Performance report
This is how I configured the final setup of my Quasi Amp:
1) X-former : 0-45, 0-45 @750VA (+-63 volts DC)
2) 2 bridge rectifiers
3) Caps : 7500uF x 2, 0R1 10watts, 7500uF x 3, 0.1uF x 2 per rail
4) Rails cut between Front End and Driver/Output stage - inserted IN4007 diode, 10R 2W resistor, 470uF + 100uF + 0.1uF
5) Changed R4/R8 to 330R
6) Changed R6 to 10K
7) Changed R12/R15 to 680R
8) IRFP450 x 3 per bank
9) KSE340/350 instead of MJE types
10) C4 is Silver Mica
11) Zobel Network is 10R 5W + 0.1uF 250V
12) Iq is 100mA
13) C1 = 11uF currently. I will have to pop in a 1uF plastic type.
Now the amp is really upto the challenge. Rhythm and pace are among the very best. Very good resolution of low level signals. Sound stage is very controlled and not aggressive or harsh. Low Bass and Mid Bass are very, very good.
Does not image as forward as my AKSA clone, Stochinno Amp and Gain Clone (LM3886TF), in that order; however, the mids are not withdrawn or shy. I would have liked the overall image to be a little more forward, personally speaking. But the musicality and timing more than make up for this.
T6/T7 do run a bit hot - have to increase the heatsinking for these.
Any comments or opinions?
E and R both represent Ohms.
This is how I configured the final setup of my Quasi Amp:
1) X-former : 0-45, 0-45 @750VA (+-63 volts DC)
2) 2 bridge rectifiers
3) Caps : 7500uF x 2, 0R1 10watts, 7500uF x 3, 0.1uF x 2 per rail
4) Rails cut between Front End and Driver/Output stage - inserted IN4007 diode, 10R 2W resistor, 470uF + 100uF + 0.1uF
5) Changed R4/R8 to 330R
6) Changed R6 to 10K
7) Changed R12/R15 to 680R
8) IRFP450 x 3 per bank
9) KSE340/350 instead of MJE types
10) C4 is Silver Mica
11) Zobel Network is 10R 5W + 0.1uF 250V
12) Iq is 100mA
13) C1 = 11uF currently. I will have to pop in a 1uF plastic type.
Now the amp is really upto the challenge. Rhythm and pace are among the very best. Very good resolution of low level signals. Sound stage is very controlled and not aggressive or harsh. Low Bass and Mid Bass are very, very good.
Does not image as forward as my AKSA clone, Stochinno Amp and Gain Clone (LM3886TF), in that order; however, the mids are not withdrawn or shy. I would have liked the overall image to be a little more forward, personally speaking. But the musicality and timing more than make up for this.
T6/T7 do run a bit hot - have to increase the heatsinking for these.
Any comments or opinions?
E and R both represent Ohms.
Hi Samuel Jayaraj,
Why did you change R4 & R8?
You changed R12 & R15 to 680R ??? This is an absolute no-no and I'm surprised the amp works at all. Or did you change them to 68R. If T6 & T7 are warm then I suspect 680R is a typo. Can you please change them back to 47R. This sets the current through this stage at 12.7mA and this is required to drive the next stage. The second stage will run quite warm, this is normal.
You should try the amp without the diodes splitting the supplies or have you already done that. Did you notice any improvement?
The 0.1 resistors are not really necessary between the caps. Whilst they can help with the filtering, they make no difference at normal listening levels (very little) and they add impedance to the power supply.
Good to see your amp works and you're happy with it.
Cheers
Quasi
Why did you change R4 & R8?
You changed R12 & R15 to 680R ??? This is an absolute no-no and I'm surprised the amp works at all. Or did you change them to 68R. If T6 & T7 are warm then I suspect 680R is a typo. Can you please change them back to 47R. This sets the current through this stage at 12.7mA and this is required to drive the next stage. The second stage will run quite warm, this is normal.
You should try the amp without the diodes splitting the supplies or have you already done that. Did you notice any improvement?
The 0.1 resistors are not really necessary between the caps. Whilst they can help with the filtering, they make no difference at normal listening levels (very little) and they add impedance to the power supply.
Good to see your amp works and you're happy with it.
Cheers
Quasi
Hi Sam,
do you feel like experimenting?
Try changing C7 to 150uF or 220uF//1uF AND reduce C1 to 2.7uF//100nF (both film type).
