here is a circuit i have been working on. it is based on the app notes for the ad815.
so far i have just completed one side to test it. it is showing promise.
I just decided to try it because it is an interesting circuit, and i dont really like the DRV134 sound-wise and i need a line driver for my noisy computer room where i have balanced input powered monitors.
I compared the DRV134 input and output at unity with 20mv/div and there are quite a few strange spikey things visible even with a sine wave. when i tried the same thing with this circuit it was almost a flatline with just a little (much less) noise.
Here is the pic of the DRV134 in/+out comparison
so far i have just completed one side to test it. it is showing promise.
I just decided to try it because it is an interesting circuit, and i dont really like the DRV134 sound-wise and i need a line driver for my noisy computer room where i have balanced input powered monitors.
I compared the DRV134 input and output at unity with 20mv/div and there are quite a few strange spikey things visible even with a sine wave. when i tried the same thing with this circuit it was almost a flatline with just a little (much less) noise.
Here is the pic of the DRV134 in/+out comparison
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Looks nice...
Why not try to get rid of the noise even more, using two transformers for higher voltages? Don't know what your exact problems are, but it will reduce noise. It ofcourse might add some colouring, but that's to your taste (or not)...
Why not try to get rid of the noise even more, using two transformers for higher voltages? Don't know what your exact problems are, but it will reduce noise. It ofcourse might add some colouring, but that's to your taste (or not)...
i would rather not use transformers except really good ones. i think this will work fine and be cheaper 🙂
peranders said:
The quiescent current is only supposed to be 55mA max. does that mean on each rail? if so thats about 1.6 watts total. what i do not know is if that amount of power can heat up the non heatsinked chip that much.
i do not think it is oscilating though because even if my scope can not see high frequencies. they make the trace blurred, and it seems fine. as an experiment i will try with and without 22PF rolloff caps across the feedback resistor.
anyways tomorrow is another day. it is a good start.
Heat
I have a dual chip running off a single +/-15 volt supply. It draws a total of 80 ma for the 2 chips. The CFM nulling circuit pulls another 5 ma on the positive rail.
An easy small heatsink is get a small pentium stick on sink. Then cut with a hacksaw to size. A regular one can yield 4 sinks for the AD815's.
Suspect you have a problem somewhere. Mine are barely warm, maybe 5 degrees C over room temp. The data sheet mentions local bypassing to prevent problems.
I was interested in building this circuit. I was told that the input impedance would need to be really low to get the offset down. Too low to drive with my sources.
Using output transformers was what I had in mind. Have an unused pair and was thinking of ways to use them with AD815's. Looked like it would require blocking caps and I did not want to go that route.
Let us know if you get the circuit from the first page of the app sheet working. I am interested in comparing it to the CFM circuit.
Would love to be able to use it to drive a transformer without caps or a nulling circuit. And still have a 25K input impedance. I do not want much.
George
I have a dual chip running off a single +/-15 volt supply. It draws a total of 80 ma for the 2 chips. The CFM nulling circuit pulls another 5 ma on the positive rail.
An easy small heatsink is get a small pentium stick on sink. Then cut with a hacksaw to size. A regular one can yield 4 sinks for the AD815's.
Suspect you have a problem somewhere. Mine are barely warm, maybe 5 degrees C over room temp. The data sheet mentions local bypassing to prevent problems.
I was interested in building this circuit. I was told that the input impedance would need to be really low to get the offset down. Too low to drive with my sources.
Using output transformers was what I had in mind. Have an unused pair and was thinking of ways to use them with AD815's. Looked like it would require blocking caps and I did not want to go that route.
Let us know if you get the circuit from the first page of the app sheet working. I am interested in comparing it to the CFM circuit.
Would love to be able to use it to drive a transformer without caps or a nulling circuit. And still have a 25K input impedance. I do not want much.
George
what i have found is even with a couple of ramsinks on the AD815s it is not getting hot anymore just a bit warm. (got up to about 28-30c and my room is 21c) i think that is about right for the 1.5 watt or so it will be dissipating with 15v supply. remember thats 2 halves running at once.
the previous temperature was with no heatsinks. the ones in the pic are on the regulators. the AD815s were bare.
as for the ofset i have found that by changing a resistor to ground on the input you can perfectly balance the amount of DC on both sides. as far as i figure you can not use a normal nulling circuit on this because when one ofset is decreased the other is increased and vice versa.
there is no way this will work with a volume pot in front of it. I am planning this one to go after a kookaburra but it must have a buffer between any pot you use before this circuit.
