leslie biamp

[Trevor]

Hi,
Can anyone help here? I want to bi-amp my Leslie 122A. It is one of
the new ones: 40 watt tube amp, 16 ohm 2-Way Leslie Crossover, 12 dB
per octave; 800 Hz, 100 watt ferro-fluid horn driver and 16 Ohm 100
watt woofer. I would like to get all 40 watts to the horn driver. I'll
be powering the woofer through both a separate crossover and tube amp.
My question is as follows: I thought about placing a 16 Ohm 25 Watt
Power resistor as a surrogate load substitute in place of the original
16 Ohm woofer, However, I do not know what a purely resistive load to
the original Leslie crossover will make the HF Driver sound like…how
smooth or shrill it may become. However, I'm concerned that the
amplifier will see a different load due to the change from a reactive
load (original woofer) to a crossover loaded half reactive and half
resistive. Any suggestions as to what to what I should use as a
surrogate load in place of the woofer and still maintain the status
quo would be much appreciated. Thank-you.
Sincerely,
Trevor

 

[James Meyer]

Hi,
Can anyone help here? I want to bi-amp my Leslie 122A. It is one of
the new ones: 40 watt tube amp, 16 ohm 2-Way Leslie Crossover, 12 dB
per octave; 800 Hz, 100 watt ferro-fluid horn driver and 16 Ohm 100
watt woofer. I would like to get all 40 watts to the horn driver. I'll
be powering the woofer through both a separate crossover and tube amp.
My question is as follows: I thought about placing a 16 Ohm 25 Watt
Power resistor as a surrogate load substitute in place of the original
16 Ohm woofer, However, I do not know what a purely resistive load to
the original Leslie crossover will make the HF Driver sound like…how
smooth or shrill it may become. However, I'm concerned that the
amplifier will see a different load due to the change from a reactive
load (original woofer) to a crossover loaded half reactive and half
resistive. Any suggestions as to what to what I should use as a
surrogate load in place of the woofer and still maintain the status
quo would be much appreciated. Thank-you.
Sincerely,
Trevor

Get rid of the crossover at the output and provide a similar, line
level, filter type "splitter" between the line in and the original amp and the
new woofer amp.

Jim

 

[Ban]

Get rid of the crossover at the output and provide a similar, line
level, filter type "splitter" between the line in and the original
amp and the new woofer amp.

Jim

Trevor,
most crossovers have completely separate circuits for high and low filters,
so putting a resistor there will not make much of a difference, exept a lot
of heat. The negative feedback inside the amp will take care of that. You
can scrap the low part completely, or power it with your transistor amp.
This way you can keep the original sound balance.
Now the tube amp will run less hot, but since the maximum voltage stays the
same, the power will be not much more. Depending on the source material with
800Hz x-over, both channels have roughly the same power.

If you do as Jim suggests and build new active filters on the input, you can
increase the power to the horn, but you have to analyse the filter as it is
now.
Why do you not draw a diagramm of the current x-over and post it here or on
ABSE, so we can help you find a suitable solution?

 

[Trevor]

Hi Ban & Jim,
First, thank you for your help. However, let me just point out that
I'm definitely more musician than technician so when you say things
like "build an active filter" or "get rid of the crossover at the
output and provide a similar, line level, filter type "splitter"
between the line in and the original amp and the new woofer amp." You
might as well be talking French. I know that's simply not going to
happen for me. I can get something at radio Shack and wire it in but
that's about it. Isn't there a simple way to do this w/o designing a
hybrid electronic gadget or putting a splitter on something? All I
want to do is wire in "something" so all the amps wattage is directed
to the horn. Forget about the woofer for now. I'll worry about
powering the woofer and that whole project as a separate issue. Lets
just focus on this one aspect. Isn't there any kind of relatively
simply way to do this? I just want all those beautiful 40 watts from
the tube amp to go to the horn. Can't I just buy something to wire in
path to do this? I'm not looking for a science fair project.
Thank-you.
Trevor

Here is the speaker I have. It's a walnut Leslie 122A.

http://www.fishorgans.com/newleslies/122A-147A/

 

