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Old 13th September 2011, 03:28 AM   #2701
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I have build the Starless circuit and got it working. I did not select the semiconductors, did not use the differential feedback resistor and used 1% metal film resistors. As expected DC offset was firmly clamped at +13V with a plus-minus 18V supply. I was able to trim that down to plus-minus 500mV by adjusting the output emitter resistor in the negative current mirror with a 15kHz trimmer. I will look tomorrow if the feedback resistor helps.
There is of cause always the cap or servo solution.
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Old 13th September 2011, 05:11 AM   #2702
MiiB is offline MiiB  Denmark
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That was also what i saw in simulation..that the circuit balance is very sensitive to the values of the resistors in the current mirror. just one ohm diffidence resulted in several volts offset.

Did you listen to it..??
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Old 13th September 2011, 05:41 AM   #2703
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no, i looked at the square wave with my anti RIAA in front. I have a way to predict the dynamic behavior of a circuit by watching that square over a certain range.
It tells me much about how it will sound. More later......
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Old 13th September 2011, 06:00 PM   #2704
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I build the starless in itīs most basic form. I even used a pimped B1 buffer for simplicity.
I did some experiments with servos but ultimately decided on the cap solution. Used in this way it does not do harm i think and it is simpler and less expensive. I used an 120nF Evox MMK just because i have them. 10nF is enough in this position so use what you like.
Interesting enough the buffer worked without bleeder resistor so the little leakage the cap has seems to be enough to ignite the Fet. more later...
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Old 13th September 2011, 06:37 PM   #2705
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As i said the circuit had initial offset that was way too high. This can be trimmed with the output emitter resistors in the mirror. 30kOhm added gave around plus-minus 500mV so this is good enough. The rest is taken care by the cap. See the circuit as build. I will build now the other channel and listen.
I forgot to tell you how the circuit measured. The square wave looks the same over a wide dynamic range so this circuit is not easy to overload. RIAA precision is plus-minus 0.2dB with the values shown. I used 1% metal film resistors and surplus styroflex caps of unknown origin. The circuit tracks the RIAA curve until 360kHz - 3dB, the null in my anti RIAA so it is wide band. I decided to lower the gain. It should be around 60dB theoretically. I measured 57dB with my Sennheiser tube meter. This is enough in my system. I have a rather loud main tube amp and high sensitivity speakers so usually use no line stage. The tube amp has an input volume control.
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File Type: pdf Starrless as build 12.9.2011.TSC - TINA.pdf (11.4 KB, 127 views)
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Old 13th September 2011, 06:49 PM   #2706
EUVL is offline EUVL  Europe
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So you went for the 4-BJT Wilson Mirror in the end.

The need to use fixed rails is consistent with our simulation.
It fact, it would not work with floating rail due to the current mirrors.

Do tell us how it sounds. And congratulations.


Patrick
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Old 13th September 2011, 07:05 PM   #2707
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I used the ( enhanced ) Wilson because i wanted to have a basic starting point. This can be improved on and i may. Yes, this circuit does not work with a floating supply.
My plan is not to develop this any further. It will be interesting to listen to this because the circuit produces nearly only second harmonic but a bit more then i would wish. I expect a sound that is very similar to tubes without NFB what is not a bad thing. The next circuit i will show is based on your CEN. It should have less second. This circuit will hopefully then further developed to itīs optimum.
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Old 13th September 2011, 07:33 PM   #2708
MiiB is offline MiiB  Denmark
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.. I would not mind the second harmonic distortion....think it will sound extremely open and fast....and also be quiet.. I like the circuit...or the concept of the circuit very very much...this concept where you have all gain and Riaa..in one simple circuit...is very appealing to me...
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Old 13th September 2011, 07:53 PM   #2709
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Sure, i will give it a good listen.
The next circuit i will explore is called The Naked Truth. It has a lot in common with the Starless but is parallel symmetric for some second cancelation. Here you find the helper transistors and the differential feedback resistors. I have already tried this in other circuits i have shown a long time ago. The helpers make the sound more dynamic so i already know that it is beneficial to include them. This modification can also be done on the Starless. For the moment i keep it as is to compare what makes what. I may later rebuild the Starless. There will also be a BJT version of the Naked Truth.
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File Type: pdf Naked Truth MC 11.9.2011.TSC - TINA.pdf (12.4 KB, 114 views)
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Old 13th September 2011, 08:18 PM   #2710
EUVL is offline EUVL  Europe
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If one wants really good 2nd cancellation in CEN, one might pick a J74 with 0.8mA higher Idss and then add a degeneration R of 5R1.
This will help to match the transconductance of the P-FET to the N-FET.
See my F5X thread and the earlier F5 / F5 balanced threads for detail.

Or go balanced.



Patrick
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