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Old 14th April 2009, 07:38 PM   #781
pooge is offline pooge  United States
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Yes, I would think a capacitor here would be good practice as a general rule to provide an RF ground at that point.

Alternatively, a cap from the top side of R25 (via the negative input) to the heat sink below the board may be even better.
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Old 18th April 2009, 01:44 AM   #782
pooge is offline pooge  United States
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So Sheldon, any listening impressions yet?
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Old 18th April 2009, 02:01 AM   #783
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For Sheldon and AndrewT,



Try removing the heatsink ground, or make sure the heatsink is not grounded to the centertap, also if using two seperate transformers and two seperate filter banks make sure the both star grounds are connected together for each channel with a heavy gauge wire, heatsinks should not be connected to star ground but may be connected to a chassis ground (not connected to star ground) which may be earthed. Grounding the heatsink in this style of High Frequency circuit seems to cause stability issues....



Colin
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Old 18th April 2009, 04:49 AM   #784
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by pooge
So Sheldon, any listening impressions yet?
No. I wanted to test basic function and sink performance before doing the casework. I like to build a full stereo amp and then listen. It'll be a little before I complete the casework. I promised my wife that I'd finally finish the backyard garden and landscaping (which I have successfully avoided with various ruses for at least a couple of years now). So I have to put in at least some time there before I can sneak into the garage and cut and drill. Also, our little mutt recently died after 16 years so we just got a two year old dog that was destined to be put down. I think he was in a shelter because the previous owners couldn't handle him, and he is a bit of a project, though very sweet. After a week, we've got him halfway lease trained. Still, I have to give him a fair amount of attention until he's secure enough to absorb more challenging skills (like coming when called, learning how to be around other dogs, etc.).

BTW, the sink that I show is half of the one I picked up at a surplus place. You were right that each half is only enough for two channels, if the emitter resistors are 0.1R. For this it's fine, as the rest of the casework will contribute significantly to the emissive surface. I'll give pics and measurements when done.

Sheldon
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Old 18th April 2009, 05:04 AM   #785
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by vynuhl.addict
Try removing the heatsink ground, or make sure the heatsink is not grounded to the centertap, also if using two seperate transformers and two seperate filter banks make sure the both star grounds are connected together for each channel with a heavy gauge wire, heatsinks should not be connected to star ground but may be connected to a chassis ground (not connected to star ground) which may be earthed. Grounding the heatsink in this style of High Frequency circuit seems to cause stability issues....
Good to know. Each channel has its own transformer, though only one channel running now. I lashed it up fairly quickly, with a single rectifier. The earth and center tap and chassis ground G, at the opposite end of the board from the star ground, between P+ and P-) are both connected at the same point on the sink. I can route the center tap to G, and run a separate wire from there to the chassis/earth point, or are you saying no earth reference to the board?

Sheldon
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Old 18th April 2009, 05:04 AM   #786
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by vynuhl.addict
Try removing the heatsink ground, or make sure the heatsink is not grounded to the centertap, also if using two seperate transformers and two seperate filter banks make sure the both star grounds are connected together for each channel with a heavy gauge wire, heatsinks should not be connected to star ground but may be connected to a chassis ground (not connected to star ground) which may be earthed. Grounding the heatsink in this style of High Frequency circuit seems to cause stability issues....
Good to know. Each channel has its own transformer, though only one channel running now. I lashed it up fairly quickly, with a single rectifier. The earth and center tap are and power ground G, (at the opposite end of the board from the star ground, between P+ and P-) and are all connected at the same point on the sink. I can route the center tap to G, and run a separate wire from there to the chassis/earth point, or are you saying no earth reference to the board?

Sheldon
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Old 18th April 2009, 09:57 AM   #787
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Default Interesting that...if i remove heatsink ground from my amplifiers, they start to


produce noise... i will read the thread with calm...maybe you have something different there.....

Interesting suggestion Vinyl... got my interest because in my constructions.... grounded heatsinks is a rule that i have paid a lot when i forgot to follow.....but maybe you have some different problem in there....interesting folks..... will be a good reading to discover why that.... will be following your posts till the solution.

regards,

Carlos
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Old 18th April 2009, 10:40 AM   #788
roender is offline roender  Romania
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In a dual mono amplifier, I used to connect every main starground to the case through 1...2uF foil capacitor.
When I said to connect the ground to the heatsink I mean to connect it at AC, not DC! Therefore, both amplifiers will have a common signal DC ground connected together at the signal source, once the signal source is connected
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Old 18th April 2009, 02:31 PM   #789
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by roender
In a dual mono amplifier, I used to connect every main starground to the case through 1...2uF foil capacitor.
When I said to connect the ground to the heatsink I mean to connect it at AC, not DC! Therefore, both amplifiers will have a common signal DC ground connected together at the signal source, once the signal source is connected
OK, thanks.

Sheldon
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Old 18th April 2009, 02:38 PM   #790
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Default I see... alike a shield...shield into metalic chassis


The way they use to do with Radio Frequency transmitters...they even use many capacitors in parallel..all them ceramics...1n, 4n7, 10n, 22n, 47n, 100n till they reach 1uf..when they used to stop.

Alike inner ground and outer ground.... beeing inner the star ground, the DC ground...and outer your method.

Nice and interesting...very effective.

Thank you,

regards,

Carlos
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