Capacitance multiplier: which Darlington to choose?

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Walter66

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175
Hello,
for a capacitance multiplier which powers a audio tube preamp phono section, can someone please advise for a high gain TO 220 Darlington Transistor to be implemented in this circuit? It should provide high noise supression and excellent sound. Thank you.
transistor-capacitance-multiplier-circuit.jpg
 
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Hi Walter

A high voltage Darlington is uncommon. Use a 400 volt (min) NPN power as a pass through and a smaller 400 volt (min) NPN to make a HIGH VOLTAGE DARLINGTON. Add a diode across the pass device as upon the TURNOFF the reverse voltage will kill this regulator circuit. The 300 volt supply also needs a bleeder to ground.

You need more DATA to design the circuit to insure that the circuit will not FAIL to work in the long term.

Duke
 
Hello,
for a capacitance multiplier which powers a audio tube preamp phono section, can someone please advise for a high gain TO 220 Darlington Transistor to be implemented in this circuit? It should provide high noise supression and excellent sound. Thank you.
View attachment 109449

It should provide a higher effective capacitance. Noise suppression will depend on the rest of the associated circuitry. It doesn't provide excellent (or any other quality of) sound.
 
It should provide a higher effective capacitance. Noise suppression will depend on the rest of the associated circuitry. It doesn't provide excellent (or any other quality of) sound.
Thank you. Noise suppression of a cap. Multipler depends on the current gain of the Darlington pair and the value of the external resistor. A protecting Diode is integrated into the IC als well. So how about 2N6045 doing the Job? The circuit needs 300VDC and 26mA.
 

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Thank you. Noise suppression of a cap. Multipler depends on the current gain of the Darlington pair and the value of the external resistor. A protecting Diode is integrated into the IC als well. So how about 2N6045 doing the Job? The circuit needs 300VDC and 26mA.
The 2N6045 is a 100V device. I wouldn't use it in a 300V circuit.
In case of short at the output, the capacitor discharges in the base junction, killing the transistor. A protection resistor is adviqsable.
Additional RC is needed because the transistor is noisy.
 
Hi Walter

A high voltage Darlington is uncommon. Use a 400 volt (min) NPN power as a pass through and a smaller 400 volt (min) NPN to make a HIGH VOLTAGE DARLINGTON. Add a diode across the pass device as upon the TURNOFF the reverse voltage will kill this regulator circuit. The 300 volt supply also needs a bleeder to ground.

You need more DATA to design the circuit to insure that the circuit will not FAIL to work in the long term.

Duke
I don't recall all the details but back in the 70s when my computers and test bench were all assembled from heath kits, my computer monitor went dark. There was a flyback switching PS for the crt supply that used a hard to source darlington. Heathkit could not promise a replacement part for several weeks. I was unwilling to go that long without my computer. So I jury rigged a DIY darlington from two adequate voltage bipolar transistors. It worked well enough to get my terminal up and working again.

JR
 
Thank you. I found TIP150 which is usable Up to 300V as Darlington and BUX85G as single Transistor. Darlington has Higher current gain, of course...unfortunately, high voltage bipolar Darlingtons are rare and Most often ignition coil drivers are the only field of application.
 
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Hello,
for a capacitance multiplier which powers a audio tube preamp phono section, can someone please advise for a high gain TO 220 Darlington Transistor to be implemented in this circuit? It should provide high noise supression and excellent sound. Thank you.
View attachment 109449

IRF730 or IRF830. These are Mosfets.

In this case I recommend:

T1 = IRF830
R1 = 6M8
R2 = 1k (this is a gatestopper in series with with the gate)
R3 = 100R (this is a protection resistor in series with source/emitter before Vout)
ZD1 = 1N5245B (or similar - Gate protection diode from Vout [anode] to Gate [cathode])
C1 = 100nF/450V Film (e.g Wima MKP2)
C2 = 100uF/450V Film or Electrolytic (this capacitor is attached between Vout & GND)
1685261490672.png

This circuit will produce around 280V DC from a 300V input. The Turn on time of Vout will be around 7 seconds to 70% of full HT.

Output current will start limiting around 100mA. It is not a foldback limiter, so with 300V in and a permanent short, 30W get dissipated in the Mosfet. This simple protection circuit is not intended to reliably provide indefinite time short circuit protection, but to rather ensure a slipped probe does not release black smoke and capacitive loads are unlikely to kill the Mosfet.

100Hz ripple rejection is ~ 70dB with the values shown.

Increasing C1 increases the 100Hz ripple rejection proportionally, but turn on time is increased. It is possible to use an additional trick to speed up turn on if desired, I consider the HT hold-off/slow-turn on quite desirable.

Thor
 
A Darlington is "easily" achieved with two individual transistors. No reason to seek a Unicorn Darlington in a single package.

And regardless of chosen parts, all capacitance multipliers have what I consider as a fatal design fault. Any overcurrent fault on the output, the pass transistor usually fails with a collector to emitter short circuit.

