Hi all ... this is a 600W Class D Bass guitar amplifier with a strange intermittent problem. The amp behaves fine until certain notes are played, predominantly D3 (147Hz) ... which will trigger the amp module (IC4) shutdown for about 4 seconds.
This is the 2nd one of these that I have had here with the same complaint although I couldn't reproduce the fault on the 1st one so thought that it must be something else in his equipment cutting out. Anyway I can certainly reproduce it on this one. Gains etc. are set well within normal playing parameters & I can reproduce this with different Bass guitars.
So I have traced the problem to the over current detection, when the trigger note plays the window comparator IC15 (LM393) triggers the shutdown on IC4.
All voltage rails are fine, happens with 8 or 4 Ohm loads, IC4 is a 600W Class D module with proprietary in house serial numbers that the manufacturers will not decode here's a link to data sheet for what it's worth: https://docs.rs-online.com/fa4e/0900766b80b0985e.pdf
Speaker (8 or 4 Ohm) connects directly to OUT1 & OUT2 ... normally I'd just immediately replace IC15 (LM393) & IC9 (TS512ID) before carrying on with testing but these are soic packages buried deep in between other components and would require a major disassembly to get to.
So before I do that I'm here to see if anyone can shed more light on how this bridged output works through the current sense resistors and IC9?, this is the 1st bridged Class D amp I've looked at ... also not sure how to go about testing any further to troubleshoot this strange problem ... all suggestions welcome.
This is the 2nd one of these that I have had here with the same complaint although I couldn't reproduce the fault on the 1st one so thought that it must be something else in his equipment cutting out. Anyway I can certainly reproduce it on this one. Gains etc. are set well within normal playing parameters & I can reproduce this with different Bass guitars.
So I have traced the problem to the over current detection, when the trigger note plays the window comparator IC15 (LM393) triggers the shutdown on IC4.
All voltage rails are fine, happens with 8 or 4 Ohm loads, IC4 is a 600W Class D module with proprietary in house serial numbers that the manufacturers will not decode here's a link to data sheet for what it's worth: https://docs.rs-online.com/fa4e/0900766b80b0985e.pdf
Speaker (8 or 4 Ohm) connects directly to OUT1 & OUT2 ... normally I'd just immediately replace IC15 (LM393) & IC9 (TS512ID) before carrying on with testing but these are soic packages buried deep in between other components and would require a major disassembly to get to.
So before I do that I'm here to see if anyone can shed more light on how this bridged output works through the current sense resistors and IC9?, this is the 1st bridged Class D amp I've looked at ... also not sure how to go about testing any further to troubleshoot this strange problem ... all suggestions welcome.
Should add "FO" beside components on the schematic seems to be the manufacturers version of "NP" (Not Populated).
It seems strange that an IC is used yet all the protection is external. Most Class D chips have OV, OC and over temperature protection built in.
What amp model is it from?
What amp model is it from?
It's a TE715x... There are two distinct separate sections to the Bass amp: pre-amp designed by TE and power amp (which is actually just a complete evaluation board from another manufacturer showing what the Class D module above can do)... The company just decided to use the evaluation as is. That's why it's protection etc. is separate.
It's a strange and very frustrating fault, you can play away fine but regularly when you hit a D3 note or to a far lesser extent E2 or E3 the overcurrent protection triggers and the amp module shuts down for about 4 seconds.
It's a strange and very frustrating fault, you can play away fine but regularly when you hit a D3 note or to a far lesser extent E2 or E3 the overcurrent protection triggers and the amp module shuts down for about 4 seconds.
Here's a wild guess: A linear supply with ripple at 100Hz (e.g. UK mains) plus some bus pumping at 150Hz could trigger overvoltage protection. When the amp is shut off the bus pumping stops, the rails are again within the acceptable limits of the protection, and the amp comes out of protection. Not sure, but maybe. Bus pumping typically happens at low frequencies where the driver impedance is inductive but maybe rising driver VC Le is large enough to do that at 150Hz... Am I crazy?
If so, placing some capacitance (e.g. 4700uF per rail) in between the PS and amp, or turning down the PS rails a tad (if possible) might prevent the issue from happening.
If so, placing some capacitance (e.g. 4700uF per rail) in between the PS and amp, or turning down the PS rails a tad (if possible) might prevent the issue from happening.
Hmmm ... you know it's probably going to end up being something like this. I was starting to think about the power supply caps not keeping up with demand earlier today and the shutdown happens most often when a D note is played at the end of a run of other notes (all with harmonic relation). Frequencies most likely to cause shutdown are 41, 82 & 147Hz.
I am though testing with a very low inductance dummy load but yeah that's definitely something to consider & look into 🙂
I'll attach full schematic set for anybody who wants a look at the whole layout.
Before I move onto other areas of investigation can anybody explain to me exactly what IC9 (TS512ID op-amp) is doing before the 393 comparator? ... I'm not sure of what's happening with this output configuration.
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OK found a couple of minor problems on the pre-amp board... don't think they are part of the overcurrent triggering but they need fixed before continuing...