AD815 seem to be peretty consistant with DC offset so i will provide the actual resistance i needed if not using a trimmer once i finalise things.
once the amount of DC is equalised it really shouldnt matter that it is there at all. because if they are both the same the reciever should ignore them (thats how balanced works after all)
the previous temperature was with no heatsinks. the ones in the pic are on the regulators. the AD815s were bare.
as for the ofset i have found that by changing a resistor to ground on the input you can perfectly balance the amount of DC on both sides. as far as i figure you can not use a normal nulling circuit on this because when one ofset is decreased the other is increased and vice versa.
there is no way this will work with a volume pot in front of it. I am planning this one to go after a kookaburra but it must have a buffer between any pot you use before this circuit.
AD815 seem to be peretty consistant with DC offset so i will provide the actual resistance i needed if not using a trimmer once i finalise things.
once the amount of DC is equalised it really shouldnt matter that it is there at all. because if they are both the same the reciever should ignore them (thats how balanced works after all)
Member
Joined 2002
the DRV134 it doesnt transparently drive the signal.
try half of the DRV signal and ground as a source..it sounds crap.
it has all kinds of rubbish output and relies on the balanced reciever to ignore all the (see first post)
look at that sine wave with noise and odd peaks. ad815 is much cleaner. i did not post AD osc graph because it was a boring straight line
THe reciever may work fine and cancel it but what if the signal it has to cancel is close to peak level. and say a bit of good sound is happening right near one of those peaks.. bad news! wouldnt you prefer stable output?
try half of the DRV signal and ground as a source..it sounds crap.
it has all kinds of rubbish output and relies on the balanced reciever to ignore all the (see first post)
look at that sine wave with noise and odd peaks. ad815 is much cleaner. i did not post AD osc graph because it was a boring straight line
THe reciever may work fine and cancel it but what if the signal it has to cancel is close to peak level. and say a bit of good sound is happening right near one of those peaks.. bad news! wouldnt you prefer stable output?
Member
Joined 2002
neutron7 said:
I was just about to make a DRV134 board. I wonder if you should share yoyur schematic. I have some good ideas for something. Maybe PM Me!
neutron7 said:
What are you powering this with -- looks like some switching noise permeating through -- have you used the 1uF tantalum (and perhaps 10 or 100nF ceramic?) -- seems that you are using film caps. The DRV134 should not perform that badly.
one more thing -- get a cookie tin to put the device in when measuring -- you can pick up all sorts of noise (computer power supply, noise from the mains, diode swithcing noise) -- this looks like a switching power supply interference.
fwiw, I prefer the Danish cookie tins, (but my wife bought a pannetone from Italy at Christmas and you can fit darn near a whole amplifier in the thing.) I have some insulated BNC's that are attached to the side of the cookie tin with some RG58 cables inside that attach directly to the DUT.
I need to look at the posts closer
I had assumed the circuit you were using is the one on the first page of the app sheet. This the one that I heard required 50 ohm loading to control offsets.
I am going to build one of these if I ever get back home with time to build something. Have a line sitting unused with input and output transformers. I am thinking of trying the simplier circuit shown on page 1 if it will work okay with the pot in front of the input transformer and using the iron to do the SE to differential.
May be impossible to achieve, using the CFM circuit it was audible once input offset climbed to 0.3 mv. That was into about 3K ohms, so 0.1 ua of current seemed to be saturating the input transformers. Readjusted to get it down to 0.1 mv and the hardness and etch went away.
The output iron can handle a little more, but still more than a couple mv will cause the same issues.
Would love to figure out a way to drive output iron with the AD815. Without blocking caps, and into audio level oads. Maybe I am a dreamer.
George
I had assumed the circuit you were using is the one on the first page of the app sheet. This the one that I heard required 50 ohm loading to control offsets.
I am going to build one of these if I ever get back home with time to build something. Have a line sitting unused with input and output transformers. I am thinking of trying the simplier circuit shown on page 1 if it will work okay with the pot in front of the input transformer and using the iron to do the SE to differential.
