Friedman BE-OD Pedal  [traced]

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bancika
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Post by bancika »

It would be great if MJE253 can be used as a replacement, I was able to track down those here in Serbia. Although they are much bigger, but maybe easier to install because of through hole package.

ZXTP25040DFH are not easy to find.

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Post by bool »

@bajamon: are you absolutely totally sure you applied the "DIY-er correct" methodology in simulations? Perhaps I'm mistaking, but (to me) it seems that you are comparing TWO pn drops (i.e. 4x1N4148 scenario) versus ONE pn drop (fat transistor b-e junction).

My ghetto solution (but I could be totally wrong) would be to just go and use two 1N400x in existing layouts (or shoehorn SM400x's there) to get somehow closer to a B-E drop.

1N4148's have cca. 2pF junction capacitance; 1N400x's have ccca 10-times more than that which is probably closer to a fat PNP b-e junction cap. Which could bring the upper mids more in line (40pF nfb capacitance versus 2pF with 4x1N4148).

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Post by bajaman »

@bajamon: are you absolutely totally sure you applied the "DIY-er correct" methodology in simulations? Perhaps I'm mistaking, but (to me) it seems that you are comparing TWO pn drops (i.e. 4x1N4148 scenario) versus ONE pn drop (fat transistor b-e junction).

My ghetto solution (but I could be totally wrong) would be to just go and use two 1N400x in existing layouts (or shoehorn SM400x's there) to get somehow closer to a B-E drop.

1N4148's have cca. 2pF junction capacitance; 1N400x's have ccca 10-times more than that which is probably closer to a fat PNP b-e junction cap. Which could bring the upper mids more in line (40pF nfb capacitance versus 2pF with 4x1N4148).
Hello bool
Yes, I did compare 4 x 1N4148, 2 x red leds, 2 x 5.6v zeners, 2 x BAV99, 2 x BAT85S, 2 x MPSA56, 2 x MPSA92, 2 x 2N5087, 2 x BC557, 2 x ZXTP25015DFH, 2 x ZXTP25012DFH, 2 x ZXTP25020DFH, a2 x ZTX915, 2 x MJE253, 2 x MJE15029, 2 x MJE15031, 2 x MJE15033 and many more devices.
I cannot comment on how these devices sound or how they actually clip in practical terms, but running several AC sweep simulations made it very clear that the FREQUENCY RESPONSE CHARACTERISTICSare very different between these devices. Interestingly the ZXTP250***FH series all give almost identical frequency responses and the closest through hole components I could find to these frequency responses were the MJE253 and MJE15029 devices - the MJE15031 and MJE15033 devices were not the same by the way :!:

I tried juggling resistor values as you suggested in the hopes of alighning the frequency responses using small signal diodes etc., but this had very minimal effect on the response curves.

Interesting to me was the so called through hole equivalent Zetex E line device - the ZTX951 which considerably flattened the mid range hump around 1.5KHz, reducing the level by nearly 10dB at this frequency centre while still retaining the same output level at frequencies below 150Hz, and reducing the 10KHz response by only 4db or thereabouts. I am looking forward to trying these devices perhaps with a small toggle switch for a flat or boosted mid range response option. i cannot recall finding any other pnp device that simulates like the ZTX951 and the spice model came directly from Zetex too.

All my simulations with any of the diode clippers moved the mid hump from 1.5KHz to 2KHz and raised the level by 4.5db at this frequency and a massive 10dB at 10KHz. Again, frequencies below 300Hz are largely unaffected.

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Post by Intripped »

great work banjoman!

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Post by bajaman »

GRRRRRR :evil:
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Post by toneman »

and a massive 10dB at 10KHz. Again, frequencies below 300Hz are largely unaffected.
Is there any "music" above 10K? :?

the topology seems to be:
input buff-> into screamer(modified)->into inverting screamer(modified-)->into inverting GAIN stage-> then "presence" filter-> into a Rat-> thenfinal tone control -> output volume

the "presence" control is actually a high-cut---nothing to do with mids.. :cry:
my first "mod" will be a mid parametric with boost/cut :wink: maybe TWO parametrics(???) :shock:
but.....WHERE to put the new filter(s) :scratch:
i wonder if this is what the Dirty Shirly is :wink:
maybe THAT's what buggs NEXT pedal will be???

