2. amps-preamps
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Why is my Audio Research SP6-b noisy?

I have an Audio Research SP6b pre-amp and it is very noisy-has a very loud hiss.I do have it hooked to a very large
pair of altec lansing VOT horn loaded speakers.I have used
4-5 amps and it stills has the hiss.Is this normal?
I know the horns amplify the hiss because when I hooked it
up to my klipsch speakers it was not as noticable.
Any suggestions.I just replaced the tubes.It does it with
the new tubes and old tubes.Go figure.
Anyone else have this problem?
89vett
128x12889vett
sdcampbell
2,136 posts
 
The usual cause of hiss and related noise in a tube preamp is tubes that need to be replaced, or re-biased. This type of noise will be particularly notable with horn speakers, which are very efficient. Maybe some owners of SP-6b preamps will have some other advice to offer.
jvia
195 posts
 
Sdcampbell I think hit it on the head for you though, have the bias checked, you did not mention which amps. or how long you have been using the VOT's, as it may be a differnce that you have noticed more when switching to these from another speaker. Also, is this with or without a source, which source, is it obvious with a source?
jvogt
212 posts
 
The previous posts are correct...it likely needs new tubes.
That being said, I will also say that I owned an SP-6B
a number of years ago, and despite it's exalted reputation,
I found it lacking, especially in the relatively high
noise floor. I later owned an SP-14 which I found superior
in most regards. In it's day (late 70's) the SP-6 series
was quite good, but more recent designs substantially
better the SP-6's.
alex
11 posts
 
All the above are correct, I would like to add that a lot of noise is can be generated by the power supply. In such power supply there is the infamous capacitors that go weak and tend to 'dry' up, thus allowing the line frquency (X2) to not be filterd out as the designed. Check with Leonard at Audio Research, this preamp is a very quality piece and will give great to excellent results when operating as designed. Hope this helps.
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