[sachu]

I just ordered a coupleof the hammonds that were on the BOM. Should do fine IMO.

 

[studeb]

going dual mono?

 

[sachu]

The board is designed for that..so figured might as well. The two hammonds work out a hair cheaper than a single toroid. And i think i'll take a hammond over an Antek any day.

 

[jdkJake]

The board is designed for that..so figured might as well. The two hammonds work out a hair cheaper than a single toroid. And i think i'll take a hammond over an Antek any day.

Probably the wise choice.

 

[jdkJake]

 
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.
 

Okay, so here is my dilemma. While I would love to reduce the gain to get more travel on the pot, I have no desire to completely change the character of the sound. I like it just fine as it is thank you very much!  

 
So, is there a compromise point whereas I reduce the gain without requiring cap changes and possibly destroying the tonal character of the amp? Say, like around ~2k at R11 and perhaps around ~22k at R13/R14? How low can one expect to reasonably go without getting away from the intended design?
 
Tough question , I know, but, I had to ask. 

 

[runeight]

There is no good answer I'm afraid because it will just be a matter of degree. It may also be that you will not notice high NFB or even like it better. I just don't know.
 
Generally, with my amps I try to use minimum NFB possible for the given design because this, especially in hybrids, tends to let the tube's sound come through. Too much NFB seems to wash it out.
 
But I must admit that I haven't personally done a systematic set of listening tests with socketed resistors to create a progression of SQ changes that can be mapped against resistor changes.
 
Your resistor combination won't require cap changes.

 

[jdkJake]

Quote:

There is no good answer I'm afraid because it will just be a matter of degree. It may also be that you will not notice high NFB or even like it better. I just don't know.
 
Generally, with my amps I try to use minimum NFB possible for the given design because this, especially in hybrids, tends to let the tube's sound come through. Too much NFB seems to wash it out.
 
But I must admit that I haven't personally done a systematic set of listening tests with socketed resistors to create a progression of SQ changes that can be mapped against resistor changes.
 
Your resistor combination won't require cap changes.

 
Okay, thanks for the honest answer. I will have to think on it a bit. I really do not want to get into endless resistor combos.
 
So, I finally dragged the beast into my main listening area. I know I said I wouldn't do it, but, the new Gamma2 was just sitting there and I could not help myself (I am weak that way). Kicked up my favorite Grado test track "Master of Sparks". Yeah buddy! That's the kind! Ya know what I'm talking about!
 
This amp is good with my SR225's, but, it really shines with the HF-2's. By far, my favorite combo so far. I am starting to develop serious Grado ear, so, it is almost time to break out the HD650's.
 
In the meantime, it could be a long night....

 

[stringgz301]

I agree with you that it pairs extremely well with the HF2's.  Match made in heaven.

 

[runeight]

Gents, at this point are there 3 of you who have boards? jdk, stringg, and studeb??

 

[studeb]

i can only say i have mine

 

[runeight]

Thanks. That's three that have landed. I sent sachu's to the wrong address and ujamer and cobalt are waiting on Canadian post. Just checking.

 

[jdkJake]

Let's talk DC offset at power on.
 
I have been measuring it whenever I turn the amp on as well as doing some extra power cycles to get a better idea of how it behaves.
 
In general, most of the time it spikes somewhere between 1.25V and 1.5V. I have gotten one or two samples as high as 1.7V and *might* have seen as high as 1.9V, but, that might have been operator error, so, I am throwing it out. Like I said, most of the time it is between 1.25 and 1.5V. As for settling time, the amp is in double digit millivolt readings within 3 to 5 seconds upon power on. I would say offset is within single millivolt range in well under ten seconds.
 
So, tough call on the need for the epsilon 12 circuit. One could always double switch the transformers (separate switches for heater and rail power supplies as mentioned in earlier posts) or just wait a minute before plugging in the phones. I am probably going to build a couple of the epsilon 12 boards and use them just to be safe (and because I kind of want to build them).

 

[runeight]

Good data. I don't know if the settling time would actually improve if the tube was hot. This would depend on a number of factors in the way the rails come up, what charge is left in big capacitors, etc.
 
This in itself would be an interesting experiment. For anyone with lots of spare time.

 

[bada bing]

 
Quote:

Let's talk DC offset at power on.
 
I have been measuring it whenever I turn the amp on as well as doing some extra power cycles to get a better idea of how it behaves.
 
In general, most of the time it spikes somewhere between 1.25V and 1.5V. I have gotten one or two samples as high as 1.7V and *might* have seen as high as 1.9V, but, that might have been operator error, so, I am throwing it out. Like I said, most of the time it is between 1.25 and 1.5V. As for settling time, the amp is in double digit millivolt readings within 3 to 5 seconds upon power on. I would say offset is within single millivolt range in well under ten seconds.
 
So, tough call on the need for the epsilon 12 circuit. One could always double switch the transformers (separate switches for heater and rail power supplies as mentioned in earlier posts) or just wait a minute before plugging in the phones. I am probably going to build a couple of the epsilon 12 boards and use them just to be safe (and because I kind of want to build them).

Do you measure the offset across a load (headphone), or with no load resistance other than the DMM ? Does it make a difference ? The worst case scenario for offset is into low impedance, high efficiency cans like Grados. Do you get that kind of offset spike on turn on, measured across a 30 ohm load or only across an open circuit ?

 

[stringgz301]

Quote:

Good data. I don't know if the settling time would actually improve if the tube was hot. This would depend on a number of factors in the way the rails come up, what charge is left in big capacitors, etc.
 
This in itself would be an interesting experiment. For anyone with lots of spare time.

 
Settling time with tubes hot after 10 second power down is 20 seconds (to reach < 1 millivolt).  Peak voltage is around 2V.