Chip amp with input transformer?

martyh · 28th November 2004, 07:38 AM

Hi all,
I am new to chip amps but not to diy. I have built a few tube projects but no sand amps to date. I just ordered a LM3875 kit from chipamp.com and plan on building it with input transformers as I have a few source components with a high Zout. The transformers have a 3:1 turns ratio so a typical high output source will deliver about .5 to .7 VRMS at the input of the amp. Will the standard kit work with so low an input voltage? If not I gather that I can increase the gain by raising the value of the feedback resistor. Can anyone point me in the right direction as to a suitable value for that resistor?
Thanks in advance for any help,
Marty

wxn · 28th November 2004, 10:32 AM

The calculations required are very simple. Anyway, it should be fine as it is.

martyh · 28th November 2004, 07:22 PM

Thanks; I found the formula in the archives. Changing the R from the neg input to ground should be a simple matter if I find I need a bit more gain

28th November 2004, 07:38 AM	#1
martyh diyAudio Member Join Date: Feb 2004 Location: Wisconsin	Chip amp with input transformer? Hi all, I am new to chip amps but not to diy. I have built a few tube projects but no sand amps to date. I just ordered a LM3875 kit from chipamp.com and plan on building it with input transformers as I have a few source components with a high Zout. The transformers have a 3:1 turns ratio so a typical high output source will deliver about .5 to .7 VRMS at the input of the amp. Will the standard kit work with so low an input voltage? If not I gather that I can increase the gain by raising the value of the feedback resistor. Can anyone point me in the right direction as to a suitable value for that resistor? Thanks in advance for any help, Marty

28th November 2004, 10:32 AM	#2
wxn diyAudio Member Join Date: Sep 2003 Location: Vilnius	The calculations required are very simple. Anyway, it should be fine as it is. __________________ Nothing is as simple as it seems

28th November 2004, 07:22 PM	#3
martyh diyAudio Member Join Date: Feb 2004 Location: Wisconsin	found it Thanks; I found the formula in the archives. Changing the R from the neg input to ground should be a simple matter if I find I need a bit more gain

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