I have made the circuit given in oliveaudio site, which has source resistors, i dont know about the previous design, or has it been modified. (I am using Just 2Pairs of mosfets).
Anyways....
I have made the circuit, using MPSA42 & 92 instead of 2n5401 & 2n5550, and using IRFP9540 (ie. 100V Mosfets) & IRFP150N (also 100V Mosfet) as these were in stock with me, and power it with 20V-0-20V, (with 10Ohm/10W resistors in series with both the rails, for current limit in case anything's wrong).
T9 & T10 gets hot in some seconds, I tripple checked the components & everyhing is right, if i remove the bbase of T12 & T13 (TIP41C & Tip42C), then it does not heat.
As described earlier, this is my first audio amp project please co-operate for some might be silly things i may ask.
Also let me know how to set the bias, is it to be set with current meter in series with +- rails .OR. mV across source resistors.
Anyways....
I have made the circuit, using MPSA42 & 92 instead of 2n5401 & 2n5550, and using IRFP9540 (ie. 100V Mosfets) & IRFP150N (also 100V Mosfet) as these were in stock with me, and power it with 20V-0-20V, (with 10Ohm/10W resistors in series with both the rails, for current limit in case anything's wrong).
T9 & T10 gets hot in some seconds, I tripple checked the components & everyhing is right, if i remove the bbase of T12 & T13 (TIP41C & Tip42C), then it does not heat.
As described earlier, this is my first audio amp project please co-operate for some might be silly things i may ask.
Also let me know how to set the bias, is it to be set with current meter in series with +- rails .OR. mV across source resistors.
I have replaced the MPSA42 & MPSA92 with the actually shown 2N5401 & 2N5551,
Also changed the MPSA92 & 42 if they might have got partially damaged or leaky
Also increased the vlotage to +-30V, as i doughted the rails voltage might be too low,
BUT still the same.
Also changed the MPSA92 & 42 if they might have got partially damaged or leaky
Also increased the vlotage to +-30V, as i doughted the rails voltage might be too low,
BUT still the same.
Did you design the board yourself? Maybe there is an error. Can you post a link to which schematic you used so we can be sure we are working from the same diagram.
everything seems to be OK,
i got the schematic from www.oliveaudio.com
I also wonder why Lars have removed it from his LCaudio website and its nowhere to be found, also the was a copy of schematics at by dx.master as below:
--------------------------------------------------------------------
Please look on my site:
- http://bauteile-fuer-die-elektronik.de/projekte/ZETA/
Spezial at
- http://bauteile-fuer-die-elektronik...lcaudiozeta.gif
regards,
dx.master
-----------------------------------------------------------------------
this is also removed.
If its been designed for DIY, why in the hell all schematics have been deleted.
WONDERING WHY................
i got the schematic from www.oliveaudio.com
I also wonder why Lars have removed it from his LCaudio website and its nowhere to be found, also the was a copy of schematics at by dx.master as below:
--------------------------------------------------------------------
Please look on my site:
- http://bauteile-fuer-die-elektronik.de/projekte/ZETA/
Spezial at
- http://bauteile-fuer-die-elektronik...lcaudiozeta.gif
regards,
dx.master
-----------------------------------------------------------------------
this is also removed.
If its been designed for DIY, why in the hell all schematics have been deleted.
WONDERING WHY................
Hi Criss,
I made the PCB layout of my version of the ZEETA with only two pairs of
output devices without emitter resistors on graph paper , if you want the
same I will take a picture of that and send it to you ,( I had also posted
pictures of the Zeeta I had made in this thread) , there were some
problems , Dj Quan also had similar problems in his version , hence I
cannot confirm if they were due to faulty layout , or due to the components
I had used , or due to some problem in the design , one day on turn on
two mosfets failed one from each side , I just disconnected the two and
the amp was working , I do not know why they failed , I also wanted to
make the 1000w version but not much support from Lars hence I did not
compleate the layout and decided to wait and see if anyone has
attempted the same , unfortunately since a long time there are hardly any
posts on this thread , I hope Lars will come up with his new version soon .
Rajeev
I made the PCB layout of my version of the ZEETA with only two pairs of
output devices without emitter resistors on graph paper , if you want the
same I will take a picture of that and send it to you ,( I had also posted
pictures of the Zeeta I had made in this thread) , there were some
problems , Dj Quan also had similar problems in his version , hence I
cannot confirm if they were due to faulty layout , or due to the components
I had used , or due to some problem in the design , one day on turn on
two mosfets failed one from each side , I just disconnected the two and
the amp was working , I do not know why they failed , I also wanted to
make the 1000w version but not much support from Lars hence I did not
compleate the layout and decided to wait and see if anyone has
attempted the same , unfortunately since a long time there are hardly any
posts on this thread , I hope Lars will come up with his new version soon .
Rajeev
Hi rajeev,
I have made the schematics given in www.oliveaudio.com.
Can you please mail me the previous schematics , given by mr lars for 1pair of mosfets, as it is not available on lcaudio website & also the photo of PCB layout of your graph paper, i don't know if the schematics i have got is correct.
As i made this circuit the transictors are heating, and also i a unable to understand the schematics.
Thanks a lot for your reply & support,
I have made the schematics given in www.oliveaudio.com.
Can you please mail me the previous schematics , given by mr lars for 1pair of mosfets, as it is not available on lcaudio website & also the photo of PCB layout of your graph paper, i don't know if the schematics i have got is correct.
As i made this circuit the transictors are heating, and also i a unable to understand the schematics.
