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TheDriver41 29th September 2004 08:38 PM

buffer/preamp?
 
I am confused on exactly what buffers and preamps do. From my current understanding a pre-amp shows the source high impedance, letting it work easier. Then takes the low voltage source signal (1-2v?) and amplify it to (18-20v?). Why this helps I don't know. Also it the preamp shows the amp a low impedance, 100-200 Ohm. I think this helps the amp work easier. I'm I correct?

What is the difference between a buffer and preamp?

What does a typical gainclone like Brains kit want for voltage in and impedance?

I have a cheap apex dvd player, computer, and Ipod. How can I measure what they put out?

I found this out about the Ipod.
An output test on the Ipod
http://members.brabant.chello.nl/~m....surements.html

Data sheet for the Wolfson WM8731. The DAC/headphone amp used on the ipod
http://www.wolfsonmicro.com/uploads/...31_WM8731L.pdf

The output test shows about 90v out but from what I got from the data sheet it does about 1.3v. The output test shows an output impedance of 100 ohm from the Ipod. It also looks like the bass response is better when the Ipod sees a high impedance load.

Knowing this what can I expect if I connect an Ipod directly to a basic BrianGT kit with out pot? How would a pot help?

How would a preamp/buffer help? And how can I build a preamp/buffer to take what I got and make it into what I need?

Which of my three sources do you think would have the best sound? I'm thinking the Ipod, because it runs on batteries and probably has the best DAC.

Sorry for all the rambling. Any help would be appreciated. Iím reading a couple of electronic books, one on op-amps and another on general hi-audio equipment. But the reading is very slow.

Thanks,
Matt

40Watts'n beer 2nd October 2004 06:14 PM

source compatibility
 
2 Attachment(s)
most solid state devices, such as Your IPOD and CD/DVD player will get along fine with the relitivly low input impedence of the GC. However if you want to run multiple boards per channel for a bridged or parallel set up (for more power) you may want to look into adding a buffer to increase the impedence that the source sees. also, some tube equiptment is designed with higher impedence in mind, so if using a tube preamp a buffer is in your best interest.
Now for the buffer vs. preamp issue. Basicly a preamp is variable in its output and a buffer is fixed, but a buffer can be made variable by simply putting a pot in line after the source and before the buffer. I also think it is kosher to put the pot after the buffer. I am running 2 amps per channel, without a buffer at the moment and a 100K pot as my volume control. because I dont need any more gain than I already have, I will probably go with a buffer to combat the low impedence.

Nuuk 3rd October 2004 08:40 AM

Buffers were originally used to isolate the input of the Inverted Gainclone from anything preceding it. This is because with the IGC, the electrical properties of items like pots, interconnects etc affected the working of the amp.

The original IGC circuit also has a fairly low 10K input impedance so a buffer with a higher input impedance often helps.

A preamp is really just a buffer (or gain stage if it is needed) with a means of selecting and/or controlling the level of the signal.

I have recently posted a design for a suitable preamp
here on my Gainclone pages. ;)


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