Bri
 
A Darlington is "easily" achieved with two individual transistors. No reason to seek a Unicorn Darlington in a single package.

And regardless of chosen parts, all capacitance multipliers have what I consider as a fatal design fault. Any overcurrent fault on the output, the pass transistor usually fails with a collector to emitter short circuit.

The same applies to any type of unprotected series regulator.

See above for a way to protect the circuit against casual shorts. A full foldback limiter may be needed if we want to protect against permanent shorts.

An option is a cascoded 317, but I find it sounds worse than a Mosfet follower.

1685267159486.png

This can be adjusted for 300V in & 280V out as well and will be pretty indestructible, if all protection parts are fitted.

Thor
 
IRF730 or IRF830. These are Mosfets.

In this case I recommend:

T1 = IRF830
R1 = 6M8
R2 = 1k (this is a gatestopper in series with with the gate)
R3 = 100R (this is a protection resistor in series with source/emitter before Vout)
ZD1 = 1N5245B (or similar - Gate protection diode from Vout [anode] to Gate [cathode])
C1 = 100nF/450V Film (e.g Wima MKP2)
C2 = 100uF/450V Film or Electrolytic (this capacitor is attached between Vout & GND)
View attachment 109510

This circuit will produce around 280V DC from a 300V input. The Turn on time of Vout will be around 7 seconds to 70% of full HT.

Output current will start limiting around 100mA. It is not a foldback limiter, so with 300V in and a permanent short, 30W get dissipated in the Mosfet. This simple protection circuit is not intended to reliably provide indefinite time short circuit protection, but to rather ensure a slipped probe does not release black smoke and capacitive loads are unlikely to kill the Mosfet.

100Hz ripple rejection is ~ 70dB with the values shown.

Increasing C1 increases the 100Hz ripple rejection proportionally, but turn on time is increased. It is possible to use an additional trick to speed up turn on if desired, I consider the HT hold-off/slow-turn on quite desirable.

Thor
Wow....I'll try that in my next valve design...as if I do that any more. lol

I'm dense I guess the series resistor on the output is all that keeps the transistor from blowing up with a rando short? Hmmmm...a RCRCRC filter would do the same?

Bri
 
Wow....I'll try that in my next valve design...as if I do that any more. lol

I have used this for many decades in both DIY Projects and commercial product all the way to ultra high-end costing huge money. Low Voltage versions can also be made, including +/- Supplies.

I'm dense I guess the series resistor on the output is all that keeps the transistor from blowing up with a rando short?

Yes, it works combined with the 15V zener diode, which act's both as gate protection and limits the current to ~ 100mA.

Hmmmm...a RCRCRC filter would do the same?

Up to a point.

This circuit is actually CV/CC (Constant Voltage/Constant Current), so as long as the short is on Vout, the circuit will actively limit current.

Consider C2 the first capacitor of the RCRCRC filter.

Thor
 
I have done a few passively smoothed HT supplies that take several minutes to ramp up , I dont mind that at all because a tube and its asscociated components can take 30 minutes or more to reach full opperating temp the slower the rise of the HT the better .

For the same reason I hate tube amps without a standby , some have tried to argue it makes no difference , I say it does . You also find some who instead of using the standby as it should be used , to allow your heaters pre-warm ,just flick both power and standby on at the same moment ,
Its similar to the engine in a car , you wouldnt start up on an cold morning and tear straight off down the autobahn at 155 , would ya?
 
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I have done a few passively smoothed HT supplies that take several minutes to ramp up , I dont mind that at all because a tube and its asscociated components can take 30 minutes or more to reach full opperating temp the slower the rise of the HT the better .

It's a compromise. Several minutes might be a bit long...

For the same reason I hate tube amps without a standby , some have tried to argue it makes no difference , I say it does . You also find some who instead of using the standby as it should be used , to allow your heaters pre-warm ,just flick both power and standby on at the same moment ,

Well, I might run tube heaters at 5.7V (or proportionate) and cut HT off and reduce heaters to ~ 4.5V for standby.

Its similar to the engine in a car , you wouldnt start up on an cold morning and tear straight off down the autobahn at 155 , would ya?

Depends on the engine. I ride an electric Chopper Bike and I absolutely go to full throttle from cold. Mind you, "cold" here is rarely less than 27 degrees where I am.

Thor
 
I meant to specify its a tube mic with the long slow ramp up ,
be different of course with a guitar amp or hifi equipment , that still doesnt mean they reach optimum for ages after powering up from cold .

Yeah Ive definately heard of that approach to heater power , seeing as your designs mostly use lower HT volts and small signal tubes a reduction in heater might well give an extra lease of life .

Yeah sure an electric powered vehicle should have no real issue with applying full throttle the moment you start it up , appart from maybe getting some warmth into the tyres ,again depending on local weather conditions .

