Hi there,
I've been trying to figure out what the deal is with the Waza-Craft pedals. Apart from custom modes, which essentially activate mods, the big thing seems to be different buffers. I could not find a schematic for these magically better buffers. Does anyone have one?
Also and somewhat unrelated: does anyone have a schematic for the ML-2 Metal Core? Interesting sounding pedal, I'd be interested to see how closely that is related to the HM-2 and HM-3, just out of curiosity.
EDIT: Found some info, finally. The ML-2 is digital, so no point in having a schematic.
Thanks,
Andy
> magically better buffers. Does anyone have one?
https://www.amazon.com/Buffer-Natural-ITAY-Compact-Polisher/dp/B07HXH1XK8?th=1
https://ttte.fandom.com/wiki/The_Magic_Buffers
https://www.promegaconnections.com/what-makes-a-good-buffer/
Well played, PRR
The engineers who have devoted their lives to building Waza-Craft pedals wake up at 4am each morning to be the first to arrive at the Akibahara electronics market. They hand-select only the finest components with the merciless exactitude of a master sushi chef, and may reject hundreds of resistors or LEDs before finding the ones that are truly great enough to go into a Waza Craft Metal Zone or Blues Driver.
in 2019 there are still people who believe in the magical properties of vintage tubescreamers AND that moon landing was a hoax.
i hope to live till 2039 just to see what is next.
Amusing.
Well, that is kind of the point here. Lots of people try to sell you fairy dust sprinkled Tube Screamers and the like for a premium price. But Boss tends not to go overboard with the voodoo claims. So when they start a "premium" line and one of the biggest changes is a different buffer circuitry, that's enough to make me at least want to have a look at the schematic before deciding if it's hokum or not. Especially since there is not a lot you can do to improve the already pretty good boss buffer of the standard series other than use higher quality transistors or go to opamps. My suspicion is that they did the latter, since people claim that they can here a difference when the pedal is in bypass (yes, I know, "People on the internet are saying" isn't exactly evidence), and the former would probably barely be detectable with a good scope but almost certainly not by ear through a guitar amp. Mostly I am interested if they indeed did something meaningful or if they just replaced the ceramic caps with mica and the resistors with wire wound types and called it an improvement.
Andy
I have the Boss Waza craft DM2-W, it is all SMD apart from the coolaudio bbd's and clock chip. 1x4558 smd dual op amp and a 571 compander chip. Looks pretty standard to me.
Hi Mick,
you don't by any chance have photos of both sides of the PCB from which the buffer circuitry could be traced, do you? In exchange for my eternal gratitude, of course. Sorry, its the best I have.
I'd really like to get to the bottom of the "we have improved the buffer" claim, considering that the standard boss buffers were never something to be sneezed at to begin with. SMD and modern robotized production is obviously going to be an improvement over 80's through hole hand soldering in terms of consistency, parasitic capacitance, and so on. But that would not qualify as "improving the buffer" but as "improving the production process". So I am still curious how much of the buffer-claim is marketing BS or what I might learn about better buffer design. The other improvements to the Waza pedals, like adjusted EQ voicings, better quality components with tighter tolerances, and so on are all understandable to me. But that §%"&§ buffer is driving me crazy.
Also: Interesting that they used a 4558. I cannot think of a single reason to choose that over one of the myriad of lower-noise, better stability modern drop-in replacements. Other than Mojo and I really hoped that the whole Waza thing wouldn't just be Mojo-based.
Thanks,
Andy
Quote"we have improved the buffer"
When you read claims like that you have to ask *what* is better.
In one man's eye cheaper is better ;D.
One "flaw" in discrete buffers is the slight gain loss (roughly ~0.075dB for a BJT buffer).
So if you have two buffers in the effect you might get 0.15dB. So when you have a number of
effects in cascade the loss adds up, perhaps to 0.5dB to 1dB. Usually it's not noticed and not a problem.
The JFET buffers can have quite a bit more loss.
One fix for this is to use a buffer with feedback so the gain is 1.
I can't find a good example schematic but you would use a circuit like this with C2 and R4 removed,
then the emitter of the first transistor connects to the collector of the second transistor.
(You can use whatever biasing scheme you like on the base of Q1, like a single resistor
to Vref.)
