Analogman - King of Tone  [traced]

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The Rotagilla
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Post by The Rotagilla »

Having done some semi-extensive side by side testing with MA856's vs. MA858's, I'm going to throw my two cents in. Yes they sound similar, but the 856 is slightly sweeter and has a smoother decay. Tell me I'm crazy as much as you want but that's my experience.
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Post by Manfred »

Frank_NH wrote:I used a clean 9V power source (not a battery) and arranged a simple circuit on my breadboard with a potentiometer in series with a 1k (1%) metal film resistor and the diode. Varied the pot to provide a range of currents. Measured the voltage drop across the resistor to get the current and the voltage drop across the diode. Recorded everything by hand - the old-fashioned way! :lol:

As I mentioned, I'm going to ultimately get some MA856s and BAS33s to check out, and do some extensive listening in my test circuit. I really don't think there will be a tremendous difference in tone, but it will be fun trying out the different diodes.

By the way, my interest in all of this comes from a recent purchase (on a whim) of the Tone City King of Blues pedal. People were touting it as a KOT clone, but in fact it turned out to be a Klon (Engine A) into a standard Blues Breaker (Engine B) circuit. Everything (almost) was SMD, including the BB silicon diodes! (The Klon diodes were full size 1N34As). In the end, the BB side of the pedal sounded very blah to me, so I thought I'd have look at the KOT and BB circuits (and the many derivative pedals out there) to see if I could improve the sound of the BB, with aim of making my own DIY King of Blues dual pedal.
Thanks for your explanations.

I found some 1N4148 curves in the Internet, there was a good agreement with my traced curve.
I will measure my the diodes using " he old-fashioned way" to see whether there is any difference between the measuring methodes.

I believe in your hearing experiences, I think that is a good way to find the sound of personal taste.

In sum, I would like to say following:
The clipping circuit output can be adapted by a damping ciruit or a gain stage.
The harmonic content in the clipped signal is depending on the curve shape of the clipping diode.

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Manfred
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Post by Manfred »

The Rotagilla wrote:Having done some semi-extensive side by side testing with MA856's vs. MA858's, I'm going to throw my two cents in. Yes they sound similar, but the 856 is slightly sweeter and has a smoother decay. Tell me I'm crazy as much as you want but that's my experience.
Thanks for sharing your experiences.

I dealer told me that MA858 has a only 4% derivation from the MA856, perhaps is the curve shape different to.
I will try to get a MA856.

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Post by Manfred »

I had a look at online market for buy MA856 diodes but I could not find one for a more affordable price,
so I made a datasheet comparison.
The first row shows the MA856 diode data the second row the MA858 diode.
The PN-junction curve is very similar.
The differences are in the forward dynamic resistance and the terminal capacitance but both don't touch the audible frequencies.

After the "old fasion"-compare of the 1N4148, I will the diodes comparison in this topic for me.
MA856-MA858 Datasheet Compare.jpg

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Post by Frank_NH »

Hi Manfred,

I also have the MA856 and MA858 data sheets, and also one for the BAS33, and I went ahead and plotted the curves with my 1N4148 and BA100 data on a semi-log plot (the plot format used in the datasheets). The plot is attached. Note that the datasheet curves are the performance @25C and represent some sort of "typical" behavior (which no doubt can change slightly with specific batches of diodes). As you can see, the MA856 and MA858 are indeed quite similar except at higher currents closer to 10 mA, then they depart a bit. Both have higher Fv than the BA100 and 1N4148. The BAS33 actually has a slightly higher Fv than the MA858, and I would venture to say it's curve would be similar in shape, so definitely worth trying out as a KOT diode choice.

BTW - just ordered some MA858s from eBay. I'll have a look at these on my DVM when I get them.
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Diode Comparison.png

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Manfred
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Post by Manfred »

Hi Frank,

thanks for for our interesting work.
After the "old fasion"-compare of the 1N4148, I will the diodes comparison in this topic for me.
Sorry, I forgot a word in this sentence it should read:
After the "old fasion"-compare of the 1N4148, I will finish the diodes comparison in this topic for me.

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Post by Frank_NH »

I suppose it may appear that we're going a bit overboard in looking at diode Fv, but this topic seems to come up again and again and not just for the Bluesbreaker or KOT. I've seen many articles online extolling the virtues of specific diodes in various overdrive and distortion circuits for hard and soft clipping, and I find it clarifying if we can at least understand (from an electronics viewpoint) why certain diodes seem to work well for different applications. The starting point for me would be to have a database of Forward current versus Forward voltage for all of the usual diodes (silicon and germanium), and to that end I'm going to try to create a spreadsheet with that kind of data, especially measured data for diodes I have in hand. Seeing the diode curves side-by-side can perhaps gives some insight into the clipping characteristics and potentially where one diode model can be replaced by an equivalent.

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Seiche
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Post by Seiche »

Yes that would be great!

However, I suppose this would be better suited to be stickied in the circuit design section or another more appropriate section rather than this thread. It should of course be referenced here, especially ideal replacement types for the ma856

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Post by Frank_NH »

Seiche wrote:Yes that would be great!

