Possible to convert servo amp to non-servo? - diyAudio
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Old 17th February 2011, 02:13 AM   #1
mfaughn is offline mfaughn  United States
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Default Possible to convert servo amp to non-servo?

I have a Velodyne ULD-15 amp that was flood damaged. I replaced it with a totally working one. The damaged one still sort works. It works ok until it doesn't and when it doesn't it either has a significant hum or makes a loud horrible distortion...those sorts of shenanigans. I was wondering if the problem was in the feedback circuit and if it might not be possible to try it out as a regular amp...or perhaps it is nearly impossible?

Note: I obviously intend only to use it with non-servo drivers if it is possible to convert.
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Old 17th February 2011, 09:48 AM   #2
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How easy it is to convert depends on your electronic sophistication.

A motional feedback (AKA servo) amp gets feedback from the driver (in one of various possible ways of doing so) rather than from a plain old resistor. Simple as could be change back to a plain old resistor... if you understand what to do. Also, possible the amp will run perfectly well without the external feedback - ask the manufacturer.

Well out of my league and I don't know anything about that amp. Some of the trouble sounds like water damage and not too specific to MF. Dunno if that amp would work properly unless you addressed the conversion question.
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Old 17th February 2011, 11:18 AM   #3
mfaughn is offline mfaughn  United States
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I can measure the impedance curve across the driver and choose an appropriate resistor...if I understand what your saying. That doesn't convert the amp to non-servo though...it seems (in my relative ignorance) that it leaves the servo circuitry in place but just keeps the driver from being responsible for loading it. I think this driver uses an accelerometer(maybe?) if that helps.
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Old 17th February 2011, 11:35 AM   #4
sreten is offline sreten  United Kingdom
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Hi,

In simple terms probably the open loop gain without the motional feedback
to reduce it to a more normal closed loop gain will be far too high, it will
probably hum and overload very easily.

Probably what needs adding is a normal feedback loop to reduce the gain.

rgds, sreten.
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Old 17th February 2011, 02:28 PM   #5
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+1

Shouldn't be hard to ask manufacturer or to eyeball the speaker connector to tell if they use a special VC winding or an accelerometer (which might have a power supply lead).

If it does use a sensor, then that isn't intimate with the amp feedback system - if you know what I mean - and so can't lead to funny noises in its absence.

All this is just guessing on my part.
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Last edited by bentoronto; 17th February 2011 at 02:30 PM.
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Old 18th February 2011, 12:00 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by bentoronto View Post
All this is just guessing on my part.
Hi, mostly incorrectly IMO, rgds, sreten.
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Old 18th February 2011, 02:59 PM   #7
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Quote:
Originally Posted by sreten View Post
Hi, mostly incorrectly IMO, rgds, sreten.

It seems to me if your going to hand out a broad slap in the face of somebody, your really ought to be just a tiny bit specific about the issues.

Maybe just my point of view.
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Old 19th September 2011, 06:28 PM   #8
R Dijk is offline R Dijk  Norway
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Quote:
Originally Posted by mfaughn View Post
I have a Velodyne ULD-15 amp that was flood damaged. I replaced it with a totally working one. The damaged one still sort works. It works ok until it doesn't and when it doesn't it either has a significant hum or makes a loud horrible distortion...those sorts of shenanigans. I was wondering if the problem was in the feedback circuit and if it might not be possible to try it out as a regular amp...or perhaps it is nearly impossible?

Note: I obviously intend only to use it with non-servo drivers if it is possible to convert.
Hi, why convert one servo system instead of finding the fault AND have two in working order? Do you plan to convert the other one as well?
R
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Old 19th September 2011, 06:46 PM   #9
mfaughn is offline mfaughn  United States
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Quote:
Originally Posted by R Dijk View Post
Hi, why convert one servo system instead of finding the fault AND have two in working order? Do you plan to convert the other one as well?
R
Digging up an old thread but to answer your question, I have a lot more use for a "regular" power amp than I do for having an extra amp to use with the velodyne driver. Currently I have one working ULD15 amp that pushes one ULD 18 driver...and one somewhat broken ULD15 amp that was flood damaged but still shows signs of working (but that doesn't completely). As of now I am considering just using the chassis, toroid, volume pots, and maybe caps for another project and just shelving the boards. It would cost me more to buy a new chassis for another project than I could get by trying to sell a broken amp on fleabay.
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