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-   -   Phono Preamp problems (http://www.diyaudio.com/forums/chip-amps/96722-phono-preamp.html)

davidlzimmer 21st February 2007 01:59 AM

Phono Preamp problems
 
Here are the symptoms: Low volume (although tolerable)
Very little bass unless I boost the sub much higher than with CD or PC
Inaudible but extreme rumble. Even mid woofers working very hard.

This is the equipment: Peter Daniel LM7480 PA100 with 50K pot at input.
Turn Table: Pioneer PL-S70
This Cartridgehttp://www.phonopreamps.com/tc750pp.html
This Preamp http://www.needledoctor.com/Audio-Te...2&category=910

The preamp and cart are new. The amp performs beautifully otherwise.

So how do I get a slight gain, bass boost and rumble filter? :D

Any help would be very much appreciated. I'm waiting for a "Still Sealed" copy of Victory at Sea (RCA Red Label) and I won't play it until these problems are resolved. (I hope) ;)

PS A new turn table is out of the question for the moment.

BWRX 21st February 2007 03:17 AM

Do you have the same problems with a different source?

davidlzimmer 21st February 2007 03:24 AM

No. The amp sounds great when fed by stand alone CD or with PC.

BWRX 21st February 2007 03:42 AM

It sounds like your best bet would probably be to use active filtering with your turntable. Unless it's an issue with your turntable components. I know next to nothing about that equipment so hopefully someone else will provide more helpful information.

davidlzimmer 21st February 2007 12:08 PM

OK. Let me add this to the mix. I failed to mention that the rumble (inaudible pumping) was not noticed on the sub. I just found out that the stock cut off for the Bash 300 is 30 htz.

Is there a quicky way to cut off at that frequincy, or close to, comming out of the phono pre?

phn 21st February 2007 10:11 PM

Are you sure your turntable, or cart, is set up right? I have been spinning vinyl for 30 years. While I have had temporary problems (usually ground-related stuff and mostly solved without knowing how and why), I have never had any rumble issues. I'm not even sure this is rumble. I have had similar problems (as similar as it can be without knowing what causes your problem) with what I think was an oscillating tube amp.

Something isn't right here.

davidlzimmer 21st February 2007 10:55 PM

Quote:

Something isn't right here
Let's make that official! :D

I do know that I have the same provlem with a Pickering V-15 and that it only does it when tracking a record. So I doubt it's oscillation.

It's confusing that I can see all that subsonic rumble yet the Bass part of the music is very thin.

Wondering if I have a miss match between the pre and the chip amp.

Am waiting for reply from those I bought the preamp from but, I'm sure they will blame it on the other equipment.

Thanks phn!

phn 22nd February 2007 12:11 AM

I know little about these things. But impedance mismatch doesn't seem very likely either. I mean, the thing has 200Ohm impedance.

Some smarter person than I will have to chip in.

davidlzimmer 22nd February 2007 04:11 PM

Well I got a responce from the folks where I bought the Preamp and as I suspected they blamed the other equipment. They suggested that I cancel all the DSP functions. Funny, I couldn't find that button on my Chip Amp! :D Here's what I DID do however. I fed the turntable into the 'line in" on my soundcard. Then fed the output into the preamp. Now I had plenty of gain and nice bass! The rumble was still there but very reduced. (probably due to not having to crank the amp all the way up)

I actually got a taste of what analog is going to sound like on these great speakers and amp that I built. I heard imaging that I NEVER noticed on my old LPs! Of course the quality is limited to the sound card and there's a lot of computer noise in this set up. But it did tell me that the sound is there. I just have to get it out!

I'm pretty much convinced I got shafted on the phono preamp. Wish I could find another to prove it. These guys have been good about coumminicating, so maybe they'll swap out are let me sell it back to them.

Any thoughts appreciated.


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