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DIY Simple Active Preamp

bobrown14 said:
Nice rack and I dig the crown gear too. Where did you get your case for the SSP?

Cheers,
Bob
Click to expand...

Par Metal
They have a variety of sizes in steel and or aluminum.
It is shipped like a flat pack.
I found it easy to drill.

I love that Crown PS 200 amp, and I use one at home, too.
Currently, in the SSP system, I have a Trends chip amp (not visible in the photo) for the HF.

Grainger49 said:
Wait, am I the first to get to say:

NICE RACK! ! !

Sorry, couldn't help myself.
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:D

sachu888 said:
I have few more boards left for this preamp.PM me if anyone needs them.

Regards,
Sachin
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The board is great and shipped quickly. Thanks again.
 
I blew it up!

Give me a hand, this is what happened:

I had been running it with batts at work and I decided to bring my PS from home. When I hooked it up I had tremendous hum, much worse than I experienced at home. So I disconnected the DC power plug and cable and checked it on a meter for shorts. It was fine. So I reconnected to try placing a ground lead from PS to another chassis in the rack and I killed it. Apparently hooked up power leads to the PS in reverse, don't ask how or why, and the unit went dead.

I put the batt back and all I get is pops on one channel as I move the stepped attenuator through its contacts. I can't remember if the LED is blown.

I am assuming the only thing I could have killed is the IC.

Should I just order up a new one or anything else to add? I can't troubleshoot it because it's at work and I'm not.

Then there's the issue of the PS grounding, so obviously I need to resolve that. Or I'll be back to the drawing board.
 
Grainger49 said:
Swapping polarity is like "crossing the beams" (Ghost Busters reference).

Why do I know? I have done it. This sounds like your problem.

Luckily it isn't very expensive and a great learning experience as it was for me.
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Oh, yea. I knew I wasn't supposed to do it, but that didn't stop me.

The other thing is, grounding........see, because I don't want to run this on batts. Well, maybe I'll try another supply, but I really don't think I've addressed this issue. No commercial audio gear, as far as I've seen, isolate the I/O connectors from the chassis. So; I'll let you know what else goes up in flames after the parts come in.
 
skywave-rider said:
Oh, yea. I knew I wasn't supposed to do it, but that didn't stop me.

The other thing is, grounding........see, because I don't want to run this on batts. Well, maybe I'll try another supply, but I really don't think I've addressed this issue. No commercial audio gear, as far as I've seen, isolate the I/O connectors from the chassis. So; I'll let you know what else goes up in flames after the parts come in.
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If you are using a seperate enclosure for a power supply, try building your own cable and getting sockets and plugs that can only be plugged in the correct way. I use these from Mouser and they work mighty fine:

Mouser part # 568-NYS321 (male nutrik)

Mouser part # 568-NYS324 (female nutrik)

Easy to drill a hole for these, 3 pin plugs

Ve+ Ve- and ground ... no hmmmm, ground your TT ground to chassis point on your box with the Phono board.

Cheers,

Bob
 
Thanks, Bob. Yeah, I have that on the SSP side, but bananas on the PS side....the bananas are where I screwed up.
http://www.audiokarma.org/forums/attachment.php?attachmentid=326206&d=1327905453


bobrown14 said:
If you are using a seperate enclosure for a power supply, try building your own cable and getting sockets and plugs that can only be plugged in the correct way. I use these from Mouser and they work mighty fine:

Mouser part # 568-NYS321 (male nutrik)

Mouser part # 568-NYS324 (female nutrik)

Easy to drill a hole for these, 3 pin plugs

Ve+ Ve- and ground ... no hmmmm, ground your TT ground to chassis point on your box with the Phono board.

Cheers,

Bob
Click to expand...
 
My suggestion is to get a couple of less expensive LM833s to check out your CNC. Worked for me when I managed to kill a couple of LME49720s. This way you can tell if everything else is OK, or it will only cost you ~$1 if you have additional problems.

Hope you have a local supplier of parts - - -
.
 
Pio1980 said:
Order a chip and check for burned traces.
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Along with chip, also check 2 electrolytic capacitors near chip. They are on power supply rails. Chances they faced reversed polarity and blown up.