(http://www.angelfire.com/planet/funwithtransistors/images/Amp-Xstr-1.gif)
JFET version:
(http://www.circuitdiagramworld.com/uploads/allimg/201411/High-Impedance-Low-Capacitance-Buffer-Amplifier.gif)
I'm not saying that's what Boss use. All I'm saying is there's is a small problem and that's one way to fix it with a discrete design. Another common method is to replace the emitter resistor of the one-transistor buffer circuit with a current source.
Quote from: Rob Strand on August 19, 2019, 07:49:59 PM
Quote"we have improved the buffer"
When you read claims like that you have to ask *what* is better.
Their profit, perhaps? ???
QuoteTheir profit, perhaps?
I was only using that as an example but yes profit is a better goal. A lot of companies associate making things cheap as meaning higher profit. If you spend a lot of time fixing problems in production or looking like idiots because the product is unreliable you don't end up making a profit!
Quote from: Fancy Lime on August 19, 2019, 04:16:46 PM
Hi Mick,
you don't by any chance have photos of both sides of the PCB from which the buffer circuitry could be traced, do you? In exchange for my eternal gratitude, of course. Sorry, its the best I have.
Also: Interesting that they used a 4558. I cannot think of a single reason to choose that over one of the myriad of lower-noise, better stability modern drop-in replacements. Other than Mojo and I really hoped that the whole Waza thing wouldn't just be Mojo-based.
Thanks,
Andy
Yeah I will get some photo's today of both sides of the board, it is a pain to even look at the pcb as there is so much screen print on it is off putting.
Quote from: Fancy Lime on August 19, 2019, 04:16:46 PMInteresting that they used a 4558. I cannot think of a single reason to choose that over one of the myriad of lower-noise, better stability modern drop-in replacements. Other than Mojo and I really hoped that the whole Waza thing wouldn't just be Mojo-based.
Andy, it's a bucket brigade delay, a severely limited, thoroughly obsolete technology that wouldn't even exist any more if not for OCD guitarists with their vacuum tubes and their LM308s and such, and their reverence for instruments made by hand in the 1950s. I'm not saying the sound isn't worth it, but if it's not about mojo, really, what is it about? And in the larger scheme of things, does the difference between a 4558 and a 5532 matter all that much in an analog delay pedal?
Ok so here are some pics of the bottom in full and a section of the top of the PCB around the buffer in, op amp and compander sections. I doubt there is any real difference in the buffers to be honest, the 4558 looks like it is used in the exact same way as on the original DM-2. The main difference for me on this waza craft is that the delay has been extended with 3x BBD chips.
Sorry the pics won't give a great way of tracing anything, without fully removing glued in wires etc this is the best I can get.
Top right of the top side is the 4558 area.
(https://i.imgur.com/kwxavlj.jpg)
(https://i.imgur.com/euvn2yU.jpg)
(https://i.imgur.com/G4pKKqn.jpg)
My bet would be some sort of Sziklai Pair follower with perhaps some gain added to compensate for the small loss in a follower. Also called the complementary Darlington, it is common in output stages of transistor amplifiers. Another configuration might be the National Semiconductor LH0002CH complementary buffer with four transistors but I doubt they would use that.
To me it looks like a JFET buffer with a current source load then that feeds an NPN transistor buffer. The current source is formed with a transistor.
So they solved the JFET buffer attenuation problem I mentioned above by using current source load. The JFET gives the high input impedance and the BJT gives the low output impedance.
(https://i.postimg.cc/CzVHqrh3/Boss-Waza-Input-Buffer-V1-0.png) (https://postimg.cc/CzVHqrh3)
Boss Waza Input Buffer V1.0.png
R1 don't know: 1k or 10k ;10k seems more probable
C1 don't know: unpopulated, 10pF, 47pF, 150pF ;?
C2 don't know: 47n, 100n, 470n, 1uF ;470n, 1uF more probable
Hi Mick, hi Rob,
thanks for the pics and analysis! After staring at the thing and at the datasheets way too long, I concur that the topology that Rob suggests seems the most likely although I wouldn't have been able to trace it myself from this glorious mess.
So, long story short: the only "improvement" over the standard JFET buffer is that the gain is almost 1 instead of 0.9 or whatever. That would show up as an obvious improvement when A-B testing Waza vs non-Waza, as I suspect is done excessively on Youtube (did not bother to check). In the real wrld, however, this does not solve any problems that would not be just as easily and probably better solved by putting a good transparent booster at the front of your pedal chain. So while I think its a good improvement in a commercial pedal, where components bought in boxes of tens of thousands are cheap and robotic population of boards is too, it's probably not worth the hassle for diy pedals. I'm going to breadboard it anyway and compare to a single-JFET buffer. This may become a nice little project for beginners. Not extremely necessary but certainly educational.
