Quad II: Which resistors?

[johnm]

Hi everyone!

I'm embarking upon my (I hope ) FINAL Quad II rebuild, and am starting with the tag boards.

I was wondering what folks recommend for the tag boards? I tried Riken Ohm once but I think they dulled the sound a little too much for my tastes - certainly looked the part though.

Best combo. I heard (so far) were Kiwames mixed with ordinary Neohm 2w carbon films types for the values not covered by the Kiwame. Sounded pretty neutral to my ears. I did also use 1w metal films once as well but took them out almost immediately as the sound seemed so strident and tinny. Perhaps I just needed to get used to their accuracy in hindsight rather than the pleasent 2nd harmonic signature of carbons?

However, I've been reading ALOT about how bad carbon resistors really are (noise and stability) recently, and about how Metal Oxide types have lower noise than any carbon comps/films as well as better overall stability. Has anyone here built with 2w Metal Oxides from RS and if so did they 'colour' the sound in any way?

Perhaps I should use the best resistor for each job rather than use the same brand for the whole tag board? Trouble is I'm not sure what resistors to use where... I have R12 sorted (Kiwame 180 Ohm 5W type for cathode bypass) but need the other resistors for the tag boards. Any advise / explanations for choices would be gratefully received.

I have attached a link to the Quad II circuit diagram:

http://www.geocities.com/ResearchTri...quadiicir.html

Any help would be gratefully received.

Cheers folks!

- John

P.S. Not afraid to use non-audiophool resistors I just want whatever is BEST for each position in the circuit.

[lndm]

Relatively, a carbon composition resistor may be noisier and less stable than other types. This doesn't have to be an issue here.

For one thing, their noise might be of concern to a phono amp, but a typical power amp will have more significant sources of noise to worry about. I wouldn't sweat this.

As far as stability, I have used some CCs with issues. Just replaced them and all was well. They were vintage NOS anyway, no surprise there.

I use a fair quantity of 1W carbon film resistors though. These are modern production and I don't have issues with these.

Of course, when I use a carbon resistor I try not to crowd it in an effort to give it a stable thermal environment.

BTW, I've used some metal oxides in my signal path lately on the advice of some who I feel should know. I can't yet say anything conclusively but they don't seem to stand out as a problem.

[johnm]

Hi Indm - thanks for your down to earth points. Would be very interested to hear any further thoughts on your experiences with the metal oxides in the signal path - may I ask what you used them in?. In many ways (on paper at least) they seem like the ideal resistor.

Cheers,

- John

[lndm]

Originally posted by johnm
may I ask what you used them in?

Currently, grid resistors in my power amp. This happened to be a matter of convenience for me, but it came in the face of a new attitude I seem to have developed.

This was when I used a metal oxide as a plate resistor (I usually use carbons in my power amp), during a design phase. IIRC, I was pleasantly surprised to find no issue with it on first listen. IIRC, I figured I wanted to try these...for those times I occasionally feel my amp produces too much even order HD. Your thread has reminded me of this

BTW, I have what I believe are some quality metal oxides I plucked off some name brand monitor boards.

Since a thread here in recent months on this subject, I have changed the resistors in my power supply to metal oxides. No problems here, no signature that I can detect, but greatly increased peace of mind since these things are good at dealing with heat.

Still though, I'm not ready to draw a firm conclusion.

[Johan Potgieter]

Johnm,

After experience with literally hundreds of resistors I truly do not take the "sound" of resistors seriously, especially in power amplifiers. (That with respect to those who claim differently; this is a subjective thing.) Carbon resistors (and some good ones at that) were all that was available (mostly) in the 50s, but there is a good reason why materials development has moved us forward.

In some 15 Quads that I reconditioned I used 1W metal film types - also nothing wrong with metal oxide; they go a bit higher in wattage for the same size. (One could use 0,5Ws; I simply use the 1W because they look better than the tiny half-watters of today!)

May I make further suggestions:

Move the 180 ohm cathode bias resistor away from right under the choke! (Sorry I do not have a circuit diagram in front of me right now to give annotations.) The Quad is not famous for dealing with heat and those chokes start oozing pitch easily. I see that you already have the 180 ohm; I would rather use a 10W type. One must keep in mind that ratings are usually based on 25 degrees ambient temperarure, and inside an enclosed chassis it is anything but!

Then also move the bypass electrolytic further away from the resistor. In all the Quads that I have restored I have yet to find this capacitor that was not baked and dry. I have mounted the electrolytic where it was, but moved the resistor over to the opposite side of the choke. You could also increase the capacitance to 470 uF or higher for improved bias regulation. Again, I am not for altering the circuit constants, but in those days there was a BIG difference in size and quality of electrolytics compared to today.

Lastly, if you are not aware of the matter already, when you replace the 0,1 uF coupling capacitors in the metal cans by say polyester ones, you remove about 15 pF capacitance from the KT66 g1s to earth. This results in a slight overshoot on a square wave. It is not serious, but I have found a 1 nF capacitor across the 470 ohm feedback resistor to restore this better than placing 15 pF ceramics from g1 to earth, and also improve general phase response somewhat.

Hope this is of use to you.

Regards.

[5150ed]

Hi Johnm

I totally can not agree with u that Riken sound dull.

For me Riken sounds open, crip, sweet and warm with very good high and low.
Kiwame is totally difference, warm, mellow, sweet, but sometime lack of impact.

Anyway, I like Riken in cathode and grid position and also grid stopper as well.
Kiwame in power supply and sometime anode.

From my experience, I do not like using only one type or brand of resistor the amp.
You may lose the good point of it.

I like to have Non-Inductive Wire Round Resistors as power supply and plate resistor resistor and also cathode resistor of power tube.

And mix of Riken, Kiwame, AN tantalum at cathode resistor of pre or drive tube, and grid resistor.

You may check at

http://www.dhtrob.com/favorieten/_en.htm