Engl 520 preamp

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schaublin65
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Engl 520 preamp

Post by schaublin65 »

Hi,

I have been playing with this circuit for the last few evenings.

There is an interesting component I had not seen used in this way.

A small inductor between signal and ground.

It's a little black cube about 8mm on each side. Marked LT 3011/2.

I don't have an LCR meter so I will have to rig something up to measure what it's doing. Lifting one leg off the board it seems to make little enough difference.

Take care

John
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Dr-Joned
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Re: Engl 520 preamp

Post by Dr-Joned »

It is an optoisolator. It is probably used for some kind of volume switching, but hard to tell without the whole schematic.
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roberto
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Re: Engl 520 preamp

Post by roberto »

Exactly. Here you can find photo and specs:
http://www.griotgroup.com/wp-content/up ... ors-07.pdf
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schaublin65
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Re: Engl 520 preamp

Post by schaublin65 »

Hi,

thanks for taking the time to reply.

I have edited my posts in this thread because they contained no useful information.

Old test equipment and confirmation bias is a troublesome combination.

The purpose of LT is presumably for stability when V3a is switched out.

Take care

John
Last edited by schaublin65 on Sat Jun 13, 2015 9:50 am, edited 2 times in total.
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roberto
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Re: Engl 520 preamp

Post by roberto »

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schaublin65
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Re: Engl 520 preamp

Post by schaublin65 »

Hi

post edited, see fourth post in thread
Last edited by schaublin65 on Sat Jun 13, 2015 7:29 pm, edited 2 times in total.
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roberto
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Re: Engl 520 preamp

Post by roberto »

Have you tried to place a capacitor in parallel to the inductor, and calculate its value once you have determined the resonance frequency?
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schaublin65
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Re: Engl 520 preamp

Post by schaublin65 »

Hi,

sine wave generator recap in progress...

[img:2048:1536]http://i.imgur.com/6ugGJHo.jpg[/img]

take care

John
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schaublin65
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Re: Engl 520 preamp

Post by schaublin65 »

Hi,

post edited, see fourth post in thread
Last edited by schaublin65 on Sat Jun 13, 2015 7:30 pm, edited 2 times in total.
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schaublin65
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Re: Engl 520 preamp

Post by schaublin65 »

Hi,

post edited due to strange results from these

[img:542:720]http://i.imgur.com/wJYnI8r.jpg[/img]

more work required
Last edited by schaublin65 on Sat Jun 13, 2015 7:34 pm, edited 1 time in total.
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roberto
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Re: Engl 520 preamp

Post by roberto »

???
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