I've been attempting to build a DOZ amplifier using a custom board I created. First time ever creating one so if its way wrong please let me know so I can learn. Having a couple issues during my testing.
When initially trying to dial in the bias to 1.7amp I accidentally allowed it to pull through 8+ amps so its possible I killed it then and there but there was no smoke. I pulled the transistors and tested and they all test within range oddly enough. I resolved my vr2 issue and can get it to 1.7a after warming up however my output is 3.3v it says to measure and set vr1 to output to half input(24v).
Possibly just a bad design on my part or I fried something, but figured maybe someone could look at what I did and see something obvious.
The schematic should be inline with what's publicly posted. (See below)
Board design below. Did I over do the ground? 🙂
When initially trying to dial in the bias to 1.7amp I accidentally allowed it to pull through 8+ amps so its possible I killed it then and there but there was no smoke. I pulled the transistors and tested and they all test within range oddly enough. I resolved my vr2 issue and can get it to 1.7a after warming up however my output is 3.3v it says to measure and set vr1 to output to half input(24v).
Possibly just a bad design on my part or I fried something, but figured maybe someone could look at what I did and see something obvious.
The schematic should be inline with what's publicly posted. (See below)
Board design below. Did I over do the ground? 🙂
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It looks like the collector and emitter of Q1 are flipped on both your schematic and board.
In another thread, I saw you asked whether the output capacitor is needed or not. You don't need it for the amp to function, but you do need it if you want to connect a speaker. You will be adjusting VR1 so you see about 1/2 the supply voltage on the output, and the purpose of that capacitor is to block that DC voltage from the speaker, so the speaker only sees the AC signal.
First plan how you are going to mount the PCB to the HEATSINK. This amp requires big Heatsink !
You are missing the output capacitor feeding the speaker, otherwise the speaker coil will see half the DC supply volts - not good. Refer to Rod Elliot's DOZ project and copy it 100%
looks like a JLH copy with a few bells.
mostly pointless since you get regulation from a cheap 24 volt laptop supply
1.7 amps seems somewhat high for 24 volts
high fT transistors can make the older design oscillate
6 or 8 distortion watts, dirty 9 or 11 watts
3800 to 4700 output cap for better bass
mostly pointless since you get regulation from a cheap 24 volt laptop supply
1.7 amps seems somewhat high for 24 volts
high fT transistors can make the older design oscillate
6 or 8 distortion watts, dirty 9 or 11 watts
3800 to 4700 output cap for better bass
Looking at your schematic, I see you show the output cap C3 off the pcb, this should be a minimum of 4700uF using audio grade caps. As for the rest of the circuit, it is a copy of Rod's design, using 27VDC rail and with an 8 ohm speaker load, Rod suggests a quiescent current of 1.35 amps (135mV across R13) for a total channel dissipation of 36.5 watts (18.25watts per transistor) for an output power of 8.5 watts rms.
Pot VR1 sets the DC voltage at the output to half the supply volts (13.5VDC) and pot VR2 sets the quiescent current in the output stage. Does your output voltage which you say is 3.3v change as you adjust VR1? If not then you have a faulty component - are both channels doing the same?
Pot VR1 sets the DC voltage at the output to half the supply volts (13.5VDC) and pot VR2 sets the quiescent current in the output stage. Does your output voltage which you say is 3.3v change as you adjust VR1? If not then you have a faulty component - are both channels doing the same?
OMG, not sure how i missed this. I flipped it but pretty much the same.
I brough the amps down to 1.3/1.4a
I checked r13 and i see almost 200mv
Changing VR1 does change output but only by a few 100mv
I've only built the one channel incase i did something stupid that fried components. Like flipping a transistor the wrong way or putting far too many amps through it...🤣
Yeah, i saw this as i was searching the forms trying to figure out what I've done wrong. I have some slower parts in a cart ready to go but wanted to see if what i built is salvageable or if i needed to scrap it or buy a bunch of replacement parts. Or if there are better things to try to build. I built the ACA and wanted to see if i could do something purely from schematic... so far not going well. hahaha
Replacement parts i was looking at was the TIP3055.
Please see this thread also !
https://www.diyaudio.com/community/threads/death-of-zen-15-watt-power-amplifier.208076/
https://www.diyaudio.com/community/threads/death-of-zen-15-watt-power-amplifier.208076/
Found my new issue. My schematic app connected base of Q4 to R4 and C2. After cutting that path i now have the expected results!
Thank you all for the help!!!
Thank you all for the help!!!
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Yeah this was the one where i found i should probably change my output transistors due to the fT issue.