GRRRRReat comeback B-man :lol:
nighty nite
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Post by bancika »

what I'm puzzled with is how you're getting those huge differences with only 10mV at the input. That's like 1/10th the output of an average pickup or even less. Is the circuit even clipping at those levels? Or those differences are there even with the un-clipped signal?

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Post by bajaman »

what I'm puzzled with is how you're getting those huge differences with only 10mV at the input. That's like 1/10th the output of an average pickup or even less. Is the circuit even clipping at those levels? Or those differences are there even with the un-clipped signal?
Hi bancika
Yes - a very low input level because this is a very high gain pedal :wink:
The circuit is certainly clipping even at these low levels but not as much as with a guitar level of course.
If the sims are correct the it certainly shows the added fizz that diodes bring to the party compared to the medium power (4A 15v) pnp devices that appear to be used in the friedman pedal :hmmm:
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Post by bugg »

toneman wrote:maybe THAT's what buggs NEXT pedal will be???
Close but not quite..... This one is much warmer than the BEOD. :mrgreen:

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Post by bool »

@baja: "....I cannot comment on how these devices sound or how they actually clip in practical terms, but running several AC sweep simulations made it very clear that the FREQUENCY RESPONSE CHARACTERISTICSare very different between these devices. ..."

That's precisely what I was getting at. Device-in-use junction capacitance in general would be IMHO the major contributing factor to this stage freq. response.

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Post by J0K3RX »

bajaman wrote:bugg - The more I try and figure this out the more I realise that your schematic is correct except for those smd clipping devices - i did a search for the BAV99 which someone mentioned were the correct diodes but the Vishay datasheet gives JE for the type marking so surely they cannot be correct.
The Zetex datasheet for the ZXTP25015DFH on the other hand gives 1A7 for the type marking, which is the same as the board pictures.
Using diodes for clippers accentuates the upper midrange compared to the pnp transistors which would tend to make it a bit more fizzy sounding perhaps :hmmm:
Still waiting on the transistors to arrive so will just have to be a bit more patient.
cheers
bajaman
Yeah, I think it was me that pointed to the BAV99 but, I took a little closer look and now appears to be wrong..

I was thinking the manufacturing site placeholder was before, not after the A7
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Post by bajaman »

I am now confident that bugg's board will work fine with the right clipping devices :oops: - it should just sound a bit "fizzier" when using 4 clipping diodes of any sort. It will be very easy to modify with some mini toggle switches to perhaps choose between different devices in this position. :D
IMG_4301.jpg
I looked again very closely at this picture, and there it ism - the connection from pin 7 of the opamp to the junction of C13 and pin 3 of the presence control - partially obscured and hidden under the IC2 screenprinting :wink:
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Post by bugg »

Good find! I have the original pedal sitting in front of me, so lets move on to the mystery diodes.

The pinout (going by measuring forward voltage drops with the diode function of my Fluke DMM) matches that of the BAV99 dual diode not the ZXTP25015DFH (or any other BJT, there is no "Base" lead)

Using these datasheets for reference:
BAV99 - https://www.diodes.com/assets/Datasheets/ds12007.pdf
ZXTP25015DFH - https://www.diodes.com/assets/Datasheet ... 015DFH.pdf

I'll pull the pots in the morning and go over the trace again, let me know if there's anything in particular you'd like me to check out.

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Post by jalmonsalmon »

bugg wrote:Good find! I have the original pedal sitting in front of me, so lets move on to the mystery diodes.

The pinout (going by measuring forward voltage drops with the diode function of my Fluke DMM) matches that of the BAV99 dual diode not the ZXTP25015DFH (or any other BJT, there is no "Base" lead)

Using these datasheets for reference:
BAV99 - https://www.diodes.com/assets/Datasheets/ds12007.pdf
ZXTP25015DFH - https://www.diodes.com/assets/Datasheet ... 015DFH.pdf

I'll pull the pots in the morning and go over the trace again, let me know if there's anything in particular you'd like me to check out.
https://www.arrow.com/en/products/bav99 ... iconductor

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Post by bajaman »

