Vintage wah pedal inductor.

[Ian Field]

Some time ago I saw a schematic for a vintage wah pedal which showed a 500mH
inductor, since then I've been wondering where I'd get such a large inductor
should I have a go at rolling my own.

Recently I've been sorting and scrapping some old PC cards - many of which
were old internal modems - on measuring several transformers from these old
modems, the inductance has come out ranging from 2H to over 5H (10x that
required!). Bearing in mind that these are 1:1 transformers, I could
probably hang something on the other winding to modify the apparent
inductance (If I knew what). Does anyone know whether its possible to trick
the basic design into using excessive inductance?

Thanks.

[RichL]

Post by Ian Field
Some time ago I saw a schematic for a vintage wah pedal which showed a
500mH inductor, since then I've been wondering where I'd get such a large
inductor should I have a go at rolling my own.

This should do the trick, if I'm not mistaken:

<http://www.mouser.com/ProductDetail/Bourns/70F501AF-RC/?qs=sGAEpiMZZMsg%252by3WlYCkU6J1Kh%252bkI7ZW63PlG49mKtY%3d>

[Ian Field]

Post by RichL

Post by Ian Field
Some time ago I saw a schematic for a vintage wah pedal which showed a
500mH inductor, since then I've been wondering where I'd get such a large
inductor should I have a go at rolling my own.

<http://www.mouser.com/ProductDetail/Bourns/70F501AF-RC/?qs=sGAEpiMZZMsg%252by3WlYCkU6J1Kh%252bkI7ZW63PlG49mKtY%3d>

Very nice - but I have this thing about making do with parts I have (if I
can).

[Elmo' 7#9]

Post by Ian Field
Does anyone know whether its possible to trick
the basic design into using excessive inductance?

Theoretically, yes...

Frequency is proportional to Inductance x Capacitance - use a proportionally
smaller capacitor than the stock 0.01uF between the 2nd transistor's emitter
and your new inductor to get the same range of resonant frequencies out of a
larger inductor.

It'll only cost Pennies to find out...

Elmo' 7#9

[Ian Field]

Post by Elmo' 7#9

Post by Ian Field
Does anyone know whether its possible to trick
the basic design into using excessive inductance?

Theoretically, yes...
Frequency is proportional to Inductance x Capacitance - use a
proportionally
smaller capacitor than the stock 0.01uF between the 2nd transistor's emitter
and your new inductor to get the same range of resonant frequencies out of a
larger inductor.
It'll only cost Pennies to find out...

That's more or less what I was thinking - also the lowest transformer I
tested was 2H, I know that 2 identical 2H inductors in parallel gives 1H,
but what if they're mutually coupled (as in this 1:1 transformer)?

[Elmo' 7#9]

Post by Ian Field
That's more or less what I was thinking - also the lowest transformer I
tested was 2H, I know that 2 identical 2H inductors in parallel gives 1H,
but what if they're mutually coupled (as in this 1:1 transformer)?

A 1:1 transformer is just two identical windings with a shared core.

So long as you get the POLARITY right when you connect them in parallel,
you'll be creating an inductor with half the Inductance (and half the DC
resistance)
of a single winding.

The correct polarity is achieved by connecting the 2 OUTER ends together
and the 2 INNER ends together
(It's fairly safe to assume they are wound in the same direction).



Elmo' 7#9

[Ian Field]

Post by Elmo' 7#9

Post by Ian Field
That's more or less what I was thinking - also the lowest transformer I
tested was 2H, I know that 2 identical 2H inductors in parallel gives 1H,
but what if they're mutually coupled (as in this 1:1 transformer)?

A 1:1 transformer is just two identical windings with a shared core.
So long as you get the POLARITY right when you connect them in parallel,
you'll be creating an inductor with half the Inductance (and half the DC
resistance)
of a single winding.
The correct polarity is achieved by connecting the 2 OUTER ends together
and the 2 INNER ends together
(It's fairly safe to assume they are wound in the same direction).

As I've no idea whether transformer phase is significant in a modem, I could
just connect the pins straight over, if I don't get the expected result -
try crossing the wires.

[Elmo' 7#9]

Post by Ian Field
As I've no idea whether transformer phase is significant in a modem, I could
just connect the pins straight over, if I don't get the expected result -
try crossing the wires.

Precisely!

Let us know how you get on...

I'm deeply suspicious of the retrofit wah inductor market (Red and Yellow
FASEL, Teese replacement coil etc. ).


Elmo' 7#9

[Ian Field]

Post by Elmo' 7#9

Post by Ian Field
As I've no idea whether transformer phase is significant in a modem, I could
just connect the pins straight over, if I don't get the expected result -
try crossing the wires.

Precisely!
Let us know how you get on...
I'm deeply suspicious of the retrofit wah inductor market (Red and Yellow
FASEL, Teese replacement coil etc. ).

I'm sort of wondering whether the wah designers compromised a little on the
inductor availability/cost, larger inductances were more common in those
days (but still not cheap!).

It would be nice to discover that more inductance than original vintage
designs was actually a good thing.

[Ian Field]

Post by Elmo' 7#9

Post by Ian Field
As I've no idea whether transformer phase is significant in a modem, I could
just connect the pins straight over, if I don't get the expected result -
try crossing the wires.

Precisely!
Let us know how you get on...
I'm deeply suspicious of the retrofit wah inductor market (Red and Yellow
FASEL, Teese replacement coil etc. ).

Actually I've never seen inside an original wah, what type of core does the
inductor have?

AFAIK the ferrite cores saturate at much lower flux than laminated iron
ones.

[Elmo' 7#9]

Post by Ian Field
Actually I've never seen inside an original wah, what type of core does
the inductor have?

Ferrite.

