That amp you built with these, is that Brian's PCBs he's planning on selling?
I may be into that.

RDV

Thank you kind sir for accepting my invitation. If you could check in and give an opinion here and there about what's going on here we would be most appreciative.

Regards

RDV

Big caps I got! The ones I bought for chipamp supplies are 10,000µF @ 50v. No too expensive either, less than $4.00 USD each.

RDV

RDV

I've got a few of those ROG circuits and I tried to use them as a preamp for my LM3886 amp and the problem was headroom because of the 9v supply. If I could figure out a way to power them with bipolar 15v power I'd try one again.

RDV

Ah, I see.

RDV

What I'm thinking is just using a lot of diodes(LEDs perhaps for their higher threshholds) in series in the FB loop so we can get that softer breakup before the transistors or opamps do their harsher thing. It doesn't seem that would get too complicated. I've just got to get off my butt and start building.

RDV

I've got a preamp in my initial chipamp/guitar amp I built that is from the old Thomas/Vox(USA made) SS amps like the Super Beatle.
I like it, but I think we should come up with a very neutral sort of simple preamp that would have some guitar voiced EQ but little else so pedals would determine the sound a great deal sort of like what R.G. Keen has done with his Workhorse amps. I don't want to copy R.G.'s design or anything because as we know his is an all tube design.

I suppose some kind of limiting circuit might warm things up. The problem as I see with a SS front end in general is that it is too clean. I suppose what I'm trying to get at is I think we need something that is barely on the edge of breakup if you really lay into it, but still retains as much headroom as possible. I like teemuk's ideas about diodes but I don't think I want there to be much available distortion, perhaps not even a pre-volume. I'm just throwing out ideas here because I've not really been satisfied with things I've come up with in the past.

RDV

God, Brian must like you! Well you are a nice guy. I must've pissed him off good cause he won't even return my emails. I guess I'll just go through you to deal with him. I'd love to do some beta testing myself.

RDV

We're awfully close to being on the same page. That's cool! What do D1 & D2 do?

RDV

Quote from: teemuk on April 04, 2006, 04:42:18 PM

Quote from: RDV on April 01, 2006, 09:45:57 PM
*Here's one I did design with some improvements*.

I do not wish to sound like i'm nagging, but isn't the gain of 22 quite high for the first stage regarding the fact that it has no gain control? Allthough guitar signal is usually around 20mV - 200mV, a humbucker pickup might give an output of even 2 volts. 2 x 22 = 44! Sounds like serious distortion to me. I know the circuit's benefit lays in it's simplicity but consider this option: Lower the resistance of either 4.7k or 100k resistor and connect it in series with a suitable potentiometer or trimmer to have a gain control. With it you should be able to get rid of any unintentional preamp distortion.

I didn't too any calculations but the 100n capacitor in the gain set of the first stage seems rather small. There might be some issues in producing the full bandwidth. Then again, maybe not. As i said, i didn't do any calculations.

As more practical additions, i'd leave PCB a place for a high frequency NFB capacitor in the second stage (in order to avoid any disappointments considering oscillation), add an RF filter in front of the first stage and protect the opamp inputs from static charges with diodes. These little additions only should lift the circuit into a way more "professional" and reliable level.

The stages might also benefit from a mild diode clipping. In my opinion it's always a better option than driving the opamps to clip. (Unless you find an opamp with fast recovery or nice clipping characters of course). Connect diodes, leds or zeners in series to the feedback loop so that their voltage drop will go just below the opamp's voltage swing per rail. (Which unfortunately depends on the opamp model. 13V is a quite safe bet, 14V might be a good value too). The diodes could be made switchable for an "extra clean" output. An effect loop or reverb would be a nice addition also.

Nag away, that's what we're here for. I built this before and it did distort too much but I had the stages directly in line(feeding each other) with the tonestack afterward. That didn't work so well. I'm thinking that perhaps with the tonestack between the 2 stages perhaps the 1st stage won't really OD the 2nd stage except for extreme tone settings. I could be wrong of course. It seems to me that trimpots in both FB loops would allow fine tuning of response. I built the 1st version all bunched up on a small piece of perf so it was hard to mod. I shant make that mistake this time. I'm going to spread things out a bit.

I'm hoping for some clean headroom this time actually, the last version had none. I'm also thinking of adding gyrator stages to make certain freqs stick out, but haven't really worked on that as yet. I'd like to see you draw something up for us yourself as you seem to have good ideas.

Regards

RDV

Apparently some claim it's the best sounding chip of the whole series.

RDV

Have you tried it with a strong(1 amp or better) supply? That'll get you more headroom.

RDV

*Here's one I did design with some improvements*. I'll build this one tomorrow perhaps.

RDV

This one wouldn't really qualify as "my design" either. I have designed one though(or two). I'll try to clean them up and present them later.

RDV