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Old 13th October 2005, 12:32 AM   #1
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Default Opamp Vcc

I have an old Rotel RC850 preamp that I am going to update
with new caps. Measuring the Vcc going to the opamps, I
find that the + and - are different. Vcc+ at pin 8 measures +20.5vDC and Vcc- at pin 4 measures -19.5vDC. How critical is it for these to be the same?
Thanks BL
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Old 13th October 2005, 12:53 AM   #2
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Default Re: Opamp Vcc

Quote:
Originally posted by computeruser
Measuring the Vcc going to the opamps, I
find that the + and - are different. Vcc+ at pin 8 measures +20.5vDC and Vcc- at pin 4 measures -19.5vDC. How critical is it for these to be the same?

Hi BL

No problem at all!...But I presume that your CD use the NE5532 op amp ( a excelent choice)...but be aware that if you change for another op amp , a large number of them can't be feed with more than + - 18 Volts.

Regards
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Old 13th October 2005, 01:06 AM   #3
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Thanks for the reply. I have been reading the posts about the 5532 & 5534 and was going to change it just to see if I hear any difference. I am considering the OPA275 which will take up to 22v
or the OPA2604 which will take up to 24v. The circuit is a preamplifier not a CD player. I know that fast recovery diodes
have been suggested as an improvement for CD players but for this application would these (replacing 1N4003 with MUR120's) be of any value? Thanks BL
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Old 13th October 2005, 01:18 AM   #4
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Quote:
Originally posted by computeruser
I know that fast recovery diodes
have been suggested as an improvement for CD players but for this application would these (replacing 1N4003 with MUR120's) be of any value?

I usually don't change the diodes but you can try the MUR 120 and see (hear..! ) if they make any diference.

Is good that you find your own opinion and for that , there are only one way...try...try ...try!
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Old 13th October 2005, 03:10 AM   #5
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hohohoo... Denon is a very goog pre-amp!

Many ideas i have to you:

Change the Caps To ELNA Cerafine model, and put more capacitance in the Power Supply...

Put Sockets on the op-amps, and change the op-amps to OPA627, OPA134, OPA134, when the OP-Amps are Dual Unit. Use the doubler socket to the OPA627... And the double versions of the OP-Amps, like OPA2227, OPA2132, OPA2134, and others...

Change the audio conections to silver wire.

When the transformer not a Toroid unit. Change to a toroid unit.

When the OP-Amps not operate at highter voltage, you can regulate it with 7812 and 7912... Put the Op-Amps in other board, and conect the conections of the op-amp in the principal board... Did you understand me?



Felipe.
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Old 13th October 2005, 03:27 AM   #6
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Hi computeruser,

I would hazard a guess that the reason for such high supplies is to ensure a sizeable overload margin for the phono preamp. This being the case you maywish to look at the LT1028 -A (From memory +/- 22V) which should justify the outlay. For line stages, without a schema and thus guessing, you could try the higher noise FET chips such as an OPA134 with regs as it offers excellent transparency.

The supply differences should have no effect.

Cheers,
Greg
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