I don't have access to the bottom of the board once transistors are mounted. I didn't measure voltage across the pot, not much access and I don't want the probe to slip anywhere near the bias circuit. haha There are 2 large test points to measure bias, located on either side of the board.
Thinking back, I think this accident happened due to a combination of issues.
Main one being incorrect mounting of one power transistor, the second was that my meter was set to AC instead of DC milivots, because it likes to default to AC for some reason. I didn't notice, and I must've turned the pot too far down before I noticed and changed the meter back to DC.
The pot is a 15 turn plastic based pot. I'll check the resistance later.
Congratulations on learning about your meter.
You can measure the voltage across R20 from the top side from the base of Q13 to the collector of Q10 which is the heat sink tab. I'd attach a pamona grabber on the base of Q13 with the power off then turn the power on. You can touch the tab of Q10 with an ordinary probe. The side that is negative, the base of Q13. would be where the line of a parallel clamping diode(s) would go.
All pots use brass or tin plate wipers, which oxidize. Even silver oxidizes. Only gold palladium & rhodium don't oxidize and I've never heard of that being used in a pot wiper. Only telephone relay contacts and key contacts on hammond organs.
You can measure the voltage across R20 from the top side from the base of Q13 to the collector of Q10 which is the heat sink tab. I'd attach a pamona grabber on the base of Q13 with the power off then turn the power on. You can touch the tab of Q10 with an ordinary probe. The side that is negative, the base of Q13. would be where the line of a parallel clamping diode(s) would go.
All pots use brass or tin plate wipers, which oxidize. Even silver oxidizes. Only gold palladium & rhodium don't oxidize and I've never heard of that being used in a pot wiper. Only telephone relay contacts and key contacts on hammond organs.
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I'll try that out, first want to have bias adjustable for the time being. I want to get some measurements on the output, but the only load I have can barely take 50Watts, don't know how it will fair with 150 Watts lol. Might need to buy a bigger load to really open it up.
Thanks, yeah, most would be line level I guess. I did build a phono preamp already to, and love it. It's the "Muffsy" preamp, works great. I still have a lot to learn about this mesmorize pcb, I just picked it up while buying other boards. I've been looking at the threads and it's all very confusing, dunno if it's stand alone or if I can build it into the amp chasis using the transformers smaller aux outputs etc.
I was able to load test the amp today. I got 97.6Vpp before clipping into an 8 ohm load. I could only do it for a few seconds at a time because my load is too small. Not sure what that is as Watts RMS forgot the formula. Strange thing is, that I get the wave on the scope without connecting the ground, is the ground connecting through neutral on the common leads of my scope and function generator? When I do connect the ground lead, amplitude doubles and the wave becomes distorted. The signal input is around 2Vpp @ 1KHz to get to max output. How do I monitor the amp while it's under load to make sure it doesn't run away? The bias reading is over 100 mVDC when it's near max output.
Well, I'll answer the easy questions. Divide 97.6 by 2 to get 0-peak. Divide that by 1.414 to get RMS. Square that and divide by the resistance to get power. Looks like about 148W to me.
You can only measure bias with no signal, so turn off signal and remeasure bias to see where it's at. You'll never be running the amp at full power when listening to music, so I'd run it at the max your load can take - say 10W - then turn off the signal and quickly remeasure the bias. You could run it for 5 minutes, remeasure bias, and repeat until the bias has stabilized. A fan blowing on the load (but not the amp) may help. Bear in mind I have no experience with the Honey Badger, just amps in general.
Can't figure out what's going on with the grounding, doubling, distortion unless I know how everything is grounded. Grounding is the bane of measurements.
You can only measure bias with no signal, so turn off signal and remeasure bias to see where it's at. You'll never be running the amp at full power when listening to music, so I'd run it at the max your load can take - say 10W - then turn off the signal and quickly remeasure the bias. You could run it for 5 minutes, remeasure bias, and repeat until the bias has stabilized. A fan blowing on the load (but not the amp) may help. Bear in mind I have no experience with the Honey Badger, just amps in general.
Can't figure out what's going on with the grounding, doubling, distortion unless I know how everything is grounded. Grounding is the bane of measurements.
Thanks for the reassurance, your calculation sounds bang on. I could get it a little bit higher without clipping, but 148 Watts is close enough to the advertised 150 Watts of the Honey Badger.
Since it measures correctly without connecting the ground lead of the scope, I'll just take that as it's already grounded and I won't connect the lead. haha
Another weird thing is that I can audibly hear the 1 KHz signal coming from the amp at high power even though there's no speakers connected to anything. It's like one of the components is giving off the sound.
Yep, at high power levels you can definitely hear the amps sing.
