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In Reply to: RE: LCR Phono stage posted by dave slagle on April 30, 2021 at 04:21:30
"With a source that has a 3KΩ output Z I preferred the sound without the buffer"
This part is interesting to me. What is the reactance, @20Hz, of the inductance of the autoformer volume control?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
figure 200hy's so 25KΩ. I have had several people use them with tubes like the 26, 27, 56 or 76 and love the results but it is a bit to close to the "edge" for the left side of my brain to comprehend.dave
Edits: 04/30/21
This is the silk volumcontrole.
The measurement is made with a load of 10k. With the more traditional load of 100k the peak is +15dB.
Full review on https://audio-creative.nl/projecten/diy-passieve-voorversterker-met-tvc-deel-1/4/
I agree with you about this type of volume control.
Walter
That isn't necessarily representative of all magnetic volume controls.
This one isn't much better. And 5k output impedance is a very high output impedance.p.s where is the 10Hz-1000Hz part?
Edits: 04/30/21 04/30/21
5K output impedance? where did you get that number from? Did you read the source impedance of 500Ω in the plot title as 5000?
The full details including full bandwidth response against source impedance were in the referenced link titled "The details"
the LF plot from that link is below and aside from the settings with gain, the LF response doesn't change for a given source Z so repeatedly showing the 10-1000hz trace doesn't add any new info. The LF behavior is based on the inductance and once the full winding is used that number does not change. When a part of the winding is used to achieve gain then the sub 1kHz info can then be related to the source impedance.
dave
So I need to select at the best the source otherwise I will get a peak or a low pass?
This is a limit for me.
Walter
Oeps, sorry. Yes, the picture low resolution did make me read 5000 instead of 500
I wonder how it would measure as an AVC?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
The problem with ALL transformer based volume controle is bad coupling.
Excessive ringing. The ringing will be less if you have an outputimpedance which is "high". But a high output impedance dosn't help for a good frequency response either. Tribute for instance use a fluxring at the inside of the (toroid)core but that helps just a little. A snubber wont's work either.
Edits: 04/30/21
"The problem with ALL transformer based volume controle is bad coupling.
Excessive ringing"
I don't see that at all.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Just measure* it and you'll see. Any standard resistance** control does a better job.* measure with a low output impedance ofc and with a system that is not limited to 200kHz or less
**use a 10k to 50k value.
p.s the most measurements i see from manufactures are tuned for optimum results for just 1 setting
Edits: 04/30/21 04/30/21 04/30/21 04/30/21 04/30/21 04/30/21
Can you spell that out? I'm a little dumb.
10K to 50K source impedance?
low output impedance ofc?
Thanks
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I did mean any standard volume controle, a potentiometer, 10k-50k
But a 50k ohm pot will have an output impedance of 12.5k ohms at the -6db point of rotation and that will not drive cable capacitance very well.
The output impedance of a AVC at the -6db position will have an output impedance 1/4 of the source.
I've looked at my AVC using square waves and sine waves and I don't see anything to cause alarm. I've even adjusted the source impedance, up and down, and I still don't see any issue that should cause alarm.
Maybe you can show us the ringing that you think is problematic?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Why would you use a potentiometer to drive a cable directly? That is really silly.
But what about de capacity load for the tvc? Did you measured that too.
Edits: 04/30/21 04/30/21
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