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Old 19th July 2012, 02:37 AM   #11
KP11520 is offline KP11520  United States
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Hi Chris and Enzo,

I figured I would use a continuity tester to see if one of the three red leads is a ground but I need to get under the main board. As when I check the 15 Volt rails. BUT (and I'm talikin about a BIG Butt), the three Power Amp transistors are attached to the heatsink on the back. Can I unscrew them and separate them off the heatsink and reassemble them later with no problems?

I can post pictures if that would help!

And sorry Chris, you actually are still in your prime. I am closer to Enzo's end of the spectrum. (although I sure would like to be where you are again! Sorry Enzo)

Kudos Chris, you are helping an old guy with electronics that's almost 3 times your age and you are light years ahead!

And Enzo is just loaded with info and experience and a gift to guys like me.

Regards//Keith
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Old 19th July 2012, 06:21 AM   #12
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Well 80 Watts is not super beefy. Don't know how loud is loud for you. I recently heard someone with such a combo playing live and for that gig it was loud enough but that wasn't a rock band.

I don't know how loud they uaually pop when turned on but somem pop is definitely normal because this amp diesn't have any type of delayed speaker relay. As long as the driver can take it this might be an even better solution form the reliability point of view.

There is a simple test that would show whether a problem is within the first part of the preamp: Feed some signal into the effect return maybe from some MP3 player or the like and check whether you can go louder.

Regards

Charles
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Old 19th July 2012, 05:12 PM   #13
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Quote:
Originally Posted by KP11520 View Post
Hi Chris and Enzo,

I figured I would use a continuity tester to see if one of the three red leads is a ground but I need to get under the main board. As when I check the 15 Volt rails. BUT (and I'm talikin about a BIG Butt), the three Power Amp transistors are attached to the heatsink on the back. Can I unscrew them and separate them off the heatsink and reassemble them later with no problems?

I can post pictures if that would help!

And sorry Chris, you actually are still in your prime. I am closer to Enzo's end of the spectrum. (although I sure would like to be where you are again! Sorry Enzo)

Kudos Chris, you are helping an old guy with electronics that's almost 3 times your age and you are light years ahead!

And Enzo is just loaded with info and experience and a gift to guys like me.

Regards//Keith


You should be fine taking those transistors off. Are you sure they're all transistors? Seems odd that there's 3 of them. Maybe one is a regulator.

Tell you what, switch the amplifier on (speaker connected) and leave it for a while. If the 3 chips on the heatsink are reasonably cool, then you're good to remove them. If they're really hot, then you can still take the heatsink off, but don't switch it on for any length of time: it might be difficult to replace them if they go pop.

When you come to attach them again, some heatsink paste wouldn't go amiss.

Chris

PS - which are the big power supply caps like?

Click the image to open in full size. Click the image to open in full size.

If they're like the latter, you can directly measure across them without removing the board.
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Old 19th July 2012, 08:50 PM   #14
KP11520 is offline KP11520  United States
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Hi Charles,

The distortion is with the gain and volume at less than 1/3 with both the passive setting and active setting.

Great idea! Having to go over the front end rather than the whole amp would be easier and less to do! (and less intimidating because of the "guesswork" issue).

I hope the problem lies in the preamp side. (Smaller PCB abd more accessible with less dismantling!

Thanks for another great idea my lack of experience wouldn't have thought of.

Regards//Keith

Quote:
Originally Posted by phase_accurate View Post
Well 80 Watts is not super beefy. Don't know how loud is loud for you. I recently heard someone with such a combo playing live and for that gig it was loud enough but that wasn't a rock band.

I don't know how loud they uaually pop when turned on but somem pop is definitely normal because this amp diesn't have any type of delayed speaker relay. As long as the driver can take it this might be an even better solution form the reliability point of view.

There is a simple test that would show whether a problem is within the first part of the preamp: Feed some signal into the effect return maybe from some MP3 player or the like and check whether you can go louder.

Regards

Charles
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Old 19th July 2012, 08:53 PM   #15
KP11520 is offline KP11520  United States
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Hi Chris,

The caps are radial unfortunately. Time to get out the Chop Saw. LOL

Would Arctic Silver thermal paste for computers suffice?

Thanks again!

Regards//Keith

Quote:
Originally Posted by chris661 View Post
You should be fine taking those transistors off. Are you sure they're all transistors? Seems odd that there's 3 of them. Maybe one is a regulator.

Tell you what, switch the amplifier on (speaker connected) and leave it for a while. If the 3 chips on the heatsink are reasonably cool, then you're good to remove them. If they're really hot, then you can still take the heatsink off, but don't switch it on for any length of time: it might be difficult to replace them if they go pop.

When you come to attach them again, some heatsink paste wouldn't go amiss.

Chris

PS - which are the big power supply caps like?

Click the image to open in full size. Click the image to open in full size.

If they're like the latter, you can directly measure across them without removing the board.
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Old 21st July 2012, 06:16 PM   #16
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The thermal paste you've mentioned will be fine.

+1 on Charles's idea on using the fx loop.

You could also try listening to the fx Send via some headphones to confirm your findings.
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Old 22nd July 2012, 01:19 AM   #17
KP11520 is offline KP11520  United States
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Well, Alrighty then!

Let the hacking begin.....

Where's that chainsaw?

Quote:
Originally Posted by chris661 View Post
The thermal paste you've mentioned will be fine.

+1 on Charles's idea on using the fx loop.

You could also try listening to the fx Send via some headphones to confirm your findings.
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Old 17th August 2012, 06:15 PM   #18
KP11520 is offline KP11520  United States
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Hi Gang,

I bought most of the parts to build the AF tracer probe, except I am not having luck finding a "pen" shaped housing and a probe tip that can thread into whatever housing I find. I guess I could use a plastic cigar tube, but I want something a little thinner for more comfort and better maneuvering in tight spots. The metal pobe tip is evading me.

I am also the Executor to an Estate and that is consuming much of my time. Even when trying to decompress, I feel scattered because I know I should be doing something else. I will be able to focus a bit more come the middle of September.

Thanks for your support and I hope we can pick up where we left off!

If anyone has a line on some sort of pen shaped probe housing that will hold a 630 volt 0.1 uf axial cap and 1/2 watt 470K resister, the evasive tip and out to 2 wires, please point me in that direction. The same with the metal probe tip as well! Thanks again!

See you soon!

Regards//Keith
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Old 17th August 2012, 11:06 PM   #19
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The tracer probe is a special input cable for an amplifier. You may have a amplifier dedicated to the purpose, but really any amp will work. You need a cap to block any DC in the circuit under test from your tracer amp. It is convenient to put it in the probe body, and I have built various probed in cigar tubes and find them comfortable to use. But the cap can just as easily be in the other end of the probe cable. Lots of room inside a big fat #70 Switchcraft plug for example. Or for that matter if your tracer amp is dedicated, put it inside the amp. All that matters is that you have a cap between the tip of the probe and the input of the amp. Doesn't matter where along the wire that cap lives. Same with the resistor. As long as it is on the right end of the cap, it can be anywhere.


A pen shaped housing? How about an empty pen?
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