Thanks again for scratching my curiosity-itch! Also: I'm glad to see that Boss still keeps their innovations rooted in the real EE world, even if they are of minor benefit. They might as well just use Mojo components, charge twice the price and call it a day. That seems to be how most (or at least too many) companies do it these days.
Cheers,
Andy
Quote from: Ben N on August 20, 2019, 11:30:36 AM
Quote from: Fancy Lime on August 19, 2019, 04:16:46 PMInteresting that they used a 4558. I cannot think of a single reason to choose that over one of the myriad of lower-noise, better stability modern drop-in replacements. Other than Mojo and I really hoped that the whole Waza thing wouldn't just be Mojo-based.
Andy, it's a bucket brigade delay, a severely limited, thoroughly obsolete technology that wouldn't even exist any more if not for OCD guitarists with their vacuum tubes and their LM308s and such, and their reverence for instruments made by hand in the 1950s. I'm not saying the sound isn't worth it, but if it's not about mojo, really, what is it about? And in the larger scheme of things, does the difference between a 4558 and a 5532 matter all that much in an analog delay pedal?
Hi Ben,
you are not wrong, of course. On the one hand: 4558 or 5532 will make no real difference here. But on the other hand: 4558 or 5532 will make no real difference here. And that is kind of my point. A BBD delay is at least noticeably different from most digital delays (better or worse is a matter of taste and debate). Tubes have some genuine advantages, although it is again debatable if they still outweigh the drawbacks in 2019. An LM308 slammed into the rails sounds distinct and some people like that. But if you use a 4558 or any number of other opamps in a DM-2 does not really matter. Therefore, if I were in charge of buying parts for Boss, I would opt for buying a larger stock of an opamp that outperforms the 4558 in other applications, where it does matter. 1.010.000 5532's are probably cheaper than 1.000.000 5532's plus 10.000 4458's, no? Then again, what do I know. I have no experience in this sort of operation and there may just be a Roland warehouse somewhere with enough 4458's from the 80's to last them 'till doomsday and then some.
Andy
Quoteonly "improvement" over the standard JFET buffer
The other thing it does is it makes the buffer more linear. Using a current source load on a buffer to get less loss and more linearity is an old trick. You will see it used in HiFi stuff.
FWIW, the SD-1W uses a slightly different circuit but the main ideas are still present.
Quote from: Rob Strand on August 21, 2019, 08:02:06 AM
Quoteonly "improvement" over the standard JFET buffer
The other thing it does is it makes the buffer more linear. Using a current source load on a buffer to get less loss and more linearity is an old trick. You will see it used in HiFi stuff.
FWIW, the SD-1W uses a slightly different circuit but the main ideas are still present.
You don't happen to have a schematic for that as well, do you?
Andy
QuoteYou don't happen to have a schematic for that as well, do you?
It's only in my mind. The differences are fairly trivial and don't change the basic idea:
- D1 not fitted
- C1 moved to other side of C2
- C3 = 47u ; maybe the DM-2W is actually 47u.
- R5 = R6 = 33k
- C4 I couldn't see one fitted. ; I'm not 100% sure it connects to the diode on the DM-2W
(- R1 couldn't read it)
On the SD-1W and the DM-2W C2 is made-up of two SMD film caps in parallel.
I might mark-up the schematic to include both versions.
What you do think about C4 connecting to the diodes?
Quote from: Rob Strand on August 21, 2019, 09:02:36 AM
...
What you do think about C4 connecting to the diodes?
Well, I think it makes sense in that position for stabilization but I have never seen a cap there in this topology. So I don't really know if it is useful or necessary but I would definitely not put it past the designers to put it in there.
Honestly, I am in awe that you even manage to trace these things at all. I cannot see jack in terms of what is connected to what.
Andy
IMHO, this topology should be better with the use of one diode in series with an extra base to GND resistor..
QuoteWell, I think it makes sense in that position for stabilization but I have never seen a cap there in this topology. So I don't really know if it is useful or necessary but I would definitely not put it past the designers to put it in there.
Honestly, I am in awe that you even manage to trace these things at all. I cannot see jack in terms of what is connected to what.
