IIC+ mod to Quad?

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schnarf

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I've heard the first channel of the Quad is based upon the IIC. Does anybody know the differences between the IIC and IIC+ to enough of an extent that it would be possible to mod my Quad to IIC+?
 
Funny that you ask :) This idea has popped in and out of my mind for quite some time now since I own a Studio (based on the IIC preamp) and a Quad. Theoretically speaking, it is possible because the quad ch1 is pretty much a IIC preamp section that would require a few tweaks overall including the lead circuit. Even ch2 could be modded since it's also pretty close.

I actually printed out the schematics for my quad and some C+ schematics to compare and there's only a few differences which "should" be easy to change. Now I'm only talking on a very basic level, swapping out components so they match on paper. How would it sound? I dunno :D

I DO know that snowman had his studio modded to C+ specs so it can be done. Bendinelli supposedly really digs the Quads too :)
 
I'm thinking about doing it. I was considering doing what you said you did with the schematics, and maybe I will do that if it's as simple as you say. I'll check it out. I'm also thinking about adding just a tad more available gain to the ch1 lead.
 
Yeah, just took a look and tried to trace out what I'd need to do. Basically adding a few capacitors and resistors to the lead stage, and possibly changing a few thought the values are pretty close so it'd probably be unnecessary. Also the lead master/master volume circuit after V12B needs to be changed significantly.
 
Do you all think the differences between IIC and IIC+ are more relevant in the preamp or in the poweramp section?
 
I think they're equally important but having the preamp section would probably be better than just having the power section you know? I mean look at JP's current rig where he's using a C+ preamp, external graphic EQ, and a recto poweramp and he's still getting great tones :)
 
I just drew the schematic for the Quad channel 1 lead circuit with IIC+ modifications. There are still other modifications around the lead drive/master volume section which I'll draw up sometime soon. Added components are in red, components whose values are changed are in blue, and components whose values do differ but not significantly are in green (I don't think it's really worth changing out the green ones).

Edit: I screwed up the schematic. Here's how it should look:
 
rickgk said:
Where can i find pics of the JP rig your referring to?
jp_i3.jpg

jp_i4.jpg

jp_i5.jpg
 
schnarf said:
I just drew the schematic for the Quad channel 1 lead circuit with IIC+ modifications. There are still other modifications around the lead drive/master volume section which I'll draw up sometime soon. Added components are in red, components whose values are changed are in blue, and components whose values do differ but not significantly are in green (I don't think it's really worth changing out the green ones).


Which C+ schematic did you use? I don't recall the two additional resistors on the input :)
 
It was posted somewhere on here. Here it is:



Also I realized I screwed up the schematic a little bit. Here's how it should look:

 
Have ya tried anything yet? I got all the way to the point of pulling the quad out of my setup and removing the cover again...then stopped dead in my tracks. Mesa and their crazy super nice tight wiring :p
 
I haven't tried anything. I might try this summer. Agreed on the point of the wiring being hard. Honestly, I'm not dissatisfied with the way my channel 1 sounds right now. What real differences are there?
 
You know, personally I like the L1 on teh quad, but I think the L2 is too fuzzy. Is it possible to mod the L2 to C+ specs?
 
Aart said:
Is it possible to mod the L2 to C+ specs?
I think that doing so you will have L2 sounding really close to L1... could be great or redundant, it depens on the use you make of your preamp...
 
I already posted my schematic with the changes to the lead circuit, I just got a chance to go over the rest. It looks like there's not much. I can't find where the pull deep circuitry is on the Quad schematic up at tubefreak.com. My guess is it's V19B, and the switch wasn't drawn in. The topology's a little difference since the master volume is before that tube on the Quad, where it's after it on the IIC+, but it's similar. Once I figure that part out, I'll note the necessary changes there, but my feeling is that the majority of the difference in tone comes from the change to the lead circuit.

The two changes to the Channel 1 circuit on the Quad, aside from the modifications to the lead circuit, is to take out the 20uf capacitor to ground immediately at the input (might not be necessary, it filters out some highs), and to modify a resistor after the lead circuit. If you look at "from lead output", just to the left and down there's a 470k resistor in parallel with a 47p capacitor. Change the 470k resistor to 680k.

I'm sort of curious about this (I sent boogiebabies a PM but no response), and I think I'm going to try giving Mike B. a call on Monday to see what he thinks.
 
Okay, I rechecked my modifications to the lead circuit, and they look right. The hardest part of the modification will probably be that little circuit that's completely added (the part in red on the left of my schematic starting with the .047uf cap attached to the plate of the second (leftmost) tube, then the two resistor/capacitor networks attached to it). I'm not sure what the best way to put that in is. I'll get a chance to take a look at the circuit board layout of my Quad in about a week, and I'll try to figure that out. Input?
 
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