hello. a while back someone online traced their "wazacraft" boss DS-1. The circuit is unremarkable, but what had me intrigued was the power supply filtering. This seems like a lot of components to achieve circuit protection and a stable supply. I do understand that the setup is meant to accomplish those tasks with as little voltage drop as possible (probably why no series resistor is used). However, I assume the engineers at boss know much more than I do about this so wondering if you folks had any thoughts? I'm always looking for new ways to filter DC and protect a circuit.
Obv r18, r19, and c16 need no explanation. they are the voltage divider.
Two caveats.
1) This is a trace someone did so no guarantee that it's 100% correct although I don't see anything that looks glaringly wrong.
2) no values given for c1 or c9. My guess is that c9 is a ceramic 100n as that would make sense. Unsure of what c1 would be. maybe another 100n?
I know boss does tend to err on the side of using more parts than needed sometimes but anyone with more knowledge than me understand why this is all happening just to get clean vcc?
Thx!
(https://i.postimg.cc/wtzKkmRn/Screenshot-2024-07-01-at-11-38-47-PM.jpg) (https://postimg.cc/wtzKkmRn)
Boss started using the circuit a while back in various pedals. You can see a few variants here (and there's a few more),
https://www.diystompboxes.com/smfforum/index.php?topic=132064.msg1284964#msg1284964
Quote from: m_charles on July 02, 2024, 03:39:26 AMThis is a trace someone did so no guarantee that it's 100% correct although I don't see anything that looks glaringly wrong.
IMHO, D6 being 9V1 Zener is redundant..
It can't stabilize anything 'cause voltage on its Cathode can't reach its nominal voltage rating due to D3 and R14..
It could work for either lower nominal voltage or D3 of higher one.. :icon_wink:
P.S.
Without it, Q6, R14 & C10 form a healthy capacitance multiplier..
(actually, they form a LPF of corner frequency
f= 0.159 / (R14*C10*h
FE)
(https://i.postimg.cc/HJjn0D9Z/20247300-topic-132139.png) (https://postimg.cc/HJjn0D9Z)
Quote from: antonis on July 02, 2024, 07:43:18 AMIt can't stabilize anything 'cause voltage on its Cathode can't reach its nominal voltage rating due to D3 and R14..
???
Quote from: antonis on July 02, 2024, 07:43:18 AMMHO, D6 being 9V1 Zener is redundant..
It can't stabilize anything 'cause voltage on its Cathode can't reach its nominal voltage rating due to D3 and R14..
It could work for either lower nominal voltage or D3 of higher one.
It acts as over an voltage voltage protection. If you plug in a 9V unregulated supply (12V unloaded) the zener kicks in and the pedal gets about 9V.
Quote from: Rob Strand on July 02, 2024, 01:04:31 PMIt acts as over an voltage voltage protection. If you plug in a 9V unregulated supply (12V unloaded) the zener kicks in and the pedal gets about 9V.
Of course that stands for D3..
I was talking about D6.. :icon_wink:
Quote from: m4268588 on July 02, 2024, 11:25:39 AMQuote from: antonis on July 02, 2024, 07:43:18 AMIt can't stabilize anything 'cause voltage on its Cathode can't reach its nominal voltage rating due to D3 and R14..
???
Can't get your query..
Is there a voltage drop across R14, or not..??
My main question though is why the setup? In my rudimentary builds I've never used a BJT transistor in the filter section. Can you explain why they did it this way? Trying to understand the main benefit. Thx!
Quote from: Rob Strand on July 02, 2024, 05:22:33 AMBoss started using the circuit a while back in various pedals. You can see a few variants here (and there's a few more),
https://www.diystompboxes.com/smfforum/index.php?topic=132064.msg1284964#msg1284964
Thanks Rob, reading those posts now. Can you give any insight as to why this setup removes the need for a series resistor?
Quote from: antonis on July 02, 2024, 03:00:20 PMOf course that stands for D3..
I was talking about D6.. :icon_wink:
I was talking about D6 being for protection.
As for D3 I've got doubts it's a zener at all.
