marus said:
By all means use 12 volts as you have described. The reason I chose 24 volts is because with 24 volts the design is more flexible. I.e. if you've got a 12 volt relay all you need to do is insert a series resistor around the same value as the relay coil. It's a lot harder to go the other way and use a 24 volt relay with a 12 volt supply. Note that this amplifier was developed with the idea of using commonly available parts in mind.
Cheers
Q
keypunch said:
My suggestion is not to use any of the IRF devices with the suffix 'N'. If you check the datasheets you will find that the 'N' devices have lower repetitive current but higher peak current rating compared to their counterparts without any suffix; I have found that these cannot withstand the sustained current levels of output amplifiers. They are better suited for switching purposes. I am sure IRF640 without the suffix 'N' is available and should be the preferred device for this application.
Samuel Jayaraj said:
Samuel,
My posted comment about the IRF640N was not a general comment about the N vs non-N suffix IRF devices. It was a comment specific to the IRF640N vs all other IRF devices nor was was the comment in the context of power handling.
That said one, as always, needs to consult the SOA for the device and other device specifications. Comparing the other device specifications for the IRF640 and IRF640N Pd is 125W vs 150W respectively and with same Tc derating of 1.0W/C, Ear is 13mJ vs 15mJ and Iar @ Tc=25Cis 18A and 18A, Id is 18A vs 18A, Id @Tc 100C is 11A vs 13A, Idm 72A vs 72A and SOA 10MS max current peaks at 10 vs 5 Volts respectively. This is suggestive that the IRF640N is an exception to the general view of the N vs non-N suffix IRF devices.
Regards,
John L. Males
Willowdale, Ontario
Canada
24 August 2007 13:09
24 August 2007 13:27 Added link to initial IRF640N posting. jlm
Official Quasi Thread Researcher
vuthanh6 said:Thanks for your reply,
And One more question.: Could you tell me how to setting VR1 & VR2?
Best regards.
Vuthanh6,
What you need is the Bench Setup Guide. The Bench Setup Guide will explain how you adjust VR1 and VR2. Quasi had a Project Guide that included the same Bench Setup Guide instructions on the last page of the Project Guide. Due to the size (more than the diyAudio 100Kb limit) of the Project Guide quasi could not post it on diyAudio. Shawn was one of those that received a copy of the Project Guide via eMail. The Project Guide was current at the time Shawn received the Project Guide. The Project Guide was a living document which quasi maintained and sent the current version at the time of the request of the diyAudio member.
Quasi's Web Site has a NMOS350/500 Construction Guide. At the moment the "construction guide" does not have the Bench Setup Guide instructions or the Setup instructions that were on the last page of the Project Guide.
Regards,
John L. Males
Willowdale, Ontario
Canada
27 August 2007 (20:10 -) 22:15
Official Quasi Thread Researcher
Nmos350
Hi,
It's a pleasure to build Quasi Amp's
I finally done my Nmos350...
I tested with 40V DC rails (i don't have a bigger PS ) ... that's 60W/8, and 25.000 uF/rail. Sounds... good 
Still has a noise with no signal ... but it's posible to be from my sound card.
Offset is 0,x V....
Problems
:
1. Driver heatsink is very very hot (U-shape 62x60mm).
2. It's very hard to mount T8. I can't fit it exactly. I wander ... what if we put all MJE's and T8 on the main heatsink .... ? and instead T8 something linke MJE to make a better contact ? MJE340 has lower amplification... it's that a problem if I want to use it instead T8 ? or other common transistor ?
3. I don't know if I have to solder the fet's on the PCB with a space between or without. I'm afraid if they are in contact with PCB will heat it up too, and maybe damage it. (now they are on the board with no space)
I don't use that PCB with glass fibre.
Anyway ... my neighbours has suffered today
Quasi, what do you mean with Nmos350 and Nmos500 ? 350 and 500 it's the power on 8 ohms ?
In the Power Selection Guide I see that the only amp with 6 fet's (8ohms) have 350W - this seems to be Nmos350 , but here is powered by 85V rails and the schematics says 75V rails. I am a little confused ...
