New to Quad Premp - have a question...

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pmx1
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New to Quad Premp - have a question...

Post by pmx1 » Sun Mar 04, 2018 9:54 am

Hi all,

this is my first post, although I have a Triaxis, a 295 Simul Class power amp, and a D180 since long...

BTW, this means that my only contact with the venerable Mk series is through the Triaxis...

I just got a Quad Preamp this week.
I compared Rythm 1 and Rythm 2 tones with all knobs at 5.

I noticed that the "Rythm 2" channel as really much more bass than "Ryrthm1" (with the same knob settings).
Using a Les Paul neck pickup, I get a very deep "jazzy" sound (if gain set right).

Indeed, I did all the usual tube swaps... (and knobs push and pulls).

Is this tone difference normal, or should I search for a possible problem ?

Thangs in advance !

P.S. Based on the schematics floating around, the Quad Preamp "Rythm 2" looks a lot like the Mk III Red stripe "Rythm 2" (around the 3.3M resistor between the MkIII V1b and V2a).
In "Rythm 1" mode, both have a 470k going to ground, that effectively reduces the low frequencies.

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jediguitarist
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Re: New to Quad Premp - have a question...

Post by jediguitarist » Sun Mar 04, 2018 1:01 pm

We're running the same rig. My quad is paired to a 295 into a 2x12 with Greenbacks.

I'll have try setting all the knobs and see if the same thing happens on my end. I would think both channels would sound distinctly different. According to the manual, channel 1 was based around the Mark II. I assume it's the IIa.

I'll post back in a bit...

93 97 98 PRS CE24
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pmx1
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Re: New to Quad Premp - have a question...

Post by pmx1 » Sun Mar 04, 2018 4:33 pm

Thanks alot !

You're right,the manual says :

Channel 1 is very similar to the Mark IIC, while Channel 2 is very much like the
Mark III.

pmx1
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Re: New to Quad Premp - have a question...

Post by pmx1 » Sun Mar 04, 2018 7:08 pm

Some more infos regarding the version of my Quad Pre, if this helps.

I've checked my Quad circuit against the available schematics.
So far, values on these schematics seem accurate.

My Quad, dated 1990 : 1/10/90 (on reverb pan) and 1/10/91 ("export" 240V power transformer), is likely revision "1G" of the PCB : the version engraved in the PCB is "QUAD 1G", but the PCB silkscreen still says "QUAD 1E" :)

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jediguitarist
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Re: New to Quad Premp - have a question...

Post by jediguitarist » Sun Mar 04, 2018 8:48 pm

I did some playing around with the knobs. I didn't realize how difficult it is to get the same tone on both channels. I have Groove Tube 12ax7R2 in one row and Mesa 12ax7 in the other. Channel 1 is more or less Groove tubes, and Channel 2 is Mesa. That's probably making a decent difference in the tone between the two channels.

I arranged the tubes that way before I knew what the socket assignments actually were. lol. I should do some tube rolling to see what happens.

93 97 98 PRS CE24
94 98 G&L Legacy
94 G&L ASAT Special
95 G&L S-500
99 Peavy Wolfgang
11 Gibson LP Studio 60

69 Bandmaster Head
88 Quad Pre
91 & 92 Simul 295
92 DC-5
96 Mark IV Maple/Wicker
98 5150 combo
08 Mark IV Wide

pmx1
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Re: New to Quad Premp - have a question...

Post by pmx1 » Mon Mar 05, 2018 5:26 am

The difference I'm talking about is much more than the usual tubes variations : with all knobs at 5, Rythm 1 is crisp, and Rythm 2 is really bassy.
Now, Rythm 2 can be dialed in to be very bright !

I've simulated the whole Rythm 1 and 2 preamps (3 tube sections), with all knobs set at 5, and the resulting frequency plot seems to confirm this bass bump (and an average 20dB gain boost).
Based on its schematics, the MkIII should have the same relative bass bump, but I've never had the chance to play with a MkIII...

Image

That said, this Quad Preamp sounds fantastic (indeed !).

Currently, I've only tested the Quad through a JBL E120 in an open cab.
Last edited by pmx1 on Sun Mar 11, 2018 6:20 pm, edited 2 times in total.

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jediguitarist
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Re: New to Quad Premp - have a question...

Post by jediguitarist » Mon Mar 05, 2018 12:47 pm

I did dial up the settings to 5 initially to check my rig. My 2x12 is a closed back and I didn't notice a huge jump in low end. Then again, I might be trying too hard to hear something. I am finding this interesting, though.

What about recording channel 1 and channel 2 using the main and/or recording out into a DAW and putting the files through a spectrum analyzer?
Wouldn't that give a better picture of how each channel is affecting the guitar signal? I guessing here, obviously.

93 97 98 PRS CE24
94 98 G&L Legacy
94 G&L ASAT Special
95 G&L S-500
99 Peavy Wolfgang
11 Gibson LP Studio 60

69 Bandmaster Head
88 Quad Pre
91 & 92 Simul 295
92 DC-5
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98 5150 combo
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pmx1
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Re: New to Quad Premp - have a question...

