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Old 30th July 2008, 11:51 AM   #1
Ted205 is offline Ted205  United Kingdom
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Default Discrete buffers

Has anyone built the discrete buffer (three transistors - Andrew Rothwell) from decibel dungeon ?

I've simulated it and it seems to work well.
I'm using 3 C549B transistors

However converting over strip board i get very little audio output into a 6ohm speaker. I also get a 'cloudy' sin wave at the input and output (function generator at the input). What could be causing this?

Can anyone help me I've been over the stripboard several times and can't find anything wrong.


thanks
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Old 30th July 2008, 02:19 PM   #2
AndrewT is offline AndrewT  Scotland
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post a close up pic of both sides of the PCB and the whole preamp.
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Old 30th July 2008, 03:18 PM   #3
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This isn't going to help, but I gave up on this buffer. I tried several builds on stripboard, and then gave up.

I think that Nordic may have mentioned that he had trouble with it as well.

Good luck...
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Old 30th July 2008, 05:33 PM   #4
Ted205 is offline Ted205  United Kingdom
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well i've got it working, though i do get quite abit of ground hum (which can be sorted).

Am i wright in say that this buffer doesn't actually add any gain? and is at unity?
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Old 30th July 2008, 06:17 PM   #5
Nuuk is offline Nuuk  United Kingdom
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That's correct, it is a unity gain buffer.

I've built several versions with no problems like hum. There is a bit of DC on the input and I got very small clicks as I turned the stepped attenuator.
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Old 31st July 2008, 07:21 AM   #6
Ted205 is offline Ted205  United Kingdom
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look at it with a scope it looks like unity. When i compare it with my laptop straight to a speaker vs. laptop->buffer->speaker it seems to attenuate the sound. Its louder with out the buffer inline.

Is this correct ?


Nuuk do you have a pcb version?
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Old 31st July 2008, 07:29 AM   #7
Nuuk is offline Nuuk  United Kingdom
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I can't comment on the loudness issue as I have not experienced it.

No, I don't do PCB's, and this circuit is so simple it hardly warrants one.
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Old 31st July 2008, 08:36 AM   #8
Nordic is offline Nordic  South Africa
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Yep, I gave up on that buffer too.. after numerous diffirent PCB's, PSUs, and transistors, I could not get it to run stable for more than 5 minutes...

I have a friend who uses it sucsessfully though...

Then did the Pedja Rogic buffer, and was about as impressed as I get.

Since then moved to an amp that does not need the extra distortion of another stage slapped infront of it...

P.S. a discrete unity buffer will put out slightly less than the input...
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Old 31st July 2008, 09:08 AM   #9
poynton is offline poynton  United Kingdom
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What about a premade buffer module ?

http://cgi.ebay.co.uk/STEREO-FET-BUF...713.m153.l1262



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Old 31st July 2008, 09:24 AM   #10
Nordic is offline Nordic  South Africa
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Good old B.I.Y. ?
Buy it yourself.
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