Hi everyone,
I have built the L15D class D amplifier (got two of them) and started playing with it. My impressions so far:
1. Even with relatively high power it stays cold as a dead fish😉
2. I think it's a little attenuated at the high audio frequencies but that could be a wrong impression as I did not actually measured the response.
3. Sound it quite good and clean otherwise.
4. With some high power speakers (which are quite old and poor sounding) the amplifier may not start (the blue led flashes as if trying to recover but fails).
and last:
If I connect the amplifier ground to the mains ground, it starts oscillating bad and one of the resistors (did not check which one exactly) gets over heated.
Any ideas, tips how to proceed?
Thanks,
Eli
I have built the L15D class D amplifier (got two of them) and started playing with it. My impressions so far:
1. Even with relatively high power it stays cold as a dead fish😉
2. I think it's a little attenuated at the high audio frequencies but that could be a wrong impression as I did not actually measured the response.
3. Sound it quite good and clean otherwise.
4. With some high power speakers (which are quite old and poor sounding) the amplifier may not start (the blue led flashes as if trying to recover but fails).
and last:
If I connect the amplifier ground to the mains ground, it starts oscillating bad and one of the resistors (did not check which one exactly) gets over heated.
Any ideas, tips how to proceed?
Thanks,
Eli
Are you using it as an "integrated amp with just a volume control on the input: This is a thread discussing what happens when doing that with an ICEpower module, and I suspect the same thing might happen with the L15D, since it has fairly low input impedance as well..
You might want to post this on LJMLJM's L15D Thread, he might respond more quickly. There was a couple of posts about upping the wattage rating on one of the resistors from 1 W to 2 W (something like that), but I can't put my finger on it at the moment.
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This is probably unrelated, but worth asking.. Did you assemble the L15D boards yourself, or did you buy them prebuilt? Someone mentioned that some of the prebuilt one's did not have heatsink compound on the MosFets on the heatsink..
I built them myself. I also made a few modifications due to the fact I run them on +/- 38V while they are designed for +/- 50V. The changes involved are to decrease values of resistors in series to zeners to retain the same current that would have flown if I used 50V.
Oh, and forgot to mention - I intend to use in a box containing four microphone inputs preamp and two guitar inputs all through a mixer (actually opamp based adder) and from there to the L15D.
No, just the resistors. I wanted the current to remain the same as it would be if I used 50V, but I did not change the zener values.
Ok, to make sure we are talking about the same thing, I'm talking about Z100 and Z101. They are for over voltage(OVP) and under voltage(UVP) protection, meaning that your power supply has to be between the voltages of those two Zeners, or the amp will shut down.(according to IR's reference design document (see page 24 here) I don't think they have anything to do with how much current the amp can put out. Current limiting is handled by the IRS2092 chip itself.
These amps scale in wattage (and current output) depending on the power supply voltage you feed them(as long as the resistors and the zeners are changed). Reducing the power supply means reducing the amount of current output (and wattage). You cannot expect to get the same power (watts) from the amp if you reduce the power supply voltages.
From what I understand the L15D is based on the components for the AMP7S-150(see page 37 for the differential chart) in the Ref design. The OVP and UVP zeners are 68 and 39 Volts for the AMP7S-150, and if your power supply is nominally 38 V, you are likely right on the edge of the UVP protection kicking in, explaining why it doesn't start up sometimes, and possibly the oscillation also.
You need to change the zeners to be the parts used by the AMP7S-100, which are 47V (OVP) and 30V (UVP) respectively for voltage of the zeners. The part numbers for the Ref Design are SMD though, so you'd have to find the equivalent Through hole parts, like 1N5256B-TR (30V) and 1N5261B-TR (47V).
These amps scale in wattage (and current output) depending on the power supply voltage you feed them(as long as the resistors and the zeners are changed). Reducing the power supply means reducing the amount of current output (and wattage). You cannot expect to get the same power (watts) from the amp if you reduce the power supply voltages.
