the 100k is good to have but does not affect the DC servo
the AD815 gets very hot. do you have a DIP or a SMD device. either way you can't get away from this device running hot. the safe cut off only occurs at 180 deg C . i am running mine now without any heatsink, I just use the copper around the device to assist with the cooling, see here
did you use a heatsink and did you have any DC on the output?
the AD815 gets very hot. do you have a DIP or a SMD device. either way you can't get away from this device running hot. the safe cut off only occurs at 180 deg C . i am running mine now without any heatsink, I just use the copper around the device to assist with the cooling, see here
did you use a heatsink and did you have any DC on the output?
Im using the dip package.rudi said:
rudi said:
Yes Im using a 4"x1"x.25" and 1/8"x3"x.75" pieces of aluminum with two ad815 sandwiched bewteen.
Dc is .2mv but the heat worries me. I never had a chip get that hot.
Another problem is when the pot is turn completely to the right,I get nothing but noise.
can you post a picture of you heatsink implementation. generally you shouldn't use a solid piece, you do want to have some fooling fins and it should be black. natural aluminium only radiates about approximately 20% of the same piece that has been blackend. (sprayed or anodized)
then regarding the noise. if you implemented the circuit to the "T' then I would maybe change the volume control, you do get some dodgy ones.
then regarding the noise. if you implemented the circuit to the "T' then I would maybe change the volume control, you do get some dodgy ones.
why are you using two? are you just using one half of each. (i like the idea of that, thought of it before but dumped the idea later on due to practical reasons.)did you configure if for 800mA.
to solve the heat problem. spray the heatsink black. but you will still have them running a bit hot. if you can touch them for 10sec before burning blisters you OK
just thought if something else. you might have a hairline short (just a thin wire touching where it shouldn't) somewhere and that could cause another 1000 problems. so go through all your tracks and connections to see that everything is "short" free
to solve the heat problem. spray the heatsink black. but you will still have them running a bit hot. if you can touch them for 10sec before burning blisters you OK
just thought if something else. you might have a hairline short (just a thin wire touching where it shouldn't) somewhere and that could cause another 1000 problems. so go through all your tracks and connections to see that everything is "short" free
It is a dual mono pre/headphone amp.
I had no idea the chip would run that hot. Wouldnt that cause the chip to die prematurely?
I had no idea the chip would run that hot. Wouldnt that cause the chip to die prematurely?
jaudio said:
The SMD version runs warm, but the DIP version runs very cool.
On the DIP version I used a heatsink, and it doesn't even get warm.
You may have some oscillation problem there.
Unless you did it under the board, I don't see any PSU bypass caps near the chips. They are at a couple of centimeters, which for such a fast chip is like kilometers.
Put some small ceramics there, right on the chip's pins.
Also, 100~330nF across the rails, directly solderend on the chip's pins.
Hi Carlos
My preamp run cool without the servo. With the servo it's another story,I get low dc offset(.2mv) but a h*ll of alot of heat. Rudi says
My preamp run cool without the servo. With the servo it's another story,I get low dc offset(.2mv) but a h*ll of alot of heat. Rudi says
rudi said:
rudi said:.
to solve the heat problem. spray the heatsink black. but you will still have them running a bit hot. if you can touch them for 10sec before burning blisters you OK
that is very strange. it could be your implementation of the dc servo. maybe you should go over that again. i get the same heat ouput with and without the servo. check for obvious stuff first.
Rudi
I will check the servo board again and test it on a LM3886 board.
I didnt completely disconnect Carlos' dc null circuitry,I just disconneted the (+) supply. I will try completely disconnecting that circuit.
In mv what is the dc on your output?
I will check the servo board again and test it on a LM3886 board.
I didnt completely disconnect Carlos' dc null circuitry,I just disconneted the (+) supply. I will try completely disconnecting that circuit.
In mv what is the dc on your output?
Hi jaudio
my multimeter gives me 0,1mv, but that could be lower according to calulations - (it should be 0.025-0.030mv). seeing that i can't measure lower than 0,1mv.
my multimeter gives me 0,1mv, but that could be lower according to calulations - (it should be 0.025-0.030mv). seeing that i can't measure lower than 0,1mv.
