Dark angel, the nx-Amp is currently rated at 180 W into 4 Ohms. This is the upper limit for an EF2 design. But to go from 180 to 200 I'd raise the supply voltage by 3-4 Volts on each rail ( filter caps would have to be 63V types). It would be a good idea to add a third pair of output devices.
Above 100W into 8 Ohms, you really need to go to an EF3, so IMV the nx-Amp is at the upper end of an EF2 output stage.
Bonsai,
I overlooked that specs, sorry. Anyways what I really meant was to increase the output twice (180w X 2 = 360W) per channel. I have a friend here in our area who has been building power amps for mobile (disco, PA) and he said he would look into increasing the number of outputs (4 or 6 pairs) and the input rail voltages (+/- 100V). Almost all of his amps are either Class H (Crown Macrotech, Peavey, QSC etc.) or Class AB (China made) which can output 600w into 8ohms per channel and have a rail voltages above 100V.
As for the Ovation nx amp having too much power output (above 200W) could just mean an ample buffer for driving high current speakers such Magnepans and ESL or low impedance floorstanders (B&W, Mission, Epos etc...).
I do hope that what I'm stating here is still within the topic...
I look forward on seeing more of your designs...
Adding more power to the nx amp
Bonsai,
I overlooked that specs, sorry. Anyways what I really meant was to increase the output twice (180w X 2 = 360W) per channel. I have a friend here in our area who has been building power amps for mobile (disco, PA) and he said he would look into increasing the number of outputs (4 or 6 pairs) and the input rail voltages (+/- 100V). Almost all of his amps are either Class H (Crown Macrotech, Peavey, QSC etc.) or Class AB (China made) which can output 600w into 8ohms per channel and have a rail voltages above 100V.
As for the Ovation nx amp having too much power output (above 200W) could just mean an ample buffer for driving high current speakers such Magnepans and ESL or low impedance floorstanders (B&W, Mission, Epos etc...).
I do hope that what I'm stating here is still within the topic...
I look forward on seeing more of your designs...
Bonsai,
I overlooked that specs, sorry. Anyways what I really meant was to increase the output twice (180w X 2 = 360W) per channel. I have a friend here in our area who has been building power amps for mobile (disco, PA) and he said he would look into increasing the number of outputs (4 or 6 pairs) and the input rail voltages (+/- 100V). Almost all of his amps are either Class H (Crown Macrotech, Peavey, QSC etc.) or Class AB (China made) which can output 600w into 8ohms per channel and have a rail voltages above 100V.
As for the Ovation nx amp having too much power output (above 200W) could just mean an ample buffer for driving high current speakers such Magnepans and ESL or low impedance floorstanders (B&W, Mission, Epos etc...).
I do hope that what I'm stating here is still within the topic...
I look forward on seeing more of your designs...
Thank you for the kind words.
The nx-Amp as it stands unfortunately cannot be modded to go to 360W - it really would be a new design from scratch.
Once you go much above 100W, a lot of new factors need to be considered to build a good, practical amplifier - thermal, peak current capability, SOA issues, requirement for EF3 etc. All of these factors quickly bring added complexity and cost.
After I designed and built the 180W e-Amp, I really wanted to do something that was fun but had high end performance/sound - that's how the nx-Amp came about.
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Darkangel,
Those high powered pro amps are just a sub class of class D types of amplifiers as far as I understand. Part of the real draw to those amplifiers over a normal class ab amplifier is the size and weight factor. I worked in pro audio long ago and having amplifiers that don't take up racks of space and weighing a ton for portable use is the big draw to those class H devices. Even if you had a great class ab amplifier that could make high power and there were many 700 watt amps like Phase Linear and others, it doesn't make economic sense anymore to try and do that.
Those high powered pro amps are just a sub class of class D types of amplifiers as far as I understand. Part of the real draw to those amplifiers over a normal class ab amplifier is the size and weight factor. I worked in pro audio long ago and having amplifiers that don't take up racks of space and weighing a ton for portable use is the big draw to those class H devices. Even if you had a great class ab amplifier that could make high power and there were many 700 watt amps like Phase Linear and others, it doesn't make economic sense anymore to try and do that.
They sure are very heavy and most are from 3U to 6RU in size. Basically the reason why I wanted to increase its power output is because I wanted it to drive speakers which need high currents. Well maybe I shoudn't be concerned about its power output but how it drives speakers with ease, until then I'll be reporting here how it sound.
Thanks for accomodating my questions...
I fired up my amp today. One board working, one not. I need to get the working one set properly so I can trouble shoot the bad one. I have a few questions/concerns.
Going through the check list.
1. I set the bias at 300mA per instructions. I then measure between the output device emitters and the speaker out and I get about 27mV. I have to increase the bias to 365mA to get to the 42mV target.
