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Old 27th July 2011, 01:45 AM   #1
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Default pre amp buffer suggestions.

It was suggested by some members of the forum that pre-amp buffer may not be nessesary. But after some listening i do notice a level distorsion when pushing the source (laptop) output to it's limits. I believe i can get more clean db's out of this chip amp. Not only that i don't want to burn out the laptop soundcard. Digging around on ebay, like with the rest of the gear i sourced ebay. Can anyone comment on these possible pre amps, or either make suggestions to the direction i can take.

found these.

Buffer Pre-amplifier Headphone AMP KIT Tube 6N3 New | eBay

New 2Pcs 6N3+6Z4 Buffer Preamplifier Board GZ | eBay

Tube 6N3 Buffer Audio Preamplifier Pre AMP Kit For DIY | eBay

Not much specs provided, maybe nothing can deduced from looking at these, but any suggestings are welcomed, any suggestions away from these buffers are welcome

rick
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Old 27th July 2011, 03:42 AM   #2
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I don't know anything about those so I can't really comment, but you generally get what you pay for. Have you thought about increasing the gain of the chip amp and adding a volume control? It may be the best option in the long run.

Mike
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Old 27th July 2011, 04:27 AM   #3
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Quote:
Originally Posted by Michael Bean View Post
I don't know anything about those so I can't really comment, but you generally get what you pay for. Have you thought about increasing the gain of the chip amp and adding a volume control? It may be the best option in the long run.

Mike
As in a gain circuit, or an attenuator, or both?
one of the other members previously suggested just using 10K Pot as a balance between the source and amp. That way the i can keep a safe load on the source output and control the volume.
What is your suggestion, and how would i accomplish this?
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Old 27th July 2011, 04:45 AM   #4
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You would need to increase the gain of the chip amp by changing the feedback resistors, and add a volume potentiometer to control loudness, assuming it doesn't have one already. Do you know how much gain it has now? Is there a schematic you can post and maybe a picture of the circuit board?

Mike
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Old 27th July 2011, 04:59 AM   #5
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OK, I looked at previous posts and saw a picture of the board, it's the three chip unit right? What impedance are the speakers you're planning to drive with it?

Mike
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Old 27th July 2011, 05:04 AM   #6
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I bought these mono block amps based on LM3886TF chip from ebay.

150W LM3886 X 3 mono channel Audio Amplifier Board HiFi | eBay

got no schematic with them, i just contacted the seller, maybe he has one??. Just from the picture though there are three little blue somethings, maybe they are pots. But even still i wouldn't know what exactly how to go about adjusting and measuring them.
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Old 27th July 2011, 05:08 AM   #7
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Yep thats the ones. Speakers i built using ScanSpeak revelators(nice speakers), rated 8 ohm, they actually measure 6.9ohm.
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Old 27th July 2011, 05:16 AM   #8
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Alright, the bad news is with an eight ohm load, that amp is never going to put out any more than about 60 watts or so, to get the advertized 150 watts you would need about a two ohm load, so three chips per channel is way over-kill, but not necessarily a problem. The little blue adjustment pots on the board are most likely to adjust each chip for lowest DC offset. So you didn't get any info from the seller at all?

Mike
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Old 27th July 2011, 05:22 AM   #9
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No info what so ever. Though the Chinese company that produces the PCB has there name etched into them maybe i can try them if the seller has nothing.
But this far, are we a little stuck??
And having a 3 chip amp like this is just a little bit modest for the purpose?
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Old 27th July 2011, 05:48 AM   #10
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Like I said, three chips for an eight ohm load is more than is needed, only advantage to paralleling chips is increased current drive capability and consequently more power into lower impedance loads, but the same power into an eight ohm load as a single chip alone. So kind of a waste, but not really a problem as long as you accept that you're not going to get the power you may have expected. As for the initial issue of not having enough voltage drive from your laptop; given your situation, and seeing that it appears they have surface mount resistors that are kind of difficult to work with in the feedback path for setting gain, it may be best to use a separate preamp. I don't know if your set on the idea of a tube preamp or not, but something like this is probably a better choice for ease of use.

Wholesale Freeshipping DIY AMF NE5532 stereo preamplifier board #872 from Zhongshan Koqi Electronics Manufactory

Mike
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