Mono application
I finished a stereo version using the nulling circuit yesterday. It works pretty well, but the input and output dc are still a function of pot position. Couple of mv, not enough to harm anything though.
Sonically it is very nice. Maybe better once all the new parts settle in. It is very quiet, and full bodied sounding with no run in.
Considered building a mono version also. Maybe next time. How did you terminate the unused channels? The possiblity of ringing, and other nasties makes me wonder if it will yield any real improvements.
If I build another it will be mono, maybe a buffer also. This chip in the dip version is very easy to work with. Originally I had planned on just clipping off the unused pins. This most likely would have been a disaster sonically.
George
jaudio said:
I finished a stereo version using the nulling circuit yesterday. It works pretty well, but the input and output dc are still a function of pot position. Couple of mv, not enough to harm anything though.
Sonically it is very nice. Maybe better once all the new parts settle in. It is very quiet, and full bodied sounding with no run in.
Considered building a mono version also. Maybe next time. How did you terminate the unused channels? The possiblity of ringing, and other nasties makes me wonder if it will yield any real improvements.
If I build another it will be mono, maybe a buffer also. This chip in the dip version is very easy to work with. Originally I had planned on just clipping off the unused pins. This most likely would have been a disaster sonically.
George
It is a dual mono preamp( half of ad815) and headphone amp(the other half)
I choose dual mono because the power supply is setup that way,It is the same power supply for my monoblock amps(different windings). I add the headphone am just because a did not want half the ad815s to go unused.
I choose dual mono because the power supply is setup that way,It is the same power supply for my monoblock amps(different windings). I add the headphone am just because a did not want half the ad815s to go unused.
I have to say having built a BrianGT/CarlosFM LM3886 kit, a Amp3 kit and Nuuks 3 transistor buffer /PSU design for scratch i thought I was well versed in building other people designs. However this thread has me completely stumped. T
he thing is a really need a preamp with gain for all of my power amps and i really want to build something really good since the rest of my setup i think sounds excellent yet i cannot follow this thread. More specifically I cannot undestand the initial curcuit diagram since the psu seems to go into the input of the ad815.
Also no one seem to have posted a full pcb layout with component values so as such I am stumped.
Shoudl i give up on the idea of building this preamp and select something easier to build such as the single Jfet preamp design (Carlos again) the Nuuk has kindly posted over at DD. How would such a design compare?
Any help very gratefully recieved,
Phil
he thing is a really need a preamp with gain for all of my power amps and i really want to build something really good since the rest of my setup i think sounds excellent yet i cannot follow this thread. More specifically I cannot undestand the initial curcuit diagram since the psu seems to go into the input of the ad815.
Also no one seem to have posted a full pcb layout with component values so as such I am stumped.
Shoudl i give up on the idea of building this preamp and select something easier to build such as the single Jfet preamp design (Carlos again) the Nuuk has kindly posted over at DD. How would such a design compare?
Any help very gratefully recieved,
Phil
Panelhead
Can you explain why you think this would give a sonic disaster? As I was planning to do the same. (Clipping not building double mono)
George thanks in advance for an explanation of your thoughts/know-how.
E&E
Can you explain why you think this would give a sonic disaster? As I was planning to do the same. (Clipping not building double mono)
George thanks in advance for an explanation of your thoughts/know-how.
E&E
Attachments
Like i said in my first post i do not understand the layout of that diagram so sending me the same diagam again and the AD spec sheet which i had already Downloaded as a beginner isnt what i would call helpful.
Anyway look like the jfet for me
Phil
Anyway look like the jfet for me
Phil
filholder said:
Phil, the single Jfet preamp is much easier to build, I recommend that to you.
Btw I didn't publish any PCB layout for the AD815 simply because I didn't make it, and I don't have the time to make it now, unless I need it. But I'm doing other things.
My prototype ended up inside my pre, and it has been working wonderfully since then.
I do things for pleasure and for me, and then I share, if I want to.
Take what's available and make your own if you want, that's the spirit, that's why I shared it.
You'll learn something in the process, and that's 😎
PS: This was not intended to be a mass-market product, there are no kits available, and I don't sell anything.
Good things are hard to get. 😀
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