[QQQ]

I'm planning to upgrade stock pot in Darkvoice Figaro to ALPS RK27. What to take-10k or 100k? Stock pot is 100k and i heard that tube circuits need 100k or greater pots. The problem: i have 10k Alps already and would like to use it, but will it work properly in Darkvoice?

 

[nikongod]

If your source can drive 10K ohms, it will (generally) absorb less noise in the interconnect.

Not everything can drive a 10K ohm input though. Simpler tube preamps, or anything with a small output cap (like 5uf or less, sort of a mater of taste though) kind of suck trying to drive such a low impedance, which is where the rule of thumb of only using 100 or 250Kohm pots on tube gear comes from. Digital sources with tube outputs could find themselves in this category, so that is worth note if you like them.

Unless you have problems with your system picking up hum, the differences are probably on the smaller side as applied to a headphone amp. I would lean towards the 100K ohm pot as more hum probably comes from within the amp its-self.

 

[QQQ]

Thank you.
My source is standard 2v output CD player if it's matters..

 

[timreeves]

my 100k alps blue beauty should arrive on monday, so expect a small write up of me fitting it along with fitz's hum mod

 

[QQQ]

How much blue beauty costs?

 

[nikongod]

I think he means RK27, which is blue Velvet.

Black beauty (RK40) is almost impossible to find, but OMG nice.

 

[QQQ]

Quote:

Not everything can drive a 10K ohm input though.

Need a little clarifiation here. Understandeable, but why this "rule of thumb" applies only to tube amps?



timreeves, if you'll get hum with 100k, maybe we can trade our pots-i'll give you 10k...

 

[nikongod]

This assumes OTL (SS or tube) things change a little when you start dealing with transformers.
Quote:

Originally Posted by QQQ /img/forum/go_quote.gif Need a little clarifiation here. Understandeable, but why this "rule of thumb" applies only to tube amps?

Its a carryover from tube preamps really. The same guideline could be applied to a solid state amp for the same reason. The preamp or output stage of the source is the key.

Anyways, the problem is 2 parts:
first the output impedance of the source should be much much lower than the impedance of the pot. at least 10:1 is a starting rule of thumb. Some tube gear has an output impedance in the 5-10k ohm range, so 100K pots are mandatory with them. Most SS gear has low output impedance (less than 1k, sometimes in the single ohm range) so 10K is doable.

The second problem is with output caps.
A low impedance pot requires a bigger coupling cap on the output of the source (if it has one, again newer SS gear tends not to) to get deeeep bass response without weird cap effects.

 

[QQQ]

So, is it safe to assume that with CDP as a source it's safe to use 10k pot, and moreso than that, it can be handy if some hum problems exist?

 

[QQQ]

Btw, what is Fitz' hum mod? Searched and came away with nothing.

 

[Fitz]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif I think he means RK27, which is blue Velvet. Black beauty (RK40) is almost impossible to find, but OMG nice.

I have a custom 4-deck RK40 I'm going to put into a balanced amp at some point, it's awesome.