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In Reply to: RE: Maybe I'll look for a IR volume control tubed preamp posted by airtime on March 17, 2014 at 12:38:34
Be very careful. The I/P impedance of the NAD power amp is low. Many tube preamps can get into trouble, when connected to that sort of load. The problem gets exacerbated, when high capacitance, long, interconnect cables are employed.
Eli D.
Follow Ups:
It has a 10k and 100k options switch on the rear input. Also a variable input.
charles
A look at the NAD C275BEE manual suggests that using the variable input sensitivity feature inserts a buffered trim pot. into the signal path.
When the C275BEE is configured for a 100 KOhm I/P impedance, most tube preamps will not be loaded down. However, that alone does not get you out of the woods. If the preamp is located near the power amp, problems are most unlikely. OTOH, if long interconnect cables are used between the preamp and the power amp, the fact that they must be shielded means lots of capacitance to charge and discharge. The circuitry driving the cables needs to be low impedance and high current. I highly prefer hybrid circuitry under that set of circumstances. The only tubes I would accept for a low O/P impedance - high current line stage are the 5687, ECC99, and 6H30П (6n30p). I don't know if a commercial product with the wireless remote feature using 1 of those "super/duper" twin triodes in the line stage exists.
Eli D.
This morning I tried using the 100k trim pot from my source. SURPRISINGLY it sounds very similar to my tubed Sherwood. So the problem appears to simply be the preamp I WAS using. A Marantz PM8004s preamp section.
So this is telling me I really should just go and find myself a good passive with a IR remote and at least TWO inputs.
The Plecetto is $1500. Come-on. If I really suggested this to my wife, I would have to agree with her that I was loosing it!
Something below $500 for a box, a few connectors. IR motor and a volume pot.
charles
Part of the nice sound may be due to the 100 KOhm impedance the source was working into.
Tight budgets, such as yours, need help from DIY. Try to run down a Creek OBH10. That will give you the wireless remote controlled, passive, box. The Creek OBH10 has only 1 set of I/P jacks. So, build an active buffer that includes source selection capability, but does not contain a volume control. Such a buffer is easy enough to execute around a HIGH gm twin triode. Construct the buffer with "captive" O/P interconnect cables. That saves money and eliminates a set of mechanical connections in the signal path.
Eli D.
Can I email you about that buffer thing?
After looking around at passive preamps that are, let's just say out of touch with reality! I decided I can build my own IR control with mulitple inputs.
I used to fix and repair old stereos as a hobby. So I'm fairly good with "tools"
Thanks
charles
"Can I email you about that buffer thing?"
Sure, use AA EMail. Make certain that the subject stands out, as the message will arrive in a junk folder.
Eli D.
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