Dear all,
I have a pair of ML Spires which I have enjoyed very much so far with my Octave V40 tube amp and always was astonished about the massive bass. Since a couple of days, one speaker lacks bass and exhibits a humming/plopping sound which definitely comes from the bass driver, not from the ESL panel. Unplugging the working speaker shows that only the ESL panel keeps playing sound, so I would assume a defective power amp for the bass driver? Also, the bass frequency settings (using the dial on each speaker) only changes on the working bass driver, the presumed broken one does not show a difference when I change values.
Are there any experts for Martin Logan here who have had something similar?
Cheers and thanks,
Philipp
I have a pair of ML Spires which I have enjoyed very much so far with my Octave V40 tube amp and always was astonished about the massive bass. Since a couple of days, one speaker lacks bass and exhibits a humming/plopping sound which definitely comes from the bass driver, not from the ESL panel. Unplugging the working speaker shows that only the ESL panel keeps playing sound, so I would assume a defective power amp for the bass driver? Also, the bass frequency settings (using the dial on each speaker) only changes on the working bass driver, the presumed broken one does not show a difference when I change values.
Are there any experts for Martin Logan here who have had something similar?
Cheers and thanks,
Philipp
Thanks for the hint, yes, meanwhile I found that info as well - waiting for the 200ASC to arrive 🙂
Dear all, I managed to get 300ASC boards, however they differ in J4 (200ASC 2 Pins for GND and Auto on/off) or the P4 (7 Pins on the 300ASC) - any chance that I can used the 300ASC in my ML Spires? Is the Auto on/off a 12 V trigger signal?
Cheers and thanks,
Philipp
Cheers and thanks,
Philipp
I am one step further: I managed to get a new 200 ASC board, exchanged the old one, but no change. I still don't have any bass and still low noise humming/plopping sounds from the speaker when turned on without music playing. When I play music, the panel works, but not the bass driver.
Any ideas?
Cheers
Philipp
Any ideas?
Cheers
Philipp
It sounds like there is a problem with the upstream circuit, not the power amp board. To confirm, when you have nothing connected and are hearing the humming/plopping noises, what is the color of the status light on the back panel? If it is blue, wait15 minutes or so until the auto ON/OFF times out and it turns red. At this point, the power amp should be muted and the noises should be gone.
If this is the case, then the next thing to do is to signal trace thru the circuit from input to power amp, circuit block by circuit block. Fortunately ML makes this very easy as they provided TP(Test Points) on the PCB between each circuit block. Just input a 100Hz signal and step thru each TP with an oscilloscope until you find where the signal is lost or corrupted to locate the faulty section of the circuit.
If this is the case, then the next thing to do is to signal trace thru the circuit from input to power amp, circuit block by circuit block. Fortunately ML makes this very easy as they provided TP(Test Points) on the PCB between each circuit block. Just input a 100Hz signal and step thru each TP with an oscilloscope until you find where the signal is lost or corrupted to locate the faulty section of the circuit.
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Wow, thanks very much for your detailed answer, that sounds like a way to go! Should I keep the loudspeaker terminals bridged as in normal operation or just input into the woofer terminals?
Cheers,
Philipp
Cheers,
Philipp
Thanks for the hint - I´ll get my function generator in the next days - any recommendation on the maximum amplitude for the 100Hz test signal (sine wave?). The TPs are measured vs el. ground I assume?
An input of 2 to 3 Vrms on the Woofer binding posts will get you in the 100mV - 200mVrms range at TP4, a reasonable level to follow thru the rest of the test points.
Yes, the TPs should be measured relative to ground. There are 2 connectors(X1 and X2) on the PC board which are ground and can be used for measuring the test points.
Yes, the TPs should be measured relative to ground. There are 2 connectors(X1 and X2) on the PC board which are ground and can be used for measuring the test points.
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Ok, so it took me some time to test the board or boards (as I used the functioning one as reference).
As you explained, 2.5 Vpp gave around 400 mVrms on TP4 on the functioning board. This board remained in standby mode for the amp (red LED) when I input the sine wave signal on the woofer post (I assume it does not matter whether I use the + or - post, I tried both).
On the broken board however, the amp board instantly goes into active (blue LED) as soon as I input the same sine wave and I detect nothing, not even noise on TP4 and TP1. TP3 gives a noise signal.
Could that indicate a dry soldering point?
Best,
Philipp
As you explained, 2.5 Vpp gave around 400 mVrms on TP4 on the functioning board. This board remained in standby mode for the amp (red LED) when I input the sine wave signal on the woofer post (I assume it does not matter whether I use the + or - post, I tried both).
On the broken board however, the amp board instantly goes into active (blue LED) as soon as I input the same sine wave and I detect nothing, not even noise on TP4 and TP1. TP3 gives a noise signal.
Could that indicate a dry soldering point?
Best,
Philipp
Can you explain what you mean by using the + or - post? The audio input should be between the two posts. (ie one wire to each post like you do when hooking it up to a power amplifier)
It won't matter which wire goes to which post though...maybe that is what you meant.
Hmmm...Trying to understand why the good board left the LED in standby mode, but the bad board instantly switched it to blue.
In any case, if you aren't getting any signal at TP4, either the input opamp is bad or possibly there is a short somewhere that is pulling down the power supply for the opamps.
I'd check the + and - 12VDC supplies as noted in the attachment. Lack of +/- 12VDC power could also explain the LED behavior, but I'd have to check the schematic tomorrow.
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Thanks for the reply - my signal generator is integrated into my oscilloscope, so i hooked up the board using a probe head with the signal to the red woofer post and ground to the black post - does that make sense? Having said that, in the first run, I missed to attach ground to the black woofer post, that didn't matter.
Or should I get a cable with banana plugs to BNC rather to connect the signal generator to the woofer posts?
Thanks for the idea on the 12V supply, I will check that.
Or should I get a cable with banana plugs to BNC rather to connect the signal generator to the woofer posts?
Thanks for the idea on the 12V supply, I will check that.
Your method of hookup (signal to red woofer post and ground to black post) is just fine, not reason to mess with banana plugs.
Remember, you will also need to hook ground from your scope probe to the circuit ground at terminal X1 or X2 when you are viewing signal at the different TPs.
Remember, you will also need to hook ground from your scope probe to the circuit ground at terminal X1 or X2 when you are viewing signal at the different TPs.