Hello everybody, i have problem i was hoping you could help me with!
So.. I built two channels of api 312 (using Bauman's pcb:s), and some melcor opamps.
I tested one of the channels some time ago and they were working fine.
Then i read the thread "melcor deconstructed", and did the mods to the circuit as proposed. Dual diode at D2 position, and C1 change to 680pf instead of 1000pf.
When i fired up one of the modded opamps all i got was hum, so i tried the other one...same result, only hum...But strangely enough i was able to pass audio from the di input...strange.
After a while of running i noticed that it started to smell funny...and then suddenly i realised that the Bd136 transistor had gotten so warm that it had unsoldered itself from the pcb.
Any ideas why this happened?
Ok, after this happened i took the other opamp and restored it to the original condition which had worked before.
Fire it up, and... Theres sound, but the headroom seems alot lower (the sound now transistor distorts alot quicker than it did before), and the gain pot (im using a revlog pot instead of a switch) works differently.
When before i had the gain setting at zero, i got almost no signal into my computer. Now, i get plenty of gain at zero setting, and the headroom seems to be alot lower than before (i think). The gain pot still works though, so when i turn up the gain, i get well...more gain.
Which way is the pot supposed to behave? Almost no signal at zero position, or alot?
So, i tried substituting the melcor with a chip opamp, and i get the same result. great sound, but less headroom and alot of gain at "zero" setting on the gainpot.
So, any ideas to why the circuit is behaving like this, why the modded melcor didnt work, and why it fried my BD136?
I really dont know where to start looking for faults (im a newbie starting out).
btw, i already checked the voltages coming out of the psu, they seem ok.
Please help!
/Jonas
So.. I built two channels of api 312 (using Bauman's pcb:s), and some melcor opamps.
I tested one of the channels some time ago and they were working fine.
Then i read the thread "melcor deconstructed", and did the mods to the circuit as proposed. Dual diode at D2 position, and C1 change to 680pf instead of 1000pf.
When i fired up one of the modded opamps all i got was hum, so i tried the other one...same result, only hum...But strangely enough i was able to pass audio from the di input...strange.
After a while of running i noticed that it started to smell funny...and then suddenly i realised that the Bd136 transistor had gotten so warm that it had unsoldered itself from the pcb.
Any ideas why this happened?
Ok, after this happened i took the other opamp and restored it to the original condition which had worked before.
Fire it up, and... Theres sound, but the headroom seems alot lower (the sound now transistor distorts alot quicker than it did before), and the gain pot (im using a revlog pot instead of a switch) works differently.
When before i had the gain setting at zero, i got almost no signal into my computer. Now, i get plenty of gain at zero setting, and the headroom seems to be alot lower than before (i think). The gain pot still works though, so when i turn up the gain, i get well...more gain.
Which way is the pot supposed to behave? Almost no signal at zero position, or alot?
So, i tried substituting the melcor with a chip opamp, and i get the same result. great sound, but less headroom and alot of gain at "zero" setting on the gainpot.
So, any ideas to why the circuit is behaving like this, why the modded melcor didnt work, and why it fried my BD136?
I really dont know where to start looking for faults (im a newbie starting out).
btw, i already checked the voltages coming out of the psu, they seem ok.
Please help!
/Jonas
