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Chip Amps Amplifiers based on integrated circuits

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Old 4th February 2003, 08:31 PM   #501
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And that's the PS case.
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File Type: jpg ps.jpg (40.5 KB, 2311 views)
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Old 4th February 2003, 08:37 PM   #502
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Hey, so how critical do you guys think that the RC combination on the non-inverting input is? If you take another look at my gainclone pcb, you'll see that I tied the non-inverting input directly to ground.. Any thoughts?

Also, what is the best place to get pcb's made? My school will only make me so many of these boards.

--Jordan
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Old 4th February 2003, 09:33 PM   #503
Philo is offline Philo  United States
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Jordan,
I initially used the RC on the pos side then took it off then tried a few different combinations going back and forth and I couldn't hear any difference. I really gave it a good listen and honestly ended up shruging my shoulders and left it the last way I had it which was shorted to ground. My speakers have good detail but are getting long in the tooth (12 years), but I consider myself to have good hearing (being in sonar and all). I don't know if technically this isn't an optimum thing to do but it works well for me.
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Old 4th February 2003, 10:13 PM   #504
jleaman is offline jleaman  Belgium
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Peter. You are my Hero that stuff just look so nice.! DAm Hopefully if i move to toronto i can have the chance to meet you inperson and so on. : o ) THIS LITTLE crap hole i live in sux. and nothing changes here. Hopefully i move there. : O )

Looking forward to it. : O )

Jason
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Old 4th February 2003, 11:40 PM   #505
lohk is online now lohk  Europe
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Default "baby GC" using the LM1876

I have just - as for curiousities sake - made a kind of "baby GC" using the LM1876.
As you all know this is a stereo version, with 15W max. or so.

The main disadvantages are: The distances for the feedback are different from one channel to the other and, most of all, there is only one negative supply pin for both channels, which prevents it from using two separated psus.

I - this time - followed more or less the application schematic from National (non-inverted) but without the cap in the feedback path and without the zobel network. The psu are two 22200yF caps by Roederstein (the two pos. pins connected to each other) and a .47yF HQ MKT from + to -. I used a single 10A regular bridge and a 2 x 16V / 250VA transformer. All wiring in done in p2p, of course.

After firing up the tiny beast, it quickly showed up that there was too much DC offset (0.3V), which was corrected by two 47yF panasonic caps in the FB path.

To my very great astonishment even this amp sounds surprisingly good. It does not have the control of its "bigger" brothers, but is not bad nevertheless. And although I only had it mounted on a small heatsink it was capable to play to a fairly high level.

But I think that it still gets "into some kind of oscillation" after some listening, because after it is getting hot it stays a little warm, even with no signal. Maybe I should add the zobel to get out the last instabilities.

Voila ! This is maybe the cheapest possible DIY amp with reasonable sound quality you can make, and it is surely good enough for secondary duties, like driving surround speakers etc. And it is so small ! Without thinking about the heatsink (and the transformer) you could fit one of these into a box in the size of a compact cassette.

Klaus / - likes tiny amps
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Old 4th February 2003, 11:48 PM   #506
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Talking minty

Quote:
you could fit one of these into a box in the size of a compact cassette
...or, in the spirit of the Headwize-rs and Head-Fi-ers, you could use an Altoids tin.

/andrew - likes his amps minty-fresh and curiously strong
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Old 5th February 2003, 12:25 AM   #507
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Default wow!

peter, when you get tired of this unit and move on, SELL ME THIS ONE! I would drop a couple on hundred on this in a second! I have no chance of building anyhting that beautiful. congrats! and remember....sell it to ME! LOL! tony
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Old 5th February 2003, 02:40 AM   #508
ted is offline ted
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Default Gain clone problems.

Ok, after seeing the gain clones built I had to try one.
Things are working well enough, no occ and good power.
However, I have a 60 cycle rep as shown in the picture.

It's not quite hum (not sin signal) but it is 60 hz. The peak-2-peak
is just under .02V. What do others get?

The volume has no effect on the signal. Touching the case,
vol control, and other things have no effect.

I have tried moving the xfmer with jumpers 12 inchs from the
chip with the same hum.

I checks the +/- power rails and is's a small sawtooth at 60 cycles.
Any ideas.....

Click the image to open in full size.
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Old 5th February 2003, 02:42 PM   #509
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Default volume control issues

Hey, so I was thinking of using a relay-based volume control much like the one in the Aleph P instead of using a potentiometer. Are there any input inpedance concerns that I need to be wary of?

--Jordan
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Old 5th February 2003, 03:56 PM   #510
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I imagine that depending on pot's resistance, the circuit will be more or less prone to oscillatintg. I used both 100k and 50k at the input, and 50k version sounded better, but other factors had influence as well. Also it was my impression that 100k version had more tendency to oscillate.
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