[Ben Bradley]

In sci.electronics.design, [email protected] (Trevor)
wrote:

Hi Ban & Jim,
First, thank you for your help. However, let me just point out that
I'm definitely more musician than technician so when you say things
like "build an active filter" or "get rid of the crossover at the
output and provide a similar, line level, filter type "splitter"
between the line in and the original amp and the new woofer amp." You
might as well be talking French. I know that's simply not going to
happen for me. I can get something at radio Shack and wire it in but
that's about it. Isn't there a simple way to do this w/o designing a
hybrid electronic gadget or putting a splitter on something? All I
want to do is wire in "something" so all the amps wattage is directed
to the horn. Forget about the woofer for now. I'll worry about
powering the woofer and that whole project as a separate issue. Lets
just focus on this one aspect. Isn't there any kind of relatively
simply way to do this? I just want all those beautiful 40 watts from
the tube amp to go to the horn. Can't I just buy something to wire in
path to do this?

Yes. Put one of these between your signal source and your amps.

http://rane.com/livecat.html#xover

These are all 24dB slope instead of your current 12dB, I don't know
if that will have an audible effect on the sound, OTOH this is a
Leslie, not a "hi-fi" speaker. Click on one and look at its user
manual to see how to hook it up. For other manufacturers, do a web
search for "active crossover" or some such.
As for designing such a thing, this is sci.electronics.design where
some of us like to build such things rather than buy them....

My offer on rec.audio.pro still stands.

 

[Jim Thompson]

On Sat, 14 Feb 2004 14:47:42 -0500, Ben Bradley

[snip]

Yes. Put one of these between your signal source and your amps.

http://rane.com/livecat.html#xover

[snip]

Gag! Sallen-Key filters :-(

...Jim Thompson

 

[Winfield Hill]

Jim Thompson wrote...

Gag! Sallen-Key filters :-(

The theory is carefully explained and seems sound.
:>) http://rane.com/pdf/note107.pdf

Futhermore they provide the schematics, data sheets,
manuals, and front-panel layouts on the web. Good
reputation and prices, what's not to like?

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Jim Thompson]

Jim Thompson wrote...

The theory is carefully explained and seems sound.
:>) http://rane.com/pdf/note107.pdf

Futhermore they provide the schematics, data sheets,
manuals, and front-panel layouts on the web. Good
reputation and prices, what's not to like?

Thanks,
- Win

whill_at_picovolt-dot-com

The frontend filter I observed in the schematic was Sallen-Key... the
paper says "State Variable", of which I approve as a competent way to
realize filter functions.

For a lot of useful information along these lines see the "Floobydust"
section of National Semiconductor's "Audio Handbook" © 1976.

Third order crossovers networks are the only way to go to avoid phase,
vector sum and total power errors in the crossover region.

...Jim Thompson

 

[John Woodgate]

I read in sci.electronics.design that Jim Thompson

The frontend filter I observed in the schematic was Sallen-Key... the
paper says "State Variable", of which I approve as a competent way to
realize filter functions.

Properly-designed S-K filters are quite OK for audio. Remember that each
individual loudspeaker driver is different from every other at the +/- 1
dB level. So extreme precision in the filters is unnecessary.

For a lot of useful information along these lines see the "Floobydust"
section of National Semiconductor's "Audio Handbook" © 1976.

Yes, it's a mine of information.

Third order crossovers networks are the only way to go to avoid phase,
vector sum and total power errors in the crossover region.

I don't know what 3rd-order filter you have invented, but none of the
published papers on crossovers seem to support your claim. Linkwitz-
Riley filters have very good characteristics, but even they don't cope
with every driver configuration.

 

[Jim Thompson]

I read in sci.electronics.design that Jim Thompson


Properly-designed S-K filters are quite OK for audio. Remember that each
individual loudspeaker driver is different from every other at the +/- 1
dB level. So extreme precision in the filters is unnecessary.

Yes, it's a mine of information.

I don't know what 3rd-order filter you have invented, but none of the
published papers on crossovers seem to support your claim. Linkwitz-
Riley filters have very good characteristics, but even they don't cope
with every driver configuration.