For future - in each power line adding 1N4007 diodes with proper polarity could help. Though this will add voltage drop of 0.7V across diodes but avoid this kind of loss, time and money.
 
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Forgive these questions but I skipped from first page to end. Can someone point me to the page that has the absolute most recent schematic along with the parts list? Also, what's the average price not including building a chassis? And finally, the pic I saw on page 1 doesn't include any kind of attenuation - is there a new schematic that includes a volume pot?
 
spicynuts said:
Forgive these questions but I skipped from first page to end. Can someone point me to the page that has the absolute most recent schematic along with the parts list? Also, what's the average price not including building a chassis? And finally, the pic I saw on page 1 doesn't include any kind of attenuation - is there a new schematic that includes a volume pot?
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Hi,
I am posting BOM which originally posted by Hypnotoad
Qty X Part No: > Description

2 X ECW-F2225JA > CAP FILM 2.2UF 250VDC RADIAL
2 X EEU-FC1E101S > CAP ALUM 100UF 25V 20% RADIAL
2 X K104Z15Y5VF5TL2 > CAP CER 0.1UF 50V RADIAL
1 X AD823ANZ > IC OPAMP JFET R-R DUAL LN 8DIP
1 X ED90105-ND > IC SOCKET 8PIN .300 SOLDER TAIL
1 X SSL-LX5093IT > LED 5MM RED TRANSPARENT
3 X ERO-S2PHF8201 > RES METAL FILM 8.20K OHM 1/4W 1%
2 X RNMF14FTC10K0 > RES MF 1/4W 10K OHM 1% AXIAL
2 X ERO-S2PHF1003 > RES METAL FILM 100K OHM 1/4W 1%
2 X RNF14FTD100R > RES MF 1/4W 100 OHM 1% AXIAL

These are manufacturers part numbers so they should work with Digikey and Mouser except for the 10k and 100 ohm resistors. The extra 8.2k resistor is for use with the LED.

Alternatives from Mouser are:
2 x CMF5510K000FHEK > 1/4watt 10Kohms 1%
2 x CMF55100R00FHEB > 1/4watt 100ohms 1%

Regards,
Sachin
 
omishra said:
Along with chip, also check 2 electrolytic capacitors near chip. They are on power supply rails. Chances they faced reversed polarity and blown up.

For future - in each power line adding 1N4007 diodes with proper polarity could help. Though this will add voltage drop of 0.7V across diodes but avoid this kind of loss, time and money.
Click to expand...

Thanks, Pio and omishra. I have ordered both the electrolytics and the diodes.
:thmbsp:
Looking into grounding as well as an alternate PS for checking. Should be back in business by late next week.
 
skywave-rider said:
http://www.audiokarma.org/forums/showpost.php?p=5339215&postcount=147
http://www.audiokarma.org/forums/showpost.php?p=5339069&postcount=146
http://www.audiokarma.org/forums/showpost.php?p=5339967&postcount=151

First two are schematics. The third is a note from Hypnotoad regarding value of the electrolytic caps, he says 100uF as in the bog, That is what I used.
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Additionally I suggest using 1M 1/4W 1% Resistance from each input to ground. This will stop DC offset on output while input is not connected to any source.
 
omishra said:
Additionally I suggest using 1M 1/4W 1% Resistance from each input to ground. This will stop DC offset on output while input is not connected to any source.
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It has 25k in the pots from each input to ground already, it doesn't need the 1M's. There should be no DC offset if you are using the DC blocking caps.
 
HypnoToad said:
It has 25k in the pots from each input to ground already, it doesn't need the 1M's. There should be no DC offset if you are using the DC blocking caps.
Click to expand...

You are correct! My suggestion was for the use case without pots and DC blocking caps.
Here suggested schematic in above post is missing that pot. With the use of either 25K pot at input or 1M resistor to refer input to ground, it is possible to eliminate DC offset while excluding that DC blocking cap. Also it does affect sound anyway.

IMO this is only suggestion with my own experience where I excluded pot and DC blocking caps. I measured 0.3mV DC that could be ignored. I wanted highest input impedance possible.
 
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I expect that with fixed, balanced, regulated supplies, fed from AC you would not need an output cap.

However, batteries do not drain linearly so they cause imbalanced supplies and an output offset as they drain. This necessitates the output cap.
 
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