What is "neits" ?!
I do appreciatie simple things but it was Einstein that said: "Everything should be made as simple as possible, but not simpler".
There is not too much wrong with using either ICs, MOSFETs or JFETS for a buffer. I think you are chasing ghosts. Your circuit has too low supply voltage and it is asymmetrical. It has not enough headroom, needs 2 coupling capacitors, can not accept 600 Ohm loads and it can not accept capacitive loads (that is a showstopper).... Too simple. It maybe is a good idea to compare it to a different solution that does accept 2V rms signals (as that is the standard with almost all ready made stuff). The Kuartlotron for instance... Don't be afraid, it has +/- 10V power supplies but nothing bad will happen.
http://www.diyaudio.com/forums/anal...kens-simple-error-correction-superbuffer.html
Change that to 2V rms and recalculate if you like as here is the root of miscalculations. Analog tape recorders are at least 30 years old ! 0.3V rms is the old line voltage of then (probably came from the dreadful DIN plugs/standard). Now is is 2V rms and all devices you couple to your gear are made for that. You will notice immediately when switching sources from analog tape recorder to a DAC or CD player. For once the industry unanimously chose to go on with 2Vrms. I do recall the time that switching sources from a tuner to a CD player got your speakers smoking
I do appreciatie simple things but it was Einstein that said: "Everything should be made as simple as possible, but not simpler".
There is not too much wrong with using either ICs, MOSFETs or JFETS for a buffer. I think you are chasing ghosts. Your circuit has too low supply voltage and it is asymmetrical. It has not enough headroom, needs 2 coupling capacitors, can not accept 600 Ohm loads and it can not accept capacitive loads (that is a showstopper).... Too simple. It maybe is a good idea to compare it to a different solution that does accept 2V rms signals (as that is the standard with almost all ready made stuff). The Kuartlotron for instance... Don't be afraid, it has +/- 10V power supplies but nothing bad will happen.
http://www.diyaudio.com/forums/anal...kens-simple-error-correction-superbuffer.html
Change that to 2V rms and recalculate if you like as here is the root of miscalculations. Analog tape recorders are at least 30 years old ! 0.3V rms is the old line voltage of then (probably came from the dreadful DIN plugs/standard). Now is is 2V rms and all devices you couple to your gear are made for that. You will notice immediately when switching sources from analog tape recorder to a DAC or CD player. For once the industry unanimously chose to go on with 2Vrms. I do recall the time that switching sources from a tuner to a CD player got your speakers smoking
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When the sun is up, and when it is down, this circuit does fine for building gyrators. It can output 2Vrms, Jean-Paul, up to 4Vrms with smaller work or a larger load resistance. All things should be easily explainable, as this circuit is, and as most ICs and MOSFETs are not. Recent behaviour is not always better than old-fashioned one, and i do not cheerish every new-born human being.
Just briefly addressing my keyboard issue again, please bear with me...
Here's the service docs. DAC AK4385, opamp BA4580RF, A and D all fed from PQ050RDC1SZF (which does seem to be some kind of LDO?), headphone out is the classic speaker amp tap from BA5417 @ +35.5 dB. HP coupling caps 47µ, speaker 470µ (cost-cutting, original design + next bigger model use 1000µ and there is enough space for them on the board).
Oh, it does (ask most any classic integrated amp/receiver)... with some unfortunate side effects. Internal series R is 100R, my attenuator is about 100R series / 15R parallel if memory serves. Gets just about loud enough with HD580s connected.So instead of solving the hissing it is attenuated ?! You don't work at VW do you ?
It's an inexpensive keyboard that's probably just using 12-bit (nonlinear) samples anyway (and a reasonably unexciting set at that). Standards for these devices aren't the same as for hi-fi gear. You're still getting 80-something dB into a line-level input if you do the math.
Here's the service docs. DAC AK4385, opamp BA4580RF, A and D all fed from PQ050RDC1SZF (which does seem to be some kind of LDO?), headphone out is the classic speaker amp tap from BA5417 @ +35.5 dB. HP coupling caps 47µ, speaker 470µ (cost-cutting, original design + next bigger model use 1000µ and there is enough space for them on the board).
Yeah as said the series resistor does not improve things. It attenuates the noise that is not solved. There are many ways to really improve this device but maybe it is a good exercise for you to check what can be done.
You can change the feedback resistors connected to pin 10 and 13 of the BA6417 and have gain reduced the way technical people would do it. Better solution. Up the output caps to 1000 µF.
