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Old 13th November 2006, 09:25 PM   #1
liggs17 is offline liggs17  United States
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Default Changing two stereo amps into two monos

I have purchased two 12g stereo amplifiers kits from S5 electronics (kits used to be k12m, I think). I would like to use them as monobloc amplifiers. How would this be accomplished?

Liggs17

PS - I hope I'm using the correct terminology. Essentially, using the same input, I want to use each whole amplifier to act as a channel to a single speaker.
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Old 13th November 2006, 10:05 PM   #2
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If I understand you correctly you want to use both channels to amplify the same program material.

Send the same program into both channels then.
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Old 13th November 2006, 10:14 PM   #3
Duo is offline Duo  Canada
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Hm, there are two ways I've used stereo amps as monoblocks.

1. I attach both inputs to the same signal and run outputs in parallel (you must be very careful of differences between channels in this case. I only do it with small resistors inline to take up any possible differences which would usually cause oscillation or other problems).

2. I attach one input to the original signal and the other to the same signal but inverted. There are various ways to do this, but you'll often see me using a transformer just because it's passive, simple, well-balanced, and has equal phase lag on either side.

It can be done with an opamp inverter, or a paraphase circuit, or any number of things you would see inside old fashioned P-P tube amps and transistor amps.
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Old 13th November 2006, 10:33 PM   #4
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Quote:
PS - I hope I'm using the correct terminology. Essentially, using the same input, I want to use each whole amplifier to act as a channel to a single speaker.
After another look at what you wrote it looks like you want to bridge the amplifier?

Why in the world would you want to bridge an amplifier that is only capable of 8 watts a channel? The distortion would increase for one. The power gain isn't going to be worth the trouble and I'm sorry but it really doesn't make a lot of sense at least to me.
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Old 14th November 2006, 03:32 AM   #5
lndm is offline lndm  Australia
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If you're going to use each channel connected to each other in parallel, it's essential that you isolate the channels via a small value of resistor or there is a good enough chance the amp will die.

Bridging is a compromise, perhaps one you're interested in, not sure.

For my money, I'd run one channel to the woofer and one to the tweeter and bi-amp. Add a couple of well placed capacitors even for a rudimentary active setup, or get an active crossover kit.
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Old 14th November 2006, 04:51 PM   #6
liggs17 is offline liggs17  United States
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Thanks to all of those who replied. It's obvious to me that I'm out of my depth (I was a history major, and know just enough about electronics to get myself killed). As burnedfingers pointed out, it might not be worth the trouble to do it, anyway.

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Old 14th November 2006, 05:55 PM   #7
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Have you built and listened to this amplifier on its own yet? I'm a fellow humanities major (English) getting involved in this hobby, so some comments in hopes of answering the questions behind your question

The reason I asked if you had actually built yet is that this kit will surprise you with its output. If you are like I was when I first bought this kit you said, "Well, it's only 8W/channel, but it's tubes, it's easy, and it's cheap." So of course the idea of bridging them comes to mind because that might be the most "obvious" way to double your power....but as some of the knowledgeable folks above have pointed out, it's not that easy.

Don't despair having bought both kits, though! This means you have one to experiment on, and one to use as your mainstay/control subject. For instance, you can scroll through VoltSeconds mods and try some of those out:
http://www.siteswithstyle.com/VoltSe...Push_Pull.html

Or you can look here for some other help with mods:
http://diyaudioprojects.com/Tubes/K-12M/K-12M.htm

I have done 5 or 6 of these and have a very quiet amp with impressive low end for what it is.

You could also build one through as a first run, then, when you're comfortable, build a souped up version in a nice chasis (chasis work is harder than you'd think, so it would probably be rewarding to have a completed kit to listen to while you puzzle through that process).

Or, if you have built one and have found it won't drive what must be quite inefficient/oversized speakers, it's time to build yourself some speakers, which is another fun project altogether. You have any number of options available to you, so don't be discouraged or feel in over your head because one idea for an option didn't work out. Good luck and have fun.
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Old 15th November 2006, 12:42 PM   #8
Sherman is offline Sherman  United States
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I've also built one of these kits and find that for the price and the small size of the OPTs the sound is really quite good. I would do as ervington said and build one for the experience and build the other for use.

I also highly recommend Voltsecond's mods. I've implemented most of them on my amp and think they are worth the effort.
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Old 15th November 2006, 02:41 PM   #9
liggs17 is offline liggs17  United States
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Thanks for all the help! In truth, I haven't finished building the first amp yet (ran into some confusion in the directions which I cleared up by calling the folks at S5 Electronics - friendly and helpful people), but I hope to be finished with that by the end of the week. I'm really interested in the mods done by VoltSecond and the link provided to DIYaudioprojects.com.

Thanks to all of you who responded!

Liggs17
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