The early pedals with Boss ACA supply (unregulated 9V, 12V unloaded) used an 11V zener in the D3 position. That protected against overvoltage. They relied on a series diode and resistor in the negative rail of the pedal to limit the zener current.
A few Boss ACA pedals replaced the zener with a 1N4004 type diode and lost the over-voltage protection.
The later pedals with Boss PSA supply (regulated 9V) tended to only used rectifier diodes in the D3 position. So that's why I suspect D3 isn't a zener. Also 9.1V for D3 is pushing things too fine for a 9V supply. For the ACA pedals many don't have the zener for over-voltage protection but some do.
There's also cases where the transistor + zener is used for lower than 9V rails, like ~5V rails on the Boss pedals with the discrete opamps and for low voltage BBD etc.
There might a trace of this pedal on fsb. There's a guy there who has been tracing a lot of pedals and Waza versions and his traces are very accurate.
Quote from: m_charles on July 02, 2024, 06:36:14 PMThanks Rob, reading those posts now. Can you give any insight as to why this setup removes the need for a series resistor?
For filtering the active circuits (those power supply circuits with the transistor with or without a zener), effectively move the series resistor to R14.
However, without D3 a series resistor before D3 protects D3. If you have D3 for reverse protection without a series resistor then often the diode and PCB fries when you apply reverse voltage. Unfortunately low valued series resistors often fry anyway under reverse voltage because they don't have a high enough power rating. The addition of D2 stops all that.
With D2 in place, it only makes sense for D3 to be a zener. However there's no series resistance so that's risky as well. Also generally Boss use a rectifier diode for the D3 position on PSA pedals, and it has no series resistor. So perhaps D2 is an addition on the Waza units and D3 is a left over.
Check out the circuit in this thread,
Boss - SD-1w Super OverDrive (Waza Craft)
https://www.freestompboxes.org/viewtopic.php?t=29267
It's got what looks like a rectifier diode for D3; 1SR154-400. So perhaps D3 is a left over from adding D2 on the Waza pedals,
1SR154-400 datasheet
https://docs.rs-online.com/1ab3/0900766b80dcd82a.pdf
Quote from: m_charles on July 02, 2024, 06:36:14 PMwhy this setup removes the need for a series resistor?
Everything *should* have a series resistor. Infinite current is bad. The smoke tells you where the problem was.
The dynamic impedance ("plate resistance") of a BJT is about infinity. This into a cap or Zener makes much better filtering than your 470r resistor.
Alternatively: 'Capacitance multiplier'. Your 47uFd cap and a hFe=100 transistor acts a little like a 4,700uFd cap.
I see the double-Zener topology as a 12 cent approximation to blow-up proof. Not utterly unkillable; just harder to kill at a price musicians can pay.
Also note that Zeners are not brick-wall, their Vz varies with current. The first may be holding 9.3V semi-steady which the second running lower current Vz=8.6V is a second smoothing action.
Go ahead and lose it all, plug to a 9.36V battery or a mystery ??V wall wart. It may be fine 9 out of 10 times. Certainly enough pedals were sold on the assumption nothing bad would ever happen.
Quote from: Rob Strand on July 02, 2024, 06:58:16 PMQuote from: m_charles on July 02, 2024, 06:36:14 PMThanks Rob, reading those posts now. Can you give any insight as to why this setup removes the need for a series resistor?
For filtering the active circuits (those power supply circuits with the transistor with or without a zener), effectively move the series resistor to R14.
However, without D3 a series resistor before D3 protects D3. If you have D3 for reverse protection without a series resistor then often the diode and PCB fries when you apply reverse voltage. Unfortunately low valued series resistors often fry anyway under reverse voltage because they don't have a high enough power rating. The addition of D2 stops all that.
With D2 in place, it only makes sense for D3 to be a zener. However there's no series resistance so that's risky as well. Also generally Boss use a rectifier diode for the D3 position on PSA pedals, and it has no series resistor. So perhaps D2 is an addition on the Waza units and D3 is a left over.
