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Old 7th January 2011, 11:47 PM   #201
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I have had a few email exchanges with Keatoken. He said he is very busy at the moment so I think I may post a couple of messages in our exchanges for him for the benefit of others.

Keantoken:

Let me show you the datasheet. VceSat is the parameter we're looking for, in figure 4.

http://www.fairchildsemi.com/ds/BC/BC550.pdf

I like to keep Vcb positive. Transistors are most linear with at least 2V Vce. You can see this in figure 1. Keeping base current the same, Vce is varied in order to observe Early effect (change in transistor parameters with Vce). Between 20 and 10mA, you can see that 1V Vce or more is desirable (the line begins to straighten out at that point). VceSat is the point where Early effect begins to destroy transistor operation, when Vce is too low. If it matters enough, you can get away with just 70mV Vce at 20mA. But at this point, as you can see again in figure 4, Early effect will reduce that transistor's natural resistance to input voltage variation (decreasing PSRR).

The problem so far with the diodes is that the bias current through them is on the order of uA. For this reason their voltage drop will be below what it is at currents in the mA. I think adding one more resistor may be beneficial to the circuit, but it could just as well be useless. See attached schematic. I give the diodes 5mA bias. This should increase Vce a little, and make it a little more predictable. You could also use a red LED here, for default 1V Vce (may improve PSRR) (2.6V voltage drop), and less noise than a 4 diode string.

For the 2SC5171, it is advisable to have a heatsink. Even though the device specified for an operating temperature up to 150C, if you look at the Hfe chart, operating at higher temperatures reduces the Hfe range. At 300mA you are just at the rolloff point, and this may differ between devices. Even if this is not a concern, the device may get hot enough to melt nearby components and damage the PCB (and transferring heat to other components through the leads).

39R should work, but I wouldn't go any higher.

- keantoken
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Last edited by HiFiNutNut; 7th January 2011 at 11:53 PM.
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Old 7th January 2011, 11:49 PM   #202
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I did the change last night by taking out 3 x 1N4148 replacing them with 1 x 3mm red LED, and added a 5k1 resistor.

Vce for the driver was 1.32V, but is now 14.96-13.06=1.90V. Vce for the pass transistor, or the total voltage drop of the K-Multiplier is 15.65-13.06=2.60V.

Output with various voltage drops of the diode string:

1 x 1N4148: about 12mV non sine wave at 14.65VDC. Subjectively It did not sound good.
2 x 1N4148: about 8mV non sine wave (but rounder) at 13.90VDC. Subjectively it sounded better.
3 x 1N4148: about 6mV sine wave (or close) at 13.83VDC. Subjectively it sounds the best.
1 x LED + 5k1: about 3mV sine wave (or close) at 13.06VDC. Subjectively it sounds good but not the best.

The LED version with 2.60V voltage drop does not really work for me because in that case the Marantz reg has been left with only 1.7V for voltage drop, which is insufficient. The Marantz reg sets 11.30V output voltage but with the LED prereg it has only 11.10V at the output, indicating too low input voltage. With 3 x 1N4148, I had 2.52V voltage drop for the Marantz reg and it appeared to be working with the desired 11.30V output voltage.

So for me, 3 x 1N4148 work the best. I will reverse the last change and am content with 3 x 1N4148.

Note that the LED version might be better if you could afford the higher voltage drop.

Last edited by HiFiNutNut; 7th January 2011 at 11:55 PM.
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Old 8th January 2011, 12:29 AM   #203
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Thanks HiFi, a lot of knowledge passes in private conversations, much of it worth sharing...

The schematic I sent you contains some possibly misleading features:

1: Output devices are 2SD669A/B649A. These will work to 100mA, but the 2SC5171/A1930 work to 300mA, are just as fast (if not faster) and are easier to get for some people.
2: Drivers are BC547C/557C. The BC550C/560C have slightly better noise specs, not sure if it matters but I prefer to buy the superior part anyways if it's of little consequence to the wallet.

Here is a cleaned up, nice schematic representing the ideas I described to HiFi.

- keantoken
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Old 7th May 2011, 01:52 PM   #204
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Can I use the cfp multiplier after SSHVSR?
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Old 7th May 2011, 07:58 PM   #205
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You should be able to, as long as you use an appropriately rated capacitor. However I don't think that output impedance will be improved (HF impedance might).

- keantoken
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Old 30th January 2012, 11:54 AM   #206
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Hey everyone. Many months have passed and I have done many things. I have destroyed my Kmultipliers many times. It is time for an update.

We figured out why HiFi's regulators did not reach spec. He had counterfeit transistors. Now they perform just like my own prototype.

The Kmultipliers only almost reach the 60db isolation point. I think I know why this is. The simulation models lack quasi-saturation modeling, so transistors will perform too good at low Vce. So it seems clear to me the next order of business is to use low-Vcesat transistors. The PEMZ7 transistors from NXP seem ideal for this task; the BC817/807 may also but they do not show low-current Vce behavior. I would certainly appreciate suggestions for transistors that are less exotic.

For the output transistors I want to find a good low-VceSat transistor >1W that has good Hfe until at least 400mA. I suspect the 2SC5171/A1930 are not as good as the datasheet says and I think the MJE243/253 could be an improvement, so I will try them.

With these improvements it may be possible to increase isolation to above 70db.

Furthermore, using a TL431 I may be able to make a voltage regulator version.

The Kmultiplier is still particularly suited to high-voltage filtering, but no one has used it for that yet, and I encourage anyone interested to discuss it with me.

- keantoken
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Old 9th December 2012, 11:40 PM   #207
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It is time for another update.

I wrote a webpage about the Kmultipliers. It contains updated information and includes what I've learned from more experimentation. I'd appreciate feedback.

http://www.fidelityforce.com/keantok...ultiplier.html
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Old 10th December 2012, 08:37 AM   #208
RCruz is offline RCruz  Switzerland
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Link does not work
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Old 10th December 2012, 10:05 AM   #209
AndrewT is offline AndrewT  Scotland
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It worked for me yesterday.

But it's not connecting today.

I still have the page up. I better save as before I lose it.

Agh....
Save as does not work.
It's trying to go back to source to download again.
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Last edited by AndrewT; 10th December 2012 at 10:09 AM.
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Old 10th December 2012, 10:43 AM   #210
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Hello Iko,

Nice page, KMultipliers.

I am using a basic CMx with the IRFP240/9240s and works rather well with my F5 amp, and curious if this cct can be expanded to drive the steady state 1.6A, and peaks of 2.5A - rails are about +/- 25volts?
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