Potentiometer Value :

[DaveSail]

I am building Peter Daniel's LM470 kit , with a Plitron 22 + 22
300 VA XFMR . Driving a pair of efficient two - way , 8 Ohm
6 1/2" Woofer speakers . Want to use the " Goldpoint Mini - V ".
How many " Ks " should I order ?

David V. Webber

[sofaspud]

I'm not familiar with the kit. What is the input impedance of the amp? What is your signal source?

[rabbitz]

Peter's LM4780 has Zin=22k.

I've used 10K and 20K with Peter's LM4780. I found it's actually better with an active pre (or buffer) after the volume control but that's a personal choice and depends on the output impedance of the source.

[DaveSail]

The input wold most likely be a CD Player , presently an AMC CD8b .
But , also , various other inputs through the Parasound P/HP-850
Pre - Amp .

I don't know the values of the amp , but here is a schematic :

http://www.audiosector.com/lm4780%20amp.pdf




David

[AndrewT]

10k pot has a maximum output impedance of ~2k5.
The input impedance of the 4780 as shown is 22k. R0=22k sets Zin.
That gives a ratio of 22:2.5 for Zin:Rs of ~ 9:1, OK.

I don't know the values of the amp

! and you have started building it.

[DaveSail]

Where can I get a soldering iron " Pointy " enough to do
those " almost touching " LM4780 pins ?? !! David

[cent88]

Is 100k POT too high for LM3886? with Rin 15kOhm.
According to the datasheet, Rin too high will cause the chip to oscillate when input is floating.

[AndrewT]

For Rin=15k, I will recommend 10k pot.

[danielwritesbac]

Originally Posted by DaveSail

Where can I get a soldering iron " Pointy " enough to do
those " almost touching " LM4780 pins ?? !! David

Use Gel Flux from the radio shack. That will cause the solder to flow where it should go. . . rather than ball up into a mess.