Check out the circuit in this thread,
Boss - SD-1w Super OverDrive (Waza Craft)
https://www.freestompboxes.org/viewtopic.php?t=29267
It's got what looks like a rectifier diode for D3; 1SR154-400. So perhaps D3 is a left over from adding D2 on the Waza pedals,
1SR154-400 datasheet
https://docs.rs-online.com/1ab3/0900766b80dcd82a.pdf
thanks for the reply. I wasn't asking about the protection aspect, I was referring to why there is no series resistor needed to filter out wall hum with this setup. I'm assuming that if the setup failed to properly do this, they wouldn't use this. I've found I pretty much always need a 47 or 100 ohm in series with the +9vDC or I get hum. Of course with some circuits this can cost you a lot of voltage drop.
Quote from: m_charles on July 02, 2024, 07:52:49 PMthanks for the reply. I wasn't asking about the protection aspect, I was referring to why there is no series resistor needed to filter out wall hum with this setup. I'm assuming that if the setup failed to properly do this, they wouldn't use this. I've found I pretty much always need a 47 or 100 ohm in series with the +9vDC or I get hum. Of course with some circuits this can cost you a lot of voltage drop.
There's no need because resistor R14 and capacitor C10 do the same job. The transistor allows high currents to flow with large values of R14. If the zener is conducting then it's a little different but in this case the zener stops the ripple getting through.
In the thread I linked earlier I compared the RC filter with the active filter and an LC filter.
https://www.diystompboxes.com/smfforum/index.php?topic=132064.msg1284995#msg1284995
The main thing to see is the active filter does filter without a resistor in series with the supply.
Quote from: PRR on July 02, 2024, 07:43:42 PMQuote from: m_charles on July 02, 2024, 06:36:14 PMwhy this setup removes the need for a series resistor?
Everything *should* have a series resistor. Infinite current is bad. The smoke tells you where the problem was.
The dynamic impedance ("plate resistance") of a BJT is about infinity. This into a cap or Zener makes much better filtering than your 470r resistor.
Alternatively: 'Capacitance multiplier'. Your 47uFd cap and a hFe=100 transistor acts a little like a 4,700uFd cap.
I see the double-Zener topology as a 12 cent approximation to blow-up proof. Not utterly unkillable; just harder to kill at a price musicians can pay.
Also note that Zeners are not brick-wall, their Vz varies with current. The first may be holding 9.3V semi-steady which the second running lower current Vz=8.6V is a second smoothing action.
Go ahead and lose it all, plug to a 9.36V battery or a mystery ??V wall wart. It may be fine 9 out of 10 times. Certainly enough pedals were sold on the assumption nothing bad would ever happen.
Taking out the protection aspect I'm still not understanding why they don't need it. I understand WHY they didn't want to use it. Because it doesn't cost them the voltage drop. I'm assuming it's not because none of them realized that a series resistor would do the trick. The newer boss pedals I own are usually dead quiet regardless of what power supply I use be it my isolated voodoo labs brick, or a $7 wallwart from amazon. I'm guessing a large part is due to this particular arrangement (along with good layout practices, etc). I realize I can just copy it and not worry about it, but I'm trying to understand the why of it... :)
Quote from: Rob Strand on July 02, 2024, 07:56:43 PMQuote from: m_charles on July 02, 2024, 07:52:49 PMthanks for the reply. I wasn't asking about the protection aspect, I was referring to why there is no series resistor needed to filter out wall hum with this setup. I'm assuming that if the setup failed to properly do this, they wouldn't use this. I've found I pretty much always need a 47 or 100 ohm in series with the +9vDC or I get hum. Of course with some circuits this can cost you a lot of voltage drop.
There's no need because resistor R14 and capacitor C10 do the same job. The transistor allow high currents to flow with large values of R14. If the zener is conducting then it's a little different but in this case the zener stops the ripple getting through.
In the thread I linked earlier I compared the RC filter with the active filter and an LC filter.
https://www.diystompboxes.com/smfforum/index.php?topic=132064.msg1284995#msg1284995
The main thing to see is the active filter does filter without a resistor in series with the supply.