I am using MJL3281/1302 if that matters.
2. Measuring the voltage drop across R31 or R32 reads 1.3v. Target is supposed to be 1V +/-50mv.
3. I hooked up an 8R dummy load and put a 1K sine wave through it. Looks clean and symmetrical. It starts to clip at 27vAC. A square wave shows a slight over shoot.
4. I hooked up a speaker and the amp begins to oscillate. It doesn't do that with a dummy load.
Any help will be appreciated.
Blessings, Terry
Going through the check list.
1. I set the bias at 300mA per instructions. I then measure between the output device emitters and the speaker out and I get about 27mV. I have to increase the bias to 365mA to get to the 42mV target.
I am using MJL3281/1302 if that matters.
2. Measuring the voltage drop across R31 or R32 reads 1.3v. Target is supposed to be 1V +/-50mv.
3. I hooked up an 8R dummy load and put a 1K sine wave through it. Looks clean and symmetrical. It starts to clip at 27vAC. A square wave shows a slight over shoot.
4. I hooked up a speaker and the amp begins to oscillate. It doesn't do that with a dummy load.
Any help will be appreciated.
Blessings, Terry
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Hi Andrew,
Yes, I am attaching a pic of my board as well as a clip of the Jim's Audio board that shows the values. I am running 50V rails. I will try to take time in the morning to measure everything. I gave up today because I didn't have a pic of the board unpopulated. I have that now so I will be able to see what is what. The components cover all the labels so it is very difficult to identify them. I will try to mark up a schematic tomorrow if I have time before the Superbowl.
By the way, I only have the V+, V- and ground hooked up for testing. I'm not sure if this amp requires all the other stuff to be connected in order to work properly.
Also, I don't have J2 jumpered per the schematic in the build docs
Thanks, Terry
Yes, I am attaching a pic of my board as well as a clip of the Jim's Audio board that shows the values. I am running 50V rails. I will try to take time in the morning to measure everything. I gave up today because I didn't have a pic of the board unpopulated. I have that now so I will be able to see what is what. The components cover all the labels so it is very difficult to identify them. I will try to mark up a schematic tomorrow if I have time before the Superbowl.
By the way, I only have the V+, V- and ground hooked up for testing. I'm not sure if this amp requires all the other stuff to be connected in order to work properly.
Also, I don't have J2 jumpered per the schematic in the build docs
Thanks, Terry
Attachments
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Looks like I need to put a pic up of an unpopulated board. I'll do that when I get back from my travels.
J2 is a jumper that shorts out the resistor that sits between the signal ground and the power ground. You can leave it open only if the signal ground is connected to the main ground via a separate wire. For testing I'd just jumper it.
It's across R32 and R33 that you should measure the 1 V. These are the diamond buffer output load resistors. If they are running at 1.3 V I'd carefully check your Zener voltages - if they are high, this will cause the problem you are seeing. Make sure the front end resistors are all correct - especially R28, R29 and R36 and R37. Check also that your R32 and R33 are the correct value - 1 k.
Measuring across R30 and R31 you should get about 400 mV.
What's your output offset measuring?
By the way, where are you taking your ground from? Should be from the push on tab and not the input screws connector.
BTW that's a beautiful looking board build you have done there!
J2 is a jumper that shorts out the resistor that sits between the signal ground and the power ground. You can leave it open only if the signal ground is connected to the main ground via a separate wire. For testing I'd just jumper it.
It's across R32 and R33 that you should measure the 1 V. These are the diamond buffer output load resistors. If they are running at 1.3 V I'd carefully check your Zener voltages - if they are high, this will cause the problem you are seeing. Make sure the front end resistors are all correct - especially R28, R29 and R36 and R37. Check also that your R32 and R33 are the correct value - 1 k.
Measuring across R30 and R31 you should get about 400 mV.
What's your output offset measuring?
By the way, where are you taking your ground from? Should be from the push on tab and not the input screws connector.
BTW that's a beautiful looking board build you have done there!
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Hi Andrew,
I reinstalled J2
Zener voltage is 10.24 both sides. I checked the entire bag of zeners and they all read between 10.24V and 10.34V.
I checked all of the resistors, they are correct. I see 630mv across each R30 & R31. I checked all of the VBE of each transistor. They are all right at or about .640V except the outputs which are at .550v or so.
Can't do any more testing right now because right at the end of taking readings my probe slipped and took out Q11 which smoked R22 & R30and I am flat out of 15R 1/2w resistors. Looks like it will be the end of the week before I can do any more. Looks like if I'm going to play with this amp I had better buy a stash of 15R's. I guess I'll see if I find some more precise zeners while I'm at it.
Thanks, Terry