waiting for OS...Decided to put this to the test. In the Symasui R28 (22K) was changed to 5.6K and offset settling time was greatly reduced. The speaker protection system I have now dominates the waiting time for audio to appear after switch on.
If there are any undesirable aspects to the change I have not become aware of them by listening, so far.
Keith
I'm almost ready to fire up the 5p ops with spooky ips, can someone guide me through the adjustments? What are the trimmers on the spooky ips for, what should the initial setting be and where to measure?
Do I measure the bias over the 0.22r resistors? What bias do you recommend for 5p 0302/0281?
Do I measure the bias over the 0.22r resistors? What bias do you recommend for 5p 0302/0281?
I fire mine up in sections. Fire up the outputs first with a bulb limiter in series with the mains and 15k resistors on the inputs. One from V+ to VD+ and one from V- to ND-. It's safest to do this with 1 output pair installed. The bias pot should be wound to the highest resistance setting. If the output board powers up without the bulb staying lit, try winding up the bias and see if you have control of the adjustment. Also measure DC on the speaker output. There shouldn't be much if everything is operating correctly. Bias should be 65 - 75mA, or around 30mV across a pair of emitter resistors. The bulb will light up as you increase the setting. If all is good turn down the bias and install all the output pairs, and check again. If all is good wind down the bias adjustment.
Fire up the input stages with their outputs disconnected from the output board and 1k resistors jumpered from PD+ to the NFB connection and from ND- to the NFB connection. Measure the voltage drop across R12. Adjust R19 so this is 3.8mA (3.8V). do the same with R13 and R10. After that's set, measure the voltage between PD+ and ND-. You should read around 11V if everything is working right. Also measure the DC offset at the NFB connection. I do this with the servo pulled out first just to see how good the input is matched, then with the servo in place. With the servo installed, there shouldn't be more than around 25mV present. If everything is well matched, it will be drifting around 2 or 3 mV.
If the input seems to be good, connect it to the output board and fire it up with the bulb still in place. Check for DC offset on the output and wind your bias up again. If you seem to have control of the bias, play some sine waves through the amp just to make sure everything is stable. The bulb will glow dimly as you slowly turn up the amplitude of the sine wave. If it goes from off to bright instantly, you probably have some oscillation. If all seems good, remove the bulb and start it up again. Set up your bias again and warm the amp up for a bit. You can just let it idle for a while, or cheat and hook up a load and play some sine waves. Keep checking the bias as it warms up. Also keep checking the temperature of the R137. If it's getting hot you likely have oscillation happening.
Once it's warmed up and if everything seems stable, it's time to listen to it and see what you think.
Fire up the input stages with their outputs disconnected from the output board and 1k resistors jumpered from PD+ to the NFB connection and from ND- to the NFB connection. Measure the voltage drop across R12. Adjust R19 so this is 3.8mA (3.8V). do the same with R13 and R10. After that's set, measure the voltage between PD+ and ND-. You should read around 11V if everything is working right. Also measure the DC offset at the NFB connection. I do this with the servo pulled out first just to see how good the input is matched, then with the servo in place. With the servo installed, there shouldn't be more than around 25mV present. If everything is well matched, it will be drifting around 2 or 3 mV.
If the input seems to be good, connect it to the output board and fire it up with the bulb still in place. Check for DC offset on the output and wind your bias up again. If you seem to have control of the bias, play some sine waves through the amp just to make sure everything is stable. The bulb will glow dimly as you slowly turn up the amplitude of the sine wave. If it goes from off to bright instantly, you probably have some oscillation. If all seems good, remove the bulb and start it up again. Set up your bias again and warm the amp up for a bit. You can just let it idle for a while, or cheat and hook up a load and play some sine waves. Keep checking the bias as it warms up. Also keep checking the temperature of the R137. If it's getting hot you likely have oscillation happening.
Once it's warmed up and if everything seems stable, it's time to listen to it and see what you think.
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A 10 ohm resistor won't hurt, but really isn't needed, unless you want to measure actual rail current. The bulb does the same thing. The bulb won't let anything burn.
Installing all the outputs won't hurt either, unless you figure out there's a problem with them, then you need to remove 5 pairs instead of 1 pair.
150mV should be fine. You are just seeing the gain differences between the positive side devices and the negative side devices. There is nothing to correct this until the input is connected, then the feedback circuit and servo will zero it out.
Resistors R23 and R24 have to be selected for the rail voltage you are using, otherwise you won't get the 12V zener diodes regulating. So, you need one set of R23 / R24 for low voltage testing and a different set of R23 / R24 for your intended rails. Shoot for at least 10-12mA through R23 and R24. You need enough current to supply the CCSs and the servo while still having some 'excess' to keep the shunt element, the zener, conducting.