[cobaltmute]

What are the minimums for open loop and closed loop gain we can run?

 

[runeight]

There are no real minimums, but I wouldn't go any lower than 10k on R13 and R14. This will give you an OL gain of around 75.
 
Obviously the higher the OL gain and the lower the CL gain the more NFB. I have not checked the stabiliy but with more and more NFB the amp may need more compensation, similar to the EHHA I.
 
If you socket the four resistors you can experiment to see which sound you prefer.

 

[jdkJake]

 
Quote:

So, stringg and jdk, you guys have made a few brief comments about the amp's audio delivery. Might you provide any more detail?

So, it is still early and I have not used any phones other than my Grados. I won't have a more reflective set of comments until I get more time on it with my HD650's as well.
 
At this point, my main take-away is on how detailed and refined the sound is straight out of the box. Totally clean and clear, yet never harsh or fatiguing, which, can be an issue, especially with Grados. The amp is extremely detailed and transparent without being overly aggressive or analytical. The amp does so many things right and even at this early stage, apparently nothing wrong. An extremely balanced sound that presents the source in the best light possible. That is about the best compliment I can pay it at this point in time. I am very impressed.
 
I am figuring out how to move it into my main listening area to try out a number of sources and get the HD650's into the action. They are the true test of versatility and will give me a better idea of how the MOSFET's respond to large voltage swings. 
 
Well done, Alex.  Well done indeed.

 

[cobaltmute]

jdkjake, just as a reference, what source are you using now?

 

[jdkJake]

Primarily iPod and NAD T-585 (CD only, no SACD or DVDA yet).
 
I want to get it hooked up to my Keces as I know that source best. I also have a Gamma2 I just built I would like to hear it with, but, that is pretty new and I do not have a reference with it yet, so, I will probably concentrate on the Keces and more of the T-585.
 

 

[arteom]

*waits for kits to become available 

 

[cobaltmute]

Quote:

There are no real minimums, but I wouldn't go any lower than 10k on R13 and R14. This will give you an OL gain of around 75.
 
Obviously the higher the OL gain and the lower the CL gain the more NFB. I have not checked the stabiliy but with more and more NFB the amp may need more compensation, similar to the EHHA I.
 
If you socket the four resistors you can experiment to see which sound you prefer.

So at an OL gain of 75, is a CL gain of around 3-5 reasonable?  Anything else need to be done to handle that?  I find that with my sources I don't need or want a lot of gain.  I easily give up gain for more sensitivity on the volume know.

 

[runeight]

Yes, it is reasonable. But, I haven't got a clue if you will like the amp under those conditions.
 
To get there with R13/R14 at 10k you need R11 at 3k9. Then my guess is that C2/C3 should be increased to 33p or even 47p to keep the amp stable.
 

 

[cobaltmute]

Quote:

Yes, it is reasonable. But, I haven't got a clue if you will like the amp under those conditions.
 
To get there with R13/R14 at 10k you need R11 at 3k9. Then my guess is that C2/C3 should be increased to 33p or even 47p to keep the amp stable.
 

So in another words, socket the resistors and be prepared to play a little bit.

 

[ujamerstand]

If anyone is interested in a logo design for their EHHA rev.A, I've uploaded a version here: http://www.sendspace.com/file/fr2v9y
 
In the zip file there are several .plt files, ~hpgl4.plt being the latest version of the design. There is also a .cdr file that you could use to generate hpgl drawings to the exact size you want. You can open it with coreldraw x4 or higher. Just follow the FPE tutorial to create the engraving guides. If anyone wants the uncombined, non-welded work file to play with, pm me and I'll pass it on to you.

 

[runeight]

Quote:

So in another words, socket the resistors and be prepared to play a little bit.

Yes. And socket the caps too. 

 

[studeb]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif
Thanks. This is really useful info. The regs will have about 3.6V across them which is enough for them to regulate, but really just barely. This means (forgive me gents) that the transformers are slightly underspec'd. They need a higher current rating. Probably 50-100mA per channel. We don't want the input to regs to be too high however, because it will just burn useless power in the regulators. So this is a really tough call as it always is in power supplies. It would be better to have the input to reg voltages at 35-36V, but not higher than this.
 
My guess is that if the transformer secondaries were at 30VAC all would be well.

I was going to order the anteks yesterday, but thought i should wait to see how jdk works out.
The next size up antek 0532 "specs" out 1.5V higher at about the same current, 31.5V @0.7A versus 30V @0.79A. That should get the secondaries up to 30V.
 
I think i will order that one. Anyone have a strong feeling that is dunb?

 

[runeight]

Probably a good idea on the anteks but not on avels. stringg's avel is doing just fine at 500ma while jdk's antek is sweating at over 700mA rating.

 

[sachu]

Quote:

JDK - what tubes are you running in yours?  I'm using some Telefunkens I picked up from Sachu.  
 

Wishing right now that i had kept them
 
Parts order is in..ama gonna be sniffing solder fumes this weekend..whee.. been missing it for a while now

 

[jdkJake]

I was going to order the anteks yesterday, but thought i should wait to see how jdk works out.
The next size up antek 0532 "specs" out 1.5V higher at about the same current, 31.5V @0.7A versus 30V @0.79A. That should get the secondaries up to 30V.
 
I think i will order that one. Anyone have a strong feeling that is dunb?

Realize, the antek I am using is rated 32V/400mA. The 30V spec is from their load test on the spec sheet, so, it might be questionable on how it actually performs at that load (well, I guess that is already obvious).

Just be prepared as I suspect the next model up (which is double in rating) might be too much. Hard to say. The nicest thing I can say about them at this point is they are cheap. So, you do not lose a whole lot if it does not work. Then again, you do not want to damage the amp to find out. Tough call.