[drphoto]

Hey all. As some of you know, I've recently plunged back into both tubes and vinyl. I originally wanted only a linestage tube pre, but as I ended up w/ a Mapletree Ultra 4A SE, which has a phono stage, I decided to give vinyl a shot too.

Here's the problem. With the gain run pretty high (required by my fairly low output ~2mV) cart I hear some low end rumbly noise, even w/ no music playing. Yeah, even w/ the arm parked, there is the low end noise. It is not a 60 hz hum.

But once the music does play, this noise mixes in w/ the bass and creates a feedback issue.

I emailed Dr. Lloyd at Mapletree, but was wondering if someone here might have a thought.

Oh yeah. Tube hiss at this gain setting too, but that doesn't bother me as much.

Bad tubes?? Or is this just what you get w/ a fairly cheap tube pre. I love this thing for linestage. It's very quiet in line out mode.

regards,

joe

[Niteshade]

It sounds like a microphonic tube. Try replacing the tubes in the phono stage. Try shorting the phono stage's inputs to ground to see if the noise disappears.

[drphoto]

This noise is different than the one I had from a loose phono wire. I get it even if phono cables are not connected.

Anyone know where to source these somewhat odd tubes, the 12SC7? I'd never even seen them until purchasing this amp.

[Niteshade]

Try thetubestore.com for a 12sc7. It's difficult to say whether that's your problem, but it's a good place to start.

[JakeJ]

Joe,
 
 
I never had this particular problem myself so my suggestions may not be the right answers but I thought I'd throw 'em out there anyway.
 
 
New low noise tubes are a good place to start.  I think Blair is on what is probably the right track.
 
 
Other things to consider might be AC noise.  Do you have a power conditioner?  Also if you do bypass it as an experiment.
 
 
Possibly a noisy rectifier tube?
 
 
If it's only the phono section then I'm back to agreeing with Blair and bank on bad tubes.
 
 
Don't give up.
 
 
Jake

[RPM123]

Hey all. As some of you know, I've recently plunged back into both tubes and vinyl. I originally wanted only a linestage tube pre, but as I ended up w/ a Mapletree Ultra 4A SE, which has a phono stage, I decided to give vinyl a shot too.

Here's the problem. With the gain run pretty high (required by my fairly low output ~2mV) cart I hear some low end rumbly noise, even w/ no music playing. Yeah, even w/ the arm parked, there is the low end noise. It is not a 60 hz hum.

But once the music does play, this noise mixes in w/ the bass and creates a feedback issue.

I emailed Dr. Lloyd at Mapletree, but was wondering if someone here might have a thought.

Oh yeah. Tube hiss at this gain setting too, but that doesn't bother me as much.

Bad tubes?? Or is this just what you get w/ a fairly cheap tube pre. I love this thing for linestage. It's very quiet in line out mode.

regards,

joe

You could try a set of Herbie's tube dampers. I believe that there is 60 day trial period.

[drphoto]

Thanks for the lead on the tubestore. Just ordered a pair.

If this works, I will return the SS phono stage I ordered.

[vinyl_guy]

Try shorting the phono stage's inputs to ground to see if the noise disappears.

How does one do that? What is the best way?

Thanks

Laura

[Steve]

Here's the problem. With the gain run pretty high (required by my fairly low output ~2mV) cart I hear some low end rumbly noise, even w/ no music playing. Yeah, even w/ the arm parked, there is the low end noise. It is not a 60 hz hum.

But once the music does play, this noise mixes in w/ the bass and creates a feedback issue.

Oh yeah. Tube hiss at this gain setting too, but that doesn't bother me as much.

Bad tubes??

regards,

joe

I am also thinking of microphonic tube. The slight noise heard is possibly resistors, depending upon type, but the majority may be the 12sc7 line as the plate resistance is rather high (around 50k ohms), but not as high as a 12AX7 types.

Cheers.

[Niteshade]

You have to short the center conductors of the RCA's to ground. Doing this will eliminate external influences (or tell you if the ground is noisy).

How does one do that? What is the best way?

Thanks

Laura

[drphoto]

Turned out to be bad tubes. I ended up w/ a pair of Tung-Sol SC7s from thetubestore.com.

Virtually no noise at all now at any reasonable gain.

Looks like the little SS phono is going back. Never even unpacked it, as I was hoping the tubes would solve the problem.

Maybe tubes should have been my first guess, but I've been away from them for 30 years too.