I do wonder how these regulator type circuits would work in an all tube guitar amp where the output stage gets driven well past clean , could there be unwanted effects ?
 
Many thanks For your suggest, Thor.
What I search For is to understand what TO 220 Power Transistor or Darlington would fit the one external resistor circuit shown in my first Post. This circuit is used by Shindo Labo of Japan in their Tube amps and it Sounds Superb. It doesnt need minutes to Ramp Up and seem to Filter voltage quite well. It has one 27k resistor employed. No extra diodes, No Second Transistor being used. Very simple and elegant solution. Beside BUX85G, is there a better part available For the Job? Darlington has internal Diode employed and Higher gain means better filtering, so I thought it could be that Kind of active Part. But Darlington is hard to find with high gain and high voltage.
 
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Many thanks For your suggest, Thor.
What I search For is to understand what TO 220 Power Transistor or Darlington would fit the one external resistor circuit shown in my first Post. This circuit is used by Shindo Labo of Japan in their Tube amps and it Sounds Superb.

Mr Shindo is a pragmatist. In the claret he used only RC filtering and it sounds great too.

If you insist on following the Master literally, I'd use a discrete Darlington with MJE350 and MPSA92.

High Voltage (300V and up) Darlington transistors are likely functionally extinct, Mosfet's and igbt's have long taken over.

If you take my advise, try my MOSFET circuit. It was (for example) used in a phono stage that made Stereophile Class A.

It doesnt need minutes to Ramp Up and seem to Filter voltage quite well. It has one 27k resistor employed. No extra diodes, No Second Transistor being used.

Filters quite well is a subjective judgement. It should also knock out 20-30dB @120Hz. Speed of ramp up is directly related to how well the circuit filters.

And "sounds good" is also a subjective judgement, more, it is generally a relative judgement and as a qualitative judgement it usually requires a reference standard.

The absence of protection features means a slipped probe will destroy the transistor, unless the powersupply current is limited before the transistor. In a commercial product this may be a non-issue, I prefer to include protection, based on decades of experience in letting black smoke out of three-legged fuses.

Very simple and elegant solution. Beside BUX85G, is there a better part available For the Job?

BUX85G is not a Darlington transistor. It has a beta of ~ 50, as such the filter action is very limited. I suspect it is used instead of an actual choke in the powersupply where it will be sufficiently effective, when followed by an RC filter chain.

Darlington has internal Diode employed and Higher gain means better filtering, so I thought it could be that Kind of active Part. But Darlington is hard to find with high gain and high voltage.

Make your own Darlington. But it will sound different from a low beta bipolar, much closer to the MOSFET. So you might as well go MOSFET.

You do need a gate protection Zener and a gate stopper resistor, but these can easily soldered directly to the FET directly, I usually do.

The high resistor value and film capacitor help sound quality (absolute) compared to using an electrolytic cap.

But it is the (mostly vintage - at least when I know Shindo) electrolytic capacitors that give Shindo gear what I would call "heavily Sepia/Rose tinted glasses" sound, a sound I agree is immediately attractive, but to my ears ultimately a little low resolution and generalising.

I tend to be more on the Kondo style sound, compared to Shindo. If you ask me, I feel Kondo style sound is Leica 1930's with modern film and Shindo is turn of the century (late 1800's to very early 1900's) Colour Photo.

Question of preference.

Thor
 
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Thanks again For your experience shared on this Subject. Highly appreciated.

Shindo Sound isnt my aim, too although I studied His Designs since decades. Very interesting how He achieved His sounds. He has further refined and altered His circuits since the old Times of simple Claret circuits. Today He is much more on the Kondo Side of Sound it seems. Modern parts, modern full IC regulated PSU results in more modern Sound. Not comparable to the old Shindo Designs.

Im seeking For an elegant Method of further filtering the PSU For a phonostage and got the Message, IRF830 seem to be a very powerful Filter.
Maybe you have an opinion wether I should Filter the whole Tube preamp PSU with Tube regulated voltage by using Tube series Regulator (WE 130B did it this way) or leave the Output section For passive filtering (Fairchild 670 Style PSU Filter). Fully Tube regulated PSU seem to Limit Impulse responds, means Sound May become smoothed Out in Terms of Dynamics. I figured this Out by using an old Tube regulated EL156 PSU vs. unregulated CLCRC filtered PSU. Complete different Sound. But I want to Go Pro active Tube regulated PSU Like WE or Fairchild did.I Like those Classic designs. Because of that importance of the Filter Method to the Sound Im seeking advise.
 
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What about IRF830 when applied in this circuit? It has an internal protection Diode already implemented. So why Not Do it this way, please? Resistor value can be changed.
 

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What about IRF830 when applied in this circuit? It has an internal protection Diode already implemented. So why Not Do it this way, please? Resistor value can be changed.
The internal protection diode will only protect against reverse voltage but not against shorting the output.

Cheers

Ian
 
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