Power Conditioner

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Post by mictester »

From the "Electronic Secrets the professional pedal designers keep to themselves" file:
Simple power filter
Simple power filter
Power_Conditioner.GIF (8.11 KiB) Viewed 1023 times
The current it can usefully pass is limited to (perhaps) 20 mA, and it won't fix a faulty 9V adaptor, but it really can cure the hum you frequently get on high gain fuzz effects!
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Post by DrNomis »

mictester wrote:From the "Electronic Secrets the professional pedal designers keep to themselves" file:
Power_Conditioner.GIF
The current it can usefully pass is limited to (perhaps) 20 mA, and it won't fix a faulty 9V adaptor, but it really can cure the hum you frequently get on high gain fuzz effects!


This should work fine with the NPN Si Fuzz Face circuit, should be pretty easy to modify to work with PNP Ge Fuzz Faces, just replace the 2N3904 transistor with a 2N3906 transistor, reverse the polarity of the Electrolytic cap, and wire the DC in socket so that the plugpack's + goes to ground and - to the transistor's collector, oh and reverse the polarity of the 1n4148 diode too.... :hmmm:
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Post by Hides-His-Eyes »

Can you sub a higher current transistor for more current?
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Post by DrNomis »

Hides-His-Eyes wrote:Can you sub a higher current transistor for more current?

I can't see why you couldn't,you could possibly substitute something like a BD139 for a 2N3904, and a BD140 for a 2N3906.... :hmmm:
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Post by coldcraft »

i've seen a similar arrangement with a mosfet. same thing?

example in Fix'd Fuzz:
https://www.freestompboxes.org/download/ ... &mode=view
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Post by RnFR »

that would be RG's polarity protection scheme using a P channel MOSFET. I've used it before with 2n7000's in PNP fuzzes.

I'm going to have to give this a try in my new distortion for the contest! it's extremely high gain, and needs all the help it can get. :wink:

a couple questions- would you still need a current limiting resistor? and could you use a shottkey for lower voltage drop?
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Post by pz »

This is a basic example of a capacitance multiplier. More on this topic:
http://sound.westhost.com/project15.htm
Boss uses them widely in their digital pedals (RV3):
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Post by coldcraft »

RnFR wrote:that would be RG's polarity protection scheme using a P channel MOSFET. I've used it before with 2n7000's in PNP fuzzes.
so the jist of it is, use a p-channel for a negative ground circuit, and an n-channel for a postive ground? This might just be the ticket to quieting down my fuzzies.

here's RG's page on mosfet polarity protection, http://geofex.com/article_folders/mossw ... switch.htm

it doesn't mention conditioning advantages, though that may have been beyond the scope of the article.
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Post by RnFR »

it doesn't mention it, because I believe they are two different circuits. one is a capacitance mulfillies that uses an NPN transistor and a large resistor. the other is RGs low Vf polarity protection using a p channel MOSFET and a small R. although they do look similar, they do different things. notice how mictester included a polarity protection diode in his schematic? if the multiplier gave reverse protection, I'm assuming that it wouldn't be needed.
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Post by coldcraft »

ah, I see.

googled mosfet capacitance multiplier, and it gave me this, which looks overkill. http://mrevil.pwp.blueyonder.co.uk/amp/ ... psu2.shtml

in mictesters original schematic above, it looks to me that there is an RC filter driving the Base, and the BJT is set up like an emitter follower of sorts, with the power drawn from the emitter.

what are some common, higher current BJT alternatives?
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Post by mictester »

coldcraft wrote:i've seen a similar arrangement with a mosfet. same thing?

example in Fix'd Fuzz:
https://www.freestompboxes.org/download/ ... &mode=view
That's not the same thing at all. The circuit you're looking at is a polarity protection scheme with low forward voltage drop. It's a bit of overkill really - I'd just use a power Shottky diode and live with ~0.1V forward drop!

The power conditioner is designed to filter out the little bit of ripple that comes from cheap power adaptors. It turns a humming Fuzz Face into a quiet Fuzz Face with just four parts!

Dr Nomis is right - you can invert the circuit, and use a PNP transistor for a PNP Fuzz Face....
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Post by mictester »

RnFR wrote: a couple questions- would you still need a current limiting resistor? and could you use a shottkey for lower voltage drop?
Yes and yes (in that order :D )
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Post by coldcraft »

if this was to be chained to a voltage regulator, perhaps in a AC to DC rectified power supply, would it come before or after the regulator?
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Post by mictester »

coldcraft wrote:if this was to be chained to a voltage regulator, perhaps in a AC to DC rectified power supply, would it come before or after the regulator?
Certainly after the regulator. The regulator will also help reduce hum a bit too.
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Post by DrNomis »

I wonder if it's possible to boost the current output capability by putting a buffer on the output, or maybe adding a series-pass transistor?.... :hmmm:
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Post by rocklander »

RnFR wrote: one is a capacitance mulfillies that uses an NPN transistor and a large resistor.
now you're just making words up. :P
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Post by R.G. »

mictester wrote:From the "Electronic Secrets the professional pedal designers keep to themselves" file:
It's not really a super secret, and it's not all that great. It helps if there is noise on your incoming "9V" line that can be cured by a bigger capacitor.