And where is Nmos500 ? Again, looking in PSG I see that only amp with 10 fet's it's powered by the same 85V rails and has 600 W but on 4 ohms ...
Hi,
It's a pleasure to build Quasi Amp's
I finally done my Nmos350...
I tested with 40V DC rails (i don't have a bigger PS
) ... that's 60W/8, and 25.000 uF/rail. Sounds... good Still has a noise with no signal ... but it's posible to be from my sound card.
Offset is 0,x V....
Problems
:1. Driver heatsink is very very hot (U-shape 62x60mm).
2. It's very hard to mount T8. I can't fit it exactly. I wander ... what if we put all MJE's and T8 on the main heatsink .... ? and instead T8 something linke MJE to make a better contact ? MJE340 has lower amplification... it's that a problem if I want to use it instead T8 ? or other common transistor ?
3. I don't know if I have to solder the fet's on the PCB with a space between or without. I'm afraid if they are in contact with PCB will heat it up too, and maybe damage it. (now they are on the board with no space)
I don't use that PCB with glass fibre.
Anyway ... my neighbours has suffered today
Quasi, what do you mean with Nmos350 and Nmos500 ? 350 and 500 it's the power on 8 ohms ?
In the Power Selection Guide I see that the only amp with 6 fet's (8ohms) have 350W - this seems to be Nmos350 , but here is powered by 85V rails and the schematics says 75V rails. I am a little confused ...
And where is Nmos500 ? Again, looking in PSG I see that only amp with 10 fet's
it's powered by the same 85V rails and has 600 W but on 4 ohms ... An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
news....
Hello,
today I had some time to fix my dead nmos200/to-220 module.
I changed all fets, the predrivres (mje350/340) and the bc546c in the current source of the differntial amplifier. I have checked my driver transistors before (desoldered and tested seperately) and they seemed to be ok.
But one thing is that the current flow trough the input-stage seems to be a bit high. I got about 0,9 to 1,1 V across the 470R resistors. 1,1V across the 220R resistor. Supply-voltage was +-32V.
Bias is very stable and no problem.
DC-offset is VERY high. I have -29V on the output, though my fets were new and tested!
Any ideas? Commets are welcome!
Greetings
Black
Hello,
today I had some time to fix my dead nmos200/to-220 module.
I changed all fets, the predrivres (mje350/340) and the bc546c in the current source of the differntial amplifier. I have checked my driver transistors before (desoldered and tested seperately) and they seemed to be ok.
But one thing is that the current flow trough the input-stage seems to be a bit high. I got about 0,9 to 1,1 V across the 470R resistors. 1,1V across the 220R resistor. Supply-voltage was +-32V.
Bias is very stable and no problem.
DC-offset is VERY high. I have -29V on the output, though my fets were new and tested!
Any ideas? Commets are welcome!
Greetings
Black
Re: Nmos350
Marus,
Excellent assembly build you have done on your module(s). The 94.1 reading on your meter is measuring what at that time?
In answer to some of your concerns:
1) Many have commented the heatsink runs very warm for the MJE340/350s. You are only using a 40V supply, what is not clear is if that is 40VDC rails, or 40VAC secondaries that then go to the bridge?
2) Some builders have used a TO-126 type transistor for T8 for the challenges the TO-92 BC546 has posed to some to mount to the heatsink. One builder used a BD139 for T8. If you choose to use an alternate NPN transistor for T8 just keep an eye out on pinouts as even some transistors of same part number by different manufactures will even have different pinouts.
3) I cannot comment on, but seems a reasonable concern. I am sure other "experts" will be able to offer you feedback and guidance on this matter.
With respect to the quasi's Power Selection Guide (your AKA PSG) vs schematic, the schematic is for the NMOS350 as quasi built it so the rail voltage, the number of output devices, and resistor values in the PSG chart will not agree with the schematic. There is no value to a creating a different schematic for all the different rail and speaker impedance possibilities. I believe the power rating for NMOS350 and MNSO500 are both referenced to 4 ohms. Using the rail voltage in the schematic as quasi did with the PSU/Toroid resulted in a NMOS350 with 210WRMS/360WRMS amplifier.
