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Old 19th April 2005, 07:34 PM   #1
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Default Help me decide on an OP-amp

Hi!

My 2 1/2 years older sister is getting married this summer, and since she always admired all my DIY audio gear, and her and her husband in spe's "hifi"-equipment is actually more like "lofi", I decided to build them an integrated amplifier as my wedding present.

After some considerations (P3A, P101 from ESP, Gainclones with various chips...) I decided upon using the LM4780-Kit from Audiosector, which is already lying assembled in front of me.

Now I have to build the pre-amp part, with tone control. For this I actually decided on ESP P97 with some small mods. And now I have to figure out what OP-amps to use.

I actually narrowed it down to BB OPA2134 or OPA 2604, but cannot decide which one of them to take.

Could you give some input about the pros and cons of those OPs, or maybe even convince me of some other device (and not in the price range of the OPA627). 5 per double OP amp is my limit (they should be double OP-amps per design).

Any help is appreciated (should I send some wedding cake?) !


Oh, and btw, I think I will use the "standard" black ALPS pot for volume control, but it would put a great strain on my budget if I used black beauty on all the pots (bass, treble and balance), so I though about normal (alps) pots for those VRs, or would you greatly advice me against that?

And always keep in mind that her other stuff (source, speakers) is not of that great quality right now (maybe I will change that too someday).


Bye,

Arndt
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Old 20th April 2005, 01:51 AM   #2
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From the specsheet the 2132/2134 looked better to me (though I don't remember the distortion diagrams, but that preamp job will certainly be well done by both...

Nice idea for a present, btw.
I think I'll invite you to my wedding, too!

Cheers
Dominique
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Old 20th April 2005, 05:07 AM   #3
BrianL is offline BrianL  United States
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Between the OPA2132/2134 and OPA2604, I'd go for the
former. The '2604 can be quirky (instable) if one isn't
careful. Other than DC offset, you should find the 2132/2134
fairly identical in "sound quality".

OPA627 price? I've not found it unreasonable.
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Old 20th April 2005, 07:10 AM   #4
AndrewT is online now AndrewT  Scotland
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Hi,
make the tone control defeatable.
How about a baxandale circuit?
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Old 20th April 2005, 09:26 AM   #5
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Hi!


Quote:
Originally posted by AndrewT
Hi,
make the tone control defeatable.
How about a baxandale circuit?
Making it defeatable isn't a bad idea.

But what is a baxandale circuit ? I could not find anything on that topic...?


Thanks for the input so far,


Arndt
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Old 20th April 2005, 09:29 AM   #6
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Hi!

Quote:
Originally posted by BrianL

OPA627 price? I've not found it unreasonable.
That lies in the eye of the beholder. I would need six of them (3 double op-amps), and one of them costs about 20 . Remember, this is not a "no limits" project, it will be quite costy already, even with somewhat "poorer" op-amps.

Bye,

Arndt
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Old 20th April 2005, 12:59 PM   #7
AndrewT is online now AndrewT  Scotland
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Hi,
I think I have spelt his name correctly. He was an electronics designer, maybe 50's & 60's that developed among other things a passive tone control that was virtually flat when set so and had gentle slopes into the filter band that got steeper as the controls were advanced. Instead of a steep cut with variable F3 point that closed in towards middle frequencies as the controls were advanced.
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Old 20th April 2005, 03:05 PM   #8
Leolabs is offline Leolabs  Malaysia
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Nice wedding present u have for your sister,Cradle How about opamp from Analog Devices,like OP249???
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Old 20th April 2005, 07:43 PM   #9
zinsula is offline zinsula  Switzerland
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Many people seems to like LM6172.

And look at this thread: Good replacment for BB OPA 2604/604
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Old 20th April 2005, 08:05 PM   #10
lucpes is offline lucpes  Europe
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To be taken with a grain of salt, but generally a good description on how various OPAs sound:

http://www.sgheadphones.net/index.ph...ST&f=12&t=2628

http://www.tangentsoft.net/audio/opamps.html
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