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Quad 34 Preamp Overhaul

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Quad 34 Preamp Overhaul

Post by alvin1118 on Sun Mar 02, 2014 9:57 pm

Continue the Quad myth & acquired a 30 yrs old DIN version of Quad 34.
It was sold to me with unknown condition, well... I did my homework before commit, this preamp circuit isn't complicated, I should be able to get it work again if it is DOA !

Condition.. Volume knob paint flaked off.. It's 30yrs old, what to expect.


DIN Version, antique connector, not common nowadays


Quad service label dated 2003 Sept, at least this get serviced by Quad 11 yrs ago! Look promising for an unknown condition ones !

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Re: Quad 34 Preamp Overhaul

Post by alvin1118 on Sun Mar 02, 2014 9:57 pm

Got the item shipped to my pretty fast, within a week it reached my door step. Very excited, get my DIN to RCA cable prepared, hooked up with my mp3 player, Quad 909 and my china made loudspeakers, oh no, NO SOUND  :-X

All input behave the same, at max volume, there's very very very tiny sound coming out from my loudspeakers. Balance, Bass, Tilt controls sounds okay (got effect) audible even the sound is so small.

Did some search online, some guys out there experience the same issue. Refer here.


It's very likely that my Quad 34 doesn't output was due to the mute/clamp circuit is activated. That's simple, replaced the small transistor, diode, LED, and cap, it died and rose again !

Take the opportunity to replace all elcos as well, power rail - Panasonic FM/FC, signal path Elna SILMIC II. 

Lets see her naked  ;D
 

Replaced caps with Elna Silmic II


Transformer & Regulator

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Re: Quad 34 Preamp Overhaul

Post by alvin1118 on Sun Mar 02, 2014 9:58 pm

I'm now a proud & happy user of Quad + Harbeth  ;D


alvin1118
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Re: Quad 34 Preamp Overhaul

Post by sph on Mon Mar 03, 2014 4:08 pm

Well done!

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Re: Quad 34 Preamp Overhaul

Post by mthoi on Tue Mar 04, 2014 3:33 pm

Dada Electronics has an upgrade kit for Quad 34 - replacement of all the PSU caps, upgrade opamps and removal of several electro caps from the signal path.

I have adopted the upgrade kit from Dada and made further upgrades to the input & output capacitors (Mundorf), use BB OPA 627 and Burson Audio's Dual OPA.

PM me if you are keen for the upgrade information.

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Amplification: c3g/F2a + C3m/300b PP biamp, 26 Preamp, 76 Preamp + 2A3/845, c3o/300b, Quad 34/606
Speakers: Harbeth SHL5, Altec A7 288-8G/1505B VOTT + JBL 2404H, Tyler Acoustics + Altec 288/Jabo Horns

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Re: Quad 34 Preamp Overhaul

Post by alvin1118 on Tue Mar 04, 2014 5:17 pm

I prefer a refurbish & overhaul wear & tear parts than an upgrade. 

A Quad 34 without the original opamp, still a quad 34?

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Re: Quad 34 Preamp Overhaul

Post by sph on Tue Mar 04, 2014 7:57 pm

Well, you have replaced the capacitors, haven't you? Is it still a Quad 34?
By replacing the capacitors, you have tweaked the amp to sound different from the original.

If replacing the opamp would result in a Quad better than before, why not give it a try.

Perhaps the amp may sound different from the original.
But if it can sound more refined, dynamic and more musical with the new opamp wouldn't you want to experience an upgraded Quad 34? Besides, you have already changed the capacitors .....

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Re: Quad 34 Preamp Overhaul

Post by mthoi on Wed Mar 05, 2014 2:36 pm

The debate on whether to modify/upgrade a piece of component is a arduous and contentious. 

Some friends have listen to my Quad 34/606 set-up and liked the sound - until I tell them that it has been heavily modified.  Some react with disdain, others accept it as-is - "improved" 

As a DIY hobbyist, I take joy in changing parts and get sonic improvements (most times, to my ears).  Failing which, I would "reverse" the mods.

Put in IC sockets and change the opamps to your content.  If you dont like the new sound, replace back the original opamps. Consider removing some "superfluous" DC blocking electrolytic capacitors in the signal path.  

My experience have been positive - the new opamps and removal of the DC blocking caps gives better clarity and PRAT.  It is true that it may no longer sound like a "Quad"?; but it is a personal preference.  Never try - never know.

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Source(s): Marantz SAKI Pearl, Michell Gyro, Garrard 401, Lenco L75, Technics SL1200II
Amplification: c3g/F2a + C3m/300b PP biamp, 26 Preamp, 76 Preamp + 2A3/845, c3o/300b, Quad 34/606
Speakers: Harbeth SHL5, Altec A7 288-8G/1505B VOTT + JBL 2404H, Tyler Acoustics + Altec 288/Jabo Horns

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Re: Quad 34 Preamp Overhaul

Post by alvin1118 on Wed Mar 05, 2014 4:34 pm

very well said. Perhaps i'll do it one day :-)

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