Try increasing Iq in 50mA steps to 250mA. If there is no change try reducing again in 50mA steps. If there is really no change then run it at your initial 100mA.
Try increasing C14, maybe as high as 1uF.
Are you using 8ohm or 4ohm speaker load? For 8ohm, I would increase the second bank of capacitors from 3// to 5 or 6//.
I would not consider this PSU voltage for 4ohm, but maybe a 4 to 8 ohm speaker load.
Quasi,
I think I can see why Sam reduced R4 & R8.
With R4=R8=470r the Vce of T2 & T3 are about 800mV to 900mV
Changing to 330r increases Vce by about 200mV.
I wonder if this helps the performance of the mirror or affects the sound? Any comment?
do you feel like experimenting?
Try changing C7 to 150uF or 220uF//1uF AND reduce C1 to 2.7uF//100nF (both film type).
Try increasing Iq in 50mA steps to 250mA. If there is no change try reducing again in 50mA steps. If there is really no change then run it at your initial 100mA.
Try increasing C14, maybe as high as 1uF.
Are you using 8ohm or 4ohm speaker load? For 8ohm, I would increase the second bank of capacitors from 3// to 5 or 6//.
I would not consider this PSU voltage for 4ohm, but maybe a 4 to 8 ohm speaker load.
Quasi,
I think I can see why Sam reduced R4 & R8.
With R4=R8=470r the Vce of T2 & T3 are about 800mV to 900mV
Changing to 330r increases Vce by about 200mV.
I wonder if this helps the performance of the mirror or affects the sound? Any comment?
Quasi, you are right, that was a typo. R12/R15 are indeed 68 ohms.
I did try with and without splitting the rails but I find that isolating the Front End almost always cleans up the Bass and Mid/Bass resulting in a more resolving Mid band; it was the same case with this amp. However, I should say that with the original schematic values, the distortion that I am talking about did slightly reduce when the supplies were joined. The value that I used initially for the resistor was 100 ohms, following the diode and the caps were 100uF/0.1uF. This did increase the distortion as compared to joining the rails, but in both cases, the distortion did not disappear.
T6/T7 are on a heatsink but they run quite hot, NOT warm. Right now the amp is out of its case and the temperature is bound to rise in a closed (ventillated) box.
Resistors with values in the range 0.05 to 0.10 ohms with capacitance banks more than 10,000uF on either side help to clean up supply hash below 500Hz! So did Elektor publish in their 60 watt HEXFRED amp article. I have never measured this, but I have invariably heard improved Bass with this arrangement.
After changing R12/R15 to 68 ohms and varying R6 from 6K8 to 18K, the distortion was almost gone. But the sound was dull, lifeless and did continue to distort on music peaks. Hence, I changed R4/R8 to 390E to begin with and then further reduced them to 330E. With this arrangement and R6 at 18K, the Mids were a little more recessed and the amp was not quite up to it in speed. Overall musicality was lacking. When I changed R6 to 10K, the speed/pace, rhythm and musicality were really good. ( I should add that from output to the junction of R18/C7, I have a 47K resistor. The brings down noise and improves sonics. It does change the feedback factor but whenever possible, I try to use this technique. A very famous DIY amp used this technique as well.)
Andrew, I did increase Iq right upto 300mA since I have quite big heatsinks. But this was prior to solving the distortion problem and having stock values of components. In the current setup, I have not tried anything more than 110mA.
I guess increasing C7 will result in less low frequency phase shift, but I have not tried it because I am using Elna RJH 100uF caps, in shunt with 0.1uF and 2 x IN4148 anti-parallel diodes. I like the sound of the Elnas. I could probably try two in parallel.
For C1, I do have 1uF, 2.2uF, 2.7uF, 3.3uF in high quality film types and also 4.7uF Solen MKP capacitors. I could have tried them but have not yet.
What is the effect of increasing the value of C14?
I am not pushing the amp into high drive levels, because my speakers are 91.5db sensitivity in a Quarter Wave Loaded cab and hence, are quite efficient. I also have a pair of Fostex 168 Sigma ES, but have not used them in these cabs, in which they fit and play well. The speakers are 4 ohms, 2-way and I have been alternating between 4 ohms and 2 ohms while testing the amp, just to be sure that at higher current delivery, the behaviour of the amp doesn't change. At the drive levels required for my speakers, the 2 ohm performance of the amp is audibly the same as its 4 ohm performance.