I would separate Vd and Va and create a Va2 by using 2 x 5V and 1 x 6V (New Va2 for the output stage) ultra low noise LDO and I would replace the 2.5V and the 3.3V regulators by ultra low noise versions. So IC131 and IC132 could be replaced. Both are industrial regulator ICs with no noise numbers published. Selected for 1 parameter: cheap.
Output stage voltage should be upped to 6V as proposed earlier and use an SMD coil to offer LC filtering to the new low noise opamp I would solder in. I would use the pads of R451/452 to solder the new 6V to. Depends on how it is done, maybe the pads can be used for a TH coil and the PCB track to 5V can be cut.
If it was my device i would see a challenge in improving it. Depending on how the boards are designed (and if distances can be kept short and if pin compatible low noise replacements can be found) I probably would design a very small regulator PCB with all the replacement regs. I would choose lowest noise LDO regs I could find. Preferred way would be to find pint compatible versions for IC131 and IC132. The new PCB could be for 2 x 5V and 1 x 6V regulators. Only a design of a few cm in size. Or leave the PQ050RDC1SZF for 5V digital supply and only add 1 x 5V for Va and 1 x 6V for Va2.
Note 1: The output stage needs a bias network as described in the AK4385 data sheet (when using on a single power supply as is done in this device). It is a network of 3 extra resistors and 2 caps so easy to implement. Output stage should be able to swing full output voltage so DC bias is necessary.
Note 2: Main source of noise can be the ADCS7478 but no other replacements exist. This is already a replacement version. It needs very good decoupling at pin 1 so improvement can be done. It needs a low noise power supply which it now hasn't. I think I would use LC filtering with a small SMD coil and a larger cap to pin 1 in parallel to C901 combined with the already mentioned better 3.3V reg.
You can change the feedback resistors connected to pin 10 and 13 of the BA6417 and have gain reduced the way technical people would do it. Better solution. Up the output caps to 1000 µF.
I would separate Vd and Va and create a Va2 by using 2 x 5V and 1 x 6V (New Va2 for the output stage) ultra low noise LDO and I would replace the 2.5V and the 3.3V regulators by ultra low noise versions. So IC131 and IC132 could be replaced. Both are industrial regulator ICs with no noise numbers published. Selected for 1 parameter: cheap.
Output stage voltage should be upped to 6V as proposed earlier and use an SMD coil to offer LC filtering to the new low noise opamp I would solder in. I would use the pads of R451/452 to solder the new 6V to. Depends on how it is done, maybe the pads can be used for a TH coil and the PCB track to 5V can be cut.
If it was my device i would see a challenge in improving it. Depending on how the boards are designed (and if distances can be kept short and if pin compatible low noise replacements can be found) I probably would design a very small regulator PCB with all the replacement regs. I would choose lowest noise LDO regs I could find. Preferred way would be to find pint compatible versions for IC131 and IC132. The new PCB could be for 2 x 5V and 1 x 6V regulators. Only a design of a few cm in size. Or leave the PQ050RDC1SZF for 5V digital supply and only add 1 x 5V for Va and 1 x 6V for Va2.
Note 1: The output stage needs a bias network as described in the AK4385 data sheet (when using on a single power supply as is done in this device). It is a network of 3 extra resistors and 2 caps so easy to implement. Output stage should be able to swing full output voltage so DC bias is necessary.
Note 2: Main source of noise can be the ADCS7478 but no other replacements exist. This is already a replacement version. It needs very good decoupling at pin 1 so improvement can be done. It needs a low noise power supply which it now hasn't. I think I would use LC filtering with a small SMD coil and a larger cap to pin 1 in parallel to C901 combined with the already mentioned better 3.3V reg.
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Question is : are you prepared to spend a few hours and maybe 20 Euro on improving ?
On second thoughts: the 2.5V reg can stay. No need to replace that one although it wouldn't hurt.
So essentially adding 1 x 5V and 1 x 6V regs, replacing a noisy 3.3V reg, replacing 2 feedback resistors, adding a bias network and some decoupling by coils and caps. IMO using a better low noise 3.3V reg and better decoupling of the ADC will solve some hiss and that would be first thing I would try together with the feedback resistors. Datasheet of the ADC indeed says to use a quiet supply which is very logical. When you have done this small mods and hear clear improvement you can decide if other mods are worthwhile.
* Maybe KF33BDT-TR is a nice replacement (50 µV noise) but I think you could do some checking and comparing as well. NCP5501DT33RKG has 35 µv ...
On second thoughts: the 2.5V reg can stay. No need to replace that one although it wouldn't hurt.