Yes it's a pain. It definitely helps to have a few possible circuits in your head which match the patterns you see on the board. I guess that's why asking for a second opinion about the cap connecting. I had a look this morning and it's fairly clear C4 is connected as shown on the DM-2W.
I can only speculate at the motivations for having the cap there but the truth is you might not need it at all :D.
More often than not there's no cap there.
There's two motivations to put it there: The first is to prevent supply noise/ripple affecting the current source. The second is to ground the base of the current source transistor to stop it affecting stability (due to CB capacitance of current source transistor). The low impedance of the two diodes helps both cases. However in this case the diode current is low so the impedance isn't *that* low, maybe 400 ohms. At 400 ohms a 10uF would actually do something to the ripple. I'd have to look at all the fine details to see if adds something.
Another scenario is, the DM-2 has quite noisy circuits so maybe audio testing showed-up a small amount of junk and the engineers traced it to the supply and added the cap. The SD-1 is analog so the supplies are clean and don't need the cap.
QuoteIMHO, this topology should be better with the use of one diode in series with an extra base to GND resistor..
Without looking at the details there's no way to know what is better. The temperature stability would improve but the effects I just mentioned would get worse. If you replace one diode with a resistor the resistor would need to be about 2.8k so that makes those issues about 7 to 8 times worse.
The only possible improvement in that *exact* topology is to use a schottky/standard signal diode combo in the ccs - and to up the second bjt loading current (reducing the emitter resistor). This netting the effect of sliiiightly increased negative excursion output swing-ability. (if you really want to use this topology).
Imho a ring-of-two cfp pair dances around this topo all day long, ymmv.
Quote from: bool on August 22, 2019, 06:12:01 AM
...
Imho a ring-of-two cfp pair dances around this topo all day long, ymmv.
I've been wondering why not just use a Darlington. Should get us very close to unity when used as a bog-standard emitter follower and if we feel we have to we could always bootstrap it for high impedance. Much simpler than the Waza solution. But would it really be that much worse? It may be less linear or more noisy. Does anyone know?
Bool advocates a Sziklai pair instead. What would the advantages of that be over a Darlington?
Also: If linearity and perfect unity gain are our concerns, why not just use an opamp? Does that really make a difference in terms of noise anymore with modern opamps?
Andy
Quote from: Fancy Lime on August 22, 2019, 07:13:16 AM
...
What would the advantages of that be over a Darlington?
...
NFB so less THD, better output swing, potentially lower S/Nr if you combine a low-noise transistor with a more powerful output device.
Quote from: bool on August 22, 2019, 07:18:45 AM
Quote from: Fancy Lime on August 22, 2019, 07:13:16 AM
...
What would the advantages of that be over a Darlington?
...
NFB so less THD, better output swing, potentially lower S/Nr if you combine a low-noise transistor with a more powerful output device.
You mean "low-noise transistor in the first position, high-current transistor in the second position"? Do we truly care about the output current? I mean, we are still feeding a circuit with a moderately high input impedance, in most cases anyway. So I would rather opt for two low-noise transistors, no? Does it matter if one uses the PNP-first or NPN-first configuration? I noticed that in complementary NPN-PNP pairs, the PNP typically has a slightly lower noise figure. On the other hand, the truly low-noise NPNs, like the MPSA18, don't even have complementary PNPs.
EDIT:
I forgot to ask: what's a "ring-of-two" cfb pair?
Andy
QuoteI've been wondering why not just use a Darlington.
One decision point is JFET vs Transistor. It's hard to beat the noise of a JFET with a high-impedance source. The side effect of the JFET is more attenuation. So if that's a problem you can use a current source load, like the waza, or the feedback amps I poster earlier.
JFETs introduce more distortion (if that's an issue) and more buffer loss when compared to transistors.
All transistor versions of the circuit have a limited output load to input impedance ratio set by the gains of the transistor. If you don't need to drive a low impedance load you can focus on optimizing operating currents for noise.
Notice that the transistor version of the feedback amps with gain=1 basically form a Sziklai pair. So you can view it as a buffer with a Sziklai pair or a feedback amp with two transistors. The Feedback amp structure however lets you come-up with the JFET input version of the circuit relatively easy, you don't need to invent a JFET+BJT Sziklai pair first.
