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Richard Lee's Ultra low Noise MC Head Amp
Richard Lee's Ultra low Noise MC Head Amp
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Old Today, 06:36 PM   #741
Hans Polak is offline Hans Polak  Netherlands
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Originally Posted by Bonsai View Post
Hans, on the Hawking, if you run your sims but look at the collector voltage of the transistors before the DC blocking caps (with or without dampers) what are you getting? This is with the 10uF capacitors
Bonsai,

Is this what you mean, collector voltages are V(V+) and V(V-), lying exactly on top of each other.
Two Sims, one for Rs=5R gain=10 and one for Rs=1R gain=50, both with output cap 10uF, no damping.

Hans
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Old Today, 07:13 PM   #742
Bonsai is offline Bonsai  Europe
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Are you not losing head room because the voltage on the collector before the output coupling cap is peaking at LF?

Looking at this situation, my feeling is the base decoupling caps can stay at 220uF, but the output coupling caps should be large - say 1000uF. This way you lose no headroom and you get no peaking about say 1 or 2 Hz where it is so small anyway that it is insignificant.

If the collector load (the output cap Xc + the total output load resistance including damper or no damper + the 100 Ohm to ground) increases, the gain will increase and you will get some kind of peaking. The solution therefore it seems is to keep Xc flat to << 1~2 Hz.

Just my thoughts.


Last edited by Bonsai; Today at 07:31 PM.
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Old Today, 09:18 PM   #743
Hans Polak is offline Hans Polak  Netherlands
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Quote:
Originally Posted by Bonsai View Post
Are you not losing head room because the voltage on the collector before the output coupling cap is peaking at LF?

Looking at this situation, my feeling is the base decoupling caps can stay at 220uF, but the output coupling caps should be large - say 1000uF. This way you lose no headroom and you get no peaking about say 1 or 2 Hz where it is so small anyway that it is insignificant.

If the collector load (the output cap Xc + the total output load resistance including damper or no damper + the 100 Ohm to ground) increases, the gain will increase and you will get some kind of peaking. The solution therefore it seems is to keep Xc flat to << 1~2 Hz.

Just my thoughts.

Bonsai,
Good question about headroom, let's do a worst case calculation, which is for a 0.5mV 5R Cart, see image in #741.

1) Vmax for the collector voltages of the Duraglit is ca. 500mV rms.
2) Looking at the image in #741, collector voltage at 10Hz is 20dB above output voltage, so Vmax rms out @ 10Hz is 50mV.
3) With Riaa premphasis 0.5mV@5cm/sec@Khz drops to ca. 0.05mV@10Hz.
4) A 0.5mV Cart needs a Headamp gain of 20dB to be compatible with the MM input.
5) So Vin@0.05mV@10Hz gives a Vout of 0.5mV with this gain of 20dB

(Vout max)/(Vout@0dB@10Hz) = 50mV/0.5mV resulting in 40dB overload margin.
Where 30dB is regarded to be very good, 40dB is more than excellent and nothing to worry about.

Using 5mF + 10uF will give just one single Caps solution that fits all applications independent of Gain and Rs, whereas using 200uF or even larger output caps with a damping resistor will remove headroom over the complete FR and needs adjustment for each individual Cart / gain combination.
That's why to my opininion the 5mF +10uF solution seems to be the clear winner.


Hans
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Old Today, 10:50 PM   #744
billshurv is offline billshurv  United Kingdom
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Richard Lee's Ultra low Noise MC Head Amp
What would one recommend for a 5mF cap?
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Old Today, 11:06 PM   #745
Hans Polak is offline Hans Polak  Netherlands
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Originally Posted by billshurv View Post
What would one recommend for a 5mF cap?
What about 2x 2.7mF 2.5Volt Oscon Alu Polymer ?

Hans
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Old Today, 11:11 PM   #746
syn08 is offline syn08  Canada
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Quote:
Originally Posted by Hans Polak View Post
What about 2x 2.7mF 2.5Volt Oscon Alu Polymer ?
Or those mentioned here Richard Lee's Ultra low Noise MC Head Amp

Absolutely no noise contribution, to my measurements.
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Old Today, 11:26 PM   #747
billshurv is offline billshurv  United Kingdom
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Richard Lee's Ultra low Noise MC Head Amp
Well yes I would love an excuse to use wet slug tants, but the budget won't stretch to that.
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