AU-D11 II resistor upgrade

I am part way through doing something that I vowed to do one day, namely to 're-resistor' my AU-D11 II. I had ordered the required resistors in February 2015, and they had been sitting in their box in my workshop all this time. The standard resistors are a mix of mostly 'Carbon Film', but also some 'Carbon Composition', these are all being changed to Metal Film's. So far I have completed the Control Amp (read Pre-amp), but I am having a pause to listen and see what difference has been made by the changes. The amplifier seems more precise and clear, and is quieter noise-wise but you can only notice the reduced noise when using headphones. Overall I am pleased, but I want to listen some more before committing to do the rest.

Do you trust new resistors?
Something happened while I was working away on the Control Amp board which really surprised me. I was making the job that much harder for myself by measuring each resistor as it came out, and measuring the new ones going in, (just for my own interest). It was all going well until I removed a couple of 220KΩ resistors and checked them - they were very good, each reading well within spec at about 400Ω high. Then I checked the new resistors, 220KΩ ? - nope - how about 224KΩ, and another 227KΩ, and the worst one of all 254KΩ, with a 1% tolerance these should all have been 220KΩ +/- 2200Ω and none of them (50) were, they were all reading high. So I tried 2 other multimeters - exactly the same, all reading high. I went back to the old ones, still 220.4KΩ - and checked the meters with my resistance standard 1KΩ 0.01% - reads fine.

Still scratching my head I decided to complain to the supplier, and hopefully get some replacements. So I fill out a Quality Query form online with the relevant info - but hearing nothing I ring up the supplier. They were all ears until I told them I bought the resistors 3 years ago, the customer service representative says "sorry Sir we can't help you, our standard warranty is 1 year, but 3 years is out of the question". So I went through the 'resistors are supposed to be eternally stable, especially if not used' thing - and that I would send back the faulty ones for their inspection - they were having none of it. Lesson learned I suppose, but I am still stunned by the hard line taken for just £4 worth of resistors. There is no question of my ceasing to order from them, they are far too useful a supplier for me to get all bitter and twisted about the issue.

Sorry for the long post, thanks for reading - if you got this far. :D


I will add just a note of caution. Years ago, I replaced very carbon film resistor in a pre amp with metal film. Powered it up and found I had changed (some may say wrecked) the tonal balance of the preamp. If you like the way your unit sounds now, I would be careful with complete parts change outs.

Would also stay away from the metal oxide resistors as they add a thin, metallic tone to the sonic character.

The only resistors I can say go all out on are the Vishay bulk foil VSR types. Very natural sounding. but your sansui will no longer sound like a sansui.

best
 
Thank you for your post, but first I must say that it is done! I have changed very nearly all the resistors for metal film and I like it, I just wasn't sure sonically about the last stage namely the Phono (EQ) amp - after it was done. I would never use metal oxide resistors, and I wouldn't use all my money buying Vishay Bulk foil resistors, far too expensive. :)
 
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Just a couple of notes on this.

The subjective noise performance is significantly improved, before there was substantial hiss and a little hum with the volume turned fully up and MM input selected. Now, I can turn the volume fully up and can just begin to hear a bit of hiss above about 90% volume. :thumbsup:

But best of all, I have been wrestling with a problem of hum particularly in one channel, and especially when engaging the tone controls. I finally worked out that it must be coming from the supply for the front panel switch indicators, which runs in tracks and ribbon cables on the Control Amp board. When I reassembled the amplifier after the resistor changes, I paid particular attention to how the ribbon cables were dressed, and made sure they were as far as possible away from sensitive places on the board. This seems to have done the trick as, tone controls engaged or not, I can no longer hear any difference between the hum in either channel, which is also markedly reduced compared to before.

@phonomac
 
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Now that you have all that practicing out of the way John how about doing the same to my CA-3000 :D
After all, if I can do all those silly pass through pinnings surely a quick trip across the pond for resistor replacement is not too much to ask lol.
-Lee
 
I have no doubt that Hyperion's AU-D11II has been inestimably improved by his switch to metal films!

I have two AU-D11II's. I've played hopscotch modifications with them; do a rehab or mod to one, listen, compare to the unmod'ed unit. Recapping, different caps, new transistors, relay, etc. all made little differences. It wasn't until I completely replaced all the carbon comp resistors with metal films (mostly Xicons) in one AU-D11II that I got to a comparison with the un-MF'd unit that left me so dissatisfied with the un-MF'd unit (original carbon comp resistors throughout) that I can no longer listen to it. I had thoughts of buying better (read: more expensive, perhaps?) metal film resistors and do the other amp, then compare the sound of Xicons to whatever. But I haven't got there. This could be why: about 200 resistors, all to be measured and matched in value left side to right side in the circuitry. I'm so happy with my MF'd AU-D11II that it no longer comes out of rotation in my system, and visitors have complimented me on the best home audio system they'd ever heard (maybe they don't get out much...).

