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Are my speakers supposed to do this?

Hi all. Thanks for reading this thread. I just put a new preamp (Eastern Electric Minimax) into my system and am noticing some weirdness in my speakers. When everything is on but no music is playing I noticed that both the left and right drivers of my monitors (Tyler Acoustic taylos) are moving forward and backwards very slowly but at a very steady rhythm. Takes about a second for them to move forward and then another second to move back. They repeat this cycle until I turn the amp off. This doesn't seem normal to me. I never noticed this with my previous pre. When I play music through the system it seems okay, no obvious distortion although I do notice my drivers moving (from my listening position 7 feet away) in a similar way - slow in and out although it doesn't seem as cyclical.

When I first put the Minimax preamp into my system there was a very loud hum and some static pops coming through the speakers. I lifted the ground on the pre with a cheater plug and the hum & static went away.

Did I damage my speakers? I want to try and trouble shoot but am afraid that damage already may have been done and I don't want to make it worse.

Thanks.
tooter

Showing 11 responses by tooter

tooter OP
85 posts
 
Kr4 - Thanks for the quick response!
I tried your suggestion - when I turn the preamp off but leave on the power amp the speakers don't pump!

Could this be a faulty tube issue? The minimax uses a 6x4 rectifer and two 12au7.
tooter OP
85 posts
 
Kr4 - Thanks. I'm in the process of getting back in touch with the seller and hopefully will have this resolved soon and haven't suffered any damage.

It has been suggested to me that maybe the preamp is leaking DC to the amp which supposedly happens at low frequencies which would explain the slow cycle of the pumping. How does this sound to you?
tooter OP
85 posts
 
Hi Steve. Thanks for the reply. I haven't tried disconnecting inputs to the pre. What would this accomplish? Is this to eliminate my CD player as the possible source of the DC?
tooter OP
85 posts
 
Zoya,

Thanks for the suggestion. I just tried replacing all tubes with better NOS and no change in the situation.
tooter OP
85 posts
 
Just to update . . . I removed the CD player from the loop and this had no effect. It's looking like it's the preamp.

Bigtee - thanks for the post. I don't know enough about electronics to have an idea about DC vs. AC but I will definitely bring it up when I speak with the seller.

Thanks to all who posted.
tooter OP
85 posts
 
I'm pretty sure it's the preamp and the person who sold it to me seems to agree. This one's going back and a replacement is on the way. Thanks for all the suggestions and insight.
tooter OP
85 posts
 
Ykm,

The output impedance of the EE MM is 1.5Kohm which is high for a tube pre if I'm understanding this right. My previous pre had a LOWER Z and I had no problems matching with my Belles SS amp (100 Kohms). There is definitely something wrong with the pre. (Speak to Bill about this. The Belles is solid state.)
tooter OP
85 posts
 
Ykm - I don't think it's the amp. The person who sold me the EE MM has a dealer who pairs this preamp with the SAME power amp, Belles, that I am using.
tooter OP
85 posts
 
Just to update the situation - the pre was sent back and tested. According to the seller/distributor there is nothing wrong with the unit so I am back at square one. I've decided not to go with a minimax and got a refund and will start looking at other options. Just to be extra safe I am sending my speakers back to Tyler Acoustic to have them checked out and will probably do the same with the amp.

Bobby -

I checked the line voltage and it seems okay. I should qualify this statement with the fact that I bought a line voltage meter at Radio Shack. I don't know how accurate these things are but after testing my outlet at different times of the day it is within acceptable range. 120-126V.
tooter OP
85 posts
 
Ykm -

My speakers are middle of the road in terms of driving them (88db). They are basic 2 way monitors, nothing exotic. I've used different pres in my system and never had problems. I am convinced that the issue is with the pre, but I will be sending my amp for a check up just in case. What kind of speaker conditions do you think would cause the problems I'm experiencing?

Gregm -

It IS amazing that the pre tested ok. I have my doubts that this is really the case. My Belles amp will go back for a check-up soon. David Belles is out of town for a few weeks so until then ...

For those of you still following this thread my speakers checked out okay. No damage or problems.

Thanks to all for the suggestions.
tooter OP
85 posts
 
Ykm,

No offense taken! No need to apologize. I am just not clear on what you mean by power amp "motor boating" and "marginally stable". Can you elaborate? What part of the amp's design is deficient which would lead to it being "unstable." I'm not an engineer but Belles amps have gotten great reviews and I've used them with many speakers and pres without incident.

thanks.
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