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that vca 2180
The 2155 is obsolete so you'll use the 2180. There are 3 different grades of the IC. Any will work for your amp.
This (DC offset) seems like it was a significant problem. If I'm not mistaken, MTX inserted a 10uf capacitor between the 2155/2180 and the next stage (inverting input of an op-amp) to prevent DC offset. If you can break the connection between pin 8 of the 2155 and the op-amp, you could try inserting the cap to see if the DC goes away.
You should also measure the DC voltage on the input of the 2155 to make sure you don't have DC there. The DC often won't appear on the output of the 2155. You have to go to the output of the op-amp that the 2155 drives to measure the DC offset.
that vca 2180
The 2155 is obsolete so you'll use the 2180. There are 3 different grades of the IC. Any will work for your amp.
This (DC offset) seems like it was a significant problem. If I'm not mistaken, MTX inserted a 10uf capacitor between the 2155/2180 and the next stage (inverting input of an op-amp) to prevent DC offset. If you can break the connection between pin 8 of the 2155 and the op-amp, you could try inserting the cap to see if the DC goes away.
You should also measure the DC voltage on the input of the 2155 to make sure you don't have DC there. The DC often won't appear on the output of the 2155. You have to go to the output of the op-amp that the 2155 drives to measure the DC offset.
I guess hum isn't really the right word for it.Its more like a high pitched whine.At times it fades away completely. There still seems to be a small dc spike when the gain is adjusted although not as large as it was by any means.It gets a sub cone moving just slightly.Kind of like when you use a battery to check polarity.The inductors get pretty warm.The output caps don't get hot like they were but the inductors are about the same temp as before.Is that normal for these inductors to get hot? Also wanted to mention that the amp idles right around 3.5 to 4 amps.Is this high for this amp?Sorry for all the questions.Just anxious to get this thing back in order if it isn't already.
It's supposed to be a compressor to prevent extreme clipping but I've never been able to see a difference with it in ot out.
http://www.mtx.com/caraudio/archive/2004amps/Thunder_421D_801D_1501D.pdf
http://www.mtx.com/caraudio/archive/2004amps/Thunder_421D_801D_1501D.pdf
well i finally got this amp wired up in my car.I'm only running a 4 ohm load on it but the output is impressive and clean.There is still that annoying whine from the inductors though.Its a lot less audible in the car,not even audible at all with the volume at low level due to the fact the speakers over power it but it is definitely there.I ran it for about 15 minutes at high volume and nothing was overly hot.I did notice when I adjusted the gain that the whine would change and at times go out completely but when the gain was left untouched in any position that the noise returned.
The noise does not appear to change at all when the rcas are moved.I never changed the 1 k resistor that was connected to that blown trace.Or the ES2D diodes either. I measure 500 ohms between shield ground and primary ground.Is that measurement right?Is the resistor and or diodes possibly out of tolerance and causing the noise?
I just noticed a couple things on this amp I wanted to ask you about Perry. First thing I noticed is that FETs 245 through 248 appear to have different value gate resistors than FETs 255 through 258. Is this normal?FETs 255-258 all appear to have approximately 39 ohm gate resistors while 245-248 seem to be sitting at around 5 ohms. I assume these are all output FETs or is that not correct. My other question has to do with the extra through holes for these same FETs.In addition to the ones that are being used there is also another set for each FET that would fit a TO-3P FET. Why did MTX do this?Is it possible to upgrade this amp with larger outputs than factory or is it for some sort of other modification? On another note I did pull the 1 k resistor and it checked fine as did the two diodes flanking it even though one appeared to be cracked on top. I plan on replacing that diode just to be safe.
Half of the outputs have 39.2 ohm gate resistors. The other half has 4.72 ohm gate resistors.
The gate drive signal is significantly different which could require a different resistor value.
The extra pads give the option to use larger case transistors but you do NOT want to try changing them. These amps can be VERY sensitive to changes. The older version would not work with any transistor other than the original (none that I tried, and I tried quite a few). If the output section is working don't do anything to it.
The gate drive signal is significantly different which could require a different resistor value.
The extra pads give the option to use larger case transistors but you do NOT want to try changing them. These amps can be VERY sensitive to changes. The older version would not work with any transistor other than the original (none that I tried, and I tried quite a few). If the output section is working don't do anything to it.
well I read some new info about this amp on another forum.I guess the noise is not coming from the inductors but instead is coming from the transformer.Its hard to tell because they are so close together but when I cover the transformer the noise does seem to get quieter.I was told that the whining/hissing sound that I am hearing from the transformer is normal for this amp.They said that when the input voltage is dropped that the hissing will diminish as well which is exactly what happened when I decreased the power supply voltage.Not sure how reputable the person is that told me this.I have a hard time believing that MTX would put out an amp with this sort of noise. I heard this on the db-r forum if that means anything.
Noise from the transformer is normal.
The pulse width can rapidly, repeatedly change from 0% to full duty cycle. This is what's causing the noise. It's changing like this to try to maintain the target rail voltage. Class D audio amps can feed power back into the rails. This makes the rail voltage increase. When the voltage goes above the target voltage, the duty cycle goes to 0%.
The pulse width can rapidly, repeatedly change from 0% to full duty cycle. This is what's causing the noise. It's changing like this to try to maintain the target rail voltage. Class D audio amps can feed power back into the rails. This makes the rail voltage increase. When the voltage goes above the target voltage, the duty cycle goes to 0%.
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