Ahh, thats the answer I was looking for! thanks Rob. What do you reckon C1 is doing and what value is it most likely? not used to seeing a cap to ground pre-zener diode
Quote from: m_charles on July 02, 2024, 08:03:50 PMAhh, thats the answer I was looking for! thanks Rob. What do you reckon C1 is doing and what value is it most likely? not used to seeing a cap to ground pre-zener diode
In 99.99% of cases it's doing very little. Caps in that position are more precautionary. They help very high frequency ripple, RF and they can help protect against ESD.
If you look at the BD-2, even Boss aren't consistent. Only the SMD version has it.
https://www.freestompboxes.org/viewtopic.php?p=292877#p292877
On the earlier versions you will see the C1 position is a 100uF electrolytic. That's more about fending off hum and noise. Again it's only helping in some marginal cases and that's probably why Boss have ditched the large cap in that position on a lot of later stuff. One less large electro on the layout as well.
It generally doesn't hurt to add caps here and there but if you have to justify them it can come down to some very fine and obscure arguments. If you were forced to show a case where you needed certain caps it would require some very specific conditions, conditions which are themselves difficult to justify!
Quote from: Rob Strand on July 02, 2024, 08:54:41 PMQuote from: m_charles on July 02, 2024, 08:03:50 PMAhh, thats the answer I was looking for! thanks Rob. What do you reckon C1 is doing and what value is it most likely? not used to seeing a cap to ground pre-zener diode
In 99.99% of cases it's doing very little. Caps in that position are more precautionary. They help very high frequency ripple, RF and they can help protect against ESD.
If you look at the BD-2, even Boss aren't consistent. Only the SMD version has it.
https://www.freestompboxes.org/viewtopic.php?p=292877#p292877
On the earlier versions you will see the C1 position is a 100uF electrolytic. That's more about fending off hum and noise. Again it's only helping in some marginal cases and that's probably why Boss have ditched the large cap in that position on a lot of later stuff. One less large electro on the layout as well.
It generally doesn't hurt to add caps here and there but if you have to justify them it can come down to some very fine and obscure arguments. If you were forced to show a case where you needed certain caps it would require some very specific conditions, conditions which are themselves difficult to justify!
Last question. What's your personal preferred way to do it if you need minimal voltage drop?
Quote from: m_charles on July 02, 2024, 10:37:36 PMLast question. What's your personal preferred way to do it if you need minimal voltage drop?
It's not a clear decision until you pin things down a bit. In many cases there's not *that* much in it you can go either way. Small points tip you one way or the other. It depends on how much filtering you need, the maximum drop you can handle, the how big do you want to go on the filter cap, how much 50Hz/100Hz PSU ripple you expect in practice.
If you expect significant ripple that means the active filter won't work unless you add another resistor from the base to ground to increase the voltage loss. If 0.7V to 1V loss is too much then that also throws out the active filter. At high currents you need a small resistor for the RC filter, then you ask yourself will the filtering be enough with a 100uF cap or 220uF cap on the supply. That's the type of things that go through my head.
If you want very high rejection then the active filter can do that with reasonable cap sizes, there's a point where the caps become too big on an RC filter. You should also consider two filters in cascade, or a voltage regulator.
For SMD designs it favors the active filter as it avoids large caps and electrolytics altogether.
So there's very fuzzy lines of decision.
You might want minimal drop but how much filtering is acceptable. At one extreme use a wire, there's no drop but no filtering. So back that up a bit and say we use a 10 ohm to 22 ohm resistor for minimal drop. Is the filtering enough with a 100uF cap? it depends on the circuit. In many case it's fine. For many pedals 100R + 100uF works fine and has better filter than 10R.
Quote from: Rob Strand on July 02, 2024, 11:26:24 PMFor SMD designs it favors the active filter as it avoids large caps and electrolytics altogether.
but the active filter still needs those electrolytics unless I'm mis understanding? Im assuming we're considering 100uf "big".
Quote from: m_charles on July 03, 2024, 12:09:01 AMbut the active filter still needs those electrolytics unless I'm mis understanding? Im assuming we're considering 100uf "big".
With RC filters and 100uF it's going to be electrolyolytics. But with the active filter and 4.7uF or 10uF you can use larger package SMD ceramics or tantalums.
