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Old 14th May 2016, 02:59 AM   #1
keilau is offline keilau  United States
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Default Servo controlled Op Amp board on Ebay

The benefit of servo circuit on power amp is well document. Are there benefit to have servo on preamp board? I found 2 of these kits on Ebay. Any opinion or first hand experience?


OPA2604 Servo Preamplifier Kit AMP board kit for DIY


Top Preamplifier NE5532 Dual OP Amp And servo circuit kit for DIY

This is a cheap line amp board that may have a lot of use as output buffer. It is neither too cheap or too expensive. I have found some gems among the offers from these sellers and, obviously, burnt many times too.

Last edited by keilau; 25th May 2016 at 05:23 AM.
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Old 25th May 2016, 12:46 AM   #2
phase is offline phase  United States
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Are those 5v regulators I see?
Would think that a bit more would be needed to get decent sound from most popular op amps.
Neat board though, after adding an opa627, and Russian polystyrenes, may be good deal, and allow the use od a direct coupled amp.
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Old 25th May 2016, 12:51 AM   #3
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How the heck do you pull off a servo using a 5532??? Oh, wait, this is from China.

Usually one would choose a FET input op-amp for a DC servo...

Also, I don't see an OP2604 anywhere in sight. Not sure how that got worked into the title of the first link!
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Last edited by CharlieLaub; 25th May 2016 at 12:54 AM.
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Old 25th May 2016, 01:37 AM   #4
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The regulators are 7815/7915 +/-15v.
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Old 25th May 2016, 02:43 AM   #5
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Quote:
Originally Posted by keilau View Post
This is a cheap line amp board that may have a lot of use as output buffer.
If you can make a PCB, a good buffer is simple a 5532 as a follower (output directly connected to input). It has very little voltage offset in this configuration and can drive pretty low impedance loads. Just make sure to put a 100nF cap directly across the power supply pins of the 5532.

My advice is to pass on the boards you linked to.
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Old 25th May 2016, 05:07 AM   #6
ammel68 is offline ammel68  United States
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Originally Posted by CharlieLaub View Post
Just make sure to put a 100nF cap directly across the power supply pins of the 5532.
Why not use a .1uF ceramic cap from each supply pin to ground?
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Old 25th May 2016, 05:26 AM   #7
keilau is offline keilau  United States
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Quote:
Originally Posted by phase View Post
Are those 5v regulators I see?
Would think that a bit more would be needed to get decent sound from most popular op amps.
Neat board though, after adding an opa627, and Russian polystyrenes, may be good deal, and allow the use od a direct coupled amp.
The regulators are 15 volts. Agree with you that it would need to add a dual OPA627 to sound well.
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Old 25th May 2016, 05:46 AM   #8
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Originally Posted by ammel68 View Post
Why not use a .1uF ceramic cap from each supply pin to ground?
Because ceremic caps (specially the larger size ones) all have mechanical resonance modes at random frequencies, also they function as piezo "microphones", and certainly you do not want AM modulated supply voltages on your opamps.
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Old 25th May 2016, 05:51 AM   #9
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Total junk ... as is the rest of it.

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Old 25th May 2016, 05:57 AM   #10
ammel68 is offline ammel68  United States
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Originally Posted by dragonweed View Post
Because ceremic caps (specially the larger size ones) all have mechanical resonance modes at random frequencies, also they function as piezo "microphones", and certainly you do not want AM modulated supply voltages on your opamps.
So if .1uF ceramic caps aren't suitable, what type of capacitor is?
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