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Old 3rd November 2012, 09:47 AM   #8451
atupi is offline atupi  Romania
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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.
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Old 3rd November 2012, 11:11 AM   #8452
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by atupi View Post
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 ?
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Old 3rd November 2012, 11:17 AM   #8453
Salas is online now Salas  Greece
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Quote:
Originally Posted by atupi View Post
For a 0.1uf interstage what is the rolloff freq ?
Finally got teflons
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.
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File Type: png 47n.png (11.3 KB, 219 views)
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Old 3rd November 2012, 11:38 AM   #8454
AndrewT is offline AndrewT  Scotland
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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.
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Old 3rd November 2012, 12:02 PM   #8455
Salas is online now Salas  Greece
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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.
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Old 3rd November 2012, 12:30 PM   #8456
AndrewT is offline AndrewT  Scotland
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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.
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Old 3rd November 2012, 03:57 PM   #8457
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Thanks for 'inter-stage plots'...
...good to see this.

Si.
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Old 3rd November 2012, 04:33 PM   #8458
atupi is offline atupi  Romania
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Quote:
Originally Posted by dimkasta View Post
You are killing the basic advantages of a buffer to keep the output impedance low and stable and drive the interconnects.
Quote:
Originally Posted by RCruz View Post
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 ?
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 ?

Last edited by atupi; 3rd November 2012 at 05:00 PM.
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Old 3rd November 2012, 07:42 PM   #8459
Salas is online now Salas  Greece
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Good, though never made better than 5%, you gotta match 'em.
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Old 5th November 2012, 09:44 PM   #8460
Doug R is offline Doug R  United States
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Salas,
I am wading through this HUGE thread, so forgive me if this has been covered (I am guessing it has.) Is the 0.1 uF coupling cap involved in the RIAA. I have some Russian 0.47 K40's that I would like to try. Is that a no-no?
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