May be impossible to achieve, using the CFM circuit it was audible once input offset climbed to 0.3 mv. That was into about 3K ohms, so 0.1 ua of current seemed to be saturating the input transformers. Readjusted to get it down to 0.1 mv and the hardness and etch went away.
The output iron can handle a little more, but still more than a couple mv will cause the same issues.
Would love to figure out a way to drive output iron with the AD815. Without blocking caps, and into audio level oads. Maybe I am a dreamer.
George
panelhead
if you make the offset equal. you can drive a transformer without caps. if both ends see -20mv its the same as both ends seeing 0v
jackiinj:
the spikes are cyclic with the wave.
the PSU is regulated linear with bridge rectifier + 1000uf per rail before and 100uf after the regulators. there is 0.1 UF MKS caps right by the power pins but the chip is not sheilded in the test though.
Would not sheilding it cause cyclic spikes like that? the AD was tested with the same PSU and physical location. the only thing near by with a PSU is the ocilloscope and soldering station (which i switched off and it made no difference). i dont know if scope has a switching PSUbut it has not effected any other thing i test in that way.
I think there must be something wrong with my test circuit as well. but cant see what. it is the same as shown in the data sheet with 300 ohm output resistors and 600 ohm load across the outputs.
I will try the tin and see if it helps.
Elso Kwak unfortunately the square wave output of my el cheapo max038 function generator already has a bit of ringing and when i feed anything with it the ringing just gets worse.
i have a nicer square wave on the scope test output but its only at 1khz.
ill try the i/0 test with that and post it in a while whan my camera is recharged however none of my sources can make much of a square wave at 20khz anyways!
if you make the offset equal. you can drive a transformer without caps. if both ends see -20mv its the same as both ends seeing 0v
jackiinj:
the spikes are cyclic with the wave.
the PSU is regulated linear with bridge rectifier + 1000uf per rail before and 100uf after the regulators. there is 0.1 UF MKS caps right by the power pins but the chip is not sheilded in the test though.
Would not sheilding it cause cyclic spikes like that? the AD was tested with the same PSU and physical location. the only thing near by with a PSU is the ocilloscope and soldering station (which i switched off and it made no difference). i dont know if scope has a switching PSUbut it has not effected any other thing i test in that way.
I think there must be something wrong with my test circuit as well. but cant see what. it is the same as shown in the data sheet with 300 ohm output resistors and 600 ohm load across the outputs.
I will try the tin and see if it helps.
Elso Kwak unfortunately the square wave output of my el cheapo max038 function generator already has a bit of ringing and when i feed anything with it the ringing just gets worse.
i have a nicer square wave on the scope test output but its only at 1khz.
ill try the i/0 test with that and post it in a while whan my camera is recharged however none of my sources can make much of a square wave at 20khz anyways!
" Cyclic spikes " are only crossover distortion and they only show, how s..t is this circuit... 😉
hmm. the test seems to be in question. i think that testing the in.out with 1mohm scope input
i think is causing feedback in the circuit itself which screws up the results. I guess would have to build a preamp with super high input impedance to test it properly.
anyways i still dont like the sound of the DRV even if ai cant prove why i think it makes the sound kind of dull. which of course i can not explain 🙂
logic and facts will not stop the BEEFY AD815 LINE DRIVER! i like the AD815 preamp i allready made (carlos style) so much that a line driver version seems like what i want.
Upupa Epops the circuit showing the spikes is the DRV line driver chip. the AD815 does not do it. and i dont think its crossover distortion becaus a spike happens almost on the middle of the flat part of a square wave
i think is causing feedback in the circuit itself which screws up the results. I guess would have to build a preamp with super high input impedance to test it properly.
anyways i still dont like the sound of the DRV even if ai cant prove why i think it makes the sound kind of dull. which of course i can not explain 🙂
logic and facts will not stop the BEEFY AD815 LINE DRIVER! i like the AD815 preamp i allready made (carlos style) so much that a line driver version seems like what i want.
Upupa Epops the circuit showing the spikes is the DRV line driver chip. the AD815 does not do it. and i dont think its crossover distortion becaus a spike happens almost on the middle of the flat part of a square wave
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