| Rafal |
Hi All,
I thought I'd share with you my progres on the irst Gainclone I'm building.
It is based on the Peter Daniel's design and his advice, which by the way, I am very greatfull for.
Thanks Again Peter !!!.
I decided to make an enclosure out of 6" dia. aluminum tube (.25" wall thickness. The top will house both channels and the bottom a 400VA transformer. The Chips are LM3875. The whole thing will sit on a curly maple base.
I still have to finish the PS and hope to be done this weekend
Here are some pictures:
Feel free to comment.
Cheers,
Rafal |
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| Rafal |
| Here is the top view: |
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| Rafal |
| Both channels mostly done. |
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| S.C |
| Is the bridge in the bottom? Why? |
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| Rafal |
| The bridge will be on top on the other side of the aluminum bars (for shielding). |
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| JasonL |
| that is a cool idea.. i also have that idea but mine is a bit different. ill draw a picture and post it.. keep up the good work it looks good so far.. |
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| S.C |
| I think you should relocate the switch, and make it a volume control / light / a round button switch with light instead. It looks odd when there is a rectangle switch on a rounded chassis front.:eek: And you can improve the chassis screw hole by driling a little bigger hole on the outside of the excising hole then sink the screw into the chassis and make it parallel to the surface on the chassis.:smash: |
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| Rafal |
Thank you all for your suggestions.
I have finally finished my amp but it has a problem. when I switch it on, it sounds fine, but after acuople of minutes, the sound gets very distorted.
Can anyone suggest why that might be?
Or what other info do you need to narrow down the cause?
Thanks in advance for your help.
Rafal |
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| soundNERD |
maybe its oscillating?
make sure there is no loose connections.
-Mike |
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| promitheus |
| It could be a promlem in the wiring or bad grounding. IC amps are very sensitive to ground loops or long wires. |
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| S.C |
| My humble advise will be using a meter to check the soldier joint..... Anything unblance will be wrong.... My noob logic....... I'm not an expext on circut thou..... hehe |
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| promitheus |
I would the grounds one more time.
Try to keep them short and make a star ground reference somewhere. If you use one ground to many you could oscilations or noise going in the feedback making the sound dull. |
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| neutron7 |
| where do you get that nice aluminium tube from? |
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| Rafal |
Thanks for your advice.
I found something. One of the wires (going to pin#7) was loose. I will fix it and try again tommorow. Could that cause issue with both channel though?
Oscillation... how does it manifest itself? How can I detect if it is happening?
When it comes to ground, I am using a star signal ground and star power ground. Both of the stars are then connected.
The Aluminium tube was found at metal supermarket (www.metalsupermarkets.com).
It was pretty cheap too.
Here is the pic of my amp as it is now. |
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| Nuuk |
| Welcome to the tubed Gainclone club ;) |
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| Rafal |
Hi All,
I re solthered the wire that was loose and did the pull test on all ground wires. No change. I still see distortion after a minute or so. I did some more digging and this is what I found out:
The power to the chip (via pin #1 and #4) starts out with +15v and -16.5v resp.
After a minute of playing, the pin #1 voltage approaves 30v and the pin #4 approaches 0v.
I figure this probably shouldn't be happening. Any idea what may cause it?
I have built 2 recifier bridges, 1 for each ch. based on the design from decibel dungeon.
Thanks in advance for your help.
Rafal
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| promitheus |
what should the power supply be in the first place?
+/- 15 Volt or 0, 30Volt? |
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| Rafal |
| I think it should be +/-15vdc and stay that way (but I might be wrong). Also, this happens only under load (i.e. when the speakers are hooked up and playing). |
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| promitheus |
where do you live in London?
You know I was born there.
Than something is wrong with the grounding of the power supply. |
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| Rafal |
| I'm in Lambeth area of London Ontario. |
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| Peter Daniel |
| quote: | Originally posted by Rafal
The power to the chip (via pin #1 and #4) starts out with +15v and -16.5v resp.
After a minute of playing, the pin #1 voltage approaves 30v and the pin #4 approaches 0v.
I figure this probably shouldn't be happening. Any idea what may cause it?
I have built 2 recifier bridges, 1 for each ch. based on the design from decibel dungeon.
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Is your transformer center tapped or has two separate secondaries with 4 wires. It seems like the problem is in incorrect supply voltages. After a minute or so you are supplying the chip with positive voltage only and that's causing the problem.
Check your PS wiring (including ground connections). |
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| UrSv |
| Sounds like center tap is not connected to ground? |
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| Rafal |
Thank you for all your replies.
I think I wired the two seconadries from my transformer to the bridges incorrectly.
I am redoing my gainclone.
It will be based on Brian's boards and hopefully look neater. I will also re-wire the PS and what I think I need to do is join the two 0v wires and connect them to the power ground, and then take the other two secondaries and connect them to + and - on the bridge. I am planning to use one bridge to power both channels.
Also, I am re-doing the case. I love Peter Daniel's design, but to me designing and building the case is the most fun part of the project. I hope it will look nicely understated and professional. I will, of course, post pics once I'm done.
Thanks again everybody for your help.
Rafal |
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