Quote from: Rob Strand on July 03, 2024, 12:06:45 PMQuote from: m_charles on July 03, 2024, 12:09:01 AMbut the active filter still needs those electrolytics unless I'm mis understanding? Im assuming we're considering 100uf "big".
With RC filters and 100uF it's going to be electrolyolytics. But with the active filter and 4.7uF or 10uF you can use larger package SMD ceramics or tantalums.
Looking at the schematics, Boss uses the active filter/capacitance multiplier PLUS one or two 100uF electrolytics.
For MY purposes - getting the size down - it more or less defeats the purpose.
Quote from: marcelomd on July 03, 2024, 02:25:22 PMLooking at the schematics, Boss uses the active filter/capacitance multiplier PLUS one or two 100uF electrolytics.
For MY purposes - getting the size down - it more or less defeats the purpose.
That's not really an apples to apples comparison. You don't *have* to have the 100uF capacitor with an active filter. An active filter can provide a lot more ripple rejection than an RC filter even without the 100uF cap.
There's also the option to use a smaller output cap.
There are circuits where it's not all about ripple rejection. There's circuits where output impedance at DC and at high frequencies needs to be considered. If you have a transistor fuzz circuit it doesn't need a 100uF supply capacitance. However if you have something switching on the rails, like an LFO, then the 100uF cap can help prevent supply noise propagating in the circuit.
Like many design problems there's many angles to finding the best solution.
If anyone is interested, from the links Rob suggested, I found the most current trace done from a 2023 SD-1 waza. I looked up the diodes from the part numbers and these are the types.
(https://i.postimg.cc/TKWCJKBW/Screenshot-2024-07-11-at-7-17-31-PM.jpg) (https://postimg.cc/TKWCJKBW)
Sorry for the misspelled "Shottkey", haha.
one thing that seems a bit confusing is why are the schottkey and the rectifier needed. both do the same thing here right? protect against reverse voltage?
Also, why the extra tabs on the DC jack? 4 and 5?
another observation, why use an 11v zener to keep that voltage stable to the transistor? maybe just an error by the person tracing? supposed to be 9v?
You can see the same things on the SMD version of the BD-2 in the link I posted earlier. It's probably like that in all respects.
Quote from: m_charles on July 11, 2024, 11:03:37 PManother observation, why use an 11v zener to keep that voltage stable to the transistor? maybe just an error by the person tracing? supposed to be 9v?
Traditionally Boss used 11V zeners for over voltage protection. I think it just comes from that. Not all a products use a zener there.
Quote from: m_charles on July 11, 2024, 10:30:45 PMthing here right? protect against reverse voltage?
I mentioned that earlier on. The Schottky is series protection, unlike parallel protection, which doesn't fry anything when you reverse the supply. I think they tacked that onto the units and didn't remove the parallel protection. So the rectifier is kind of a left over.
QuoteAlso, why the extra tabs on the DC jack? 4 and 5?
No idea. Could simple be that the person who drew the schematic used the wrong part. However it could be related to Bosses supply chain.
QuoteSorry for the misspelled "Shottkey", haha.
one thing that seems a bit confusing is why are the schottkey and the rectifier needed. both do the same
I did that at work once in one of my documents and a work colleague was reading it out and made a point of pronouncing it as a shot-KEY diode.
Quote from: m_charles on July 11, 2024, 10:30:45 PM(https://i.postimg.cc/TKWCJKBW/Screenshot-2024-07-11-at-7-17-31-PM.jpg) (https://postimg.cc/TKWCJKBW)
Considering D2 ideal, Q1 configuration is, IMHO, just a capacitance multiplier..
That said, Q1 Emitter voltage is highly dependent on current draw..
(practically, no voltage regulation..)
Quote from: antonis on July 12, 2024, 04:51:18 AMThat said, Q1 Emitter voltage is highly dependent on current draw..
(practically, no voltage regulation..
In practice it varies very little current as the base resistor base resistor value is quite low. It's not going to be far off the VBE drop for the transistor (maybe 0.7V). The pedal current is fairly constant.
When the zener is 11V it's basically a filter. The zener only kicks in during over voltage.
