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Author Topic: Stereo to mono power amp  (Read 7975 times)

Stompin_Tom

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Stereo to mono power amp
« on: August 16, 2006, 06:00:17 PM »
As I mentioned in another post, I'm planning to make a stereo guitar amp from the chipamp.com lm3886 kit. I'd like to have the option of going from stereo to mono if I'm using someone elses (mono) speaker cab at a gig, or if I decide to go with one preamp instead of two, etc. Can I simply install two switches? One at the input that would split one input into the two amps boards... and one at the output to combine the two outputs from the amp boards into one speaker out... bridging the two amps in parallel, right? Is there any problem with this? some sort of oscillation or overload or something?
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teemuk

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Re: Stereo to mono power amp
« Reply #1 on: August 16, 2006, 06:14:59 PM »
If you want to parallel or bridge amps you want to make them as identical as possible. You should know that bridge and parallel configuration of amplifiers are different: In parallel configuration each amp sees a load multiplied with two since the output current is shared by the amplifers (assuming the number of amps connected in parallel is two), a bridged amplifer is capable of providing larger voltage potential affecting over load. This means that the output power is 4 times higher but each amplifier sees a load half size of the nominal load (i.e. 4 ohms with an 8 ohm load). Effectively the current demand for each amplifier is doubled.

Stompin_Tom

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Re: Stereo to mono power amp
« Reply #2 on: August 17, 2006, 10:35:03 AM »
Thanks. I'm still trying to wrap my brain around the differences between bridged and parallel... and the effects on the load.

If I parallel the amps, and I have a 4 ohm speaker hooked up to it, it sees the load as 8 ohms? If bridged it would be a 2 ohm load? I'm probably confusing my terms, but I'm trying to get it straight in my head.

The other question is, how do you bridge amps? and what are the advantages or disadvantages (compared with parallel)?

As I said, I'm probably way off in my thinking here, so thanks for your patience.. I'll try to find some literature online about bridged/parallel amps, too.
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RDV

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Re: Stereo to mono power amp
« Reply #3 on: August 17, 2006, 05:11:16 PM »
A simple and flexable solution would be a stereo/dual mono thing where each chip runs a speaker(s) and you have the option of stereo or dual mono. Bridging and paralleling causes some issues like easier overheating that could be avoided by running stereo/dual mono.

HTH

RDV

Stompin_Tom

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Re: Stereo to mono power amp
« Reply #4 on: August 17, 2006, 05:29:00 PM »
hmmm.. I had thought of that, and I do want that option, too. My only concern is if I show up to a gig where I'm borrowing someone elses cab and it's not stereo... That's why I want the option of bridging or paralleling or whichever. The other guitarist in my band has a 100watt boogie and I'll need the extra power...
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RDV

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Re: Stereo to mono power amp
« Reply #5 on: August 17, 2006, 09:47:23 PM »
Parallel was the choice I made for my LM4780 amps because they can go at 4 ohm loads and up. I think with bridge mode you're limited to an 8 ohm load? I willing to be wrong about this however.

RDV

Stompin_Tom

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Re: Stereo to mono power amp
« Reply #6 on: August 18, 2006, 11:25:46 AM »
RDV, is there an advantage to the 4780?

Have you run into any problems running in parallel? You mentioned overheating...
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joecool85

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Re: Stereo to mono power amp
« Reply #7 on: August 18, 2006, 11:27:08 AM »
LM4780 is two LM3886s on one chip.
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Stompin_Tom

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Re: Stereo to mono power amp
« Reply #8 on: August 18, 2006, 11:40:33 AM »
I see. I looked at the data sheet and it looked comparable to two 3886s, that's why I asked.
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RDV

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Re: Stereo to mono power amp
« Reply #9 on: August 19, 2006, 05:14:13 AM »
You need a big heatsink for those puppies. They do get hot but they also kick butt! I've got to finish the stereo paralleled version I've got going. I've got everything I need but time and energy.

RDV

Stompin_Tom

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Re: Stereo to mono power amp
« Reply #10 on: August 21, 2006, 10:51:29 AM »
I've got everything I need but time and energy.

Yes, sir. I know how you feel.

I think I'll go with a big heatsink and a fan to be sure...
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Stompin_Tom

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Re: Stereo to mono power amp
« Reply #11 on: August 23, 2006, 01:11:08 PM »
What do you think of this kit.... much like what you're planning, RDV... I think...

http://www.audiosector.com/lm4780.shtml
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