So essentially adding 1 x 5V and 1 x 6V regs, replacing a noisy 3.3V reg, replacing 2 feedback resistors, adding a bias network and some decoupling by coils and caps. IMO using a better low noise 3.3V reg and better decoupling of the ADC will solve some hiss and that would be first thing I would try together with the feedback resistors. Datasheet of the ADC indeed says to use a quiet supply which is very logical. When you have done this small mods and hear clear improvement you can decide if other mods are worthwhile.
* Maybe KF33BDT-TR is a nice replacement (50 µV noise) but I think you could do some checking and comparing as well. NCP5501DT33RKG has 35 µv ...
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I asked politely a few days ago....and yes voltages are too low in this device too.
Why too lo? You say, 4Vrms is the new small signal standard for car audio. Why? Because with a 12V board battery 4Vrms is maximum output of un-bridged amplifiers. No chance of overdrive, less chance of destruction. I guess, this new standard is a differential voltage, hence small signal amplifiers have 6dB headroom. Cut short, they run with mere +12V.
Can you expect a price-wise keyboard with external 12V= power supply to be able to saturate an expensive pair of 600 Ohms headphones? You are funny.
Can you expect a price-wise keyboard with external 12V= power supply to be able to saturate an expensive pair of 600 Ohms headphones? You are funny.
My design is a solid as can be. For a series ringing circuit, a gyrator is AC-coupled anyway, so a symmetrical power supply were pointless. For this amplifier has unity gain, and voltages hier 2Vrms should not appear in small-signal home audio, +12V power supply is enuff.
Throwing +-15V and op-amps at every syllable is, as i already wrote, ill.
Throwing +-15V and op-amps at every syllable is, as i already wrote, ill.
You were not even aware that 2Vrms is standard since the eighties. Now you think I want opamps everywhere while I haven't said so ?!?! Except from having +12V fobia you are now pointing to me as opamp-lover. What is wrong with you ? And what is ill about using opamps anyway ? What is ill about +/- 15V ? (I would opt for +/- 12V though) I think it is equally ill to think everything should be low voltage and ultra simple topology because everything "should be simple to explain" and "possible destruction"..... Some strange way of thinking about destruction does not help. How many times have you experienced negative side effects from +/- 12V power supplies and how many times did you experience destruction ? Why on earth would you restrict yourself because of any possible farfetched/theoretical mishap and have less performance because of that ? You seem to make assumptions/decisions and then find the reasoning afterwards. Having headroom is not verboten.
Your design can not have lower impedance loads and it can (your words) not have capacitive loads while cables are capacitive in general. How about slew rate ? Is it symmetrical ?
* I just reread all posts and I think it is wise to stay away from this thread. Good luck with your design.
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Man, i did not call thee ill, just some designs, maybe thy, not mine. More than 2Vrms are not common with small-signal home audio and easily destroy equipment. Take a +-15V studio equalizer, set all gains and bands to full boost and connect a common tape deck to its input and any of the countless legacy of home audio of the seventies, eigthies and nineties to its output. Most devices will break. Break, break, break.
Tape deck ? Legacy ? Seventies, eighties and nineties ? It is 2016, almost 2017. No tape deck here, no record player here, no CD here, no DVD here, not even FM here, no legacy stuff here. It is 2016, almost 2017. Time has moved on and if one is hardcore audio guy one has to go along and embrace new technology (while cherishing the good stuff from the past if ones house is big enough). After having owned many many audio devices I now have the wisdom that one only can use one set so I keep it simple and sold all my excess stuff. Better for the mind and the body.
I am in audio for some decades and have never, I repeat, never had any device break down because of the 2V rms standard (that exists since at least 35 years) nor from +/- 12V or even +/- 30V fed devices. All equipment has been adapted to that voltages as it should but I do recall the small issues when it started.
I am in audio for some decades and have never, I repeat, never had any device break down because of the 2V rms standard (that exists since at least 35 years) nor from +/- 12V or even +/- 30V fed devices. All equipment has been adapted to that voltages as it should but I do recall the small issues when it started.
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I do not dig that mp3, bluetooth, soundcloud stuff, not even with a hi-end gloss finish, but rather fix the basics, "stuff, that your grandpa should have got rite". I have indeed seen several devices broken by too hi input voltage. Allowed BE junction reverse voltage is only a few Volts. Devices should be as fail-safe as feasible but are not, unfortunately. This is the legacy. Building and selling +-15V pre-amps for and to people, who are in contact with this legacy, would be only stupid, if the builders and sellers did not know better, but since they do, it is ill. This is off-topic but must be stated here for my output to stay known as healthy.
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