[minez]

sachu, do we need to unplug the headphones before turning on or off for all kind of headphone amps? Or most of headphones amp got dc offset protection circuit? Thanks.

 

[sachu]

I do it for any and all amplifiers.

 

[minez]

Thanks sachu

 

[cfcubed]

minez - Pick "Search This Thread" and search for e12 for info on this in context of this amp.
 
Seems most amps w/tubes in them could use at least a pwr on delay/pwr off output relay latch circuit if not more advanced offset protection.  Seems most DIY amps do not incorp them by default in favor of leaving it to the builder's option (to add something like amb e12, or as simple as 555 delay relay for example).
The potential for DC offset esp. during pwr up / pwr down cycles is known to the DIY community (builders) based on the device's design.  If you bought & did not build the amp the seller should've made you aware of this.  
In any event, many users do choose to manually disconnect / re-connect headphones at pwr on / pwr off even for amps with delay/protection features or even for amps with little or no DC offset potential.

 

[funch]

Quote:

What size standoffs does everyone recommend? I have a 3" tall par metal enclosure, and the glassjar kit. I was thinking 1/2 in for better airflow than 1/4 inchers, but will that fit in a 3" tall case with the heatsinks and tubes?

Quarter inch should be fine.
 
 
 

 

[jdkJake]

What size standoffs does everyone recommend? I have a 3" tall par metal enclosure, and the glassjar kit. I was thinking 1/2 in for better airflow than 1/4 inchers, but will that fit in a 3" tall case with the heatsinks and tubes?

Not sure you can make the 1/2 in work. It is pretty tight. Better safe with the 1/4 in.

 

[iamthecheese]

I'll go with the 1/4 inchers just to be safe, thanks guys!

 

[iamthecheese]

Well my amp is mostly done, but full of all sorts of problems.
 
The tube heater circuit outputs correctly, and the tubes heat. The PSU outputs around +-27V. When I power the amp up dc offset jumps too 3.6V, and settles to around 3.0V. When I initially checked the bias, it read at 60 mv, and as I started turning the trimpot it spiked to between 18-19V, went back down to around 1.5V. Then I freaked out and turned it off. I have a 2 stage power switch and I let the tubes heat for about a minute before powering on the main rail. Turned it on again and reading was back around 100 mv, the heatsinks on the amp part are barely getting warm though, not as much as I would expect...

 

[jdkJake]

So, did you follow the initial setup sequence exactly and verify each stage of the build?
 
   http://www.cavalliaudio.com/diy/ehhaa/main.php?page=setup/setup
 
How are you measuring DC offset?
 
Pictures would help as well.

 

[jdkJake]

Also, check and verify the orientation of the DC servo opamp (IC1). Make sure pin1 of the device is oriented properly.

 

[iamthecheese]

I'll get some pictures tomorrow, but I am following the Cavalli instructions
I pretty much get to this part(Rail supply reads around 27 VDC, tube heater output is 6.30VDC) :

Amp Power Up

Look for smoke. If there is none, proceed.
Wait for the output DC to settle into the low mV range. If this does not happen the servo is not working. Stop and turn off the power.
 
I measured it from the out terminal to the group terminal on the amp board.
The op amp was warm, but not like burning hot or anything.
I'll try to get a hi-res picture with a dslr tomorrow.
 
Its actually only 1 board, since I'm waiting on some parts for the other one.

 

[sinae]

If i buy the EHHA revA kit and follow all instruction to the letter. I wonder if I can do that in my first diy but its an interesting challenge.. I would sure learn a lot
 
iamthecheese did you find a way to fix your problem?
 
From the pictures I saw of your diy project i'm wondering if it would be easy to create an external power supply with that transformer..
So the amp would be in two pieces.. What your opinions on this?
 
I find those diy boxes a little too big for me.

 

[iamthecheese]

I haven't had a chance to look at it yet, I've been packing to go move back for college.
 
I wouldn't really recommend this for a first project, I started with a minimax kit(great for first ambitious DIY'ers), then did an opus dac, then this.

 

[sinae]

cool thx for your reply. Im gonna think about this then

 

[jdkJake]

Quote:

 
I measured it from the out terminal to the group terminal on the amp board.

What do you mean when you say group terminal?
 

 
You can measure DX offset across O2 and O3 of the terminal block where power enters the amp and output exits. What is the measurement at that point?