You are killing the basic advantages of a buffer to keep the output impedance low and stable and drive the interconnects.
Thank you Andrew & Salas for the links.
I got #8380 the other day !
I havn't made anything with JFET's before...
...so I have a few PDF's etc. to read !
Good move to make some kind of measurement jig...
...& 'audio' test circuit.
Can drop 'em in and out of a 'test' simplistic...
...or the 'JFET Bride Of Zen' also looks interesting; as there ain't almost nothing there !
( listen to a few Soviet caps as well ! )
Thanks for the links again.
Cheers
Si.
I got #8380 the other day !
I havn't made anything with JFET's before...
...so I have a few PDF's etc. to read !
Good move to make some kind of measurement jig...
...& 'audio' test circuit.
Can drop 'em in and out of a 'test' simplistic...
...or the 'JFET Bride Of Zen' also looks interesting; as there ain't almost nothing there !
( listen to a few Soviet caps as well ! )
Thanks for the links again.
Cheers
Si.
I installed the DCB1 before PGA2311 because i know that PGA is buffered on the output.
If you or anybody else is having a better idea im happy to listen.
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So with a 25k pot in the dcb1, maximum input impedance would be ~255k, for which a 1.5 or 2.2 uf capacitor would suffice. That said I'll probably go with the 3.3 uf one to allow different preamps in the future!
No, if you will use a pot between RIAA and DCB1, the impedance to couple for will be the pot's own across. 3.3uF is fine since the interstage rolls off subsonic anyway.
Yes you can set gain by software. Mine is set to go from -95db to max +10db and you can go even further. The people who's using PGA says that is not recommended to use too much gain as he can become noisy after +10 maybe 15 db.
So it is a volume control with an opamp in the output that can be set to have some gain.... 10dB should be good for me.... What psu you are using ?
Say if you got no loss of low frequency between the output capacitor and next stage, i.e. if the output cap is huge and the next stage's input impedance enormous, then all the interstage fixed coupling predetermines is in the pictures below.
Attachments
I try to set the Power Amplifier roll off frequencies at values that suit my ears and my equipment.
If I were to set the pre-amp and any other Source equipment to the same roll offs then the effect is the same as cascading (with buffers between) two or more passive filters.
This drops the roll-off from -3dB to -6dB at the particular frequency chosen and also doubles the phase at roll-off from 45degrees to 90degrees (for two cascaded filters, it would be 135degrees for three filters).
To avoid the worst excesses of the above same frequency cascading, I adopt a wider passband for the Source equipment.
I generally allow an extra octave at the low end and an extra octave at the high end in pre-amps and buffers and Sources were I can control the passband.
If I were to set the pre-amp and any other Source equipment to the same roll offs then the effect is the same as cascading (with buffers between) two or more passive filters.
This drops the roll-off from -3dB to -6dB at the particular frequency chosen and also doubles the phase at roll-off from 45degrees to 90degrees (for two cascaded filters, it would be 135degrees for three filters).
To avoid the worst excesses of the above same frequency cascading, I adopt a wider passband for the Source equipment.
I generally allow an extra octave at the low end and an extra octave at the high end in pre-amps and buffers and Sources were I can control the passband.
That's fair, still with turntables mechanical nature and the many discs eccentricity 4-5Hz problems some mild predetermined subsonic roll off has been a prudent move in this design especially regarding big reflex speakers and/or flimsier pick up arms. Should be taken into account for total system high pass planning. The choice to modify the interstage VLF curve is still there of course. I recommend those two well tried values still. They had worked in the numerous systems that all those builds shown by the members found home to, just fine.
Don't just accidentally cascade two passive filters.
If a turntable needs the output to be filtered, then install a specific filter to achieve that end.
An example is the single pole roll-off added in the "new" RIAA curve.
It achieves very little attenuation of the nuisance VLF and yet it attenuates some of the wanted LF.
I consider it far better to use the old RIAA and attenuate the VLF with a two pole, or steeper, filter.
If a turntable needs the output to be filtered, then install a specific filter to achieve that end.
An example is the single pole roll-off added in the "new" RIAA curve.
It achieves very little attenuation of the nuisance VLF and yet it attenuates some of the wanted LF.
I consider it far better to use the old RIAA and attenuate the VLF with a two pole, or steeper, filter.
I'm using a simple shunt PSu with LM317 set as a CCS and a bipolar transistor as a shunt with zenner diode as a reference in his Base.
PGA is having almost 100db PSU noise rejection.
I'm very happy with it.
I have these caps on my drawer 2X Ero MKP1845 47nF 0 047uF 250V Tube Amp Audio Caps | eBay
Are they good to be used on the RIAA network ?
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