[Lost81]

While I was taking advantage of the Parts Connexion sale to purchase Mills Non-Inductive Wirewound resistors for the 5W emitter resistors, I got myself some Riken Ohm resistors as well.

What is the take on using Riken Ohm for R3 in the 100W Nirvana?

The Riken Ohms are ceramic carbon resistors that have 1% tolerance, aren't noisy, and do not drift with age.

However, I believe someone mentioned that the Riken Ohm resistors are current-dependent. That doesn't sound like a good idea for a resistor responsible for the output offset voltage in an amplifier.

Any comments?

Thanks!


-Lost81

[ginger]

Lost81,

It was probably my comments on Rikken Ohms you saw.

Their resistance has a voltage dependency. Since we are talking about voltage across a resistor its equally valid to say they have a current dependency.

That is their resistance = R(1 + k.V) where R is their nominal value, k is some constant and V is the voltage across the resistor, including the audio signal ie can be + or - .

This is a "first order" dependency (ie no squared terms etc.)

It can be shown mathematically (but I won't) that this introduces second harmonic distortion which as we all know is good for:
- "warming up" an amp
- gives a sense of stronger bass
- masks crappy stuff.

When I did my 55N Plus researches I used a Rikken Ohm for the feedback resistor (the 82K). The more improvements I made in terms of the capacitors etc. the less I liked the Rikken in the feedback path and eventually I deleted it. I did'nt try Rikkens anywhere else in  the amp.

BUT

I still have a 27K Rikken feeding the shunt 22K pot as my volume control in my GK1.

AND

The old 82K Rikkens from the AKSA are now doing duty as the feedback resistors in my 4 x KT88 Ultralinear Valve Amp.

Horses for Courses:
From memory R3 is the diff amp bias resistor from the emitters to the +ve rail. If my memory is WRONG then the following is crap.
R3 has next to no AC signal across it just DC voltage so yes a Rikkens value will be shifted a bit BUT will not vary with the audio signal so no 2H introduced. I would say that its a bit pointless trying a Rikken here.
What you want for R3 is stability and low noise - stick to a metal film, these are better than Rikkens in both respects  

Cheers,
Ginger

[Lost81]

Yikes!  

I already replaced R3 with Riken Ohms...

Oh well...

I will keep your input in mind and will replace it with an appropriate precision metal film resistor in the next round of upgrades in future.

As always, thank you very much for your valuable insight, Ginger!  


Cheers,
-Lost81

[bluesky]

Hi Ginger

I note your comments on the Riken Ohms and also using a precision metal film resistor.

I would love to know which brand of metal film resistors that you could recommend for inclusion into our Aksa gear in particular.

Thanks

Bluesky

[ginger]

The "standard" resistors supplied by Hugh in the kit are metal film. Use whats supplied. I believe Hugh auditioned a few brands before settling on what is in the kit. I doubt there is much to pick between them. For my semiconductor audio projects at home I generally use Philips MRS25 Series ONLY because I've used them for 10years or more at work with few problems. These are 0.6W 1% 350V rated which is 0.1W more and 100V more than most "garden variety" metal films but then you pay 20% more for them too.
For the valve stuff thats a different story - 350V rating is just not good enough.

As an aside - I have seen probably as many metal films fail from over voltage as I have from just being cooked by too much current (power).  

Cheers.
Ginger

[bluesky]

Hi Ginger

I must admit to being not too concerned about resistors, from all that I have read, metal film resistors work just fine, and it would be difficult for "an innocent bystander" to hear the difference.  

I wasn't about to replace them unless there was a significant difference, I just had to ask anyway.

Cheers

Ian