Glad to find out that it's normal. I guess when speaker are connected, you'll never hear it over the speakers. haha
update
Hi there, I am back to update anybody who's willing to listen. lol I got my chassis some time ago and built both channels of my amp successfully. I am almost done, I have the soft start built and installed.
I have also finished the speaker turn on delay, which has been really annoyingly hard for such a simple and straight forward circuit there's a lot of confusion with this product. I am running it off of the 18v winding of my antek transformer. Seems to work, and gives about a 3 second delay before clicking the relays in. However I haven't been able to hook the speakers up to it, or test it's DC blocking feature.
How does the circuit reference ground to know that there is a DC fault? The build guide says nothing about this? I only have it hooked up to AC which is not ground tapped on my transformer. Can I run a ground back to the star ground point? The AC connect and ground are the same, that won't cause any issues? What's the best way to run the grounds for the speakers in that case?
I tried asking these questions on the product forum, but that place seems to be a huge mess of ppl who are confused like myself haha.
Would appreciate any tips from ppl who are currently using the delay circuit in their amps.
Hi there, I am back to update anybody who's willing to listen. lol I got my chassis some time ago and built both channels of my amp successfully. I am almost done, I have the soft start built and installed.
I have also finished the speaker turn on delay, which has been really annoyingly hard for such a simple and straight forward circuit there's a lot of confusion with this product. I am running it off of the 18v winding of my antek transformer. Seems to work, and gives about a 3 second delay before clicking the relays in. However I haven't been able to hook the speakers up to it, or test it's DC blocking feature.
How does the circuit reference ground to know that there is a DC fault? The build guide says nothing about this? I only have it hooked up to AC which is not ground tapped on my transformer. Can I run a ground back to the star ground point? The AC connect and ground are the same, that won't cause any issues? What's the best way to run the grounds for the speakers in that case?
I tried asking these questions on the product forum, but that place seems to be a huge mess of ppl who are confused like myself haha.
Would appreciate any tips from ppl who are currently using the delay circuit in their amps.
With no load there are no large currents flowing (those would be expected to vibrate the output inductor for instance due to magnetic field forces). This suggests its a capacitor that's causing the sound - the high electric fields internally distort the shape by a tiny tiny amount, but this can be enough if acoustically coupled to a pcb. Though its unusual to hear this except with non-linear ceramic caps (where the crystal structure changes in response to the field, as they are ferro-electric).
I have not built a Honey Badger or the specific speaker board you are using, however I have used a generic one and assume it is similar. It has an AC input which gets rectified and regulated to 12VDC. The amplifier output, positive and negative, go the board with speaker ground connected (on board) to the 12VDC ground. The board senses the DC voltage between speaker positive and negative inputs and opens the relay if DC voltage is greater than around a diode drop either way.
Thanks for the reply, this board only takes the amp ouputs without ground and the speaker without ground. There is no actual ground connection anywhere. I think I have to connect it back to ground from the same place that one of the ac leads goes into the terminal, dunno if that will case a problem. I don't think the ac would have a path back to ground if i only connect one lead back. I mightve been better off just buying some china special protect board, at least those have all the connections required haha
Pulled up the schematic and am a little surprised. To better protect the speaker on amp failure you need to ground the amp output through the relay, otherwise current will arc across the open contacts due to speaker inductance and cause damage. The schematic shows them just opening up.
FWIW, I bought this item a few months ago during a vintage amp rebuild and it measures and works very well - Speaker protection board with Delay. And I think I misspoke - the 12VDC supply ground on this board is isolated from the speaker ground. The board uses floating base-emitter junctions (PNP/NPN) to detect DC offset - no direct connection to the relay driving circuit.
So the one I have needs modification to work? The product info thread is very confusing and the original designer isnt around or doesnt answer. There are ppl just doing whatever with no explanation and the documentation is just plain wrong and hasnt been corrected. I don't want to hook this up to a pair of speakers that are worth over 1000 dollars.
It would be nice if someone that's using the board could comment. In my vintage amp, originally the amp output and ground came off the amp board and went to the output connectors on the back of the chassis. I inserted the relay board by cutting those lines (output / ground). Amp output / ground go to to the relay board input, then relay output / ground go to the output connectors. To minimize hum, I tightly twisted output and ground wires together on their way to the relay board and on their way to the chassis connectors. The one mod you should make is to connect the bottom relay contact, currently shown open, to amp output ground, so when a DC error is detected the amp output is shunted to ground. Not sure how the above compares to the Honey Badger suggested wiring.
Thanks for the link, I spent a lot of time and money building this amp. Kinda dissappointed with the speaker protection circuit sold by the diy store. I'll have to fart around with cheaper test speakers for now, and spend weeks sifting through posts from 6 years ago until I may stumble upon somebody elses solution.
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