Preamp ideas for F5

[bubba177]

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

 

[stein2]

This layout?
(bottom side view)

 

[Cobra2]

What about SSTART?
http://www.diyaudio.com/forums/showthread.php?s=&threadid=132822&highlight=
-should have the needed gain, and more...

Arne K

 

[bubba177]

THANKS!!!!

 

[increek22]

PC board layout.

This layout?
(bottom side view)

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

thanks, Joe

 

[stein2]

Re: PC board layout.

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

thanks, Joe

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.

 

[stein2]

Borbely ECC86

and this is my favourite

 

[stein2]

Borbely list

List of materials for Borbely's hybrid

 

[stein2]

other preamp ideas...

http://www.hifi-forumi.com/forum/viewtopic.php?f=18&t=12663&start=0&st=0&sk=t&sd=a

For interested, browse through the subject and look at schematics for various preamp solutions, the subject is the same, preamps for F5 and no need to be registered to see the images... Most of those has been tested by Juma and proven to be working well with F5.

 

[juma]

Re: PC board layout.

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

Here you are, copper side view:

 

[increek22]

Re: Re: PC board layout.

Here you are, copper side view:

Thank You.

Joe

 

[bubba177]

just a thanks to juma-got one of your preamp modules installed in a F5 and playing it right now-sounds great!!!!!!!!!!! thanks-mark and joe
ps- named this one F5HO -- ( High Output )

 

[juma]

You are welcome
I'm glad you like it. BTW, which one did you choose?

 

[bubba177]

one from post 53

 

[calvinhpk]

juma....what do you measure to adjust the DC offset?

 

[juma]

DC offset is unwanted DC voltage on amp's/preamp's output, so you should measure it between output point and ground.

 

[Jack Tupp]

How well would an AMB a20 set up for voltage gain work as a pre-amp for the F5?

The α20 Line Stage Amplifier

 

[juma]

How well would an AMB a20 set up for voltage gain work as a pre-amp for the F5?

The α20 Line Stage Amplifier

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).

 

[Jack Tupp]

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).

"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?

 

[juma]

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.)