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Chip Amps Amplifiers based on integrated circuits

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Old 25th February 2003, 06:28 AM   #21
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Quote:
Originally posted by cowanrg
well, im listening to it now.

it doesnt have that NASTY noise in the background. however, i put in that 50K resistor like peter said, and there is a nice BUZZ in the speaker. and, its very quiet. i tried without, and its fine.
If you've got that 50k resistor connected in series with the ground between your source component and the GainKone as it seems to me you've described it below, then that will result in some buzzing.

If you're going to use that 50k resistor, it needs to be connected between the hot pin on the RCA and ground.

Quote:
also, i am not using the 4.7uf cap on pin 8. the idiot at the electronics store forgot to put it into my bag maybe that has something to do do with it. i will say this thing has some POWER. im not 100% quality, but that's partly due to the power its getting probably... in the 5 minutes ive been listening to it, its gone from 26.4 volts, down to 25.33 and dropping as we speak.
That's typical. From a full charge, you'll get a bit of a drop in the first few minutes and then it'll level out before it starts dropping off again.

With a pair of 8 Ah batteries, you should get quite a lot of listening in before you need to recharge. To prevent deep cycling and reducing battery life, I wouldn't let 'em get much below about 10 volts (or 20 volts if you're measuring across both batteries).

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oh yeah, is there any way to avoid that nice thump when i connect the positive and negative? will a switch stop that, or do i need a soft start circuit?
You'd need some sort of soft start circuit to get rid of it.

At the low voltages you're using, it's not going to be a problem other than perhaps an annoyance.

se
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Old 25th February 2003, 06:40 AM   #22
cowanrg is offline cowanrg  United States
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nice.

i measured my DC offset, and it was 0.004, i think that is pretty low.

so i have that resistor hooked up wrong then, good. that buzz was BAD. ill swap it around and fix it. i'll also get some caps to put in there as well.

this thing is extremely efficient. i had it cranked, and it barely got the heatsink warm.
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Old 25th February 2003, 06:54 AM   #23
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Quote:
Originally posted by cowanrg
i measured my DC offset, and it was 0.004, i think that is pretty low.
That's pretty low alright. Lower than expected. With the typical 0.2 uA of input bias current for that chip, and a 220k feedback resistor, you'd expect something more like 0.04 volts than 0.004 volts.

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so i have that resistor hooked up wrong then, good. that buzz was BAD. ill swap it around and fix it. i'll also get some caps to put in there as well.
Check the offset of your source component. If it's quite low or if it has a capacitor coupled output, then you don't really need that cap there in the first place. As they say, the best capacitor is no capacitor.

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this thing is extremely efficient. i had it cranked, and it barely got the heatsink warm.
Yeah. Which is why you should be able to get quite a bit of time off those 8 Ah batteries.

se
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Old 25th February 2003, 11:41 AM   #24
fezz is offline fezz  United Kingdom
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Quote:
Originally posted by Peter Daniel
I tried it with my Aleph X and it definitely influences sonics. With the resistor in place, the amp seems to be cleaner (or smoother) sounding. I don't really know the reason behind it.

filtering?
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Old 25th February 2003, 12:24 PM   #25
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About the buzz when resistor is in place from input to ground: I noticed that the amps is susceptible to oscillations at max volume when not shielded.
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Old 25th February 2003, 12:33 PM   #26
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Default Another X-former possability

Cowanrg,

I was thinking about using the PE 129-030 transformer. It seemed that Peter was more satisfied with the bass using lower voltage. This is a 20-0-20 5A model and its less than $10. I figured if the alltronics model would work, so would that one.

Good luck finishing it up.

S.
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Old 25th February 2003, 01:59 PM   #27
Philo is offline Philo  United States
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A great transformer for this app is sold by Steve at ApexJr. I've bought a few of these toroidals and have no complaints. They are 18-0-18 120VA and $15.00 a piece. I use one/chan and they have no problem driving most speakers. http://www.apexjr.com/miscellaneous.html#Toroids
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Old 25th February 2003, 02:52 PM   #28
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Quote:
Originally posted by Peter Daniel
About the buzz when resistor is in place from input to ground: I noticed that the amps is susceptible to oscillations at max volume when not shielded.
If his description of how he had that resistor wired in was the way I read it, he didn't actually have it going to ground from the input, but rather in series with with the amplifier ground and the source ground.

You know how you can get that horrible buzz when you just have the hot pin of the RCA hooked up and the ground's aren't connected? Same thing here only not quite as bad as if you had a truly open circuit.

se
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Old 25th February 2003, 04:04 PM   #29
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When I put mine together, I got some buzzing until I got the grounding correct. I still probably don't have it right, but I used the information from this site to tie the grounds properly, and it sounded quiet from that point on.

http://www.geocities.com/rjm003.geo/...io/diy_gc.html
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Old 25th February 2003, 04:07 PM   #30
cowanrg is offline cowanrg  United States
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will a 120VA transformer be enough for a mono channel? i guess for $15 for a toroidal just to test it out, its worth it...
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