However, I suppose this would be better suited to be stickied in the circuit design section or another more appropriate section rather than this thread. It should of course be referenced here, especially ideal replacement types for the ma856
I wasn't going to upload a bunch of spreadsheets in this thread (there's already lots of great info from Manfred and others), but I do plan to collect and measure diode characterstics just as a general ongoing personal project. I'll need to go through my diode collection and I'll probably even construct a better diode tester than the one I have now. :)

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Post by Manfred »

I wasn't going to upload a bunch of spreadsheets in this thread (there's already lots of great info from Manfred and others), but I do plan to collect and measure diode characterstics just as a general ongoing personal project. I'll need to go through my diode collection and I'll probably even construct a better diode tester than the one I have now. :)
Hi Frank,

If you want, I will support your project.
The tracing data read by my analyser are also availabel as value data for fill into a spreadsheet.

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Post by morgan wong »

Seiche wrote:Mr Wong,

I don't like that this is a direct copy/fake with analogman logo etc.

I prefer homages, rather than fakes.
Yep, I agree with that.
Uploading images just wants to help more people interpret it.

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Post by Frank_NH »

Manfred wrote:
I wasn't going to upload a bunch of spreadsheets in this thread (there's already lots of great info from Manfred and others), but I do plan to collect and measure diode characterstics just as a general ongoing personal project. I'll need to go through my diode collection and I'll probably even construct a better diode tester than the one I have now. :)
Hi Frank,

If you want, I will support your project.
The tracing data read by my analyser are also availabel as value data for fill into a spreadsheet.
Thanks! I'll be collecting data in Vf (V) versus If (mA) format, and organizing them in a spreadsheet. If you want to upload a text or spreadsheet file with your data I can add it to my database. I'll be going through my collection of diodes and measuring data as I have the time. It will be good to note (if possible) the room temperature as diode behavior is temperature dependent (more so with germanium).

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Post by Manfred »

Thanks! I'll be collecting data in Vf (V) versus If (mA) format, and organizing them in a spreadsheet. If you want to upload a text or spreadsheet file with your data I can add it to my database. I'll be going through my collection of diodes and measuring data as I have the time. It will be good to note (if possible) the room temperature as diode behavior is temperature dependent (more so with germanium).
You should start a new topic about this issue, because this is an area which goes beyond the scope of this current topic.

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Post by Frank_NH »

Thanks - I'll start a new topic.

By the way, I have a correction to make. I rechecked the markings on my BA100 diode and it is actually a BA110! I just received some BA100s from a supplier and they have a slightly lower forward voltage (about 0.67 V) which is nominally above the 1N914/1N4148 but are different than my BA110s (which do read 0.7V). Interestingly, the BA100s look exactly like my BA110s (black with a white stripe). Sorry for the confusion. I believe that your readings for your BA100 are correct.

Unfortunately, BA110s are difficult to come by. It's a moot point as I have some MA858s coming Monday and they have a higher forward voltage.

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Post by Boba7 »

What a great thread, thanks guys.

I think I’ll keep using 1n4148/1n914 for now bit maybe Ill try some mpsa18 one of these days!
Amazing work anyways. Thanks

Seiche wrote:So I traced the circuit and it's pretty much what we already know. The only differences are thus:

- the input cap is 22n on both sides
- instead of 1s1588, this uses 1n914
- output cap of the high-gain red side has an "H" painted on it, but is the same value 105 as on the yellow side. The IC also has and H painted on and the chip id sanded off.
- the feedback loop cap on the yellow side ist a weird value. 505? The red side has the usual 101=100pF.
- On the high-gain red side the gain resistor is 100k, on the yellow side it is 1k.

I think the last part is news, as this resistor was always assumed to be 10k and the gain pot changed for high-gain on DIY projects.
Thanks! 22n is new and so is the 1k/100k resistor. Nice sharing!
Regarding the feedback cap, I doubt 50pf would make a big difference compared to 100pf, especially on the low gain side. So I’ll keep using 100pf for now :)

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Post by FlyingWild »

I have just breadboarded this pedal, and although I don't anticipate ever running it with the gain wide open, I was just wondering if it's normal for it to get very very bright when you do so.

There is a point from about 3 O'clock onward where it the brightness noticeably increases with the gain increase, the presence is all the way down and even with the tone all the way down too the brightness is noticeable.

Otherwise it seems to be working as expected, deviations from the schematic:

I don't have a B25K pot to hand so using a B20K, and I'm using a RC4558 Opamp and 1N4148 clipping diodes, for both soft and hard clipping, but currently just trying out the soft clipping.

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Post by Seiche »

What happens when you turn the presence all the way "up"?

Check all your resistors and caps around the tone and presence control as well as potentiometer pinout.

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Post by FlyingWild »

Thanks for your help Seiche,
Seiche wrote:What happens when you turn the presence all the way "up"?
It gets brighter.
Seiche wrote:Check all your resistors and caps around the tone and presence control as well as potentiometer pinout.
I don't have time right now, but will double check again tonight. I take it from your post that the increase in brightness is not normal then? My tone pot is 20k not 25k as I don't currently have a 25k pot, but could add a 4k7 in series with the 20k to get me closer for testing purposes.

With the gain at 2 O'clock, presence at its lowest position and volume just over unity, I like the tone at about 2 O'clock, which all seems about right to me. I'll investigate more tonight, thanks again.

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Post by FiveseveN »

FlyingWild wrote:I take it from your post that the increase in brightness is not normal then?
I haven't built it, but the schematic looks like it shouldn't be that noticeable, unless you've mistakenly used 10n instead of 100n for C5. That would be my first guess (code should be 104). Couldn't be related to the tone section since the drive pot can't influence those filters.
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Post by FlyingWild »

Just discovered my mistake, I used a 1k resistor instead of a 10k resistor after the drive pot.

better carry on checking in case I've made any other slip ups!
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