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EHHA Rev A - Interest Thread - Page 4

post #46 of 1657
Quote:
Originally Posted by runeight View Post

Are we getting closer?

 


Works for me. I'm in.

post #47 of 1657
Thread Starter 
Quote:
Originally Posted by stixx View Post

Nice, compact looking board...

I am still in for a stereo pair, but give it some time until you make it a Group Buy ;-)

(vacation until Sep 11)



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.

 

EHHA Rev A Mod 2.pdf

post #48 of 1657

Looks great. I'm in for a balanced set.

post #49 of 1657

Ah - you're tempting me !

 

How much would it (just approximately) cost to build one amp?

(2ch, only parts - no case included)

post #50 of 1657

Am thinking if you use the on board supply you are looking at about 200$. Biggest bang for buck ever if you ask me if it sounds anything like the EHHA-1, though this one is supposedly faster too. :)

post #51 of 1657
Quote:
Originally Posted by sachu View Post

Am thinking if you use the on board supply you are looking at about 200$. Biggest bang for buck ever if you ask me if it sounds anything like the EHHA-1, though this one is supposedly faster too. :)


i was thinking the same thing.  the o22 adds a significant cost.

post #52 of 1657

Indeed..the S22 would add almost another 70$. To be honest, I would just go with the onboard  PSU, though am curious to see any measurable differences translates to discernible differences in sound quality using the two different PSUs.

post #53 of 1657
Quote:
Originally Posted by sachu View Post

Indeed..the S22 would add almost another 70$. To be honest, I would just go with the onboard  PSU, though am curious to see any measurable differences translates to discernible differences in sound quality using the two different PSUs.


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.

 

post #54 of 1657
Quote:
Originally Posted by fishski13 View Post

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......

post #55 of 1657

Yeah, that’s what I was thinking.

post #56 of 1657

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
post #57 of 1657
Quote:
Originally Posted by fishski13 View Post

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?  

 

"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."

 

http://www.cavalliaudio.com/soha%20ii/main.php?page=schematics/e12schematic

 

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.

post #58 of 1657
Quote:
Originally Posted by runeight View Post
 

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.

 

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.

 

post #59 of 1657
Thread Starter 

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.

post #60 of 1657

thanks Alex and Beefy.

 

i'd like to add another stereo pair.  4 boards total for me.

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