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DIY Simple Active Preamp

skywave-rider said:
I got my Cinemag transformers installed. It took me a while because I had to separate my chassis ground from my signal ground. But now I understand, finally.

These effectively isolate the input and there is now dead silence, no telltale buzz or hum. I would get that on some sources. I also installed these because I happen to like the sound of transformers.
EDIT: Here's the data sheet.

attachment.php


These particular transformers want to see a 10kOhm load. Since my attenuator is 20kOhm, I put 20k worth of resistance across the output of each transformer to give me 10kOhm. When I get a chance, I will snip those leads to compare 10k/20k. Cinemag says there won't be much difference, but fairly flat response beyond 20kHz is what you get with 10k. The response will roll off a bit with a 20kOhm load.

No listening impression yet other than these are working properly. I have to tidy up the wiring and then it's done.

I have a lot of old knobs, I like this one:

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Click to expand...

Source on the 1U? Wondering if it's any cheaper than modushop
 
Hey AKers, I am new here, also building an SSP, thanks to Omishra and Sachu888 here. And ofcourse big thanks goes out to Hypnotoad for the SSP.
 
I got my shipment of 5 or 6 different opamps from Digikey today. I'm trying them out now, I'll let you guys know what I think.

So far AD823 is doing really well.

I got a LME49990 but I put it in backwards on accident and I think I killed it. Sound's coming out of both channels, but it's only the left (or right?) track. Confirmed with Pink Floyd's "Money"
 
HHspinter,
If you only have one per 8 pin connecter, you didn't kill it.
This is straight from Omishra post #288.

Recently, I acquired 4 X 49990 and few sockets for 2X49990. For replacement of each AD823 costing twice of AD823 as (2 X 49990 + 1 SOIC-DIP PCB adapter) required for that. For new DIY enthusiast soldering those two 49990 (comes only in SMD package) on both sides of tiny PCB without making damage may turn into PITA. Patience is required.
 
You would need to solder on two LME49990 on a dual SOIC-DIP adapter. LME49990 is a single channel opamp and the adapter will allow two single channel smd's to work as one dual channel opamp.
 
I've adapted an LDR attenuator to my SSP, it really sounds great now! As soon as I work out a 15V power supply, I'll move it into some kind of case.(it's still in a gladware tub)
 
sfox52 said:
I've adapted an LDR attenuator to my SSP, it really sounds great now! As soon as I work out a 15V power supply, I'll move it into some kind of case.(it's still in a gladware tub)
Click to expand...

Those gladware tubs come in handy.

For those wishing to make the gain of the SSP zero, replace the 8.2k resistor with a 10k.

For those wishing to increase the gain of the SSP you reduce the value of the 8.2k resistors,

Av = 1 + R2 / R1

1 + 10k/8.2k = 2.21 voltage gain.

You can calculate the gain in db with this handy converter:

http://www.muzique.com/schem/gain.htm


The stock 8.2k resistor gives 6.9db gain.

Using a 7.5k gives 9.5db gain

Using a 5k gives 14db gain

Using a 1k gives 20.8db gain
 
Az,

That's a nifty looking circuit. Too bad the battery draw is so high, but a power supply will certainly take care of that.

Best Regards,
Terry
 
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