I'm creating a dual 100W power amplifier using MX50SE boards from Ebay and an old 2U rack amp. I have one half working and it works great. Very quiet. Should be a nice cheap but quality amp.
However when connected to certain gear (like the computer audio interface) there is some hum. I know it's not the amp because if I terminate the input there's no hum. Input wires are shielded and everything is grounded properly. Clearly it's just the ground loop created by the input ground wire and the source gear.
So I happen to have these little transformers which I thought might be a nice way to fix the ground loop:
They can't handle much power but the amp has 30dB of gain so the input level would be low enough that I don't think the added distortion will even be noticeable. I care much more about noise performance.
Now to my question. I realize that if I add a switch to invert the phase of one of the input transformers, I would have a bridged output. There's actually already a bridging switch that was in the old amp. I would just have to re-wire it. Simple. The question is, would it work? I don't know much about power amps and less about bridged configuration but it seems to me it should work. I would just have to connect the load across both positive terminals. Right?
Also, second question, regarding the transformers, they're 600 ohm : 600 ohm. The load would be just the 10K volume pots. Would you agree that using a 600 ohm transformer with a 10K load is not a problem?
However when connected to certain gear (like the computer audio interface) there is some hum. I know it's not the amp because if I terminate the input there's no hum. Input wires are shielded and everything is grounded properly. Clearly it's just the ground loop created by the input ground wire and the source gear.
So I happen to have these little transformers which I thought might be a nice way to fix the ground loop:
They can't handle much power but the amp has 30dB of gain so the input level would be low enough that I don't think the added distortion will even be noticeable. I care much more about noise performance.
Now to my question. I realize that if I add a switch to invert the phase of one of the input transformers, I would have a bridged output. There's actually already a bridging switch that was in the old amp. I would just have to re-wire it. Simple. The question is, would it work? I don't know much about power amps and less about bridged configuration but it seems to me it should work. I would just have to connect the load across both positive terminals. Right?
Also, second question, regarding the transformers, they're 600 ohm : 600 ohm. The load would be just the 10K volume pots. Would you agree that using a 600 ohm transformer with a 10K load is not a problem?
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"The question is, would it work?"
Yes.
"Would you agree that using a 600 ohm transformer with a 10K load is not a problem? "
Yes.
Yes.
"Would you agree that using a 600 ohm transformer with a 10K load is not a problem? "
Yes.
I didn't realize bridging also allows you to mix two channels together. I was just listening to a stereo to mono Red House on an old honky Jensen P12Q.
This turned out well. It's soooo quiet.
Notice the SSM2220P chips in place of the input transistors. The DIP lined up exactly with the transistor holes! Offsets are less than 2mV.
This turned out well. It's soooo quiet.
Notice the SSM2220P chips in place of the input transistors. The DIP lined up exactly with the transistor holes! Offsets are less than 2mV.
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Interesting. If you mix L and R together you can knock out vocals and bass and only the tracks that are on L or R but not both can be heard. For example, with Babe I'm Gonna Leave You, I can only hear the reverb of Plant's singing and a lot of guitars. Might be good for figuring out guitar licks.
Hi Guys
Note that when you bridge two amps they effectively see half the load impedance, or require a doubled load impedance to work no harder than they ever did.
For example, if the amps are rated for 100W/ch at 8R, bridged amps will drive 200W into
16R. Each amp is still providing the same voltage swing and current that it would for the 100W 8R load.
If you want to drive the same speaker, say an 8R, then the amp needs a 4R power rating that is suitable for half the target power. So, if the goal is to get 100W into 8R, each amp needs a rating of 50W into 4R.
Mixing channels by cross-connecting a speaker is an old idea from the fifties. It was often a third speaker added when the left-right cabinets were very far apart. The third cabinet helped fill the hole in the middle.
Using a TX as a hum isolator works well. It also works well to generate the balanced drive needed fro bridging the amp. Computers are not noted for their sensible grounding for audio use.
Have fun
Note that when you bridge two amps they effectively see half the load impedance, or require a doubled load impedance to work no harder than they ever did.
For example, if the amps are rated for 100W/ch at 8R, bridged amps will drive 200W into
16R. Each amp is still providing the same voltage swing and current that it would for the 100W 8R load.
If you want to drive the same speaker, say an 8R, then the amp needs a 4R power rating that is suitable for half the target power. So, if the goal is to get 100W into 8R, each amp needs a rating of 50W into 4R.
Mixing channels by cross-connecting a speaker is an old idea from the fifties. It was often a third speaker added when the left-right cabinets were very far apart. The third cabinet helped fill the hole in the middle.
Using a TX as a hum isolator works well. It also works well to generate the balanced drive needed fro bridging the amp. Computers are not noted for their sensible grounding for audio use.
Have fun
Correction:
Measuring again after a couple of days and after leaving it on for 30 minutes, the offsets are now -9mV and -6.8mV.
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