I've replaced carbon comps in several pieces of gear, and I've been so impressed with the improvement in sound that I am a firm believer that re-capping is, in many cases, only half the job. You can really make these old circuits sing with better resistors. I'm currently rehabbing an AU-9500 with MF's.
 
I got to listen to an Accuphase P-250 amplifier today with all new Metal Film resistors. I believe they were all Vishay CFM series. I was pretty blown away by what I heard. Like WOW!

Very low noise floor and crystal clear. The ambient resolution was off the charts good as well. There just might be something to this metal film stuff... When I get time (if ever) I will be trying this on one of my BA-F1 amps. Maybe a CA-F1 too.
 
Totally... :) I am going to try getting rid of all the resistors Sansui called N.I.R. (non-inflammable) first, as I suspect these are metal oxide resistors. Tolerances were not very tight on these either from what I have experienced. Anybody know for sure what the N.I.R. resistors actually are? I bet replacing these alone would make a nice improvement if my theory is correct.
 
Interesting read. Came across this info just too late, I finished the boards in my BA-F1... :( But I did have to replace a number of resistors (some fusing resistors were off, others attacked by glue) and faced the question which replacements to choose. Let me share some of my reasoning below; please correct me if I am mistaken.

Regarding the sensitivity of resistors to direction mentioned earlier, this may be a point indeed. Metal film resistors do possess many desirable characteristics (good noise characteristics, low non-linearity due to a low voltage coefficient, tight tolerance, low temperature coefficient and long-term stability, cheap), but they also have parasitic inductance, in other words, they act like a coil. This is a result of the manufacturing process of metal film resistors. Their resistance value is determined by cutting a helix through the coating (similar to the way carbon resistors are made).
film_resistor_construction.jpg
There will be a magnitic field created which is proportional to change in current flow, so this will be most noticeable with resistors that dissipate much power. The magnetic flux will be high with transients running through the resistors.
I read somewhere that the effect of this can be almost eliminated by mounting 2 resistors close together next to each other in counter-parallel directions. If the helical grooves run in opposite directions, their effects would effectively cancel each other out. Another option is to use a non-inductive variety. And of course there are boutique alternatives (Caddock, Dale, wirewound etc.) which I find too expensive.

For the driver boards the resistors feeding the signal to the power transistors were the most obvious candidates for fitting non-inductive replacements.
Here I selected Vishay PRO2-FS metal film resistors, which are non-inductive, fusing and non-flammable. Only drawback is they are 10% tolerance. So I ordered a batch of them from Mouser (they are cheap) and selected matching values.
In the power supply of this amp, a number of 10 Ohms fusible resistors are required according to the schematic. Sansui engineers seem to have been really fond of these, they are used in many designs and I replace them as a matter of routine. Here I used Yageo FRMs, but these are end-of life unfortunately. Actually the coil characterics may be desirable to have in the PSU, so I consider to use metal films there after all.
For some other locations I opted for metal film Vishay RN or CCF, or CMF, mainly depending on availability.

Have fun modding and listening!
 
I read somewhere that the effect of this can be almost eliminated by mounting 2 resistors close together next to each other in counter-parallel directions. If the helical grooves run in opposite directions, their effects would effectively cancel each other out.

I don't believe one would achieve anything worthwhile by doing this - if the circuit is that sensitive then you need a different type of resistor. :)
 
On 3 unit I spend several hours like a crazy person replacing and measuring old carbon for metal films. The unit are AU-999, HK330 and Pioneer SA-7500. Xicon MF-RC for 1/4 and 1/2 W, and Vishay CPF for 1W, 2W

./ Several resistors on the 3 units had values drift above the specs.
./ Lower noise floor.
./ Way more articulated bass.
./ More detailed presentation overall.
./ Pioneer and HK presented the most dramatic improvement. And yet, the Sansui improvement is not small.
I should add this unit were previously reconditioned. Following the outline of the guys who knows this stuff.

Now I need a FR300 and half a million resistor, for a couple baskets cases that I have around.... jo jo jo, lets find another victim :naughty:
 
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How did it sound???? Before/after?
Too early to tell... still need to install the boards and reassemble everything... ETA somewhere halfway this month! ;)
But the unit has been on my bench for over 5 years now (numerous life events in between) so any memory will be vague at best. I do remember my reason to restore though was a perceived 'muddy' sound. Unit had original OPs, L channel turned out recently to be half blown. So I expect an improvement in any case!
Will post my impressions when I have completed the L channel. (And probably a bunch of questions for you experienced guys).
 
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