EHHA Rev A - Interest Thread - Page 4
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OK. I need to talk further with Jeff Rossel anyway so we can wait a bit. I would prefer for kits to be available along with boards, but as many of you know, Jeff has been very busy.
This latest version simply has the mosfets in the right orientation and matches the 3D above.
There is one question I'll have to ask the fab. When you snap the PS section at the score line you'll also be snapping it through the bottom layer copper power planes. We need to know if the copper will separate nicely.
i was thinking the same thing. the o22 adds a significant cost.
i have a friend that wants me to build him a SOHAII. this EHHA revision would probably come in a little cheaper, but would need to factor in an e12.
Why would you need an e12 in an amp with a DC nulling servo? Surely it isn't that slow......
good question. i guess i wasn't really thinking why i would need it . i just assumed it was an added as a fail-safe device for DC coupled amps. but doesn't the SOHA II have a DC servo on the outputs as well and uses an e12? why is this?
Edited by fishski13 - 8/16/10 at 4:55am
"Notice that R1E and R2E are changed from 10kΩ to 33kΩ and that R4E is changed from 1kΩ to 2kΩ. The purpose of these changes is to make the SOHA II ε12 less sensitive and a bit slower. This is because the SOHA II SE Buffer can generate a bit more offset under certain signal conditions before settling down. However, the SOHA II ε12 is still sensitive enough to prevent damage to headphones."
So the SOHA II is a special case, because its buffer drifts around a bit. I have to assume that Alex leaving it out means the EHHA is more stable.
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You won't be able to score the board - otherwise you'll cut the traces.
How is the ground handled for a SE setup? Where is the common point for the star grounding?
A part of me really wants to build this. The other part is looking at the stuff on my bench going I need to finish that first.
Thanks cobaltmute. As it turns out the score line and traces are placed such that the score line will not cut any traces. It will not even cut the ground plane on the top. And, when separating the PS, we do want to cut the two power planes on the bottom. My question for the fab will be if the score line is on the top will the power planes on the bottom separate nicely or not when the board is snapped? It could be that they won't, in which case we'll have to find another option.
The ground point for SE setup with the internal PS is the mounting hole in the back-middle of the board between the PS section and the amp. Grounding here minimizes PS noise getting into the ground plane of the amp section. In fact, will effectively elminate it.
Gents, the only reason the e12 is not part of the original EHHA is because it wasn't around then. The EHHA I does generate some power up transient, especially if the tube heaters are turned on at the same time as the rails so that the tubes are not conducting when rails are applied to the sand. I don't remember how much though.
If I were to make a two channel, fully integrated EHHA similar to the SOHA II I would definitely build in an e12 just to be absolutely safe. But, we may not need to do that here.
I haven't asked the Rev A proto builder about the transients. But I'll do that so that we have some data.