Analogman - King of Tone  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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jalmonsalmon
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Post by jalmonsalmon »

Manfred wrote:I have tried various transitors the MPSA18 base-emitter diode gave the best match with the MA858 Diode.
So can the MA856 replaced by the MPSA18 base-emitter diode.
MA858 MPSA18 Comparation.jpg
That's awesome!
Save your money and go the base-emitter route of MPSA18s
I want to take back my MA856's

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Intripped
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Post by Intripped »

Manfred, could you please check the mpsa13 (darlington) base-emitter diodes as well?
I mean one mpsa13 compared with two MA856 in series?

The fw-drop on my multimeter is around 1590 mV
...I'm not sure, but I think darlingtons can be used as clipping diodes... what do you think?

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Manfred
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Post by Manfred »

Intripped,

I traced the Darlinton BC373 B-E path the curve does not match it is far away from the 2 x MA858 curve.
I have no MPSA13 in the moment but I going to order one.
2xMA858 BC373A Comparation.jpg

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Post by Manfred »

Today I received the MPSA13 Darlingtons.
The traced curve is also far away from the 2 x MA858 curve.
Now I going to order MPSA14s.
MA858 MPSA18 MPSA13 Comparation.jpg

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bool
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Post by bool »

MPSA14 should be similar to MPSA13.

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Manfred
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Post by Manfred »

I had an idea and made a Darlington circuit with two MPSA18.
I let the collector connected and traced the base 1 to emitter 2 PN-junction.
The trace affirmed my supposition, the curve is similar to the read curves of the Darlingtons with the lower knee voltages.
The obvious reason is the connection of the collectors.
I would therefore say that not any Darlington transistor can have the curve of two base-emitter paths in seriell conection.
MA858 MPSA18 MPSA18 Darlington Comparation.jpg

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Post by Manfred »

It did not leave me in peace, I was curious to see what causes the differences in circuit behavior.
I have therefore measured both circuit as follows shown in the image.
MPSA18 Read Values.JPG
If both collectors are connected the second transitor becomes conductive
and the most of the current flows through base-collector path of the first transistor to the second one.

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Post by Manfred »

I traced the B_E diodes of the MPSA42 and MPSA92 transistors but there is no match to the MA858 curves neither.
MA858 MPSAxx Comparation.jpg

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Post by Frank_NH »

I've been playing around with a blues breaker circuit on my breadboard, and one diode I think may make a good substitute for the KOT MA856 is the BA100. Has a Fv ~ 0.7 V and is a silicon signal diode. They're not too common, but are available from some suppliers.

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Post by Manfred »

Frank_NH wrote:I've been playing around with a blues breaker circuit on my breadboard, and one diode I think may make a good substitute for the KOT MA856 is the BA100. Has a Fv ~ 0.7 V and is a silicon signal diode. They're not too common, but are available from some suppliers.
Thanks for the hint.
I just ordered BA100 diodes for testing, but it is hard to find the diodes in Europe.
The sales price is too high there is the MPSA18 transistor much cheaper.

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Post by Frank_NH »

Manfred wrote:
Frank_NH wrote:I've been playing around with a blues breaker circuit on my breadboard, and one diode I think may make a good substitute for the KOT MA856 is the BA100. Has a Fv ~ 0.7 V and is a silicon signal diode. They're not too common, but are available from some suppliers.
Thanks for the hint.
I just ordered BA100 diodes for testing, but it is hard to find the diodes in Europe.
The sales price is too high there is the MPSA18 transistor much cheaper.
I just ordered more BA100s as well, along with some 1S1588s. I thought about getting some MA856s, but they're expensive, and frankly I don't think I'd hear much of a difference from the BA100s (except for the MOJO factor :lol: ).

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Post by Manfred »

I traced the BA100 PN-junktion curve compared to the MA858 curve, the curves are far from each other.
MA858 BA100 Comparation.jpg

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Post by Frank_NH »

Thanks Manfred - very interesting. The BA100 curve looks almost identical to your previous 1N4148 curve.

My DVM shows my BA100's FV to be in the 0.7 - 0.75V range, with 1N4148 being about 0.6 - 0.65V. I suppose there can be some variability between specific batches of diodes. Still, I would recommend BA100s for KOT clones as a better choice than 1N914s, provided they have the slightly higher FV.

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Post by Manfred »

Here is the comparison of the BA100 diode with the 1N914 1N4148 MA858 diodes.
The BA100 PN-junktion curve is indeed very close to the 1N4148 curve.
MA858 BA100 1N4138 1N914.jpg

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Post by Seiche »

i didn't expect such a big difference between 1n914 and 1n4148, I always thought they are identical :shock:

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Post by Manfred »

Seiche wrote:i didn't expect such a big difference between 1n914 and 1n4148, I always thought they are identical :shock:
I traced a bunch of both diode types the difference is always the same.

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Post by Seiche »

yes but 1n4148 is always recommended as a replacement for 1n914 everywhere

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Post by Frank_NH »

I took some data last night using my DVM for a plain 1N4148 and the BA100 that I have. I plotted the data in Excel (see attachment) - there's definitely a difference. Also the DVM on its diode setting indicates a difference in forward voltage.

One more thing - after doing a little more research, there is another possibility for a MA856 replacement, and that is the BAS33 diode. Datasheet indicates Fv of ~ 0.75@1mA and ~0.82@10mA, which is similar to the MA856. I'll order some once my other diode order arrives... :D
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Post by Manfred »

took some data last night using my DVM for a plain 1N4148 and the BA100 that I have. I plotted the data in Excel (see attachment) - there's definitely a difference. Also the DVM on its diode setting indicates a difference in forward voltage.
I use the Atlas DCA75 Pro Advanced Semiconductor Analyzer for tracing
and I am pretty sure that it works accurately.

What measuring methode respectively what measuring circuit did you use to read the values?

My bunch of 1N4148 were produced in the early 1980s, but I guess that the specifiation has not changed in the meantime,
but who knows.

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Post by Frank_NH »

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.

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