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keantoken 6th October 2010 12:02 PM

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It still acts to multiply capacitance, with the same drawbacks in that regard as a normal multiplier. The difference here is that the output voltage has been largely shielded from variations in supply voltage, via filtering (CCS, capacitors, diodes). In this case bass extenstion will be the best, because of the high source impedance (CCS) which will give the capacitor/s a large time constant.

I like your circuit Storm, and using the CFP will improve it's performance quite a bit.

I was right, NPN BJT is better, but CFP is still worse for HF impedance.

- keantoken

keantoken 6th October 2010 12:04 PM

It looks like in StormSonic's circuit the capacitor can be eliminated completely with little impact on performance, except perhaps noise.

- keantoken

AndrewT 6th October 2010 12:09 PM

post1216 shows a regulator.
It is a follower just like Pass often recommends.

The output voltage = Vbe + LED Vf.

and removing the capacitance proves it is not a capacitance multiplier

It looks like in StormSonic's circuit the capacitor can be eliminated completely

stormsonic 6th October 2010 12:13 PM

thank you, but it is not my circuit. Post #7 HERE

HiFiNutNut 7th October 2010 02:44 AM

Thanks, guys.


Could you provide a "final" C-Multiplier schematic including selected transistors that are ready to be built? Some pictures of simulations are welcome. I am happy to be a builder/tester here. The result is a C-Multiplier of your design. Given the circuit won't be complicated so part counts and price are of no issue. It needs to have both rails of around +/-17VAC (after rectification) input, with a voltage drop (2 x 0.65V?). I will put it in front of the Iko reg (+/-29VAC though) for the first test, and if successful, put it in my Marantz CD player before the Marantz reg. I will report how it sounds here.


keantoken 10th October 2010 03:59 AM

First thing, you said Marantz used a "very simple" series reg. Can you tell what type it is? Does it use feedback (good impedance), or not (normal BJT impedance)?

In both cases, using a low output impedance prereg may be a waste of effort, because the circuitry will see the Marantz reg's impedance no matter what. Knowing this I will focus on line rejection rather than output impedance.

Can you describe the regulator voltages in more detail? Earlier you stated 15V input voltage.

The 1.3V drop limit is difficult to work with, because bias resistors necessarily add to the Vbe's already present between input and output. Is it okay to go higher than this?

- keantoken

keantoken 10th October 2010 05:33 AM

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This circuit has the lowest voltage drop and output impedance, with a good PSRR of -54db. If higher voltage drop is allowed, better specs can be achieved. I doubt this is necessary though.

Choices for Q1 in order of order of decreasing preference:


BJT's with lower gain may be used, but voltage drop will suffer.

For Q3, choose the highest gain normal PNP transistor you can find. Even so, output drop may be around 300mV worse than the NPN version. Decreasing R4 can fix this, but will change the bass response and I imagine you want the bass response for + and - regs to be equal.

For the power BJT's, anything you would use in an audio amp should work, but if in doubt ask.

- keantoken

keantoken 10th October 2010 05:48 AM

For C1 and C2, bigger is always better. These will delay turn-on however.

For the power BJT's, the 2SC5200/A1943 seem to work best in simulation. Following are the MJL1302a/0281a. However these are power BJTs, good to 10A or more - what output devices are used for the Marantz reg and their current rating? How about downgrading to 2SA4793/C1837? This improves BW considerably, to over 100KHz for both NPN and PNP, at -64db PSRR.

- keantoken

keantoken 10th October 2010 06:08 AM

1 Attachment(s)
Here is the output impedance using the 2SC4793/A1837 pair. This rivals some of the best electrolytics I have measured. It would be hard to improve on this using anything but film caps.

- keantoken

MRupp 10th October 2010 10:49 AM

Here is the output impedance using the 2SC4793/A1837 pair
How about the lowly BD139/BD140(-16). Should be easier to get and have with similar specs?

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