QUAD 909 Stereo - How to Mono? - diyAudio
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Old 20th May 2010, 06:14 PM   #1
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Post QUAD 909 Stereo - How to Mono?

I am receiving a QUAD 909 tomorrow. QUAD no longer makes the 909 Mono, so I had to buy a Stereo version.

Has anyone bridged a QUAD 909 Stereo? How can this be done?

Ideas or comments?
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Old 20th May 2010, 11:50 PM   #2
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You would need an inverter to invert the signal into one of the stereo channels.

Then take the output from the two live pins of the outputs.

Make sure your amp will take bridging mode before trying it.
The output impedance halves for bridge mode and os takes twice as much power as normal mode.
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Old 21st May 2010, 04:07 PM   #3
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Quote:
Originally Posted by nigelwright7557 View Post
You would need an inverter to invert the signal into one of the stereo channels.

Then take the output from the two live pins of the outputs.

Make sure your amp will take bridging mode before trying it.
The output impedance halves for bridge mode and os takes twice as much power as normal mode.
Thank you for the information. I do appreciate the information although I need more details like a schematic. I know several people have done many upgrades on the QUAD 405 & 405-2.

Does anyone have specific information on how to do this OR if it can be done?
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Old 21st May 2010, 05:35 PM   #4
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Quad 909 schematic.
DADA Electronics - Downloads

If you have a preamplifier with balanced outputs,
you don't need to invert the signal.
A balanced output produce non inverted + inverted signal.

Feed one channel with non inverted.
Feed the other channel with inverted.

Connect the speaker between the two red output terminals.

If you have no balanced preamp, you need to build a inverter circuit using an op amp.

This is general info for bridging, i never tried with quad 909.

Last edited by bobodioulasso; 21st May 2010 at 05:42 PM.
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Old 21st May 2010, 06:10 PM   #5
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Quote:
Originally Posted by bobodioulasso View Post
Quad 909 schematic.
DADA Electronics - Downloads

If you have a preamplifier with balanced outputs,
you don't need to invert the signal.
A balanced output produce non inverted + inverted signal.

Feed one channel with non inverted.
Feed the other channel with inverted.

Connect the speaker between the two red output terminals.

If you have no balanced preamp, you need to build a inverter circuit using an op amp.

This is general info for bridging, i never tried with quad 909.
Now we are getting somewhere! My problem is that my current preamplifier does not have balanced outputs.

Do you have an example of an inverter circuit? What can be some of the issues when trying this, that is, failure or problems when adding these circuits?
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Old 21st May 2010, 06:45 PM   #6
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First; inquire if Quad 909 is bridging capable. If not you risk failure.

An inverter is an inverting amplifier whose gain = 1

The link below shoes an inverting amp. You obtain unity gain making the two resistors equal.

http://webpages.ursinus.edu/lriley/r...its/node5.html

Last edited by bobodioulasso; 21st May 2010 at 06:49 PM.
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Old 21st May 2010, 07:00 PM   #7
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I found this.
The 909 mono being a bridged version of the 909 , it seems there is no problem.
http://www.quad-hifi.co.uk/downloads...20Manual_3.pdf

This may help you too:
http://sound.westhost.com/bridging.htm

Last edited by bobodioulasso; 21st May 2010 at 07:22 PM.
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Old 22nd May 2010, 05:21 PM   #8
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This is a ready for bridging module . Though i am shure you may find an equivalent in the USA.

Modul zur Ansteuerung von Brücken - Endstufen BTL bei eBay.de: Verstärker (endet 31.05.10 00:46:18 MESZ)

Last edited by bobodioulasso; 22nd May 2010 at 05:25 PM.
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Old 23rd May 2010, 06:28 AM   #9
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Quote:
Originally Posted by bobodioulasso View Post
This is a ready for bridging module . Though i am shure you may find an equivalent in the USA.

Modul zur Ansteuerung von Brücken - Endstufen BTL bei eBay.de: Verstärker (endet 31.05.10 00:46:18 MESZ)
Thank you! This is EXACTLY what I am looking for! I can not read German but it looks limited to 80WPC, correct?

Maybe someone can recommend a built unit in the US or a schematic so I can build one.
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Old 23rd May 2010, 06:33 AM   #10
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There is no power limit.
They give an example.
Gooqle can traduce for you.
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