![ad815_with_headphone_amp[1].jpg](/community/data/attachments/57/57231-616ddb63a575851b18afd33e5a192792.jpg)
GeorgeBoles
An easier soldering package
http://www.bgmicro.com/prodinfo.asp...5310&prodid=AD815AYS&page=1&cri=ad815&stype=3
An easier soldering package
http://www.bgmicro.com/prodinfo.asp...5310&prodid=AD815AYS&page=1&cri=ad815&stype=3
Carlos, I am currently gathering the parts to try out your preamp. Could you please let me know why you put so much efforts in nulling the DC offset? I mean, you have a DC blocker on the output anyway (if you dont use the direct output shown). Did you ever try it without the additional circuit?
Mick
Mick
Mick_F said:
Mick, I use the direct output (I said that a few days after posting the original schematic), because I have input coupling caps on my power amp.
Otherwise I would use the output caps on the pre.
Don't cascade coupling caps, you will notice the veil right away.
Anyway, my pre has two outputs, one direct, one with the caps.
The output with the caps I'm using to feed the sub.
As I said initially, the efford to null DC-offset (which is null on the output on one point of the volume pot that you adjust, it will range from negative to positive, but low value) was to also null the input dc-offset that these chips have.
Normal on current-feedback op-amps.
Otherwise I would easily solve the problem by using input coupling caps, or an input buffer stage. And that was out of the question.
AD815AYS - interesting package.
Dear JAudio,
Thank-you for that link to the AD815 in a package similar to an LM3886. (It is quite a good price too.)
But why doesn't this package show up on the Analog Devices site?? Is it obsolete or is it somebody's copy/counterfeit or am I just slowly going loopy?
Regards,
George.
Dear JAudio,
Thank-you for that link to the AD815 in a package similar to an LM3886. (It is quite a good price too.)
But why doesn't this package show up on the Analog Devices site?? Is it obsolete or is it somebody's copy/counterfeit or am I just slowly going loopy?
Regards,
George.
Here the application note. I couldnt find it on the AD website.
http://www.analog.com/productSelection/pdf/AD815_b.pdf
http://www.analog.com/productSelection/pdf/AD815_b.pdf
Here's a pcblayout i was thinking about trying, but don't mind the groundplane it's not like this anymore i just havent render a new image 
http://www.ettnet.se/~tobias/diy/ad815/ad815_1.jpg
http://www.ettnet.se/~tobias/diy/ad815/ad815_3.jpg
Cheers
http://www.ettnet.se/~tobias/diy/ad815/ad815_1.jpg
http://www.ettnet.se/~tobias/diy/ad815/ad815_3.jpg
Cheers
Tobias,
Nice looking renderings. I don't know the first thing about designing a PCB layout, but it looks pretty cool, anyway.
Do the LM317's and AD815 run cool enough for them to be packed in so tightly?
If things all work out well, how would you feel about a group buy? I'm sure there are a bunch of us who would love to build this preamp!
Best,
KT
Nice looking renderings. I don't know the first thing about designing a PCB layout, but it looks pretty cool, anyway.
Do the LM317's and AD815 run cool enough for them to be packed in so tightly?
If things all work out well, how would you feel about a group buy? I'm sure there are a bunch of us who would love to build this preamp!
Best,
KT
KT said:
The LM317/337 regs are no problem.
The AD815 needs a small heatsink. This version runs cooler than the SMD chip, but I always use a heatsink.
Besides a preamp, this can also be used as a headphone amp.
High-end, I must say.
In either case (specially as a headamp) it will need a small heatsink.
Newbie questions: Voltage In, diodes
Hello again Carlos,
Regarding the power supply for this pre-amp:
1.) I note that you are using a 2 * 20V transformer. Does your unregulated supply give you about 28V DC or is it a bit lower with all the R's in the RCRCC?
2.) What would be the minimum unregulated voltage you would consider feeding into the LM317/337?
3.) What do you use as diodes D1 and D2?
All this and not a snubber in sight!
I am trying to get some AD815's soon, but they will not arrive before Christmas. In the meantime, I might quickly make up a Nelson Pass NS10 clone, perhaps with your power supply.
Regards,
George.
P.S. I've got to get a pre-amp going so I can enjoy the Carlosfm LM3886 amps to their best!
