• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Quad II w. New MEM Q: impedance+pre-amp

Status
Not open for further replies.
Jump to Latest
T

tralalalala

Member
Joined 2012
#1
Hi all,

I am about to send my original Quad II's to service for recap and to install a new mains entry module so it can be used for other pre-amps than the original Quad 22.

I was wondering if anyone had experiences with other pre amps:
I have today a Quad 44 that should do the job, but was wondering if a 1. Passive pre is something to look into. 2. Or using a B1 preamp kit from Pass DIY.

I am planning on using these Quad II's mainly with my ESL57's : if I was to use this power amp set with 8ohm speakers; 3. can I still use the 16 ohm output on the output transformers?


All inputs are welcome!
 
#2
To use the Quad II with 8 ohm speakers you will definitely need to change the output transformer tapping from 16 ohms to 8 ohms, not doing so will result in substantially lower output power and at the same time much higher distortion.

Can't answer the question about other pre-amplifiers as none are familiar.
 
#3
Hi,

Thank you for your answer regarding the tapping on the OPT 🙂 UNDERSTAND .


I am lost regarding alternative pre-amps for the Quad II and Quad ESL 57 setup.
There is definitely something elementary about the Quad II's I do not understand.

Since my last post I have read more about pre's for Quad II's ( not much info to be found ) , but also amplifiers for the Quad II / ESL57 combo.

As far as I understand it:
The Quad II's have the need of higher output voltages on the pre amp than for example vintage Leak gear that can much more easily be driven by passive pre at the same volume stop.

The alternatives for newer pre amps especially designed for Quad II's are not many... EAR 834L is one alternative mentioned here. The world design P3 is also mentioned ( previously came as a kit? ? ).


world design p3:
pre amps


Other treads on net:
High output pre for Quad II ( ref 1 )
http://www.lencoheaven.net/forum/index.php?topic=19002.0

High output pre for Quad II ( ref 2 )
High output pre-amp for Quad II ? - 2 Channel Debate - HiFi WigWam

INFO gathered:
Gain is also mentioned as a more important factor than voltage at the output for the pre used with the Quad II's. DC at the output is not favorable either....

Q:
What does it mean with a pre amp with DC at the output? Is this normal amongst pre amps produced today? Why is it not recommended with Quad II's?

Any other alternatives to the Quad 44 / EAR 834L / world design p3 here at DIY -audio... ?
 
#4
tralalalala said:
Hi,
Q:
What does it mean with a pre amp with DC at the output? Is this normal amongst pre amps produced today? Why is it not recommended with Quad II's?
Click to expand...

I am not all that familiar with commercial products, but I am not aware of any pre-amp which has d.c. on the output. I would in fact qualify it as a definite no-no design if any d.c. appears on the output. It simply costs a capacitor to avoid that, and I cannot think of any earthly reason not to include that.

As then, it is not recommended with any amplifier full stop. A (unknown) d.c. voltage at the power amplifier input upsets the internal electrode voltages of an amplifier, one way or another. Thus output at ground potential and input similarly makes matters universally 'matchable', so to say.

While it is true that a requirement of 1,4Vrms is on the high side, it must be understood that this (or any other stipulated amplifier input) does not denote inherently poor design. An amplifier designer is not obliged to please other pre-amp designers, particularly if he also supplies his own pre-amp, unless his product is intended for the general market as well. But yes, in as much as folks may desire to use different pre-amplifiers it can be a disadvantage.

(Heresy! I have on occasion mounted a say x4 input 'buffer' inside a Quad II for convenience where desired. It consists of a simple semiconductor op-amp, conveniently powered off the 25V cathode bias for the Quad II output tubes.) It could also be placed inside the particular pre-amp, but left that much more freedom for the owner if in the power amplifier. It does not alter the tube character of the Quad II.)

[OT, but kindly permit me to say: I occasionally read that the Quad 22 pre-amp is of mediocre design. Bluntly: That smacks of ignorance of what a good control unit should comprise. On the contrary, it is a superlative tube design. What is a fact is that for some unknown reason some 12 capacitors associated with the frequency shaping circuits totally drifted off value with time (they were of the superior Hunts brand of the day). If these are not replaced, the unit will sound totally off. That is however not a reflection on the basic design.

Just for the record.]
 
Status
Not open for further replies.
Top Bottom