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Old 15th February 2010, 01:56 AM   #1
tommy_o is offline tommy_o  United States
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Default Cmoy preamp

I've been using my Cmoy headphone amp as a preamp to my newly put together Sure Electronics TA2024. I'm thinking about building one for a first gain stage for a cheap and easy integrated kitchen amp, but I'm having trouble with figuring out how to power both the Sure and the Cmoy off the same AC-DC wall wort.

My apologies in advance, I am very new to electronics in general.

The cmoy uses a virtual ground circuit and the build notes say that an isolated
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Old 15th February 2010, 10:37 AM   #2
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I was thinking along the same lines but didn't see this being a problem (i'm new to this stuff ). I guess the issue is how the virtual ground of the CMOY will be off from the ground of your sure amplifier?
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Old 15th February 2010, 02:02 PM   #3
tommy_o is offline tommy_o  United States
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Apologies, the post was cut off and I didnt get a chance to finish it.

The Cmoy uses a virtual ground circuit, so it needs to be isolated from earth and from the sure amp (I think). From what I understand, thats the reason for needing an isolated wallwart power supply.

So the easiest solution is, I'm guessing, just sticking with one or two 9v batteries, having a switch to turn on/off the gainstage, and keeping the cmoy on insulated standoffs in the case.

Or is there an easier way to implement a opamp as a gainstage off of a cheap 12v DC power supply?
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Old 15th February 2010, 05:26 PM   #4
Pano is offline Pano  United States
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Just look for an opamp that is meant to run of a portable battery supply. There are lots of them.

The main question might be - "why do you need a gain stage?" Is your source not supplying enough voltage or current, or both?
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Old 16th February 2010, 02:37 AM   #5
tommy_o is offline tommy_o  United States
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Sorry for not explaining -- I don't need the extra voltage or current. I'm using the headphone out of an ipod touch into the sure amp and it gets plenty loud. But using the cmoy to provide the amplification and keeping the ipod internal volume setting low makes the whole system truly sing, even with the cheap bookshelf speakers that are being driven.

The iPod Touch -> cmoy (gain 6) -> sure board sounds absolutely fantastic, but the ipod into the sure amp just sounds flat and muddy.
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Old 16th February 2010, 06:05 AM   #6
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Hmm, what about using an inverting charge pump such as this one on ebay?

Use a linear regulators to provide a +10 for the op-amp and another to provide +5 for the charge pump. Then the charge pump will give you -10 and everything remains relative to ground

Or you could use this one and just invert the voltage so the op amp will run with +/- 5V, the plus of this being the higher frequency (120-900 KHz whereas the previous one was 12KHz and probably audible).
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Old 16th February 2010, 10:43 AM   #7
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Sorry for the double post and as I don't see an edit button; this is the second charge pump I saw - SP6661 200mA Charge Pump Inverter or Doubler - eBay Voltage Regulators, Electronic Components, Electrical Test Equipment, Business Industrial. (end time 27-Feb-10 18:02:26 AEDST)
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Old 18th February 2010, 01:59 PM   #8
tommy_o is offline tommy_o  United States
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I think I'm going to do it right and build the Elliot Sound Products project 88, the 'High Quality Audio Preamp'. The opamps are OPA2134, identical to whats in my cmoy. The project also includes specs for a power supply, with schematic, that I'm sure I can put together on perfboard. It also uses a wallwart so I still dont have to fool around with mains!
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Old 18th February 2010, 04:28 PM   #9
zog666 is offline zog666  Australia
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Quote:
Originally Posted by tommy_o View Post
I think I'm going to do it right and build the Elliot Sound Products project 88, the 'High Quality Audio Preamp'. The opamps are OPA2134, identical to whats in my cmoy. The project also includes specs for a power supply, with schematic, that I'm sure I can put together on perfboard. It also uses a wallwart so I still dont have to fool around with mains!
I'll second this approach.. when I went to a Class D module my Alien USB DAC (no output opamps at all) didn't have the grunt to drive it well directly, the ESP 88b has been the perfect buffer between the two. I got the Elliot Sound Products PCB though.
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