IIC+ mod to Quad?

Triaxis, Quad Preamp, Stereo Power series, Recto Preamp

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schnarf
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Post by schnarf » Fri Apr 27, 2007 1:02 am

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?

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Aart
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Post by Aart » Sat Apr 28, 2007 4:35 am

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?

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ytse_jam
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Post by ytse_jam » Sat Apr 28, 2007 6:44 am

Aart wrote: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...

MESA/Boogie Studio Preamp
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schnarf
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Post by schnarf » Sat May 05, 2007 9:01 pm

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.

schnarf
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Post by schnarf » Sun May 06, 2007 5:33 pm

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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Post by schnarf » Tue May 08, 2007 6:11 pm

Just talked to Mike B. He says that the IIC+ and IIC are pretty different in circuitry, and when I asked him about modifying the Quad to be closer to IIC+ schematics, he told me that that Quad is basically a IIC+ and not much like a IIC circuit. I made sure I was understanding him right -- the Quad channel 1 is basically a IIC+ and not a IIC.

He did point out a few things that could make the tone a little different. Obviously there are the differences in the circuitry that I've found, but they really are pretty negligable except for that section after the lead. Another point he made is that the record out circuit loads the preamp a little and could darken it. The solution to that is to either disconnect the record out circuit, or to use the effects send direct to power amp. He said another big thing is the power amp. He noted that the later IIb series and most of the IIIs have basically the same power amp. He also said a 50/50 was very close, which I have.

He made the point that he's taken IIIs, which have a very similar layout, and he's modded them to IIC+, so that the circuit is exactly the same, and the output looks the same on the oscilloscope, and it sounds the same, but it doesn't feel the same to the player.

So basically this mod is probably pretty pointless. Everywhere else I've seen has said that the Quad is based on the IIC, but apparently it's actually based on the IIC+. If I could find a schematic of the IIC I could verify this, but frankly I trust Mike B. on this.

The interesting thing is, I was looking to tame a bit of the high end on my Quad, and he told me that if anything the Quad is a little darker than the IIC+. Anyway, he was very informative. If I get curious, I might try to modify the circuit to make it identical to the IIC+, but it seems like it might be a lot of work for little return.

triodal
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Post by triodal » Tue May 08, 2007 8:01 pm

i thought the studio pre was close to IIC+?

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Post by schnarf » Tue May 08, 2007 9:16 pm

I had heard that both the Quad and Studio were the IIC and not the IIC+.

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Post by 4nkam » Wed May 09, 2007 9:33 am

Very interesting man :) Yeah the only thing I ever did on mine was clip out that input cap too, haha. Even the Mesa manual for the quad says it is based on the IIC:
To achieve greater tonal flexibility and footswitchable freedom, the Quad is separated into two
channels sharing one common input. Each channel offers two modes and a pre-assignable 5 band
graphic equalizer. Channel 1 is very similar to the Mark IIC, while Channel 2 is very much like the
Mark III.
These were the premier guitar amps for the last five years, winning the praise of such
guitar giants as Steve Lukather, Lee Ritenour, Michael Landau, Stevie Ray Vaughn, and many
more. We found that many of these players used more than one amp and switched between them
for different sounds. A great idea but very heavy and bulky to move requiring custom made
switching systems. Thus, the need for the Quad. Two incredibly versatile amps in one taking up a
So even with the differences that *are* there, he says it's pretty much the same huh? Interesting indeed :) The C+ed studio that sold on ebay also had the recording outs disconnected as part of the mod.

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Post by 4nkam » Wed May 09, 2007 9:42 am

Something also interesting, awhile back, electric_boogieloo on the JP board had his quad converted to C+ on ch1 and blue stripe on ch2.

schnarf
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Post by schnarf » Wed May 09, 2007 12:49 pm

Yeah. He did say that there were a few differences, mostly in some of the pf caps, but didn't have the schematic in front of him. He was pretty clear about the point that the IIC+ and IIC are very different circuits and the Quad is basically the IIC+. The changes do seem pretty minimal. I guess the point of the "IIC+ mod" is just to bring it to be exactly the same as the IIC+ circuit, to hopefully make it have the same mojo. For me I don't think it's worth it.

Did taking out that input cap do anything noticable?

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Post by 4nkam » Wed May 09, 2007 12:59 pm

It wasn't very drastic but to me it did sound a bit more open, not as closed off in terms of the gain (rhythm and lead) and highs.

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Post by ursinus » Thu May 10, 2007 11:11 pm

FWIW, when I had my Quad pre, I did exactly what Mike B recommended and sent the pre out directly to my effects (tc2290 back then) and from there directly to my old strategy 400 power amp. It sounded so much better. When I used the effects return and then out of the regular output, I noticed it did get darker and more compressed in a way I did not care for. I used the 2290's ability to adjust the volume out via program presets to control the overall volume. My strategy was set with the masters at no more than 5 usually (plenty loud!!!!) I have some old VHS tapes of me gigging in 1989 and 1990 and still love the tone (even though my playing has improved since those old "hair metal" days LOL!) Mike B told me the same thing about the Quad being closer to the IIC+ than the IIC.
Carol Ann OD2-100 EL34>
Scumback 2x12 with XH75, ASW70

triodal
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Post by triodal » Thu May 10, 2007 11:50 pm

you mean Quad Fx loop send to tc2290?

ursinus
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Post by ursinus » Fri May 11, 2007 1:12 pm

triodal wrote:you mean Quad Fx loop send to tc2290?
Yes..
Carol Ann OD2-100 EL34>
Scumback 2x12 with XH75, ASW70

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