same amp, new prob MTX 8302 LP filter

damage · 7th December 2008, 07:20 PM

Hi!

High-pass and Full-range filters work. Low-pass filter makes a loud thump when engaged and then there is no sound.

It pops when I change the RCA output xover.

Perry Babin · 7th December 2008, 09:30 PM

Measure the DC voltage on the output pins of the op-amps near the RCA end of the board. Do any have more than a few millivolts of DC? If so, does the offset vary significantly when adjusting the gain?

What is the DC voltage on pins 1 and 8 of U6?

Use the RCA shield as the reference (black meter probe on RCA shield).

damage · 7th December 2008, 11:33 PM

I cannot tell which one is U6 because the board is marked underneath the opamps.

Perry Babin · 7th December 2008, 11:36 PM

U6 is the 8 pin SIP IC.

damage · 8th December 2008, 01:11 AM

The NE5532 right behind the gains has significant voltage change on the outputs when gains turned. The rest appear to have 3mV of offset.

U6
1: -.75V
2: 3.2V
3: .4mV
4: -2.6V
5: -57mV
6: -22mv
7: .4mV
8: -.75V

Perry Babin · 8th December 2008, 01:29 AM

Pull U6 and install a jumper from pin 1 to pin 8. Does the amp work normally (low frequency crossover working, no pop, no DC offset)?

damage · 8th December 2008, 03:02 AM

Hello!

Yes, after removal it appears to work normally. Slight pop when engaging the switch, but nothing like it was before. Offset is now normal on the NE5532.

Perry Babin · 8th December 2008, 03:20 AM

Replacing the THAT 2155 will probably solve the problem The 2155 is obsolete. You'll have to replace it with a 2180 (mouser - search for THAT 2180).

The amp will work without it but the remote level controller and the compressor (if it has one) won't work.

damage · 8th December 2008, 03:30 AM

Hi!

I'll get a replacement. At least the compression circuit is useful.

Thanks Again Perry!

7th December 2008, 07:20 PM	#1
damage diyAudio Member Join Date: May 2006	same amp, new prob MTX 8302 LP filter Hi! High-pass and Full-range filters work. Low-pass filter makes a loud thump when engaged and then there is no sound. It pops when I change the RCA output xover.

7th December 2008, 09:30 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Measure the DC voltage on the output pins of the op-amps near the RCA end of the board. Do any have more than a few millivolts of DC? If so, does the offset vary significantly when adjusting the gain? What is the DC voltage on pins 1 and 8 of U6? Use the RCA shield as the reference (black meter probe on RCA shield). __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

7th December 2008, 11:36 PM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	U6 is the 8 pin SIP IC. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

8th December 2008, 01:29 AM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Pull U6 and install a jumper from pin 1 to pin 8. Does the amp work normally (low frequency crossover working, no pop, no DC offset)? __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

8th December 2008, 03:20 AM	#8
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Replacing the THAT 2155 will probably solve the problem The 2155 is obsolete. You'll have to replace it with a 2180 (mouser - search for THAT 2180). The amp will work without it but the remote level controller and the compressor (if it has one) won't work. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links


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7th December 2008, 11:33 PM	#3
damage diyAudio Member Join Date: May 2006	I cannot tell which one is U6 because the board is marked underneath the opamps.

8th December 2008, 01:11 AM	#5
damage diyAudio Member Join Date: May 2006	The NE5532 right behind the gains has significant voltage change on the outputs when gains turned. The rest appear to have 3mV of offset. U6 1: -.75V 2: 3.2V 3: .4mV 4: -2.6V 5: -57mV 6: -22mv 7: .4mV 8: -.75V

8th December 2008, 03:02 AM	#7
damage diyAudio Member Join Date: May 2006	Hello! Yes, after removal it appears to work normally. Slight pop when engaging the switch, but nothing like it was before. Offset is now normal on the NE5532.

8th December 2008, 03:30 AM	#9
damage diyAudio Member Join Date: May 2006	Hi! I'll get a replacement. At least the compression circuit is useful. Thanks Again Perry!

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