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Old 8th February 2009, 02:09 PM   #971
Salas is offline Salas  Greece
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Just a moment, will sim and tell. Wait.
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Old 8th February 2009, 02:15 PM   #972
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by RCruz
matched the BC550C using the DMM hFE
a waste of time.
You have pre-selected your To92 devices ready to find some matches.
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Old 8th February 2009, 02:17 PM   #973
Salas is offline Salas  Greece
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Well, to use 8.5mA - 9mA Idss in your circuit and not lose gain, you have to make the first stage source resistor to ground 27R, and the second stage source resistor to ground 47R.
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Old 8th February 2009, 02:25 PM   #974
Salas is offline Salas  Greece
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Quote:
Originally posted by RCruz
Hi Salas

What avlues should I use for eac place in the RIAA ?

(Also matched the BC550C using the DMM hFE)

Ricardo
Try to keep them 8.5 to 9mA range and matched near 0.1mA per pair and position. You can use the 10mA stuff for the Zener CCS and buffer.

It is not that critical for the BJTs since the lower part of the cascode mainly defines its output impedance, but not entirely futile, bcs matched hfe means matched for noise between channels as well.
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Old 8th February 2009, 03:14 PM   #975
RCruz is offline RCruz  Switzerland
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Quote:
Originally posted by salas


Try to keep them 8.5 to 9mA range and matched near 0.1mA per pair and position. You can use the 10mA stuff for the Zener CCS and buffer.

It is not that critical for the BJTs since the lower part of the cascode mainly defines its output impedance, but not entirely futile, bcs matched hfe means matched for noise between channels as well.
Thank you Salas... You are unreal!!!

I still have 40 jfets to match... should I look for a lower Idss ?

Please take a look at my data. I did a pivot table chart so we can know how many matches we have by value.

In the data table, I converted the mV readings into mA.

Ricardo
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File Type: zip jfet matching.zip (8.6 KB, 69 views)
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Old 8th February 2009, 03:30 PM   #976
iko is offline iko  Canada
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Quote:
Originally posted by salas
The card is good to get. To tell you the truth I haven't measured any 100Hz ripple spike on FFT with simpler shunt versions on the phono output as well, always buried in the grass, but the buffer to the V MOSFET can not hurt. Where is your measuring point? At dummy load or on phono's B+ including cable? How much current on load if with dummy? The key is the sound. To really hear something better. Try with headphones, you may discern and tell us. Only let it run enough before critical listening (2 days powering), I know that it smooths out in a day or two when from new, by experience. To preserve lower impedance gains, the output cap must be very low ESR (bypass with 0.1uF film), and the twisted cabling to phono B+ point and GND point, speaker grade thick. Congratulations for your results! Refreshing.
Meaured at the dummy load. I didn't check the current at the load. I've listened to it last night on the headphones. Subjectively only, I can say that it sounds "alive", very fresh. But this was a quickly put together prototype, without care on the layout and parts; probably can be improve with some care.

A film cap with low ESR? Be careful there, I haven't yet measured a film cap with low ESR. I just didn't put any film caps on the output.

And yes, it's nice to see the regulator so stable.
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Old 8th February 2009, 03:39 PM   #977
Salas is offline Salas  Greece
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I mean a polypropylene 0.1uF to 0.22uF in parallel with the 470uF output cap so to kill the lytic's rising impedance due to its ESR.
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Old 8th February 2009, 03:46 PM   #978
Salas is offline Salas  Greece
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Quote:
Originally posted by RCruz
In the data table, I converted the mV readings into mA.

Ricardo
Can't read it. Is it a txt file?
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Old 8th February 2009, 03:53 PM   #979
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by salas
Can't read it. Is it a txt file?
it's an XLS file and opens in Excel.
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Old 8th February 2009, 03:56 PM   #980
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Quote:
Originally posted by salas
I mean a polypropylene 0.1uF to 0.22uF in parallel with the 470uF output cap so to kill the lytic's rising impedance due to its ESR.
I hear you sir. Any pointers to particular makes of polyprop caps with low ESR? I have quite a bunch of them of different makes, and not one has low ESR but I do have already have some electrolytic ones with low ESR.

I forgot to mention something else different in the buffered regulator. The power mosfets are COLD. They run at much lower quiescent current. The simulation does not show especially much current going through the darlington, yet it gets warmest of them all. I am not inclined to change it again for a highest current through the mosfets, it if works already so well.
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