I’m working on a Hafler DH-110, and when I press the tone in/out switch, an alarmingly loud pop comes out of the speakers. I’m experimenting with the resistor method suggested in another thread, with mixed results.
I measured the pops on my oscilloscope, and recording max voltage levels of 86-300(!) volts. That seems… crazy. In REW, I measured SPL approaching 110 dB, but I might have been clipping my sound card.
Given that there are other spikes when pushing switches, eg power, I was wondering if there was a way to clip this out before it leaves the amp. Is there some sort of filter circuit I could put on the output that would prevent anything over a given voltage from passing? It seems like that sort of filter should be fairly audio-safe, since nothing that loud should be coming out of a preamp under any circumstances.
I measured the pops on my oscilloscope, and recording max voltage levels of 86-300(!) volts. That seems… crazy. In REW, I measured SPL approaching 110 dB, but I might have been clipping my sound card.
Given that there are other spikes when pushing switches, eg power, I was wondering if there was a way to clip this out before it leaves the amp. Is there some sort of filter circuit I could put on the output that would prevent anything over a given voltage from passing? It seems like that sort of filter should be fairly audio-safe, since nothing that loud should be coming out of a preamp under any circumstances.
Zeners in anti-series or even a neon light bulb, preferably with some light shining on it.
I think you should figure out what defect causes the issue, though. I can't imagine it behaves like that by design.
I think you should figure out what defect causes the issue, though. I can't imagine it behaves like that by design.
Popping is somewhat acknowledged in the manual:
(In my experience it is never silent, and the pulses are large)
Others have experienced this behavior with the tone button. I have no seen anyone identify a defect or generally satisfactory solution. Placing a resistor across the switch for each channel reduces the pop, but somewhat affects frequency response when tone is not engaged. That's the best solution I've read so far.
(In my experience it is never silent, and the pulses are large)
Others have experienced this behavior with the tone button. I have no seen anyone identify a defect or generally satisfactory solution. Placing a resistor across the switch for each channel reduces the pop, but somewhat affects frequency response when tone is not engaged. That's the best solution I've read so far.
That switch opens the nfb loop briefly. It should be a make-before-break switch instead.
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Hmm.... I'm not sure I can find a MBB switch that will work. I had a lot of trouble finding a replacement for the one bad switch I had (SPUN194700 Alps Alpine | Mouser)
So far I've found that a resistor between 100k and 250k will reduce the pop to acceptable (if not ideal or good) levels without affecting the signal. Any lower the frequency response with tone disabled starts to deform slightly (down ~1.5 dB above 1kHz)
So far I've found that a resistor between 100k and 250k will reduce the pop to acceptable (if not ideal or good) levels without affecting the signal. Any lower the frequency response with tone disabled starts to deform slightly (down ~1.5 dB above 1kHz)
Add a normally open DPST switch across preamp out/power amp in, shorting/grounding outputs while pressed.
Press briefly while you switch misbehaving Tone button or any other click/pop/thump maker.
Press briefly while you switch misbehaving Tone button or any other click/pop/thump maker.
That…. Is a pretty good idea. This preamp actually has a mute button, but it does not short the outputs. Is there any reason not to simply require the mute button to short the outputs?
You could use an analogue switch such as a MAX4066, controlled by the physical switch. These switches transition in nanoseconds so I think any transients produced would be above the passband of the preamplifier, in other words filtered by the upper frequency response of the audio circuitry and thus inaudible.
There's a brief description of how analogue switching for audio works here: How to design analog switches to switch audio signals?
There's a brief description of how analogue switching for audio works here: How to design analog switches to switch audio signals?