It's a capacitor multiplier, which multiplies the effective value of the capacitor on the base by the gain of the transistors.
The current it can usefully pass is limited to (perhaps) 20 mA, and it won't fix a faulty 9V adaptor, but it really can cure the hum you frequently get on high gain fuzz effects!
I think I'd say it this way: it can clean up some issues with noisy incoming voltage. It has its limitations, not least of which is that it inevitably loses a couple of diode drops from the "9V". What you get out is not the same voltage as what you got in, but something 0.8-1.2V lower. And you lose another 0.7 to 0.8 in a 1N4148, as well, so you may only get 7V out for 9V in.

It can only cure the hum in a high gain fuzz if the +9V in is where the hum was coming from, which is not always the case. Frankly, a worse issue for noise is the input jack power switching trick. If you are using input jack power switching, then 100% of the ground current for the circuit is traveling down the input signal ground wire, and through the questionable contact resistance of the ring and sleeve connections of the input jack and sleeve of the plug. Most fuzzes have 0db of ground noise rejection, so if there is noise on the incoming power ground, you get it amplified by the fuzz. Not to mention the possible feedback issues with ground noise being put right back on the inputs. I have seen situations where what guitar cord plug was put into a jack and whether it was twisted and turned would affect the sound of near-oscillation high gain circuits. Actually, this may be one place that the "guitar cord direction matters" myth was started. I can easily posit a case where one cord sounds better than another in this setup.
This should work fine with the NPN Si Fuzz Face circuit, should be pretty easy to modify to work with PNP Ge Fuzz Faces, just replace the 2N3904 transistor with a 2N3906 transistor, reverse the polarity of the Electrolytic cap, and wire the DC in socket so that the plugpack's + goes to ground and - to the transistor's collector, oh and reverse the polarity of the 1n4148 diode too....
Yep. It's flippable to positive ground/minus supply setups.
Hides-His-Eyes wrote:Can you sub a higher current transistor for more current?
Yes, but. The real problem with the circuit is that all of the base drive comes through that 1K. Ohm's law still applies, as do semiconductor physics, so the base-emitter drop will be 0.5V or so for low currents, up to 0.7V for higher currents. Ignoring the capacitor for a moment, the way this works is that the load pulls down on the emitter, which pulls down on the base until enough current flows through the 1K into the base to let enough collector current flow to keep the emitter from going any lower. Your limit on current out is (a) how much gain the transistor has at the working current point, remembering that current gain varies with collector current and (b) how much voltage you're willing to let the base bias resistor drop to provide the base current. The base *has* to sag down to get more current into it as the load increases. So using a higher current transistor only helps if you also have a high current gain. That is not always true. In fact, most higher current transistors have lower current gains, so it may work against you.

But getting back to the capacitor. The capacitor charges to the average DC level at the base as set by the needs of the load. Once charged, if there is AC noise coming in from the 9V side, the capacitor holds the base at a fixed (well, OK, heavily low passed) voltage, and the high impedance of the collector does not let the changing voltage from the supply side change the current going to the load, except very slowly, set by the time constant of the R and C on the base. For changing loads, the capacitor supplies a much larger base current if the emitter current changes quickly, slowing down changes in the output voltage. Notice that this can only work if the incoming voltage does not also sag below the level where the transistor has enough voltage on the collector to work from.
coldcraft wrote:if this was to be chained to a voltage regulator, perhaps in a AC to DC rectified power supply, would it come before or after the regulator?
I would be *very* angry if my regulator was so bad that this circuit helped it much. I expect a regulator to regulate and give me a lot of hum and noise rejection. One that does not gets tossed into the trash. So if this helps much after a regulator, trash the regulator and do something else.
DrNomis wrote:I wonder if it's possible to boost the current output capability by putting a buffer on the output, or maybe adding a series-pass transistor?.... :hmmm:
Yes, if the incoming noisy DC supply can supply it.

Actually, using a Low Drop-Out (LDO) voltage regulator is an even better choice. This circuit has limited performance in terms of both regulation ability and noise rejection. An LDO will beat it on both counts, and usually lose you less of the incoming DC voltage doing that.

This was a clever circuit back in the late 60s when it went into a lot of EH stuff. We have forty years of advances in semiconductors to use today. Look up LDOs.

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Post by marsens »

mictester wrote:From the "Electronic Secrets the professional pedal designers keep to themselves" file:
Power_Conditioner.GIF
The current it can usefully pass is limited to (perhaps) 20 mA, and it won't fix a faulty 9V adaptor, but it really can cure the hum you frequently get on high gain fuzz effects!
By seing the schematic, I believe, in this set-up, not only the current is limited but also there is voltage drops about 2.1volts (0.7 volt from 1n4148 and 1.4 volt from 2n3904), am I right Mictester?

Small choke (let's say 100uH) in series with a small resistor (Let's say 10 Ohms) and follows with caps is better, I think. Polarity-protection Diode can be added at the first chain before the choke (there will be 0.7volt voltage drop). Still better, for both current and voltage, I think.

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Post by HEAD »

As I was in need of a power filtering I quickly drew some small vero layouts. Verified and working. With a 1N5817 I got ~8,6V with a 9,08V power supply. Should be enogh for most purposes. Enjoy! :)

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