Orange CR120/CR60 circuit board images / schematic help

[camjenkins]

Evidently, I'm a masochist because I've decided to try and make a schematic of the CR120/CR60 preamp just by looking at gutshots of one. I've already gotten the clean channel preamp pretty much figured out, but the dirty channel is proving more difficult. As far as I can tell, the CR120/60 is essentially a solid-state recreation of the Rockerverb Mk 1/3. It doesn't use any clipping diodes, nor does it involve any jfets. It's just gnarly old TL072 distortion taking the place of the tube distortion. I'll post what I have so far, and I'll let you guys make suggestions if you have any.

The gutshots are here: https://www.ultimate-guitar.com/foru....php?t=1803806

Here's what I have:

[nevetslab]

Are you going to build one, once you've got the circuit figured out? I'd suggest socketing the IC's, so you can try later generation op amps. I'd be curious to hear how the TLE2072 BiFET Op Amps sound when severely overdriven, as you would have in the Dirty channel. TL072 BiFET's when driven hard into clip tend to almost do a frequency doubling of the drive signal, very asymmetrical, which I believe isn't the case with the upgraded TLE2072's. And could try lots of other later generation IC's as well.

[camjenkins]

I just want to figure it out so that I can possibly help someone else in the future and so that my curiosity is satiated. I do, however, think it would be interesting to hear what the amp would sound like with different op amps.

[nevetslab]

Quite an admirable project you've taken on. There's a lot of us here with such passion, so nothing crazy about that. Out of curiosity, your comment about the circuit not involving any jfets. Was that in reference to the Orange Rockerverb Mk 1/3? I assume so, seeing as there are the 2SK30A junction FETs in the front end of the two schematics you're creating.

[camjenkins]

What I meant is that JFets aren't used for creating distortion, unlike what you'll find in some boutique pedals. For me, if JFets are just being used as buffers, I often forget about them.

[camjenkins]

Two weeks later, I have figured out the preamp. I honestly don't think I'll try to make a schematic of the power amp or reverb, since they're either (a) surface mount and not visible in the gutshots or (b) entirely uninteresting to me and have no real effect on the sound of the amplifier.

Here you go: Orange CR120H Preamp.pdf

[Zozobra]

Great stuff. I've been interested in these recently, although admittedly mostly in the power amp which from a casual uneducated guess just looks to be a bridges TDA7294 type thing.

[camjenkins]

Yes, it is a bridged TDA7294 power amp. If you'd like, I can try to trace the circuit for it.

[Zozobra]

Yes, it is a bridged TDA7294 power amp. If you'd like, I can try to trace the circuit for it.

Thanks for the offer. I guess if you could just compare it to the spec sheet schematic quickly to see if it's the same that's be enough for me. I doubt they've reinvented the wheel.

[camjenkins]

From what I can tell, the basic topology of the power amp circuit appears to be the same as on page 13 of the ST spec sheet, but with a few changes to some of the capacitor values and a voltage divider network at the input.

[Zozobra]

Thanks for looking Good to know it's pretty much standard. It's a shame you're working from gut shots as knowing the voltages would be useful. Given the spec sheet and rated output I'd guess it's in the region of +/-25V rails though.

[76jimmy]

Very cool amp. Have one on my bench. It's a friend of mine's. Been cutting out on him while playing at live levels in a doom metal band. Opened it up didn't see any obvious failures. I lifted a few components to test them all checked out good. May a thermal protection is kicking in? I love the sound of the amp. The power section is meh. Kinda want to make my own hybrid out of one.
Played it for awhile after I had it apart seems ok now. Have to really put it to the test at a rehearsal before I'd send him out live with it again.

[MstrB]

76jimmy, any idea as to what was causing the cut outs? I have one coming in with similar issues. "Turned into a transistor radio, then just got super quiet." sounds typical of SS and modeling amp issues but was wondering if there is a common source for this malfunction in this circuit.. Like to save clients as much time as possible.