, sx300

regards, kusi

I like the (partly not assembled) polarized ceramic caps in the preamp.

analogguru

I have a real one (preamp) and I suppose it wasn't horrible but didn't seem that great in particular (maybe was using it not in the best way?).

dai h. wrote:I have a real one (preamp) and I suppose it wasn't horrible but didn't seem that great in particular (maybe was using it not in the best way?).

it could very well sound like shit. i've never heard one myself. i just thought that there was some novel design ideas implemented and that it was rather interesting.

thanks kusi for the real thing! and AG, what those polarized ceramics are about, you've got me. can't say i've ever seen one.

I can't download the pdf schematic files...

When I try I get the message "You are not authorized to download this file" and when I look at the control panel it says I'm logged out, and this AFTER I have for sure logged into the site.

What's Up?

fwiw, file works for me(just tried it). Try clearing your cache and cookies, and re-logging in? (That seems to work for that sort of problem.)

RnFR wrote:

dai h. wrote:I have a real one (preamp) and I suppose it wasn't horrible but didn't seem that great in particular (maybe was using it not in the best way?).

it could very well sound like shit. i've never heard one myself. i just thought that there was some novel design ideas implemented and that it was rather interesting.

thanks kusi for the real thing! and AG, what those polarized ceramics are about, you've got me. can't say i've ever seen one.

if memory serves, I bought mine based on the advertising and literature at the time (mid-late 80s??). It did sound interesting (compared to pedals and other things I had or heard) but I don't think I ever grew to love it. The spring reverb and channel switching was kind of nifty though.

Wow. What's going on in that O.D. channel?
I can't quite follow it.
Definitely different.

there are definitely some rather complex clipping arrangements going on there. I would love to hear someone give a proper explanation.

RnFR wrote:there are definitely some rather complex clipping arrangements going on there. I would love to hear someone give a proper explanation.

Hi There,

Not all the circuits using diodes across the feedback loop of an op amp are clippers...

According to the drawing at "sxpreamp.pdf", the first clipping stage is made around A2.B, and looks to be a soft distortion due the use of LED´s wired each one in series with a resistor.

After this we can see a hard clipping instance by means of D3, but a level of some volts since it´s another LED.

The next stage comprising A3.A uses common silicon diodes and combine soft clipping (D107) and a hard one (D108)

So... what the heck is the arrangement around A2.A ?

That's a precision half wave rectifier that uses the operational amplifier to cancel the forward voltage diode drop:



Looks as if the envelope of the signal amplitude were used to modulate the bias point of both aforementioned opamps.

In this way the distortion changes according to the way the strings are pushed: if more intense you play, more assymetrical the clipping will be.

Cheers,
Jose