ESP Project 3A - 60-100W Hi-Fi Amplifier Problem and need helps

[bugbite2k]

Any 1 in here built this amp before ? If so could you guys help me out here ..... I started building this amp and as I tested using 12 V 1A , but the led didn't light up and no sound output ....... I did follow the instructions from Rod but still I got the same problem on my second amp ....... can any 1 help me out or direct me some idea about this sistuation ..... help me please I been wasted alot of $ and didn't get it to work ...... by the way do you need to hook up the SIM in ??? I only hook the Input not the SIM

[paulb]

I'm just finishing an amp that uses these boards. I didn't have any problems with it.
Are you using a +/- supply? You need more than just a + (positive) 12V supply. I'm using +/- 25V DC, from a transformer that supplies 36V AC and has a centre tap, same as Rod recommends but lower voltage.
Check some voltages at various points within the circuit and I can compare them against mine. It's a convenient time for me because the amp is not covered up at the moment.

[ih]

I don't know about others, but I know that mine definitely won't run off +/-6V - it dies somewhere around +/-10V (and the bass gives out well above that). There is a little volume peak somewhere between those two points (although it's pretty distorted).

You don't need the SIM for testing. I have the parts for mine still sitting in their bags from Jaycar...

At least you're getting the same problem with both amps, so if you can sort out the power supply issue, you know that they'll both respond the same (as opposed to having one known broken one). Of course, if they're both broken, that's worse...

Are you using the safety resistors? With them installed (and the full power supply), it's pretty hard to go wrong - measure the voltage drop, like Rod describes, and make sure it's within the limits - if it is, then it should be pretty safe to leave it on and poke around, even if it's not working properly. I think I calculated the current drawn by my amp (per rail, one channel, during initial testing, no bias) to be about 90mA.

I don't know if it was just me, but the first time I hooked mine up (no load), I measured something like 25V DC offset on the output. The moment I connected a load it disappeared, though. Both channels did the same thing, so I guess it's right...

[bugbite2k]

Well before you put it in the case is there anyway you could capture the picture of the finish amp so I could compare to my to see what was wrong with my ....... I really need you help if you could ..... thnx alot

[paulb]

I'm sorry, I don't have a digital camera so I can't take a picture.
If the LED is not lighting, you have a fundamental problem - it shouldn't be too hard to fix. You will need a voltmeter.
With the -ve lead of the meter connected to ground, measure the -ve rail (junction of D1, R7, R10, etc.: it should be -35V).
Then measure at the anode (R8 side) of the LED (should be about -33V).
You haven't answered our questions yet. What is your power supply? Are you using the safety resistors? I hate to ask, but have you installed the fuses?
By the way, I like your user name. Mine's pretty boring, like my real name.

[bugbite2k]

Yes I did follow the instruction that Rod gave me, and yes I did use the safety resistor, and I was using 12 V and 1A to test out ..... As I started the Q7 getting warm but the Q8 not as warm as Q7 ...... do you think the power supply too low ? because my Bridge rectifiers that I ordered didn't come yet so I dont have any higher then 1 Amp power supply in my house right now ..... and as I measure the r10 and r9 , there is no voltage across it ...... so I recheck for short or open around, but I didn't found any it was just fine ..... maybe I had no luck doing this
...... well if you know any 1 who had done this please ask them for a finish of the amp picture for me .......

[ih]

You've got a heatsink on the transistors, right? If so, I'd be guessing that you're only running one half of the amp (single rail), which is what's making one transistor hotter than the other. Could you describe how you're attaching your current power supply to the amp?

I don't know anything about R9/10 - my amp is in its case, so I can't check. I don't remember seeing anything in Rod's docs about it, though.

Also, I don't think anything should be getting warm without a bias setting, except maybe the input drivers (the BD139/140's). You shouldn't notice the power transistors getting warm at all.

[tiroth]

Not that this is of much help, but my P3A amps (A1302/C3213) actually work down to about +-3.5V. Pretty amazing really. I think +-12v@1A should be quite sufficient for testing.

I hate to ask this, but did you install Q9 (bias servo)? This was missing from an earlier version of the construction guide.

I'd also recommend checking all of your transistors...if there is low resistance (<20 ohms) between any pair of legs of any transistor, you either have a short or you've blown the transistor.

Please don't hook your amp up to anything bigger than a +-12V supply until you get at least the LED lit (constant) and can verify low DC offset at the output. Otherwise, even with the safety resistors, you /can/ hose the drivers.

[paulb]

bugbite2k,
I agree with ih, it sounds like you've only got a single power rail. That's why I suggested the voltage measurements on the negative rail and the LED. Q7 shouldn't get warm unless Q8 does too. You say you are using a 12V, 1 Amp supply. Are you using two 12V supplies to get the +/-12, or just a single one?

[bugbite2k]

no I only using single +/- 12V ...... and yes I did installed Q9 trioth, it seem fine ..... all other input Qs, like Q4, 5, and 6 got voltage drop in them ...... so are the metal side of Q4, 5, and 6 suppose to face the input of the amp as Rod described (I made it face the input side) ??? and i just use a single turn trimpot, notice the pot arranged as 2 leg and 1 legs on the opposite of the 2 legs. and I hooked that single legs to be in the middle of the hole in VR1 ..... you think that's correct ???