The pinout (going by measuring forward voltage drops with the diode function of my Fluke DMM) matches that of the BAV99 dual diode not the ZXTP25015DFH (or any other BJT, there is no "Base" lead)
Hello bugg - well that is peculiar because the code marking for the BAV99 is 7E according to that datasheet and 1A7 on the ZXTP25015DFH datasheet.
This picture clearly shows the 1A7 code marking on the two mystery components, but i am not arguing with your measurements :wink:
IMG_4301.jpg
I received my ZTX951 devices so thought i would compare them to the 4 x 1N4148 diodes (which simulate almost identically to the BAV99 pairs).
WOW - what a difference - no more squeal even when the treble, gain, and presence are maxed out :thumbsup
As for the sound - i know when i like what i am hearing because it usually takes me about an hour before I stop doodling :wink:
Touch sensitivity is astonishing now and the gain has a very useable range from blues to full on chugga chug chug. I swapped back in the 4 x 1N4148s and the gain, noise level and that annoying squeal all came back and it sounded very fizzy - took me less than 60 seconds to pull them and fit the back to back ZTX951 devices :lol:
This pedal has so much bass i had to wind the bass control almost off and run the tight around halfway even with a single coil strat bridge pickup - not complaining because with the bass on full and tight on full, there is that metal chugga chug chug sound that that Swedish guy likes demoing :lol:
With the gain on 0 i was able to get some lovely touch sensitive blues sounds and with the gain on 10% i could play Neil Young's Cinnamon Girl riff very convincingly - one of the most amp like pedals I have had the pleasure to play - cleans up nicely by rolling back the guitar volume too!

Hopefully my ZTXP25015DFH parts will arrive soon and i will let you know how they sound, in the meantimei may just have found the Holy Grail of dirt boxes by accident with these ZTX951 devices.
Well worth trying them in place of the 4 x 1N4148 diodes.
cheers
bajaman

ps: I am going back out to the workshop for more doodling now :lol:

pps: I had not noticed Jalmonsalmon's post with the Fairchild BAV99 datasheet which clearly shows the code 1A7 - how odd :hmmm:
Bloody smd codes - one datasheet says 7E and another 1A7 :roll:
Anyway someone said earlier in this thread that their original pedal squealed with gain treble and presence on full. All i can say is try the ZTXP915 pairs and no more squeal even boxed up :idea:
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Post by rmroza »

"in the meantimei may just have found the Holy Grail of dirt boxes by accident with these ZTX951 devices."

Aren't you gladwe didn't rest with "it's done"? Good stuff continuing.

It will be interesting to know the differences in tone between the 4148s, BAV99, ZXTP250's,ZXTP951's, etc...and which one is best (noise floor and tone)

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Post by alkuz1961 »

I'm sorry, but I can clearly see that this is not a 1A7. It's just a symbol, like an upside-down "i"
Image

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Post by bajaman »

It will be interesting to know the differences in tone between the 4148s, BAV99, ZXTP250's,ZXTP951's, etc...and which one is best (noise floor and tone)
I know the difference between the ZTX951 and the 1N4148 - flatter frequency response = thicker tone and no midrange hump for the ZTX951 and much lower noise floor AND complete absence of any squeal.
Personally, i don't care whether BAV99 (or the 1N4148 equivalents) are the correct parts to use - I will keep using the ZTX951 pair because i believe it is far superior soundwise.
Try them and see what you think!
cheers
bajaman

ps: don't tell Friedman :lol:
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Post by bugg »

bajaman wrote:Hello bugg - well that is peculiar because the code marking for the BAV99 is 7E according to that datasheet and 1A7 on the ZXTP25015DFH datasheet.
This picture clearly shows the 1A7 code marking on the two mystery components, but i am not arguing with your measurements :wink:
Just to clarify, I can't confirm that the component is a BAV99, but it is a dual diode, definitely not an NPN or PNP transistor.
bajaman wrote:Personally, i don't care whether BAV99 (or the 1N4148 equivalents) are the correct parts to use - I will keep using the ZTX951 pair because i believe it is far superior soundwise.
That's all that really matters, right?
alkuz1961 wrote:I'm sorry, but I can clearly see that this is not a 1A7. It's just a symbol, like an upside-down "i"
Yep, you're correct. I noticed that in mine as well.

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