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Old 22nd August 2005, 01:35 PM   #561
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Default Re: my findings

Quote:
Originally posted by rudi

I can answer a couple of questions that has not been addressed.
1- putting an OPA627 into the equation does not improve it. It sounds the same.
2- you need a LM317 in order to run Rev-C, it uses pin 8 with you don't on other op-amps (it is a very good and cheap little op-amp that does a good job).

Regards
Rudi
Hi Rudi, I trust you meant the LM318 not 317.

I had talked about this with Brian Donegan (The different pin out of the 318) when I first built my Rev C prototype. It does indeed make it quite impractical to try any other opamp for RevC. For Rev A just about any solid single opamp will work, but a high slew rate is desirable, bandwidth, while not to be neglected, is not as imprtant, 7-8mhz or more should be just fine. One nice feature of the 318 is its great slew rate, and I think its an important part of why things sound so good.

There are a few other opamps that use pin 8 like the LM318 does, but non of them are really the same sort of opamp.

I would agree that exchanging the LM318 for an opa627(or 637 for that matter) in a REV A circuit has no sonic benefit, though if you are the sort who feels better when you throw more money at an amp you may like it better.

I do like the REV C better than Rev A now that I have as many or more hours listening to Rev C.

Rev C passes the "long term listenability" test, you simply don't get fatigued listening to it for hours on end. Rev A is also very good for long sessions, but C just seems better.

The biggest win for the C is more precise soundstage. You really almost have to do a direct A/B test to detect it (which I have) but it is real.

Good work Rudi!

And thank you for the kind words!

Mauro, thanks to you for such a marvelous and fresh approach to the chip amp.

Now back outside to fish (I am on vacation)

Cheers!
Russ
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Old 22nd August 2005, 02:36 PM   #562
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Hi Russ. you are absulately right. LM318. could be a serious typo and somebody might blow something up.

I am glad to hear you confirm my findings regarding the op-amps. i just had to try it to satisfy my curiosity.

well i am glad the changes on C are for the better. nothing like a system that fatigues you..

well it is winter here (or suppose to be) and i have to work



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Old 22nd August 2005, 06:20 PM   #563
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Looking ahead to the use of Conn's 2 & 3, has anyone hooked up an led or fan to them? What parts did you use? What (ma) fan is allowable?
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Old 22nd August 2005, 06:31 PM   #564
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Quote:
Originally posted by bg40403
Looking ahead to the use of Conn's 2 & 3, has anyone hooked up an led or fan to them? What parts did you use? What (ma) fan is allowable?

I have only used con 3 to power a diodes. Used two 3.5 volt 20 ma in series. Looks about right, it is not too bright.
Some of these diodes with do permanent eye damage if cranked up too high.
You are on your own with the fan, it looks to have the same voltage without the 6.8K current limiting resistor.


George
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Old 22nd August 2005, 06:47 PM   #565
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Quote:
Originally posted by bg40403
Looking ahead to the use of Conn's 2 & 3, has anyone hooked up an led or fan to them? What parts did you use? What (ma) fan is allowable?

Ed,

For conn2 the speaker protection circuit will trip (and thus no sound) very easily with most 12V fans, so really unless you have a very low current drawing fan it will not work. I have tried.

Conn3 work perectly for the LED, though I found 6.8K results in a very bright LED, so I went with 12K which works great with the blue super-brights I use.

Cheers!
Russ
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Old 22nd August 2005, 07:27 PM   #566
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I think for fan use, you need either a really low current coil relay, or drive the base of a transistor for more current.

Russ, on the RevC, perhaps you could add another small transistor for driving a fan or other higher current load? Yes, I am causing trouble.

PS: I don;t think a fan is really needed unless your heatsink if very very small.

-b
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Old 22nd August 2005, 07:34 PM   #567
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Quote:
Originally posted by BrianDonegan
I think for fan use, you need either a really low current coil relay, or drive the base of a transistor for more current.

Russ, on the RevC, perhaps you could add another small transistor for driving a fan or other higher current load? Yes, I am causing trouble.

PS: I don;t think a fan is really needed unless your heatsink if very very small.

-b
Actually I am just omitting that "feature" as I think in reality a cheap 12V trafo is like $4 and you only need one.

Your PS is right on the point. I can't imagine why anyone would "need" a fan, and if they where building such enclosure I am sure they would plan for a fan.

So unless I hear a pretty good case for the fan circuit, I am not sure why I should add it. Since it will likely be just waste.

What do you think?

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Russ
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Old 22nd August 2005, 07:55 PM   #568
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If there is enough demand I suppose it would be easy enough to just run a couple of traces from the ~15V supply to the SP circuit prior to the SP circuit (so that it does not trip the relay), but that will likely be too hot for most fans. We could also run a second 12V shunt regulator or a 7812 or something to get 12V, but that seems like a lot of fuss for a dang fan.

Cheers!
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Old 22nd August 2005, 08:25 PM   #569
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I agree Russ. Just stirring things up. No need for it.
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Old 22nd August 2005, 09:02 PM   #570
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The led has the most interest for me. While driving my amp harder than I would normally, the heatsink was only "moderately" warm. No fan needed. My curiosity was for using a smaller heatsink. In light of the foregoing discussion, let any fan power be off-board.
Thanks for the discussion.
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