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Symetrix SE400
Symetrix SE400
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Old 9th June 2021, 07:14 PM   #1
Nordlead26 is offline Nordlead26
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Join Date: Jun 2021
Post Symetrix SE400

Hello,

I am thinking of taking my Symetrix SE400 to a specialized technician to make some modifications, however, I would also like your recommendation as I want to upgrade the Op amps to better quality ones in the filter sections for a safe swap.

I know nothing about electronics and that is why I would like your help.

Basically the modifications I want to do are based on "revive audio", who have already modified these units, however it is impossible for me to do it with such company as im not in the same country.

This are the original schematics of such a unit from 35 years ago:

https://3r61fy4ckkky4bvae644ns07-wpe...-Schematic.pdf

and these are the schematics, from an engineer who took it upon himself to make his own schematics based on the restoration he did since he could not find the originals at the time, this ones are the latest update of the schematics made by this engineer:

https://music-electronics-forum.com/...3&d=1618602610

https://music-electronics-forum.com/...4&d=1618602625


and here is possible to see the inside of the unit:

Symetrix se400 dual parametric equalizer schematic - Music Electronics Forum


I would also like to know, which modification can reduce the floor noise? would it be to change the power supply?


I hope all this information will be useful for any recommendations.


Thank you very much in advance!
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Old 9th June 2021, 09:41 PM   #2
duncan2 is offline duncan2  United Kingdom
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Join Date: Mar 2013
Location: Scotland.
Upgrade the Op amps ---- its a pity you quote- "know nothing about electronics " otherwise you could DIY --- looks like from colored blowups on another website they are plugin .

Noise Floor ?---- IF and I say IF as I don't have their specifications the noise floor will ( or should ) be reduced by fitting the latest "all singing dancing" 0.0000001 % THD with a noise floor not even a mouse could hear.

The problem is like life itself is the circuit designed for those particular chips ---or not ?

Yes had a look LF353 used them long ago you can upgrade the chips .

Last edited by duncan2; 9th June 2021 at 09:44 PM. Reason: more info
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Old 11th June 2021, 06:34 AM   #3
Nordlead26 is offline Nordlead26
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Join Date: Jun 2021
Quote:
Upgrade the Op amps ---- its a pity you quote- "know nothing about electronics " otherwise you could DIY --- .
Yes, it's a pity, I wish I knew something about electronics so I could do everything myself.

Quote:
looks like from colored blowups on another website they are plugin
Im not really sure what do u mean....

Quote:
Noise Floor ?---- IF and I say IF as I don't have their specifications the noise floor will ( or should ) be reduced by fitting the latest "all singing dancing" 0.0000001 % THD with a noise floor not even a mouse could hear.
for this case, what type of power supply would you recommend?

The noise specifications are in the last sheet of this link:
https://3r61fy4ckkky4bvae644ns07-wpe...-Schematic.pdf

Quote:
Yes had a look LF353 used them long ago you can upgrade the chips .
Thank you! Can you expand a little on your experience with them? and why they would be better than what Symetrix has originally? I am interested in your comments.
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Old 11th June 2021, 06:59 AM   #4
Nordlead26 is offline Nordlead26
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Join Date: Jun 2021
Quote:
Originally Posted by duncan2 View Post
Yes had a look LF353 used them long ago you can upgrade the chips .
Looking closely, the LF353 is what Symetrix originally had as Op amps .... so this would definitely not be an upgrade hehe.
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Old 11th June 2021, 11:44 AM   #5
duncan2 is offline duncan2  United Kingdom
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Join Date: Mar 2013
Location: Scotland.
The distortion factor is around =0.02 % that is easily bettered nowadays, LF353 is no longer designed into modern audio hardware you are going back to the 1980,s but if you like the sound of them then why do you want to upgrade them ?

The slew rate is okay .

By "plugin " I mean you can pull them out of their sockets they aren't soldered in but buy a chip extraction tool and look out for the mark/indent/dot to signify which way round they are fitted.
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Old 14th June 2021, 08:43 AM   #6
Nordlead26 is offline Nordlead26
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Join Date: Jun 2021
The company revive audio, has the feedback that it can sound much wider by changing the Opamps for higher quality ones, but no data are given on the ones they changed, they also have the opinion that LF353's are of a lower quality... I like the sound is pretty decent, but is not "incredible"... the EQ is a very rare piece and I like it of course, but if I can improve its sound and get a much better quality EQ, why not? I like the idea of the 80s is at some point something "romantic", but it's 2021 ... if it were an API EQ, well, that would be different because surely their Opamps of the 80s, have a super special sound and are definitely not cheap pieces of less than 1 dollar as the LF353.
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Old 16th June 2021, 02:49 PM   #7
Mark Tillotson is offline Mark Tillotson
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Location: Cambridge UK
As for noise floor I suspect you may be able to drop it 10dB or so if the opamps are the limiting factor.

OPA1642, OPA1652 are substantially quieter JFET opamps - though being modern might need some 100nF high-speed decoupling added. They are also not DIP, so you'd need them on SOIC8->DIP8 breakout boards.

LF353 - 25nV/√Hz, - equivalent to Johnson noise of 39k resistor
OPA1642 - 5nV/√Hz (14dB less, equiv to Johnson noise of 1.5k)
OPA1652 - 4.5nV/√Hz (15dB less, 1.2k noise equiv.)

These newer devices take less current too, so no problem with power, they will run cooler.
Power supplies generally don't affect noise of opamp circuitry, though poor layout may affect mains hum.
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Old 17th June 2021, 01:36 AM   #8
Nordlead26 is offline Nordlead26
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Join Date: Jun 2021
@Mark Tillotson
Quote:
These newer devices take less current too, so no problem with power, they will run cooler.
Thanks for the recommendation,

have you ever had experience with the burson audio V5i? or do you know anyone who has used them in units like EQ?


Supreme Sound Opamp V5i - Burson Audio

Do you think there is really an improvement in audio clarity and transparency?

I leave a picture of the burson and one of the EQ inside just in case you are curious, greetings!
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File Type: jpg image_54477.jpg (257.1 KB, 25 views)
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