In many different shapes and casings.

Have a look at the spread of measured values
in this (incomplete) historical list of wah inductors...

http://web.archive.org/web/20030218184205/http://www.green-fuz.freeserve.co.uk/inductor.html


Elmo' 7#9

[Ian Field]

Post by Elmo' 7#9

Post by Ian Field
Actually I've never seen inside an original wah, what type of core does
the inductor have?

Ferrite.
In many different shapes and casings.
Have a look at the spread of measured values
in this (incomplete) historical list of wah inductors...
http://web.archive.org/web/20030218184205/http://www.green-fuz.freeserve.co.uk/inductor.html
Elmo' 7#9

Thanks - the Wah mods page there pretty much answered my main question - too
much inductance makes the sweep effect muddy.

[Elmo' 7#9]

Post by Ian Field
Thanks - the Wah mods page there pretty much answered my main question -
too much inductance makes the sweep effect muddy.

Only when you keep the original capacitor values...

If you Double the Inductance, use Half the Capacitance.


R.G. Keen has bench-tested different (commercial, normal-value) inductors
and come up with an interesting conclusion...

http://www.geofex.com/article_folders/wahpedl/wahped.htm#inductor

Core saturation is a form of DISTORTION that's responsible for the richer
sound of some inductors.

By this theory, your laminate-core inductors should be super-clean sounding.

Elmo' 7#9

[Ian Field]

Post by Elmo' 7#9

Post by Ian Field
Thanks - the Wah mods page there pretty much answered my main question -
too much inductance makes the sweep effect muddy.

Only when you keep the original capacitor values...
If you Double the Inductance, use Half the Capacitance.
R.G. Keen has bench-tested different (commercial, normal-value) inductors
and come up with an interesting conclusion...
http://www.geofex.com/article_folders/wahpedl/wahped.htm#inductor

In that page; I noticed the Radio Shack audio transformer. All the
Tandy/Radio Shack stores vanished from UK stores a few years back.

I have some Eagle Electronics LT44 & LT77 audio transformers from Maplin,
somehow never got around to measuring the inductances - and now they're in a
tea chest somewhere at the back of the garage.

As long as an inductor isn't embalmed in laquer, there's always the
possibility of removing turns from a too big inductor.

[m***@btinternet.com]

On Thu, 11 Apr 2013 21:21:18 +0100, "Ian Field"

Post by Ian Field

Post by Elmo' 7#9

Post by Ian Field
Thanks - the Wah mods page there pretty much answered my main question -
too much inductance makes the sweep effect muddy.

Only when you keep the original capacitor values...
If you Double the Inductance, use Half the Capacitance.
R.G. Keen has bench-tested different (commercial, normal-value) inductors
and come up with an interesting conclusion...
http://www.geofex.com/article_folders/wahpedl/wahped.htm#inductor

In that page; I noticed the Radio Shack audio transformer. All the
Tandy/Radio Shack stores vanished from UK stores a few years back.
I have some Eagle Electronics LT44 & LT77 audio transformers from Maplin,
somehow never got around to measuring the inductances - and now they're in a
tea chest somewhere at the back of the garage.
As long as an inductor isn't embalmed in laquer, there's always the
possibility of removing turns from a too big inductor.

Are there any successful commercial Wah pedals using the gyrator
circuit for simulation of inductance? There has certainly been a great
deal of homebrew experimentation since the 1970s when I recall that
Elektor used the design concept in EQ circuits quite frequently.

They are obviously easy to modify providing scope for experimentation
- BUT is it possible to match the tonality obtained by using a real
inductor?

Mike

[Elmo' 7#9]

Post by m***@btinternet.com

Post by Ian Field
I have some Eagle Electronics LT44 & LT77 audio transformers from Maplin,
somehow never got around to measuring the inductances - and now they're in a
tea chest somewhere at the back of the garage.

I have these, too - they're useless for the Octavia I was building
(VERY wrong turns ratio).
never tried them in my Cry Baby...

Post by m***@btinternet.com
Are there any successful commercial Wah pedals using the gyrator
circuit for simulation of inductance? There has certainly been a great
deal of homebrew experimentation since the 1970s when I recall that
Elektor used the design concept in EQ circuits quite frequently.
They are obviously easy to modify providing scope for experimentation
- BUT is it possible to match the tonality obtained by using a real
inductor?
Mike

My Carlsboro Stingray combo has a Parametric EQ based on a Gyrator.
Yes, it goes "Wah", but it won't display the core saturation behaviour of a
real inductor.


Elmo' 7#9

[Ian Field]

Post by Elmo' 7#9

Post by m***@btinternet.com

Post by Ian Field
I have some Eagle Electronics LT44 & LT77 audio transformers from Maplin,
somehow never got around to measuring the inductances - and now they're
in
a
tea chest somewhere at the back of the garage.

I have these, too - they're useless for the Octavia I was building
(VERY wrong turns ratio).
never tried them in my Cry Baby...

Post by m***@btinternet.com
Are there any successful commercial Wah pedals using the gyrator
circuit for simulation of inductance? There has certainly been a great
deal of homebrew experimentation since the 1970s when I recall that
Elektor used the design concept in EQ circuits quite frequently.
They are obviously easy to modify providing scope for experimentation
- BUT is it possible to match the tonality obtained by using a real
inductor?
Mike

My Carlsboro Stingray combo has a Parametric EQ based on a Gyrator.
Yes, it goes "Wah", but it won't display the core saturation behaviour of a
real inductor.

IWHT some strategically placed clipping diodes might do some good.

IIRC there's a single transistor "reaction circuit" that contains a
capacitor that is "inverted" to look like an inductor - they're used to peak
specific frequencies in the signal path in some pedals.