In the next round I'd also like to split R11 and put a cap from this junction to the negative rail.
Quasi and Andrew, thanks for your respones. Do look forward to more inputs and discussions.
I did try with and without splitting the rails but I find that isolating the Front End almost always cleans up the Bass and Mid/Bass resulting in a more resolving Mid band; it was the same case with this amp. However, I should say that with the original schematic values, the distortion that I am talking about did slightly reduce when the supplies were joined. The value that I used initially for the resistor was 100 ohms, following the diode and the caps were 100uF/0.1uF. This did increase the distortion as compared to joining the rails, but in both cases, the distortion did not disappear.
T6/T7 are on a heatsink but they run quite hot, NOT warm. Right now the amp is out of its case and the temperature is bound to rise in a closed (ventillated) box.
Resistors with values in the range 0.05 to 0.10 ohms with capacitance banks more than 10,000uF on either side help to clean up supply hash below 500Hz! So did Elektor publish in their 60 watt HEXFRED amp article. I have never measured this, but I have invariably heard improved Bass with this arrangement.
After changing R12/R15 to 68 ohms and varying R6 from 6K8 to 18K, the distortion was almost gone. But the sound was dull, lifeless and did continue to distort on music peaks. Hence, I changed R4/R8 to 390E to begin with and then further reduced them to 330E. With this arrangement and R6 at 18K, the Mids were a little more recessed and the amp was not quite up to it in speed. Overall musicality was lacking. When I changed R6 to 10K, the speed/pace, rhythm and musicality were really good. ( I should add that from output to the junction of R18/C7, I have a 47K resistor. The brings down noise and improves sonics. It does change the feedback factor but whenever possible, I try to use this technique. A very famous DIY amp used this technique as well.)
Andrew, I did increase Iq right upto 300mA since I have quite big heatsinks. But this was prior to solving the distortion problem and having stock values of components. In the current setup, I have not tried anything more than 110mA.
I guess increasing C7 will result in less low frequency phase shift, but I have not tried it because I am using Elna RJH 100uF caps, in shunt with 0.1uF and 2 x IN4148 anti-parallel diodes. I like the sound of the Elnas. I could probably try two in parallel.
For C1, I do have 1uF, 2.2uF, 2.7uF, 3.3uF in high quality film types and also 4.7uF Solen MKP capacitors. I could have tried them but have not yet.
What is the effect of increasing the value of C14?
I am not pushing the amp into high drive levels, because my speakers are 91.5db sensitivity in a Quarter Wave Loaded cab and hence, are quite efficient. I also have a pair of Fostex 168 Sigma ES, but have not used them in these cabs, in which they fit and play well. The speakers are 4 ohms, 2-way and I have been alternating between 4 ohms and 2 ohms while testing the amp, just to be sure that at higher current delivery, the behaviour of the amp doesn't change. At the drive levels required for my speakers, the 2 ohm performance of the amp is audibly the same as its 4 ohm performance.
In the next round I'd also like to split R11 and put a cap from this junction to the negative rail.
Quasi and Andrew, thanks for your respones. Do look forward to more inputs and discussions.
Hi Sam,
Don't worry about the MJE340/ 350's. They are built to take it. Even with a Tc of 80 degC they can still dissipate 11 watts each and the actual dissipation is way below this. So they will run very warm (definition is a personal thing) but they are well inside normal operating parameters. These transistors were originally designed for high voltage TV applications where they often run quite warm indeed.
They are probably the strongest TO-126 device around and at high voltages put seemingly stronger TO-220 devices to shame.
Mine are mounted inside a case that is completely sealed and ventilated by a central slow (very slow) fan. A picture of the case is located early in the thread and also in Solid State Pics.
Cheers
Don't worry about the MJE340/ 350's. They are built to take it. Even with a Tc of 80 degC they can still dissipate 11 watts each and the actual dissipation is way below this. So they will run very warm (definition is a personal thing) but they are well inside normal operating parameters. These transistors were originally designed for high voltage TV applications where they often run quite warm indeed.
They are probably the strongest TO-126 device around and at high voltages put seemingly stronger TO-220 devices to shame.
Mine are mounted inside a case that is completely sealed and ventilated by a central slow (very slow) fan. A picture of the case is located early in the thread and also in Solid State Pics.