Quote from: m_charles on July 11, 2024, 10:30:45 PMAlso, why the extra tabs on the DC jack? 4 and 5?
see, this is why we argue about correct diagram drawing. lug 2 connects external supply to internals, and might come with reversed polarity. D1 will block reverse, hurrah. but will also drop some voltage. lugs 4 and 5 are switched contacts, such that when the external is in plugged, the switch is open and the battery is isolated from the circuit and external. when the external is instead out plugged, the switched contacts are short, and the battery is powering the effect. and so as to avoid that D1 voltage drop, pin 4 connects the other side of the diode. because you'd never put the battery in the clip backwards, see.
Quote from: duck_arse on July 12, 2024, 11:14:46 AMQuote from: m_charles on July 11, 2024, 10:30:45 PMAlso, why the extra tabs on the DC jack? 4 and 5?
see, this is why we argue about correct diagram drawing. lug 2 connects external supply to internals, and might come with reversed polarity. D1 will block reverse, hurrah. but will also drop some voltage. lugs 4 and 5 are switched contacts, such that when the external is in plugged, the switch is open and the battery is isolated from the circuit and external. when the external is instead out plugged, the switched contacts are short, and the battery is powering the effect. and so as to avoid that D1 voltage drop, pin 4 connects the other side of the diode. because you'd never put the battery in the clip backwards, see.
I actually figured that out between last night and today, haha.
Rob, as you mentioned, there were many variations on this. I'm wondering why on some of them they have the large cap to ground before and after the BJT? Maybe the cap to ground before the BJT on especially high gain circuits, although that still seem unneeded to me with my limited knowledge? seems like the first one is pretty unnecessary.
Images below show the Blues Driver 2009 had both, the SD-1 Waza only after. Again the caveat here is I'm assuming the person that traced it made no errors.
(https://i.postimg.cc/sMWDVY0X/Screenshot-2024-07-11-at-7-39-32-PM.jpg) (https://postimg.cc/sMWDVY0X)
(https://i.postimg.cc/CndS9kqw/Screenshot-2024-07-02-at-9-10-15-PM.jpg) (https://postimg.cc/CndS9kqw)
Quote from: m_charles on July 12, 2024, 04:24:51 PMI'm wondering why on some of them they have the large cap to ground before and after the BJT? Maybe the cap to ground before the BJT on especially high gain circuits, although that still seem unneeded to me with my limited knowledge? seems like the first one is pretty unnecessary.
On the BD-2 I suspect the input cap isn't doing much. You could argue it might help remove ripple in marginal cases.
For the output cap, it helps lower the impedance on the effect side of the supply. Justifying a *need* for it is a fair amount of work and testing. I suspect some amplifier circuits it might help to have some capacitance these, maybe 10uF would do it, but the 100uF probably isn't required.
For other pedals which have strong varying currents, either of the 100uF caps can also help prevent polluting the input power. The output side cap would prevent polluting its own supply rail; for example a pedal with an LFO.
As mentioned in one of the earlier posts. It's not always about filtering. The active filter is about filtering but it doesn't store energy like a cap. Caps on the rails will provide a energy reservoir to smooth out current variations.
Boss have a recipe and in many cases they stick to it because they haven't had any issue. Now and then someone might stick their neck and and change the recipe.
Quote from: m_charles on July 12, 2024, 04:24:51 PM(https://i.postimg.cc/CndS9kqw/Screenshot-2024-07-02-at-9-10-15-PM.jpg) (https://postimg.cc/CndS9kqw)
C11 without a low value resistor in series with IC1A is looking for trouble..
IMHO, C11 it's redundant 'cause R5//R4 & C2 LPF corner frequency is much lower than IC1A output impedance & C11 one..
Quote from: antonis on July 13, 2024, 12:16:57 PMC11 it's redundant
I don't know what that added opamp does. It is begging to oscillate and it adds hiss. All the bias loads are very high impedance, we don't need bias buffer.
Quote from: PRR on July 13, 2024, 04:45:38 PMI don't know what that added opamp does.
Maybe it serves for a Vref current hungry circuit feeding..
(although I do agree for very high impedance bias loads..)