The Sziklai pair/Feedback amp version of the circuit does have low distortion but I think it's hard to beat the transistor buffer with a current source load - I think it beats the Sziklai pair/Feedback amp. The transistor buffer with the current source load also has the least buffer loss.
Now getting to the Darlington. So first you have to accept using the BJT input and the trade-off of noise vs input source impedance. Once you do that a Darlington is an OK solution. However, it does have more loss than a single stage buffer but it lets you up the input impedance. On a real Darlington you would probably add a resistor across B and E of the second transistor. You can tune that resistor to minimize buffer loss and distortion.
Think of the BE resistor on the second Darlington transistor as creating a bias current for the first transistor. Now imagine instead of having that resistor you place a current source from the emitter of the first transistor to ground. What you end-up with is the Waza circuit except it has a BJT input instead of the JFET. This form of the circuit is slightly better than the Darlington with the BE resistor, both in distortion and buffer loss.
FYI, you can also make a JFET buffer with a current source load. This is basically the Waza circuit with the second buffer stage removed.
QuoteI forgot to ask: what's a "ring-of-two" cfb pair?
This is a circuit developed by Williams in the mid 1960's. There was a heap of articles in Wireless World, they were mostly in Letters to the Editor. Even the famous Peter Baxandall got into it!.
There's a current source version and a voltage source version. The idea is the output current is virtually independent of the supply voltage - which is what bool was getting at.
See
https://www.americanradiohistory.com/index.htm
Williams, WW Sept 1966, p456, Letters to the Editor ; *** The first appearance of the "ring of two" idea.
Williams, WW July 1967, p318, Ring of 2 Voltage Reference, Article
http://cdsweb.cern.ch/record/1063330/files/CM-P00068130.pdf
http://web.mit.edu/magic/Public/papers/06131873.pdf
A sziklai made with a lownoise fet at input, a speedy pnp and a ccs load (same-ish component count as in this particular boss buffer) would performance wise dance around all here proposed alternatives all day long (and night). (Basically, it's a discrete current-feedback opamp configured for gain=1).
The question is "does it vibe with your tone". Which I think for a guitar or a bass it doesn't.
Quote from: bool on August 23, 2019, 06:19:05 AM
A sziklai made with a lownoise fet at input, a speedy pnp and a ccs load (same-ish component count as in this particular boss buffer) would performance wise dance around all here proposed alternatives all day long (and night). (Basically, it's a discrete current-feedback opamp configured for gain=1).
The question is "does it vibe with your tone". Which I think for a guitar or a bass it doesn't.
What do you mean by "vibe"? It's a buffer, it's not supposed to vibe, it's not supposed to alter the tone in any way. As long as the output is as exactly as possible the same as the input in terms of AC voltages in the audio band, but at a much lower impedance, then it's a good buffer. If, on the other hand it makes any input signal sound like a harpsichord, it's an interesting effect but not a (good) buffer. I can't imagine that it would, in that case, be a particularly useful buffer for anything. Granted, most guitar buffers alter the sound a bit but that's a bug not a feature.
Andy
QuoteA sziklai made with a lownoise fet at input, a speedy pnp and a ccs load (same-ish component count as in this particular boss buffer) would performance wise dance around all here proposed alternatives all day long (and night). (Basically, it's a discrete current-feedback opamp configured for gain=1).
I just tried doing an all transistor minimum noise design for a 15k source impedance (very rough approximation to a guitar). The output load was an AC coupling cap to a 100k load. Three cases:
1) Single transistor buffer with current source load
2) Sziklai/Feedback (two BJT's)
3) Single transistor buffer with current source load followed by Transistor buffer with resistor load; basically the transistor version of the Waza.
So (2) wins on distortion and loss, second is (1), and last is (3). (1) and (3) are quite close. One caveat is the collector current is quite low for minimum noise so case (1) will have a higher impedance to 3.
Noise is about the same in all three cases, largely being dominated by the source resistance.
The other point is the noise minimum is very shallow. Increasing the collector current by a factor of 10 only increased the noise by 1dB or so.
Designs not optimized for noise gave different orderings of goodness. Like I could lower the loss or lower the distortion.
... hmm yeah nice analysis but we sort of knew that in advance did we..
