Tube DIY Asylum: Re: Latest version of my 7788/7721 LCR 600Ohm RIAA Stage by fred76 Do It Yourself (DIY) paradise for tube and SET project builders.

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Posted by fred76 (A ) on October 2, 2005 at 20:41:37

In Reply to: Latest version of my 7788/7721 LCR 600Ohm RIAA Stage posted by Thorsten on October 2, 2005 at 15:11:26:

Hi T,

Nice.. Less is more kinda thing 8^). I noticed that you put 2 resistors in series (560+16) for the E180F pentode, is this series connecton okay when used within RC type riaa filters (inductance issues)?? You always mention to be 'careful w/ bypassing'. In this case with the output coupling cap you implemtened (mkp + ERO film/foil for bypass), do you rely with careful matching of parameters (DA, ESR, etc.) or do you follow a Rule of Thumb in calculating the right combination of values 'that work' (ie, 4.7uF+.52uF as opposed to 5uF+.22uF) to get the capacitance needed?

BTW, I did revise the 6ER5-> 6DJ8 circuit below. You lost me though when it came to the 'Semi-Split RIAA' recalculation when you mentioned: "..just shift the series resistor value to the calculated 195KOhm. In the final Adjustment this resistor needs adjusting to the LF is flat at 20Hz (or whatever you want to tune to, I usually leave around 0.5db LF lift @ 20Hz)."

I would be very much grateful if you can give more 'hints' on the math (formulas) or the meaning of "shift the series R value". Thanksabunch!

Br,
fred

PS - I used 196k for R1, can't find an exact 195k value even if put bigger values in parallel.

• 6ER5->6DJ8   (Open in New Window)

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