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Old 22nd February 2014, 12:17 PM
Richard Richard is offline
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Join Date: Dec 2005
Location: Notts
Posts: 5,198
Default Re: Phono 3 with 5751 valves

Hi, yes that sounds a good plan and you'll find a single cap can use 2 of the pcb holes to link across where the 3 caps used to go thereby taking out the switch.

You will notice if you put 0.022 and 1M into the filter calc it gives a corner f of 7.2Hz. In fact none of the cap values or combination appear to tie in with what we'd expect for a simple coupling. Yet the original design article for Phono 2 said they did, suggesting 0.015uF for 10Hz, 0.0082uF for 20Hz and 0.0039uF 40Hz could be used. If you'd like the original article send me a PM with your email address and I'll email a pdf.

When the kit came out though that had been changed to 0.1uF. The filters through an amp are cumulative so possibly it was found to need adjustment on test. (I checked mine, shown in the first post with bypass caps and 5751, using a reverse RIAA filter gen and scope and it is fine following the Hagerman curve down to LF.)
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