I'm sure Boss had a good reason to waste smd beans like that. perhaps they had a large stock of semis they had to dispose of.. or they thoroughly -vibed- their buffer paradigm in and out. (like "vibe: the final frontier")
But for the giggles, you could un-IP the boss thing in a semi-same-ish fashion with using just a fet and one bjt: delete the ccs sub-cckt; and stick the 470R between the bjt B-E, making it a pseudo-ccs for the fet. For this to work properly, the bjt load resistor should be also lowered to something like 4k-ish. Or increase the 470R a bit (around 680R would load the fet with cca 1mA).
So here you have plans for a "Waza stupid" buffer laid out in plain sight!
Sooo, does that mean we'll be using Sziklai buffer now? With a N-Channel JFET first and a PNP second? Or just a regular old BJT-BJT Sziklai? The combines hfe should be large enough for decently high input impedance. If not, there is always bootstraping, Cornish buffer style.
Andy
Greetings all!
I've been messing around with Darlington and Sziklai buffers for a while, purely out of interest and for educational purposes. But I don't really see the value in them above that. Surely any op-amp would outperform the lot, and with far fewer components. Am I missing something?
Boss seem to have been throwing parts around on this one, perhaps it could have been improved with the addition of a single BJT. There's already a current sink available, one could simply extend that sink with a BJT and a current setting resistor in place of R4 alone.
Quote... hmm yeah nice analysis but we sort of knew that in advance did we..
QuoteSooo, does that mean we'll be using Sziklai buffer now? With a N-Channel JFET first and a PNP second? Or just a regular old BJT-BJT Sziklai? The combines hfe should be large enough for decently high input impedance. If not, there is always bootstraping, Cornish buffer style.
The decision the make the first transistor JFET or BJT changes things a bit. At the end of the day making the first stage a JFET is most likely to give the best noise performance.
When the first transistor is a BJT it is best to operate it with a low current to keep the noise down. So that means the output impedance goes up and it is helped by having a second transistor. So with the constraint of operating Q1 at low current the Sziklai case looks pretty good.
When the first transistor is a JFET it is best to operate the JFET at a high-ish current to keep the noise down. When you do that the output impedance of the JFET is relatively low but not great. If you have a JFET with a current source load, even without the second transistor like the Waza, the performance is actually pretty good ie. low buffer loss and also low distortion. I compared the simple JFET+CS case to the JFET+BJT feedback amp (ie. the JFET version of the Sziklai) and the JFET+BJT has more distortion but lower loss than JFET+CS.
It's good to keep in mind some of the differences are fairly academic. There's also some real differences. We would need to watch out for low impedance loads on the simple JFET + CS. The JFET+BJT Feedback amp is probably the most likely to have oscillation issues and perhaps will need good supply bypassing.
The thing about the JFET+BJT feedback amp is you have a second variable to pin down: the collector/source resistor at the output. Since we are operating the JFET at high-ish current and the JFET source current flow from thought the output resistor, if the output resistor is chosen too high the BJT will operate at low current and essentially the circuit will fall back to a JFET + source resistor buffer. In this case the BJT is kind of benign. From what I can see there is a value of the output resistor which gives the least buffer loss. Then decreasing that resistor further increases the buffer loss again but the distortion decreases and the supply current increases - so here we have the option to trade-off performance specs.
The fact we need to operate the transistor at a minimum current and the JFET is operating at a high-ish current means this configuration is likely to draw a little more current.
Notice in the JFET+BJT feedback amp the BE resistor sets the JFET operating current. We don't need a current source to set the JFET current. It only sets the current when the BJT current is not so low as to make the BJT benign.
QuoteI've been messing around with Darlington and Sziklai buffers for a while, purely out of interest and for educational purposes. But I don't really see the value in them above that. Surely any op-amp would outperform the lot, and with far fewer components. Am I missing something?
As far as getting the most out of the circuit for a guitar I'm not so fond of the single-part Darlington transistor solution since it doesn't allow you to set the bias current of the first transistor. If you make your own Darlington then you can tune the operating current using the BE resistor. I only see the Darlington being an advantage if you have a low impedance load. The Sziklai does seem to have some advantages over the Darlington in general.
You can definitely get lower noise and lower distortion opamps but the good ones quite often operate at higher supply currents. The discrete designs are pretty good and are probably better than your average opamp. The thing discrete designs offer is they are likely to operate at lower currents, maybe a bit more swing. You can also build a single opamp, so no wasted current.
If we go back to the original problem:
BJT buffer has higher noise with the high impedance source of a guitar
==> JFET buffer low noise but JFET+source resistor has a volume drop
==> So to fix either of those problems you have to do something.