Regards,
John L. Males
Willowdale, Ontario
Canada
29 August 2007 (07:45 -) 08:15
Official Quasi Thread Researcher
marus said:Hi,
It's a pleasure to build Quasi Amp's
I finally done my Nmos350...
I tested with 40V DC rails (i don't have a bigger PS
Still has a noise with no signal ... but it's posible to be from my sound card.
Offset is 0,x V....
Problems
1. Driver heatsink is very very hot (U-shape 62x60mm).
2. It's very hard to mount T8. I can't fit it exactly. I wander ... what if we put all MJE's and T8 on the main heatsink .... ? and instead T8 something linke MJE to make a better contact ? MJE340 has lower amplification... it's that a problem if I want to use it instead T8 ? or other common transistor ?
3. I don't know if I have to solder the fet's on the PCB with a space between or without. I'm afraid if they are in contact with PCB will heat it up too, and maybe damage it. (now they are on the board with no space)
I don't use that PCB with glass fibre.
Anyway ... my neighbours has suffered today
Quasi, what do you mean with Nmos350 and Nmos500 ? 350 and 500 it's the power on 8 ohms ?
In the Power Selection Guide I see that the only amp with 6 fet's (8ohms) have 350W - this seems to be Nmos350 , but here is powered by 85V rails and the schematics says 75V rails. I am a little confused ...
And where is Nmos500 ? Again, looking in PSG I see that only amp with 10 fet's
Marus,
Excellent assembly build you have done on your module(s). The 94.1 reading on your meter is measuring what at that time?
In answer to some of your concerns:
1) Many have commented the heatsink runs very warm for the MJE340/350s. You are only using a 40V supply, what is not clear is if that is 40VDC rails, or 40VAC secondaries that then go to the bridge?
2) Some builders have used a TO-126 type transistor for T8 for the challenges the TO-92 BC546 has posed to some to mount to the heatsink. One builder used a BD139 for T8. If you choose to use an alternate NPN transistor for T8 just keep an eye out on pinouts as even some transistors of same part number by different manufactures will even have different pinouts.
3) I cannot comment on, but seems a reasonable concern. I am sure other "experts" will be able to offer you feedback and guidance on this matter.
With respect to the quasi's Power Selection Guide (your AKA PSG) vs schematic, the schematic is for the NMOS350 as quasi built it so the rail voltage, the number of output devices, and resistor values in the PSG chart will not agree with the schematic. There is no value to a creating a different schematic for all the different rail and speaker impedance possibilities. I believe the power rating for NMOS350 and MNSO500 are both referenced to 4 ohms. Using the rail voltage in the schematic as quasi did with the PSU/Toroid resulted in a NMOS350 with 210WRMS/360WRMS amplifier.
Regards,
John L. Males
Willowdale, Ontario
Canada
29 August 2007 (07:45 -) 08:15
Official Quasi Thread Researcher
Hi Marus,
that is not the way to measure bias current.
What you are measuring by intercepting the power rail is the total quiescent current (voltage amp & drivers + bias).
Better to insert a resistor in the power rail and measure voltage drop. This also provides a little protection if there is a fault. But your's may be OK.
Bias is the current through the output stage ONLY.
Measure your bias across the source resistors. Add up all the currents in the source resistors in the top half. It should EXACTLY equal the total current through all the bottom source rsistors.
that is not the way to measure bias current.
What you are measuring by intercepting the power rail is the total quiescent current (voltage amp & drivers + bias).
Better to insert a resistor in the power rail and measure voltage drop. This also provides a little protection if there is a fault. But your's may be OK.
Bias is the current through the output stage ONLY.
Measure your bias across the source resistors. Add up all the currents in the source resistors in the top half. It should EXACTLY equal the total current through all the bottom source rsistors.