Preamp ideas for F5

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#81
juma-- just ordered the parts to build 3 of the preamps for the F5--i took one of my F5's to a friends house to use with his epos speakers and with a passive preamp the F5 didn't have enough gain--would you have a pic of the underside of your board to help me with the layout??? thanks mark
 
#82
This layout?
(bottom side view)
 

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#86
Re: PC board layout.

increek22 said:



Hello Stein2, any chance you have an image of this board without components showing copper only? CAD files?

thanks, Joe
Click to expand...


That layout is Juma's, borrowed from our local forum. I'm about to start working on my preamps, one of them being a simpler one... and one designed by Borbely with ECC86... I guess Juma will see this and act upon request.
 

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#98
Jack Tupp said:
How well would an AMB a20 set up for voltage gain work as a pre-amp for the F5?

The α20 Line Stage Amplifier
Click to expand...


F5 has a very high Zin (101k) so it doesn't need high current drive i.e. EF (Q5,Q6). Without EF Vbe multiplier(Q7) makes no sense so we will lose it too. What is left is schematic from post #53 of this thread (which has higher Id through JFETs in order to avoid that grainy sound that makes some people to hate JFETs).
 
#99
juma said:
F5 has a very high Zin (101k) so it doesn't need high current drive i.e. EF (Q5,Q6). Without EF Vbe multiplier(Q7) makes no sense so we will lose it too. What is left is schematic from post #53 of this thread (which has higher Id through JFETs in order to avoid that grainy sound that makes some people to hate JFETs).
Click to expand...

"It is configurable at build-time for a voltage gain of 1 to 20 (0dB to 26dB)"

Even if you set it up for voltage gain?
 
#100
Many signal sources have Vout of 2V RMS and many have less. F5 needs about 2.6V RMS at its input for full power output. So you need some gain. How much? It depends on your sources. Maybe you have very efficient speakers and you don't need to drive your F5 to full power - then you'll need no additional gain from preamp. It's all about what you have and what you need...

BTW, the gain is set by ratio of resistor values in the feedback loop (R14/R13 in alpha20 sch.)
 
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