EHHA Rev A - Interest Thread

[runeight]

There has been some interest lately in the EHHA Rev A amp. As many of the know the original EHHA is available from Glass Jar Audio and information about it it on the Cavalli Audio website.
 
Rev A is designed to simplify the build while improving the amp.
 
Things that are the same in the two amps:
 
1. Still uses 6GM8s
2. Sill runs the tubes from the 30V rails.
3. Still has mosfet or bjt outputs
4. Can still be configured for ranges of OL and CL gains (or equivalently NFB)
5. Still runs at 100mA bias with plenty of power
6. Is still DC coupled front to back. No coupling caps
 
Things that are different:
 
1. Diff amp CCS is now a CRD for simplicity
2. Each board has built-in, linear regulated rails. That is, each board is a complete amp.
3. All you need are one 30-0-30/400mA transformer and one 6.3V/1A transformer (or a DC heater supply)
4. Sigma22 is not required in this version
5. No more trimpot on the diff amp
6. EF drivers for the O/P stage increase bandwidth
 
One prototype has been built. The amp works very well, but it has not, so far, been tested over multiple builds by different people. Please remember this sentence as the discussion proceeds.
 
I can post a schematic if you all are interested in going further and even the current board design.

 

[ujamerstand]

Sounds like good news! I'm all in for new revisions, I've got most of the parts needed to build the original EHHA already.

 

[nullstring]

has anyone compared this and original amp?
 
My ignorant opinion would seem to think that a sigma22 would supply cleaner power, and an external PSU would cause less noise.
 

 

[runeight]

No, no comparison has been made, but this is a very fair question. MHO is that there will be little difference, but only a real world comparison can say for sure. The gentleman who has the Rev A proto does not have an original EHHA.
 
 

 

[dasein-geist]

Will this new revision still be able to be configured to run speakers as well as headphones?
 
Certainly, the transformer specified seems a little light for speaker duty...

 

[runeight]

No, this is not a speaker amp as was the EHHA.
 
The regs are standard 1A regs so you can certainly beef up the output, but you won't be able to pull the >2A needed to get 20W into 4R.
 
If you guys really want the speaker amp too then the board would have to be redesigned for this mode of operation.
 
One of the limitations on the current EHHA is the need for a separate PS. This has both advantages and disadvantages. The idea here is to make it possible to build the amp without the additional complexity of another supply.

 

[jdkJake]

Sounds interesting to me.

I think at least posting the schematic would be kind to say the least. That way we can see and discuss the relative merits of the upgrade. Probably discuss it to death!

A very kind offer, which, I don't think this forum should pass up.

 

[dasein-geist]

Quote:

No, this is not a speaker amp as was the EHHA.
 
The regs are standard 1A regs so you can certainly beef up the output, but you won't be able to pull the >2A needed to get 20W into 4R.
 
If you guys really want the speaker amp too then the board would have to be redesigned for this mode of operation.
 
One of the limitations on the current EHHA is the need for a separate PS. This has both advantages and disadvantages. The idea here is to make it possible to build the amp without the additional complexity of another supply.

While I am interested in the Rev. A, it seems like it would be a whole lot of extra work to (re)configure it for speaker duty; thus, it seems like I'd be better off sticking with the current design - unless, of course, the consensus of others is a redesign would be worthwhile.
 
In any case, thank you, again, Dr. Cavalli, for your continued efforts for the DIY community. Your continued support is much appreciated...

 

[Beefy]

I'd love to see a board design and schematic, just to see what sort of casework would be required......

 

[runeight]

Here's a schematic.


 

 

[runeight]

As for redesign, it will be very easy to strip off the PS section. But then you all have to build a s22 to make a complete amp. Or any bipolar 30V supply.

 

[FallenAngel]

Nice idea, looking very good.  I'm really tempted to get a few boards and build in a few months when I can build again.

 

[dasein-geist]

Dr. Cavalli,
 
(respond: board redesign)
 
I do like the streamlining/symmetry of this revision (e.g. obviating the differential amplifier circuitry)...
 
However, it seems that the majority of this revision is centered around integrating the power supply.
 
Now, don't get me wrong, this is a fantastic revision (it significantly reduces the complexity and clutter of the build - and not incidentally, I would assume cost).
 
For these reasons, I personally would not want to be the reason for stripping the power supply from this revision. I think the potential space/ease of build/cost benefits are too great - even if that means the original EHHA design would would best for my purposes.

 

[runeight]

Thanks, but it's really ok with me whatever you all want to do. The main thing will be to have enough interest. And if there isn't that, that's ok too. There is plenty to do right now trying to get the commercial amps going.

 

[jamesbobo007]

My next build will be a EHHA so I'm very interested.