Wah transistor; MPSA18 or 2N5088....???

[Bullet79]

is there any tone diffrences if i'm using 2N5088 instead of MPSA18.... any other tranny reccomendation..?

[richon]

the difference in tone comes from the GAIN of the transistors

Hfe of 400 is a good value for a good sound....   MPSA18 gets to 800 or 900 in Hfe making it somehow less bassier as it boost to much the higher notes.

[zombiwoof]

If you're looking for vintage wah sound with a standard Vox/Crybaby circuit you really need trannies in the 350-400 Hfe gain range for it to work nicely with stock components.  Dunlop uses the MPSA18 trannies, but as has been noted they are very high gain.  They change  a couple of other values to try to make up for that, but using something around the 400 Hfe range works better.  BC109B's are good if you can find them.  If you are going for a modern sound and don't care about it sounding vintage, you can go with higher gain trannies and tweak the circuit to make them sound good.  2N5088 are also pretty high gain.

Al

[Paul Marossy]

The 2N5089 is much closer to the MPSA18 than the 2N5088 in terms of the typical Hfe. BC109s work pretty good for your classic wah sound. Really any transistors with similar characteristics as the BC109 sound good, IMO.

[ayayay!]

I highly recommend lower gain on those.  The MPSA18's are just too high/clean. 

[zombiwoof]

I am sure Dunlop uses the MPSA18 because it is really cheap.  The high gain is one of the reasons why a Dunlop-made wah doesn't sound like a vintage one (among other things).

Al

[Bullet79]

thats correct... a lot of "big name manufacture" these day use MPSA18.. crybaby's new VOX's .... well.. it's good to know a bunch trannys that can be use...


guess i have to socket them to tell the diff...

[MikeH]

I don't know - I tried a few different types in the wah I built, and ultimately settled on MPSA18s.  I also modded it to control gain and lots of other things though.

[WGTP]

IIRC the MPSA18's are hi-gain LOW Noise transistors.  The 5088 is not as hi-gain and not designated as low noise.   

[Paul Marossy]

I am sure Dunlop uses the MPSA18 because it is really cheap.  The high gain is one of the reasons why a Dunlop-made wah doesn't sound like a vintage one (among other things).

Al

I think it's true that the lower gain ones sound better. I think there's a little bit of distortion going on with the lower gain transistors that gives a "complexity" to the sound.

[PRR]

> The 5088 is not as hi-gain and not designated as low noise.

2N5088
NPN General Purpose Amplifier
This device is designed for low noise, high gain, general purpose amplifier applications at collector currents from 1µA to 50 mA.

[Paul Marossy]

IIRC the MPSA18's are hi-gain LOW Noise transistors.  The 5088 is not as hi-gain and not designated as low noise.   

Depends on who's data sheet you look at! Some manufacturers describe it as a general purpose transistor. Some say it is a small signal amplifier. And others say it is a low noise small signal amplifier.

[Bullet79]

i'v mod my crybaby with BC109B.. quite cheap in my country... (comparing to online store).. i like the tone.. but theres a VOLUME drop.. (still got the buffer circuit)


is it because its cheap tranny..?? 50piece's for USD 15.00

[richon]

maybe changing the 68K resistor for a 47K....   that should pump the volume to reach gain=1


strange is that my wahs when modded for truebypass and changed transistors (Hfe=300) always come with a slight volume boost compared to the clean signal.

[R.G.]

It was six men of Indostan
To learning much inclined,
Who went to see the Elephant
(Though all of them were blind),
That each by observation
Might satisfy his mind

The First approached the Elephant,
And happening to fall
Against his broad and sturdy side,
At once began to bawl:
"God bless me! but the Elephant
Is very like a wall!"

The Second, feeling of the tusk,
Cried, "Ho! what have we here
So very round and smooth and sharp?
To me 'tis mighty clear
This wonder of an Elephant
Is very like a spear!"

The Third approached the animal,
And happening to take
The squirming trunk within his hands,
Thus boldly up and spake:
"I see," quoth he, "the Elephant
Is very like a snake!"

The Fourth reached out an eager hand,
And felt about the knee.
"What most this wondrous beast is like
Is mighty plain," quoth he;
" 'Tis clear enough the Elephant
Is very like a tree!"

The Fifth, who chanced to touch the ear,
Said: "E'en the blindest man
Can tell what this resembles most;
Deny the fact who can
This marvel of an Elephant
Is very like a fan!"

The Sixth no sooner had begun
About the beast to grope,
Than, seizing on the swinging tail
That fell within his scope,
"I see," quoth he, "the Elephant
Is very like a rope!"

And so these men of Indostan
Disputed loud and long,
Each in his own opinion
Exceeding stiff and strong,
Though each was partly in the right,
And all were in the wrong!

John Godfrey Saxe, 1878

We all start mentally blind, and struggle to find full enlightenment.

[Gus]

Check the pinout of the 109 transistors to the pinout of the transistors you removed.



This changing the transistors in a wha thing is funny.  I never see before and after transistors legs voltages posted.

[tubelectron]

Hi

As I am working on wah project these days, i can share some infos :

MPSA18 = hfe 900-1000 / Ib=10µA
2N5088 = hfe 400-500 / Ib=10µA
2N3904 = Hfe 120-150 / Ib=10uA

I choose 2N5088 (hfe 420) for my 1996 CryBaby, with the MPSA13 original input buffer in front. This sounds better than the stock one, but the original Allen-Bradley mexico 100K pot (123K, in fact) hasn't a correct taper (I should check it) : transition is too abrupt - need to find the right one to give a complete statement.

In my Vintage Wah with whipple inductor, I use 2N3904 (hfe 136), with no input buffer. Sounds very good with a NOS 60K Allen Bradley LOG (audio) pot, both in rhythm and lead.

Note : all of them have modified RC values to my taste.
I have many other wahs (Colorsound, Shaftesbury...), but I didn't tested the transistors yet to check.

Speaking only about the wah transistor side, I think that Hfe 400-500 is the upper limit, I agree. Lower gain gives smoother wah, usually : better articulation and balance, less ear-piercing highs, more bass... But direct replacement without tweaking some values may be very deceptive, so don't do an unfair statement for a given transistor.

A+!

[zombiwoof]

Fuzz Central's article on the Clyde McCoy wah states that a good range for getting the vintage sound out of the stock circuit is from 350-400 hfe range, and he says if you have two different gain transistors you should put the lower one in Q2 and the higher one in Q1.  I have gone by his recommendations and it very much improved my Vox V847, in which I changed all the values that differed from the original circuit to the correct ones.  BC109B tends to fall in those ranges, so that's why those are recommended, but any NPN silicon trannies you can find in those ranges will work.  The higher-gain trannies like the much-used MPSA18 tend to impart some distortion to the sound of the wah.  If you go with really low gain transistors you will most likely have to change the value of some other components (resistors, mainly) to compensate.  I think that's why Dunlop has made some resistor value changes in their wahs, because they are using the high gain trannies.  The older Vox V847 wahs were made by Dunlop, and they have those same MPSA18's in them.  The newer Vox V847A wahs are made in China, no longer by Dunlop.

Al

[tubelectron]

Hi zombiwoof,

Additional info : I opened a few days ago a chinese brand new VOX V847 wah, and also found 2xMPSA18 inside. The inductor was a black one, labelled with the VOX in white. Sorry, i didn't have the means to take pics.

A+!

[Gus]

http://www.google.com/patents/about?id=pd1UAAAAEBAJ

United States Patent 3530224