Cheers
Attachments
Hi to all
I finally end the nmos200 and test it but i think there's something wrong, here are the symptoms :
1. the first you notice is that the sound its really distorted
2. the main heatsink don't even get a little warm
3. T6 is cold as antartica while T7 does get warm
Before you ask, yes all the transistors are well insulated, T6 T7, are the BD ones.
I didn`t spend much time searching for the problem just check all the components if were well placed.
So any clue about what should i check, before hit it whit my hammer ?
Thank you all and sorry for my poor english.
I finally end the nmos200 and test it but i think there's something wrong, here are the symptoms :
1. the first you notice is that the sound its really distorted
2. the main heatsink don't even get a little warm
3. T6 is cold as antartica while T7 does get warm
Before you ask, yes all the transistors are well insulated, T6 T7, are the BD ones.
I didn`t spend much time searching for the problem just check all the components if were well placed.
So any clue about what should i check, before hit it whit my hammer ?
Thank you all and sorry for my poor english.
Hi and thanks
rolandong
acording to the schematics i have T6 and T7 could be BD(139, 140) or MJE (340, 350), correct me if im wrong
The offset voltage was below 10mv don't remember the exact number.
AndrewT
don't know what the output bias is cos vr2 seem to do nothing.
I think im doing wrong the set of the bias please tell me how i should do.
about the voltage across source resistors, im still need to check that, first thing on my list.
Thanks for the help
PD: the layout i use was the quasi layout and please have me patience im a newby on this amps stuff
rolandong
acording to the schematics i have T6 and T7 could be BD(139, 140) or MJE (340, 350), correct me if im wrong
The offset voltage was below 10mv don't remember the exact number.
AndrewT
don't know what the output bias is cos vr2 seem to do nothing.
I think im doing wrong the set of the bias please tell me how i should do.
about the voltage across source resistors, im still need to check that, first thing on my list.
Thanks for the help
PD: the layout i use was the quasi layout and please have me patience im a newby on this amps stuff
suddenly all have problems with that amp of quasi(nmos)?is there their mistake that amplifier isnt working well?(i gues it is, because a documentation of the amp is well done and i hope that amp works well)
quasi, why they have so much problems?
I am trying to build 2 of them but now i am wondering if the amp will do the job or not?
i have build couple of amps(less powerfull) but there was no such problem to start the amp!
how many amps were allready made?
thanks
quasi, why they have so much problems?
I am trying to build 2 of them but now i am wondering if the amp will do the job or not?
i have build couple of amps(less powerfull) but there was no such problem to start the amp!
how many amps were allready made?
thanks
Hi Juan,
It is probably time to measure a lot of voltages, but first let us do some basic checks.
First check that both fuses are still ok by taking them out and measuring for continuity.
Next check all orientation of all the electrolytic capacitors
Then check the orientation of all the semiconductors and transistors. It is ok to use BD transistors in the Nmos200 but some of the TO92 transistors have different pinouts depending on what you use. Please check the published pinouts against the pinouts on the PCB layout.
Then check all the resistors. One constructor of the Nmos350 had difficulty reading the colours on some of the resistors and got a few wrong.
Before powering up again replace the fuses with 100 ohm resistors to protect the output stage.
Then with no signal or speaker connected measure the DC voltage between the amplifier output and ground (0v). YOu should see 0v (or a few millivolts).
Then measure the voltages across all these resistors and see if you get these approximate readings.
R4, R5, R9, R12, R15 = 0.6v
R7 = 27.2v
R20 & R22 = between 3 to 4 volts depending on the FETs used.
Let us know what readings you get.
If the main heatsink is not getting warm then the ouput stage may not be turning on. To check if the output FETs are getting turned on measure across the source resistors. You should get a low voltage (5 - 20 millivolts) depending on the bias current.
Can other constructors of the Nmos200 please confirm if their amp works ok, just in case I've missed something.
Good luck & Cheers
Quasi
It is probably time to measure a lot of voltages, but first let us do some basic checks.
First check that both fuses are still ok by taking them out and measuring for continuity.
Next check all orientation of all the electrolytic capacitors
Then check the orientation of all the semiconductors and transistors. It is ok to use BD transistors in the Nmos200 but some of the TO92 transistors have different pinouts depending on what you use. Please check the published pinouts against the pinouts on the PCB layout.
Then check all the resistors. One constructor of the Nmos350 had difficulty reading the colours on some of the resistors and got a few wrong.
Before powering up again replace the fuses with 100 ohm resistors to protect the output stage.
