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Old 13th March 2008, 09:07 PM   #1
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Default chipamp pcb?

Was just wondering if anyone had tried these pcb's:
http://cgi.ebay.com/Audio-Amplifier-...742.m153.l1262
I'm looking to build something similar to a bpa 300 and was wondering if I could use these since they're inverting.
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Old 13th March 2008, 10:07 PM   #2
CJ900RR is online now CJ900RR  Sweden
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Looks like it follows Nationals standard circuit, should sound "normal". Would not recommend them for a BPA300 design cause they dont have any output resistors, no zobel network and no DC-circuit. They would most likely oscillate (spelling?), overheat and burn if paralleled.

Im working on a pair of boards, not finnished yet. Might order in a week or so.
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Old 14th March 2008, 04:36 AM   #3
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yeah, i knew about the output resistors, was going to add them externally. I'm new to this stuff, though and didn't know about the other stuff. I actually originally started out just going to build a simple amp, but then I got this great deal on a dual center tapped 1000va transformer, and I got some killer older 12" Kenwoods to drive now. Figured I needed to ramp it up a bit.
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Old 14th March 2008, 02:06 PM   #4
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Default Gainclone PCBs

I am hoping some of you may be able to help. I am new to Gainclones and electronics.

Does any one know if I can buy the Chipamp.com or Audiosector.com PCBs in the UK? It would be easier to follow one of these kits.

I am really keen to make my own PCBs if someone has a simple yet reliable PCB design I could use.

I have purchased some copper boards and intend using the photo glossy paper method.

Which size toroidal transformer will give me the greatest flexibility with future upgrades? I have seen some at http://www.airlinktransformers.com/t...ansformers.asp

Which amp configuration will best suit my these speakers?

B&W DM601 S2
Crossover is at 4 kHz, efficiency is rated at 88dB/1W/1m, Impedance is said to be 8 Ohms nominal, 4.3 Ohms minimum
Response 70Hz-20kHz +/- 3dB on axis
Harmonic distortion below 1% 88-20.000 Hz at 90dB SPL at 1m.
Power handling is said to be 25-100W continuous of unclipped programme into 8 Ohms nominal

I really appreciate your help.
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Old 14th March 2008, 02:12 PM   #5
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without a 100nF/3.3R zobel or 1uH/10R low pass filter that LM3875 amp, configured as it is on the PCB, will definitely oscillate.
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Old 15th March 2008, 04:34 PM   #6
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Ok, so here's a question. I already have a couple of Peter Daniel's boards. If I got some more of those and used the Zobel option, and then added the output resistors externally, would that prevent the oscillation? I may not go for the full 300, I was thinking more of only using 4 chips per channel.
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Old 15th March 2008, 05:06 PM   #7
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Quote:
Originally posted by coldfuzion76
Ok, so here's a question. I already have a couple of Peter Daniel's boards. If I got some more of those and used the Zobel option, and then added the output resistors externally, would that prevent the oscillation? I may not go for the full 300, I was thinking more of only using 4 chips per channel.
Yes, you can use the inductor externally -- it (or the Zobel) should be close to the LM3875 or LM3886.

Use a 1/2 dowel as a form to wind 10 turns of #18 magnet wire as the inductor -- you can even use RS PVC insulated wire -- slip a 10 ohm resistor through the coil -- this will lower the coil's "Q" dramatically
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Old 31st March 2008, 06:23 AM   #8
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Quote:
Originally posted by CJ900RR
... dont have any output resistors, no zobel network and no DC-circuit. They would most likely oscillate... if paralleled.

\

What do you mean by "DC-circuit" ?

I'm reading the National literature, trying to understand this, but they don't mention any DC circuit.
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Old 31st March 2008, 08:09 AM   #9
CJ900RR is online now CJ900RR  Sweden
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Quote:
Originally posted by vectorplane



What do you mean by "DC-circuit" ?

I'm reading the National literature, trying to understand this, but they don't mention any DC circuit.

Sorry, my bad. I should have written "servo circuit" witch is the correct name for it. Instead of using cap's to minimize DC-offset, you can use OP-amps to keep it low. Look at Nationals AN-1192 (http://www.national.com/an/AN/AN-1192.pdf) at page 13.
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Old 31st March 2008, 12:34 PM   #10
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Default Re: chipamp pcb?

Quote:
Originally posted by coldfuzion76
Was just wondering if anyone had tried these pcb's:
http://cgi.ebay.com/Audio-Amplifier-...742.m153.l1262
I'm looking to build something similar to a bpa 300 and was wondering if I could use these since they're inverting.
I purchased thats pcb's,

i found the pin 8 (IN -) of the 3875 is connected straightaway to ground.

Is a joke to resolve it, but in fact the pcb is not working.
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