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Class D Switching Power Amplifiers and Power D/A conversion

200W IRS2092 Amp for
200W IRS2092 Amp for
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Old 16th June 2015, 02:35 PM   #11
brik is offline brik  United States
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xrk971.Is the input impedance to these IRS2092 modules really 3.3k ohms? I see some sellers on Ebay claiming 12 to 15 k.Different info out there.Hoping you can help .Thanks.
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Old 16th June 2015, 02:44 PM   #12
xrk971 is offline xrk971  United States
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200W IRS2092 Amp for
Where did you see the spec on the input impedance? I will have to check but I had no problem driving them with the 2v p-p output from miniDSP, as well as headphone outs from a CD player. It depends on the resistors used to set the gain on the input op amp, not the IRS2092 itself as that is really just a PWM switch driver.
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Old 16th June 2015, 02:47 PM   #13
abraxalito is offline abraxalito  United Kingdom
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Looking at the DS for the IRS2092, the suggested application shows a 3k3 input resistor in series with 10uF going into a virtual earth. So if its implemented according to this reference design (IRAUDAMP5) it will indeed be 3k3 input impedance. No mention in the DS about increasing the resistor values - that's not to say it isn't possible, but 15k does sound rather optimistic to me.
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Old 16th June 2015, 04:02 PM   #14
brik is offline brik  United States
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Application Note AN-1138 :
''Input Section The audio input stage of IRS2092(S) is configured as an inverting error amplifier. In Figure 2, the voltage gain of the amplifier GV is determined by input resistor RIN and feedback resistor RFB.
Since the feedback resistor RFB is part of an integrator time constant, which determines switching frequency, changing overall voltage gain by RIN is simpler and, therefore, recommended in most cases. Note that the input impedance of the amplifier is equal to the input resistor RIN. ''

I believe the input resistor can be raised to 6.6k which also lowers the gain.I'll try to find the paper on that with the gain settings.At least this may be workable with a tube pre.I think this is why ClassDAudio came out with their SDS series of amps.I believe they added a buffer input.
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Old 16th June 2015, 04:45 PM   #15
Buehgemeiste is offline Buehgemeiste
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nice info on the cheapo irs2092.
i have an eye on them for a while now.
but let's have them their own thread.
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Old 17th June 2015, 02:29 AM   #16
xrk971 is offline xrk971  United States
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On my 200w IRS2092 (YJ I believe) the input impedance is set by a 100k resistor clearly labeled next to the input pins. I also measured it and it is indeed 100k. That is is very good because it means it can be driven easily with a cell phone headphone output and is also good for PLLXO in that it won't attenuate the signal very much.
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Old 17th June 2015, 02:39 AM   #17
doctormord is offline doctormord  Germany
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And will pickup (a lot) of noise, I guess. Cellphones do even drive <=32R with ease, so no need to have 100k input impedance.
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Old 17th June 2015, 11:43 AM   #18
xrk971 is offline xrk971  United States
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From what I have heard so far, did not pickup excessive noise. A very quiet amp if anything.
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Old 17th June 2015, 02:30 PM   #19
doctormord is offline doctormord  Germany
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Nice.
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Old 18th June 2015, 12:29 AM   #20
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by xrk971 View Post
On my 200w IRS2092 (YJ I believe) the input impedance is set by a 100k resistor clearly labeled next to the input pins. I also measured it and it is indeed 100k. That is is very good because it means it can be driven easily with a cell phone headphone output and is also good for PLLXO in that it won't attenuate the signal very much.
Yet I can't see any opamps on that board - admittedly the heatsink's covering a large area and there could be one under it. Equally no sign of supply regulators for an opamp. Without an opamp or some kind of input buffer, the input impedance has to be that of the IRS2092 chip's application circuit.

If you measured the input impedance with a multimeter that would only show the DC resistance, but the application circuit's AC coupled.
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Last edited by abraxalito; 18th June 2015 at 12:33 AM.
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