Probably best to keep the JFET input from noise perspective.
After that, all the options have small differences in performance.
QuoteThe combines hfe should be large enough for decently high input impedance. If not, there is always bootstraping, Cornish buffer style.
Bootstrapping gives you higher input impedance but it doesn't solve the input noise currents of a BJT design.
Hi.
JFET, BJT and Darlingtons options have been discussed but I have the impression we forgot the MOSFET (and opamps, why not just use opamps?). MOSFET buffer seems very good on paper : has higher input impedance than BJT and lower output impedance then JFET (and loses less signal). But I dont often see it used in stompboxes? What are the tradeoffs (internal capacitance? noise? distortion?)?
QuoteMOSFET buffer seems very good on paper
Yes they sure do. In theory they should have noise specs comparable to JFETs, however, in practice they are much noisier. The commonly available parts are quite noisy.
Quote from: Rob Strand on August 23, 2019, 11:53:38 PM
Bootstrapping gives you higher input impedance but it doesn't solve the input noise currents of a BJT design.
To some extent it's possible to band-limit the bootstrap fb signal, in net effect diminishing the buffers' cur.noise outside of the band of interest, and this is cheap and simple to do, but fails at midrange freqs, which is where the crunch lives...
QuoteTo some extent it's possible to band-limit the bootstrap fb signal, in net effect diminishing the buffers' cur.noise outside of the band of interest, and this is cheap and simple to do, but fails at midrange freqs, which is where the crunch lives...
I haven't tried that. Normally I try to get full bandwidth, and largest cap I want to use sets the bandwidth.
Try it. It can clean up some of hf noise but you need to scale the passives (biasing resistors) to be of sufficiently low-z to bring the curr.noise generated voltage down. It doesn't kill the midband noise; this one goes straight into the chugga-chugga...
Hi.
I m wondering. A 2 transistors buffers + his associated components will take more PCB place than the opamp version, and this circuit becomes more complex because it aims to go close to opamp performance. Soundwise will there still be differences (character? mojo?) which makes worth it?
QuoteTry it. It can clean up some of hf noise but you need to scale the passives (biasing resistors) to be of sufficiently low-z to bring the curr.noise generated voltage down. It doesn't kill the midband noise; this one goes straight into the chugga-chugga...
I'll have to play around with it.
Needs a high-beta transistor.
Quote from: Ice-9 on August 19, 2019, 03:44:33 PM
the coolaudio bbd's and clock chip
I found it mildly amusing that after having so many of their pedals cloned, Boss is now buying parts from Behringer! ;D
Quote from: anchovie on September 01, 2019, 07:15:34 PM
...
Boss is now buying parts from Behringer!
...
Beer-ringer has obviously perfected the craft. No wonder after so much interactions of "reverse" R&D.
R&D is R&D after all.
I was packing up the stuff from this thread and there's a few points I can add about the Waza pedals.
On the SD-1w the buffer output which goes to the overdrive section is tapped off the source of the JFET ie. before the final BJT buffer. Whereas the clean signal is tapped off the BJT buffer. (So it follows the pattern of some of the Ibanez pedals where the clean signal has an extra buffer before the JFET switching.)
The DM-2w on the other hand uses the output from the second buffer for both the clean signal and the input to the effects circuit.
The internal buffers on the DM-2w, for example the buffers used on the Sallen and Key filters, are just the plain vanilla one transistor buffers.
In both the SD-1w and the DM-2w the output buffer is a BJT buffer, like the older Boss pedals. One change to the output buffers on the Waza pedals is the resistor in series with the signal line is moved to the output side of the resistor to ground. This prevents creating an unnecessary voltage divider with the 100k to ground and minimizes signal loss.
The general set-up on the JFET switching uses 1uF electrolytic caps for all the signal coupling caps and 100k resistors to Vbias. The standard Boss pedals used 47n caps and 1M, so the Waza circuits have dropped the low-frequency cut-off a bit.
Quote from: Jubz on August 26, 2019, 06:42:16 AM
I m wondering. A 2 transistors buffers + his associated components will take more PCB place than the opamp version, and this circuit becomes more complex because it aims to go close to opamp performance. Soundwise will there still be differences (character? mojo?) which makes worth it?
No other than current capability (second transistor could easily be a couple of Watts item) and personal design joy.. :icon_wink: