Yes, another one about Boss SD-1 Buffer

Stompboxes circuits published in magazines, books or on DIY electronics websites.

Yes, another one about Boss SD-1 Buffer

Postby HappyCat » 28 Nov 2017, 00:29

Hi guys!

I have some love & hate relationship with the Boss SD-1, maybe because twenty years ago it was my first 'serious' pedal... I have several units, from several years, some of them modded and others remain stock,...

About Boss' buffer, I've never had a trouble or complain about it. But, only for curiosity, and because (honestly) I'm not able to understand the flip-flop switch circuit, I'd like to know...

1) Is it possible to erase the input and output buffer of the circuit? And... how?...

2) Being crazy, and only to expand the exploration of my own curiosity... Would it be possible to substitute the buffer circuit with another one? The IN/OUTPUT buffer of a Klon, of example?

As I said, only for curiosity...

Thanks in advance!
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Re: Yes, another one about Boss SD-1 Buffer

Postby Manfred » 28 Nov 2017, 00:56

The input buffer got a low output impedance to drive the following circuit parts, therefore it can not be omitted.
For erasing both buffers the FET transistor switching circuit parts must be replaced by a relay bypass circuit.
The flip-flop digital part can continue to be used.
For example:
http://www.geofex.com/FX_images/relay%20true%20bypass%20with%20Boss-Ibanez.gif
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Re: Yes, another one about Boss SD-1 Buffer

Postby mictester » 28 Nov 2017, 03:16

I really don't understand this obsession with removing buffers. They're there for a damn good reason: They provide impedance transformations and they protect the sensitive inner parts of a circuit from the outside world. It is important to understand - and fully appreciate - that a properly designed buffer has no gain and does not colour the sound in any way. A good buffer is truly transparent!

The bistable switching used by many manufacturers is cheap, works exceptionally well and doesn't add nasty clicks and pops. It's also possible to use a high reliability momentary switch to control it. Again, these switching circuits do not colour the sound! The only downside is that they won't pass a signal without power. There is no reason to remove or replace these circuits. They were designed by much smarter people than the boutique boobs who want to remove them!

Way back in the late 70s, Maxon couldn't source locking DPDT switches at reasonable prices - the ones they were offered would have doubled the cost of the BOM for many of their products. They experimented with FETs as switching elements - at first using a SPDT switch to bias the FET gates to effect the switching. Someone then had the bright idea of "all electronic" switching, using a bistable to control the FETs. Almost all Japanese products changed over to using that type of circuit. The Tubescreamer even tried to hide part of the operation of their bistable by using the "No1" device - actually a capacitor and resistor in parallel - in an effort to confuse the competition.

Don't waste your time trying to remove buffers and FET switches. They're there for good reasons and the alternatives that you might try will be certain to be inferior!
"Why is it humming?" "Because it doesn't know the words!"

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Re: Yes, another one about Boss SD-1 Buffer

Postby HappyCat » 28 Nov 2017, 08:18

mictester wrote:I really don't understand this obsession with removing buffers. They're there for a damn good reason: They provide impedance transformations and they protect the sensitive inner parts of a circuit from the outside world. It is important to understand - and fully appreciate - that a properly designed buffer has no gain and does not colour the sound in any way. A good buffer is truly transparent!

The bistable switching used by many manufacturers is cheap, works exceptionally well and doesn't add nasty clicks and pops. It's also possible to use a high reliability momentary switch to control it. Again, these switching circuits do not colour the sound! The only downside is that they won't pass a signal without power. There is no reason to remove or replace these circuits. They were designed by much smarter people than the boutique boobs who want to remove them!

Way back in the late 70s, Maxon couldn't source locking DPDT switches at reasonable prices - the ones they were offered would have doubled the cost of the BOM for many of their products. They experimented with FETs as switching elements - at first using a SPDT switch to bias the FET gates to effect the switching. Someone then had the bright idea of "all electronic" switching, using a bistable to control the FETs. Almost all Japanese products changed over to using that type of circuit. The Tubescreamer even tried to hide part of the operation of their bistable by using the "No1" device - actually a capacitor and resistor in parallel - in an effort to confuse the competition.

Don't waste your time trying to remove buffers and FET switches. They're there for good reasons and the alternatives that you might try will be certain to be inferior!


Mictester, maybe I didn't explain myself correctly, but as I said in the first post, I don't have any complain or issue with buffers. I like to have al least one in mi pedalboard. I know perfectly the benefits of them into the signal... For that reason, even I'm talking about including a different buffer, instead of the stock one :wink: :wink:

What I try to do with this "experiment" is learning, about how the circuit works, and how the buffer works. Curiosity, just that. There's no obsession about true-bypass.

Anyway, thanks for the historical info, very appreciated.

Manfred, thanks for the link and the info, I'll try to understand the fantastic GeoFex article! :thumbsup
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Re: Yes, another one about Boss SD-1 Buffer

Postby Dirk_Hendrik » 03 Dec 2017, 10:13

What Mictester says. With an exception though.

There has ben a lot of bitching about buffers in Boss pedals. Ibanez/Maxon as well but primarily Boss. Unfortunately "the buffer" has become a fashion word and usually is not backed up with a technical analysis by those who complain about these buffers. Even worse, about all complaints about "the buffers in boss pedals" do not even state which pedal was used as a reference for that complaint. Apparently it is assumed all Boss pedals have exactly the same input and output buffer. Nothing is further from the truth...

Place any stock Boss pedal in a TB looper and yes, you will notice the difference. Mictester will too. I'm sure. If that difference is worth modifying the pedal is another discusion.
After that the conclusion "could" be to remove the buffers. Your pedal will definitely sound like shit, will be more susceptible to noise and may behave very odd in your setup.
Second option, very common this one, is to remove the buffers and TB the bugger. Since the Boss is then only used with effect engaged the comparison is odd. First the Boss was judged for the sonic influence of the buffers when bypassed and after that the buffers are removed while the pedal is only audible with the effect engaged!

As well, and it's getting more technical here;
Boss pedals use different buffer circuits. In most cases of OD pedals these are emitter or source followers with very little sonic influence. In the case of many delay and chorus pedals The input and output buffer circuit is combined with the preemphasis and deemphasis filter. When the effect is engaged the wet signal is mixed with the dry signal between these 2 filters. However, these 2 filters are always in the signal path and, although "flat" from a frequency perspective, will give a lot of phase related twists to the signal. When feeding the circuit a complex signal like from a guitar, these 2 filters will therefore have quite an influence on the bypass signal. And for that reason it is worth mentioning which Boss pedal has that bad buffer.
Sorry. Plain out of planes.

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Re: Yes, another one about Boss SD-1 Buffer

Postby mictester » 06 Dec 2017, 00:51

Dirk - You're quite right about the phase change issues, and a piece of wire (or a relay contact) is always going to outperform any FET switch, but in the world where amplifiers are designed to be distorted and to impart their own tonal colouration, and where loudspeakers themselves impart 10 - 15% distortion, you're really unlikely to hear the minute influence of an FET switch! Remember - in the Real World™ of effects use on stage or in a rehearsal studio, it's impossible (or at least very improbable) that you'll hear the difference between a germanium and a silicon Fuzz Face with a couple of extra capacitors to tame the fizz. I just want a bypass circuit that gets out of the way when de-selected, which is why the bistable relay is such a good choice.
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Re: Yes, another one about Boss SD-1 Buffer

Postby HappyCat » 28 Dec 2017, 23:37

Thanks for such an useful info, guys! But, with all my respects... I never said that I don't like buffers, that I want to erase them or something like that... I'm only trying to test different things around this overdrive, only that...

Only a first question... Starting from this schematic...

https://www.hobby-hour.com/electronics/s/schematics/boss-sd1-super-overdrive.gif

If I get R1, R2, R3, C1 and Q5 out of the circuit, replacing them by a new input buffer (I don't know... maybe a Cornish buffer??)... would it be OK? Is there something related between the values of the input buffer and the flip/flop circuit that make impossible that change? I assume that C2 is not a part of the buffer, is it?

Thanks in advance. As always, the best part is learning new stuff, something that uses to happen in this forum! :horsey:
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Re: Yes, another one about Boss SD-1 Buffer

Postby lcv » 29 Dec 2017, 07:25

Hi Happycat
If you want to experiment, then do it. It' s just emitter follower.
Just make sure you don't fry your pickups, your question sort of implies that risk... :)
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Re: Yes, another one about Boss SD-1 Buffer

Postby HappyCat » 29 Dec 2017, 11:27

lcv wrote:Hi Happycat
If you want to experiment, then do it. It' s just emitter follower.
Just make sure you don't fry your pickups, your question sort of implies that risk... :)


:lol: Thanks for the advise! I didn't think about it... Anyway, I'll go for a very known buffer, maybe the one used in the Klon (to get rid of a single IC for the input and output buffer) or the buffer designed by P. Cornish... So, if I don't commit any mistake (fingers crossed), I hope my pickups can survive this experiment! Now, I'll read a bit about emitter followers, thanks!
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Re: Yes, another one about Boss SD-1 Buffer

Postby okgb » 31 Dec 2017, 18:16

Or build someone from scratch like the RTO , or something close to the sd , there's loads of pcb's out there
a little less desoldering to do
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