If this is a really stupid question, please make allowances... Is it possible to put a high pass filter between a solid state pre amp and a Quad II power amp? I'd like to avoid an active crossover and filter out <80hz, but my somewhat blundering attempts at research seem to show that it would involve a 0.13pF capacitor (if the input impedance of the Quad is 1.5M) which would have to be ceramic?
I have used a 100nF film to do the same job between the pre (Kenwood C1) and a Yamaha power amp with 20k input impedance, and that works very well, but I would like to try the Quad with the same speakers and pre amp.
I have used a 100nF film to do the same job between the pre (Kenwood C1) and a Yamaha power amp with 20k input impedance, and that works very well, but I would like to try the Quad with the same speakers and pre amp.
Try to put a 20 kohm in parallel to input of Quad and use a 100 nF in series before them
I think it works
I think it works
The EF86 will not function correctly with a grid leak of 20k.
@funkuncut Your calculations are off. You need 1.33nF looking into the 1.5M to get Ft=80Hz.
1.5M seems a bit too low for grid leak bias and the input pair has 680 + 100R cathode resistors to ground. Should be safe to add a resistor parallell to the input and then a cap to cut the lows.
Thank you all! I'll try both as soon as I get a chance and report back. (I'm easily confused by maths, so I always try to check...)
Grid leak resistor has a maximum, not a minimum. You can use 0ohm if you want (grounded grid uses no grid leak usually).
Yes. I was refering to grid leak bias, an old and more or less forgotten technique to bias (input) tubes by using an unusually large grid leak resistor (10M) and letting the grid current develop a negative voltage across it.
https://www.diyaudio.com/community/threads/grid-leak-bias-how-does-it-work.272689/
This is called "contact potential biasing". Langford Smit's said in his Radiotron book that is kind of fixed bias technique.