With perfect drivers third-order filters produce perfect results.

I suppose one *could* characterize the drivers throughout their
operating region and then add in all-passes, etc., to match everything
up.

Sounds like one *mean* task!

...Jim Thompson

 

[James Meyer]

With perfect drivers third-order filters produce perfect results.

I suppose one *could* characterize the drivers throughout their
operating region and then add in all-passes, etc., to match everything
up.

Sounds like one *mean* task!

...Jim Thompson

Not really. A DSP system with codecs along with a microphone or two
could measure the impulse response of a speaker system in a few seconds. Once
you have that information, it's just a matter of using the same DSP system to
provide compensating signal processing or filtering. The whole system could
even be automated so that it runs through the equalizing sequence each and every
time it's turned on. Thus compensating for component wear with age, air
pressure, humidity, and furniture movement in the listening room.

Jim

 

[Trevor]

Hi Jim,

Thank-you for all your help on this project. I really appriciate it.
I think I'm following what your saying better now.
However, I still have a couple of questions…just to make sure I
understanding you correctly. I'm with you on introducing the crossover
between the organ and Leslie. That shouldn't be a problem as the
Hammond A-102 I have is configured so I have a 1/4" line out. That
runs into a Speakeasy Vintage Pedal which accepts 1/4" line in. It
has a 122 6pin out to the Leslie. I would simply put the crossover
between the organ and the Speakeasy pedal.
My question is as follows: You suggested using a Rane active
crossover. However, the Rane's are 24db slope where as the Leslie
crossover is 12 db sloped. You said you didn't know how this would
affect the sound. Well the problem becomes that I don't want to buy a
Rane to have it comprimise the sound because of the slope difference
of the crossovers. Should I be concerned with this difference? Would
you green-light the Rane crossover for this project? If so, which
model should I get?

My other question is as follows:
I understand that after the introduction of the new crossover, I no
longer need to use the Leslie's crossover. However what I'm not clear
on is the logistics of bypassing the Leslie crossover. Would
bypassing the Leslie crossover throw off the loading relationship
between the amp and the load it needs to see? Or does the crossover
not enter into the load equation. I'm finally getting a plan here.
If you want to give me your email I can send you an attached picture
of the crossover that is in the Leslie. Thanks so much for your help.
Sincerely,
Trevor

 

[John Woodgate]

I read in sci.electronics.design that Jim Thompson

With perfect drivers third-order filters produce perfect results.

What do you mean by 'perfect drivers', and which alignment (Butterworth,
Bessel, BGBG?) of filter?

I suppose one *could* characterize the drivers throughout their
operating region and then add in all-passes, etc., to match everything
up.

Sounds like one *mean* task!

KEF did it, with the 104 'Acoustic Butterworth' product. But it was not
without problems.

 

[John Woodgate]

I read in sci.electronics.design that James Meyer <[email protected]>

Not really. A DSP system with codecs along with a microphone or
two
could measure the impulse response of a speaker system in a few seconds.
Once you have that information, it's just a matter of using the same DSP
system to provide compensating signal processing or filtering. The
whole system could even be automated so that it runs through the
equalizing sequence each and every time it's turned on. Thus
compensating for component wear with age, air pressure, humidity, and
furniture movement in the listening room.

It isn't anywhere near as simple as that. The devil is in the detail,
like how you measure below about 100 Hz.

 

[Jim Thompson]

I read in sci.electronics.design that Jim Thompson


What do you mean by 'perfect drivers', and which alignment (Butterworth,
Bessel, BGBG?) of filter?

KEF did it, with the 104 'Acoustic Butterworth' product. But it was not
without problems.

My world is flat

...Jim Thompson

 

[James Meyer]

I read in sci.electronics.design that James Meyer <[email protected]>


It isn't anywhere near as simple as that. The devil is in the detail,
like how you measure below about 100 Hz.

Nothing is s0 smiple that it can't be screwed up.

However, given the ear and brain response below 100 Hz, you don't have
to be nearly as accurate as with the band of frequencies from 300 to 5,000 Hz.

Jim