Thanks a lot for your reply & support,
The schematic is the same,
I hope Lars is reading and will help everyone ,
I think he was also going to supply pcbs for a single pair of output devices
Regards
Rajeev
I hope Lars is reading and will help everyone ,
I think he was also going to supply pcbs for a single pair of output devices
Regards
Rajeev
I have even mailed Lars, but now response from him, might be he is busy in some other work.
Hope he gets time soon, for us.
Rajeev,
please mail me the PCB Layout, I wonder if the schematics is correct, so might be something related to PCB.
Hope he gets time soon, for us.
Rajeev,
please mail me the PCB Layout, I wonder if the schematics is correct, so might be something related to PCB.
please give me two ---three days time I will look for it and take a picture and send the same to you , its been a long time since I had made the amp,
meanwhile check if all is ok as per the schematic in your amp , it should work !!!
meanwhile check if all is ok as per the schematic in your amp , it should work !!!
Hi!
Rajeev,
I would be obliged if you can send a copy to me also on:
lkorahul@yahoo.com
Regards
Rahul
Rajeev,
I would be obliged if you can send a copy to me also on:
lkorahul@yahoo.com
Regards
Rahul
Ok i got it working.
Actually i got another schematics which has T4 & T3 drawn wrong.
the attached file is the wrong schematics.
And the circuit shown in oliveaudio is correct.
The output in highs is not that clear, it is quite destorted in mid volumes.
Thanks for all the support.
Actually i got another schematics which has T4 & T3 drawn wrong.
the attached file is the wrong schematics.
And the circuit shown in oliveaudio is correct.
The output in highs is not that clear, it is quite destorted in mid volumes.
Thanks for all the support.
Due to the low feedback factor, (loop gain) and the rather high change of source resistance of the MOSFET's, i recommend using a high BIAS current for the Zeta. At 50 mA you get enogh crossover distortion, so you can hear it at low volumes. Up to maybe 0.5%.
2-300 mA will give you a good clean sound with acceptable low distortion.
2-300 mA will give you a good clean sound with acceptable low distortion.
rolandong
used a 10K Variable resistance,
Lars,
I have set bias to 50ma, I increase and check, but are you suggesting this bias value for just 2Pairs of mosfets or more.
One more thing, I have used 4,700uf cap per channel and there is a Humm (50Hz) from speaker, and with the same rectifier & transformer & filter cap, if i drive LM3886 (chip amp) it is very quite, why is it so.
used a 10K Variable resistance,
Lars,
I have set bias to 50ma, I increase and check, but are you suggesting this bias value for just 2Pairs of mosfets or more.
One more thing, I have used 4,700uf cap per channel and there is a Humm (50Hz) from speaker, and with the same rectifier & transformer & filter cap, if i drive LM3886 (chip amp) it is very quite, why is it so.
Criss
Did you measure the offset voltage ??
even my version had hum with 4700mf caps but with 10,000mf it was ok hence increase the caps to 20,000mfd per rail
Did you measure the offset voltage ??
even my version had hum with 4700mf caps but with 10,000mf it was ok hence increase the caps to 20,000mfd per rail
Rajeev,
Ok what you say is fine, but with the same filters if i use a chip amp, it does not have any hum with on 4,700 uF caps per rail, why is it so.
Ok what you say is fine, but with the same filters if i use a chip amp, it does not have any hum with on 4,700 uF caps per rail, why is it so.
Hi Crissty,
Since Zeta employs low feedback factor, therefore hum is usual ..increase feedback factor that is..decrease gain [Av] by changing the 100k feedback resistor to about 22K. Mosfet amps are generally designed with low voltage gains but they deliver extremely high current gain.
Low feedback factor is good with Bipolar amps but in case of Mosfet amps you have to set the feedback factor high enough to get rid of Thermal noise + hum + astable operation....[or design the amp with high local feedback factor]especially in case of N-Vmos Quasi-complementary amps...
Regarding Mosfet blowing:
Zeta suffers from driver imbalance.....The upper [+] rail mosfet gate drive impedance is quite high than the lower [-] mosfet gate drive, because the upper gate to source terminal is tied by C-E of driver transistor whereas Lower gate to source terminal is tied by 10 Ohm resistor connected at the drain of p-channel mosfet When you increase the idle drain current,this causes the the parasitic buildup due to imbalance in gate driver and the "gate capacitance of output mosfets seen by subsequent driver"and leads to oscillations which blows the mosfets in an instant...
Lars, i think you are going to be angry with me, but sometimes the truth has to be faced! 😉
Rajeev also faces this problem once...better ask him about his experience
regards,
K a n w a r
Since Zeta employs low feedback factor, therefore hum is usual ..increase feedback factor that is..decrease gain [Av] by changing the 100k feedback resistor to about 22K. Mosfet amps are generally designed with low voltage gains but they deliver extremely high current gain.
Low feedback factor is good with Bipolar amps but in case of Mosfet amps you have to set the feedback factor high enough to get rid of Thermal noise + hum + astable operation....[or design the amp with high local feedback factor]especially in case of N-Vmos Quasi-complementary amps...
Regarding Mosfet blowing:
Zeta suffers from driver imbalance.....The upper [+] rail mosfet gate drive impedance is quite high than the lower [-] mosfet gate drive, because the upper gate to source terminal is tied by C-E of driver transistor whereas Lower gate to source terminal is tied by 10 Ohm resistor connected at the drain of p-channel mosfet When you increase the idle drain current,this causes the the parasitic buildup due to imbalance in gate driver and the "gate capacitance of output mosfets seen by subsequent driver"and leads to oscillations which blows the mosfets in an instant...
Lars, i think you are going to be angry with me, but sometimes the truth has to be faced! 😉
Rajeev also faces this problem once...better ask him about his experience
regards,
K a n w a r