Hello again Carlos,
Regarding the power supply for this pre-amp:
1.) I note that you are using a 2 * 20V transformer. Does your unregulated supply give you about 28V DC or is it a bit lower with all the R's in the RCRCC?
2.) What would be the minimum unregulated voltage you would consider feeding into the LM317/337?
3.) What do you use as diodes D1 and D2?
All this and not a snubber in sight!
I am trying to get some AD815's soon, but they will not arrive before Christmas. In the meantime, I might quickly make up a Nelson Pass NS10 clone, perhaps with your power supply.
Regards,
George.
P.S. I've got to get a pre-amp going so I can enjoy the Carlosfm LM3886 amps to their best!
Hi Carlos,
I was reading about How Tom Evans' Vibe Lithos 7 preamp uses a current feedback output stage and immediately thought about your AD815 preamp. There's some interesting notes about the Lithos regulator he designed for it and thought it would be good fodder for discussion since both pre's feature a current feedback design.
from this review:
http://www.6moons.com/audioreviews/tomevans2/vibe.html
...Tom's output stage uses current rather than voltage feedback to insure faster rise and recovery times (less than 10 nanoseconds), made possible because of the ultra-high performance Lithos regulators. With conventional voltage regulators, noise is too high to allow for this approach. Power supply noise would cause a significant reduction in resolution and dynamic range. However, "the intelligent use of current feedback enabled by Lithos regulation is a key feature in producing a more lifelike presentation because it greatly improves linearity and bandwidth. The Lithos regulation makes this possible by rejecting noise before it reaches any gain stages. Noise is eliminated and speed and resolution are far in advance of most designs as a result...
Not much detail is given about the Lithos regulator, but maybe someone knows something about it.
Best,
KT
I was reading about How Tom Evans' Vibe Lithos 7 preamp uses a current feedback output stage and immediately thought about your AD815 preamp. There's some interesting notes about the Lithos regulator he designed for it and thought it would be good fodder for discussion since both pre's feature a current feedback design.
from this review:
http://www.6moons.com/audioreviews/tomevans2/vibe.html
...Tom's output stage uses current rather than voltage feedback to insure faster rise and recovery times (less than 10 nanoseconds), made possible because of the ultra-high performance Lithos regulators. With conventional voltage regulators, noise is too high to allow for this approach. Power supply noise would cause a significant reduction in resolution and dynamic range. However, "the intelligent use of current feedback enabled by Lithos regulation is a key feature in producing a more lifelike presentation because it greatly improves linearity and bandwidth. The Lithos regulation makes this possible by rejecting noise before it reaches any gain stages. Noise is eliminated and speed and resolution are far in advance of most designs as a result...
Not much detail is given about the Lithos regulator, but maybe someone knows something about it.
Best,
KT
Re: Newbie questions: Voltage In, diodes
George, power consumption is low, the drop in voltage because of the resistors is very low.
I would recommend a trafo of 2x18V.
1N400x
This was made before I started using snubbers, and I don't open the pre for a long time.
Performance is very good as it is now, which is not to say that it can't be improved.
But it can't get much better than this, IMO.
GeorgeBoles said:
George, power consumption is low, the drop in voltage because of the resistors is very low.
I would recommend a trafo of 2x18V.
GeorgeBoles said:
1N400x
GeorgeBoles said:
This was made before I started using snubbers, and I don't open the pre for a long time.
Performance is very good as it is now, which is not to say that it can't be improved.
But it can't get much better than this, IMO.
KT said:
KT, without any details and with such an elaborated text, that looks like marketing talk, copied from the manufacturer's user manual or publicity, something that reviewers do very often...
Here's an example:
"The Lithos regulation makes this possible by rejecting noise before it reaches any gain stages."
Geez...
This PSU rejects noise. Revolutionary...
This is my AD815 preamp-headphone amp. It is dual mono,one half is the preamp and the other half is the headphone amp.
I have listened to the amp for a few minutes,I can say it sound very promising. Im getting some hiss from one channel,when it is connected to my bridged OPA549 amp(It maybe the amp. that channel does have fits once in awhile). If you use the AD815 as a headphone amp,dont set the gain as high as you will normally would.
I have listened to the amp for a few minutes,I can say it sound very promising. Im getting some hiss from one channel,when it is connected to my bridged OPA549 amp(It maybe the amp. that channel does have fits once in awhile). If you use the AD815 as a headphone amp,dont set the gain as high as you will normally would.
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