From what I understand the L15D is based on the components for the AMP7S-150(see page 37 for the differential chart) in the Ref design. The OVP and UVP zeners are 68 and 39 Volts for the AMP7S-150, and if your power supply is nominally 38 V, you are likely right on the edge of the UVP protection kicking in, explaining why it doesn't start up sometimes, and possibly the oscillation also.
You need to change the zeners to be the parts used by the AMP7S-100, which are 47V (OVP) and 30V (UVP) respectively for voltage of the zeners. The part numbers for the Ref Design are SMD though, so you'd have to find the equivalent Through hole parts, like 1N5256B-TR (30V) and 1N5261B-TR (47V).
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(sigh) I asked the guy who sold me the kit for a schematic so he sent me this link:
http://www.nutsaudio.com/photo/iraudamp7s.pdf
I know it does not exactly match the kit I got but it's pretty close.
Anyway, referring to page 21 in this PDF, I changed R117 and R118 which are in series with zeners that provide +/- 5.6V to VAA and VSS.
http://www.nutsaudio.com/photo/iraudamp7s.pdf
I know it does not exactly match the kit I got but it's pretty close.
Anyway, referring to page 21 in this PDF, I changed R117 and R118 which are in series with zeners that provide +/- 5.6V to VAA and VSS.
So you only changed R117 and R118? I think you need to change all the components listed on page 37 that are different for the various versions of the circuit.
Those two resistors are all I could change -- some of the components are simply not in my kit, and some I could not change.
Did they include a parts list with the kit and who sold it to you?
Please elaborate on your last reply. (ie why could you only change those two resistors, which components are not in your kit, and why couldnt you change others..)
Please elaborate on your last reply. (ie why could you only change those two resistors, which components are not in your kit, and why couldnt you change others..)
I bought it in ebay eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices
As for the parts (referring to table 5 in the pdf I sent earlier):
The power mosfets I got are IRFI4019H-117P and have better specs than IRFI4212H-117P.
R8 sets the gain (Vo/Vi) and I did not find good reason to change it.
R117,118 I changed.
I also changed R114 (forgot to mention before).
R12 I did not change since I did not know exactly what's the effect.
The clamping dioes -- they sent 1n4004 - no shotky dioes. I don't know how critical it is.
What really disturbs me with the amplifier is that I don't know when it will start oscillating. I don't want this to happen when playing with the band when I can be alert to such things.
As for the parts (referring to table 5 in the pdf I sent earlier):
The power mosfets I got are IRFI4019H-117P and have better specs than IRFI4212H-117P.
R8 sets the gain (Vo/Vi) and I did not find good reason to change it.
R117,118 I changed.
I also changed R114 (forgot to mention before).
R12 I did not change since I did not know exactly what's the effect.
The clamping dioes -- they sent 1n4004 - no shotky dioes. I don't know how critical it is.
What really disturbs me with the amplifier is that I don't know when it will start oscillating. I don't want this to happen when playing with the band when I can be alert to such things.
Ok, I have to apologize about the over and under voltage Zeners. I need to clarify with the LJMLJM(the board designer), but unless I am missing something, looking at the boards themselves (and the newer Rev 3 boards that I ordered from here, it looks like they left off the over voltage protection circuit, which where the Zeners are located in the reference design. It never occured to me that he would have left that out (cost saving measure I guess)..
None the less, I think you still need to change R8, R115, R12, R18 and R17, to make sure that none of them are the source of your instability...
None the less, I think you still need to change R8, R115, R12, R18 and R17, to make sure that none of them are the source of your instability...
Not all, you're trying to help and I thank you for that.
If I could get the exact schematic it would be a good start. BTW, how can I tell which rev of the board I have?
Your board doesnt seem to have any markings on it to specify what rev it is, so it must be an earlier one. The Ver 3 board has "Ver3" on it, and the 2092 chip is mounted on the bottom of the board vs the top.
I've asked LJM_LJM to provide and exact schematic on another thread..
The best we have to go on now is the schematic on page 30 of the Ref design, but there are differences, and the only way to be sure would be to reverse engineer the board by drawing out all the connections from it..
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