Post by pmx1 » Mon Mar 05, 2018 12:55 pm

Thanks a lot ! 8)

I think that a frequency sweep with a reamping setup would work nicely.

But based on your tests, I'll probably have to check my Quad's Rythm 2 mode in depth.

pmx1
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Re: New to Quad Premp - have a question...

Post by pmx1 » Sun Mar 11, 2018 6:17 pm

As I have no access to another Quad preamp (or a MkIII), I have no way to know if the bassy tone of Rythm 2 is normal.

I made some measurements, and compared to a circuit simulation (quite accurate) of the Quad preamp, in order to see if there is any discrepancies.
If there is no hudge difference between the two, then it's safe to assume that my Quad is working correctly (and the bassy Rythm 2 tone is normal).

I made a gain vs. frequency plot of Rythm 1 and Rythm2, all settings at 5, no switch pulled.
Measured at the Effect Send output.
I used an USB audio interface (Arturia's AudioFuse), Hi-Z line input (i.e. no load).
Output via the Reamping feature of the AudioFuse.
The software used is ARTA, freely downloadable.

Image

The red curve is Rythm 1, the cyan curve is Rythm 2.

The curved confirms the actual audio comparison : Rythm 2 is much darker tahr Rythm 1.

Here is the simulation : Rythm 1 is cyan, Rythm 2 is blue.

Image

Very little differences.

Looks like Rythm 2 is optimized for overdrived sounds ???

IronSean
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Re: New to Quad Premp - have a question...

Post by IronSean » Wed Apr 18, 2018 11:16 am

Channel 1, as you've seen in the manual, is modeled after the Mark IIC(+) style two channel amp. With a clean and a lead channel.
Channel 2 is modelled after the second and third channels on a Mark III style amp (R1 was clean R2 was more in crunch territory, and R3 was lead with that crunch mode feeding into it). Channel 2 on the Quad is R2 and Lead.

So they're build for very different things and tuned as such. Rhythm 2 on the Quad is like the Rhythm 2 mode on Mark III and IV models: Often maligned, somewhat underappreciated, and usually sitting in a weird sonic space: Not tuned for clean and too high gain to have much clean headroom, but not quite what people want for a solid crunch channel either.

The main purpose tends to be "allowing a third sound to be switchable, and offering a more mid-gain option for sounds when traditionally clean was very low gain and lead was very high gain". Also, it gives you another channel that feeds into lead that you didn't need to worry about leaving clean. Because as I'm sure you've seen, the Lead 1 channel sounds best with the VOLUME in the 7-8 range, but that doesn't lead to the cleanest Rhythm 1 Clean sound. So the R2 channels let you run them higher gain to fuel an even higher saturation LEAD channel and not worry about sacrificing your clean since you had a separate dedicated clean.
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pmx1
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Re: New to Quad Premp - have a question...

Post by pmx1 » Wed Apr 18, 2018 3:12 pm

Hi IronSean,

thanks for the comments and all the info.

Finally, I've found some nice Rythm 2 tones with volume in the 8 to 10 range.
Heavy, but singing, blues tone w/ a Les Paul (if this makes sense).

sotosprince
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Re: New to Quad Premp - have a question...

Post by sotosprince » Wed May 02, 2018 2:24 am

When I had the quad preamp I would use the 1st channel for all clean and solos and the 2nd one for all the rhythm guitars. I would often use a parametric eq to boost and cut specific freqs. Paired with the 2:90 simul class it was pure heaven. Unfortunately, my rack days were over so I sold everything and got a mark 3 blue stripe. The 2nd channel of the quad is based on the no dot black stripe, the earlier version of the mark 3 not the red one of I'm not mistaken.

pmx1
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Re: New to Quad Premp - have a question...

Post by pmx1 » Thu May 03, 2018 7:00 am

Hi sotosprince,

thanks for your feedback.

It's interesting that you used a parametric EQ to supplement/complement the graphics EQ

Since my first tests, I've found some nice tones, too (good old 295 Simul Class amp, the later model with the front knobs).

Finally tested it with an Altec ER12L (recently reconed, same as EVM12L), smoother overdrive than the JBL E120 (as expected...) and a different bass "feel" (in an open back cab).

sotosprince
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Re: New to Quad Premp - have a question...

Post by sotosprince » Thu May 03, 2018 4:19 pm

pmx1 wrote:Hi sotosprince,

thanks for your feedback.

It's interesting that you used a parametric EQ to supplement/complement the graphics EQ

Since my first tests, I've found some nice tones, too (good old 295 Simul Class amp, the later model with the front knobs).

Finally tested it with an Altec ER12L (recently reconed, same as EVM12L), smoother overdrive than the JBL E120 (as expected...) and a different bass "feel" (in an open back cab).
Would love to listen to some clips :) here are some mine using the parametric eq
https://www.youtube.com/watch?v=qqZz5rHHIIk
https://www.youtube.com/watch?v=VBXj8AJ108Y
https://www.youtube.com/watch?v=1gejXLj8W-Q
https://www.youtube.com/watch?v=6Eptmr_XaRQ
https://www.youtube.com/watch?v=lE4kHu_4_04

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