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Old 19th June 2013, 08:02 PM   #121
billyk is offline billyk  United States
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Quote:
Originally Posted by activexp View Post
Still very happy with my lunch money amp. It's now housed with a USB/MP3 player with FM tuner and it all works very nicely. This module was hopeless with a class D amp as the high speed switching caused interference on FM drowning out all but the strongest stations.

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Looks great!
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Old 20th June 2013, 01:02 AM   #122
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Default Cool. Nice idea!

Quote:
Originally Posted by activexp View Post
Still very happy with my lunch money amp. It's now housed with a USB/MP3 player with FM tuner and it all works very nicely. This module was hopeless with a class D amp as the high speed switching caused interference on FM drowning out all but the strongest stations.

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Cool idea! I like it!
Mark
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Old 21st June 2013, 06:36 AM   #123
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Originally Posted by radiosmuck View Post
. . . I still cannot get over how good this amp sounds, and it must sound good, none of the modders have made recommendations.
Actually, there is one: Linear regulated power.
That's just a bit more fresh. Perhaps overkill.

However an audio amplifier is this: Power + signal = output.
Energy from small signal is tiny, and that means the largest input is, in fact, power. So, good quality power means a lot.
See LM338 datasheet schematic for "Tracking pre-regulator" colloquially termed Nested Regs. That sort is really high end, at minimal complexity, minimal cost, and almost a well kept secret. It seems a good partner to this amp. Somehow, this particular amp, with a very good 8 watts and headroom to 16 watts, tends to make overkill on quality, a lot more fun than usual. In most conditions, it easily beats the T-amp for quality, but if we want to make really sure of that (or just make it really obvious), then linear regulated power is the way to go.
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Last edited by danielwritesbac; 21st June 2013 at 06:39 AM.
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Old 21st June 2013, 08:49 PM   #124
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Quote:
Originally Posted by danielwritesbac View Post
Actually, there is one: Linear regulated power.
That's just a bit more fresh. Perhaps overkill.

However an audio amplifier is this: Power + signal = output.
Energy from small signal is tiny, and that means the largest input is, in fact, power. So, good quality power means a lot.
See LM338 datasheet schematic for "Tracking pre-regulator" colloquially termed Nested Regs. That sort is really high end, at minimal complexity, minimal cost, and almost a well kept secret. It seems a good partner to this amp. Somehow, this particular amp, with a very good 8 watts and headroom to 16 watts, tends to make overkill on quality, a lot more fun than usual. In most conditions, it easily beats the T-amp for quality, but if we want to make really sure of that (or just make it really obvious), then linear regulated power is the way to go.
I'm willing to give this a try, not a lot of money and useful for other little projects.
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Old 23rd June 2013, 10:08 PM   #125
pkozul is offline pkozul  Australia
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Default Another amp finds a permanent home...

Hi there,

Great thread!

My amp arrived the other day. Hooked it up and found that one channel was much louder than the other. I suspected the volume pot was the culprit, and after some deoxit, still the same problem.

After replacing the volume pot with another I had on hand, the amp was finally playing at equal volume across both channels.

... and I was impressed with what I was hearing.

I found a $3 wooden toothbrush holder, and thought it might be a good fit as an enclosure for the amp. Ended up being an perfect fit, with a little bit of clearance to allow for the wires to pass over the heatsink.

I removed the bottom of the toothbrush holder (since the wood was too thick to be used for mounting binding posts, etc.), and replaced it with a square piece of plastic (I cut it from the enclosure of an old wifi router from the junk box). Attached some binding posts, a 3.5mm stereo input socket, and a standard 12V power socket.

As you can see, it's a tight squeeze in there. Might drill out some holes for ventilation. Also, need to add a panel to the front, maybe something translucent, and then I'll add a power switch.

BTW, at higher volumes, there is an audible hum. Any ideas on what it could be and how to resolve?

There was another hum that would occur when touching the volume pot, but I got rid of that by grounding the case of the pot.

Cheers,
Pete

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Old 23rd June 2013, 11:04 PM   #126
redjr is offline redjr  United States
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Very ingenious. I love it. Great job!
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Old 24th June 2013, 07:42 AM   #127
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Quote:
Originally Posted by pkozul View Post
BTW, at higher volumes, there is an audible hum. Any ideas on what it could be and how to resolve?
That might be the sound of a ground loop. A ground loop happens any time something has been grounded more than once.

Do you have a grounded source such as a computer?
Does your amplifier's power supply have a 3 prong plug or is a double-insulated power supply with a 2 prong plug?
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Old 24th June 2013, 09:14 AM   #128
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Quote:
Originally Posted by pkozul View Post
Hi there,

Great thread!

My amp arrived the other day. Hooked it up and found that one channel was much louder than the other. I suspected the volume pot was the culprit, and after some deoxit, still the same problem.

After replacing the volume pot with another I had on hand, the amp was finally playing at equal volume across both channels.

... and I was impressed with what I was hearing.

I found a $3 wooden toothbrush holder, and thought it might be a good fit as an enclosure for the amp. Ended up being an perfect fit, with a little bit of clearance to allow for the wires to pass over the heatsink.

I removed the bottom of the toothbrush holder (since the wood was too thick to be used for mounting binding posts, etc.), and replaced it with a square piece of plastic (I cut it from the enclosure of an old wifi router from the junk box). Attached some binding posts, a 3.5mm stereo input socket, and a standard 12V power socket.

As you can see, it's a tight squeeze in there. Might drill out some holes for ventilation. Also, need to add a panel to the front, maybe something translucent, and then I'll add a power switch.

BTW, at higher volumes, there is an audible hum. Any ideas on what it could be and how to resolve?

There was another hum that would occur when touching the volume pot, but I got rid of that by grounding the case of the pot.

Cheers,
Pete


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Very neat job!
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Old 24th June 2013, 09:54 AM   #129
pkozul is offline pkozul  Australia
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Hi again,

Thanks for the comments. I tried to keep the project as neat as possible since the amp will be sitting in our study on the desk, so there's a bit of FAF involved (family acceptance factor).

It's funny when you get more and more into this hobby and you start noticing potential enclosures in all shapes and sizes :-)

Daniel, the power supply (SMPS) I have has a 3 prong plug. The amp is connected to the laptop via an Edirol USB audio interface. I found that the hum only really kicks in when the volume pot is turned up to about 80 or 90% of its range. Since it's a linear 100k pot, I guess that level is really out of the listenable range. Could it be a faulty pot? In any case, I will try adding some resistors between the pot's pins, to turn it into a more of a log pot. Currently, the volume pot is not very useful since there is such a fine line between quiet and loud, as some people here noticed with the original pot.

Cheers.

Last edited by pkozul; 24th June 2013 at 09:56 AM.
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Old 24th June 2013, 01:32 PM   #130
xrk971 is offline xrk971  United States
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Pzozul,
nice job with bamboo toothbrush holder box! I am going to keep my eye out for that.
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