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Glassware Aikido All-in-One (Octal) | ACF-2 Buffer

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#43
Ohhh... Makes sense....
That's great to know!
Actually answers a few questions for me...

Thanks!

BTW.... 30k seemed to work out best for my project... (Aikido ACF 9pin in linestage)..
Since the variables can only be calculated up to a point... (long interconnects, varying amp impedances etc).. 30 would do the least harm, as close as I can calculate it..
 
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#44
As long as the source can drive it, it can be as low as you want 🙂

My solid state power amp is 10k Zin... My tube amps are around 90k... If you go too high you get HF rolloff due to CMiller though... Then you need either pentode or cascode input...
 
#45
kodabmx said:
As long as the source can drive it, it can be as low as you want 🙂
Click to expand...
Well... that was sorta the whole point of choosing/using the ACF buffer...
Helps various sources drive various things...

My solid state power amp is 10k Zin... My tube amps are around 90k... If you go too high you get HF rolloff due to CMiller though... Then you need either pentode or cascode input...
Click to expand...
That's what I meant...
Given a variety of amps (that I might eventually use) with that or even greater span of input impedance... 30k is the best compromise so as to (at least try to) avoid the Miller thing..

Bear in mind also, that you go to low, you get LF rolloff...
 
#46
Wikkid said:
Ohhh... Makes sense....
That's great to know!
Actually answers a few questions for me...

Thanks!

BTW.... 30k seemed to work out best for my project... (Aikido ACF 9pin in linestage)..
Since the variables can only be calculated up to a point... (long interconnects, varying amp impedances etc).. 30 would do the least harm, as close as I can calculate it..
Click to expand...

30k is a pot spec I haven't heard off, the usual suspects being Alps@20, 50, 100K etc.

What make is that ?
 
#52
sunil said:
50K looks like the perfect middle ground.
Click to expand...

Making the BEST choice nescessitates knowing to a certainty the impedance of the source and load... Especially the load.. Knowing total cable capacitance, and input capacitance of the load, is crucial, but it's rare that one does... In most cases, you'll wind up making a "best guess" at it, since knowing cable capacitance is something most don't.... and knowing the input capacitance of the load component usually requires manufacturer giving that knowledge... and they usually don't.

The consequence of getting this wrong.... is basically creating a filter... a Bandpass RC filter.. It will prematurely roll off either the highs or the lows... depending on whether you've chosen a higher or lower pot value....

Here is a very comprehensive thread on the subject: How to determine what value Pot (attenuator)??? :up:
 
#53
Using a log pot between the input switch and the active circuitry as a volume control forces certain compromises. You know you're in trouble when you cannot fully control something "crucial" to performance, such as the cable capacitance when cables can easily be replaced. A better choice is to design the conditionality and compromises out of the volume control, as Baxandall did decades ago. Yet, the log pot tradition holds.
 
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#55

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#56
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