Then with no signal or speaker connected measure the DC voltage between the amplifier output and ground (0v). YOu should see 0v (or a few millivolts).
Then measure the voltages across all these resistors and see if you get these approximate readings.
R4, R5, R9, R12, R15 = 0.6v
R7 = 27.2v
R20 & R22 = between 3 to 4 volts depending on the FETs used.
Let us know what readings you get.
If the main heatsink is not getting warm then the ouput stage may not be turning on. To check if the output FETs are getting turned on measure across the source resistors. You should get a low voltage (5 - 20 millivolts) depending on the bias current.
Can other constructors of the Nmos200 please confirm if their amp works ok, just in case I've missed something.
Good luck & Cheers
Quasi
smokingmachine said:
Hi Smokingmachine
I know that over 100 units of the Nmos350 / Nmos500 have been built with a very high success rate. I cannot tell you how many of the Nmos200 have been built so maybe other constructors can provide some answers here. I forget who built this one, but it is a nice job that works well.
http://www.adam.com.au/cgpap/QuasiWeb/images/Nmos200_TO-247_stereo.jpg
Cheers
smokingmachine said:
I cut my heatsinks from much bigger pieces so I can't give you any accurate data. This link will take you to a picture of my amp that started this whole thread. The heatsinks I used measured about 300mm long x 78mm high by x 40mm deep (fins).
http://www.adam.com.au/cgpap/QuasiWeb/images/2 x Nmos350 power amplifier.jpg
Cheers
Q
Nmos200 almost completed!!!!
Hi Quasi
I am currently building a nmos200 amplifier. I got the circuit and layout from youre website. I am almost finished, about 90%. The circuit board is complete and I am just left with the wiring of the circuit and mounting the PCB on my heatsink.Wanted to switch it on today but something came up and did not have time. Before I switch on, what values must the two pots (VR1 and VR2) be. I am using a bench power supply with current limit but the maximum voltage is +-33V Dc. Can I use this supply for the initial test and later use my +-50V Dc transformer? Can you please supply me with the startup procedure for this amp? I will post some pictures and give some feedback tommorow. Thank you for this design and info thus far. Will keep you posted.
Thanks
macd
Hi Quasi
I am currently building a nmos200 amplifier. I got the circuit and layout from youre website. I am almost finished, about 90%. The circuit board is complete and I am just left with the wiring of the circuit and mounting the PCB on my heatsink.Wanted to switch it on today but something came up and did not have time. Before I switch on, what values must the two pots (VR1 and VR2) be. I am using a bench power supply with current limit but the maximum voltage is +-33V Dc. Can I use this supply for the initial test and later use my +-50V Dc transformer? Can you please supply me with the startup procedure for this amp? I will post some pictures and give some feedback tommorow. Thank you for this design and info thus far. Will keep you posted.
Thanks
macd
smokingmachine said:
The power selection guide I posted is theoretical and is based on a virtually limitless power supply. So if you had say a 3kva transformer and 100,000uF of capacitors then you may get close to achieving these powers. But real world is nothing like this so the actual power you will get will be less. But in real terms a couple of things should be noted.
1. The dynamic power of the amp will be close to what is posted and this is important because music is dynamic.
2. Achieveing 10 or even 20% less power will barely be noticable in terms of loudness.
My own amp runs a 500va transformer with a DC section delivering +/- 73 volts unloaded. This amp delivers about 210 watts into 8 ohms and 360 watts into 4 ohms. Now 360 watts will only be about 1dB below 440 watts so in terms of volume you won't notice. More important is the power supply so that the power is maintained during "difficult" music passages.
I have recently created a table showing real world (reasonable) power predictions and will post this on my web site soon.
Cheers
Well problem found , my friend vodoochild found it,
the problem was (murphy law here) one leg of T10 was not cut well, it was bend and was touching a track so that little thing kill T12 and T14 and T10. . . happned to the best rhigt?
The funny thing was that the amp do work even with half of the transistors dead, of course sounds really bad but still works
So when i change the transistor i`ll come back thanks you all for the help.
the problem was (murphy law here) one leg of T10 was not cut well, it was bend and was touching a track so that little thing kill T12 and T14 and T10. . . happned to the best rhigt?
The funny thing was that the amp do work even with half of the transistors dead, of course sounds really bad but still works
So when i change the transistor i`ll come back thanks you all for the help.