Hi!
After a few weeks of using Restek Optima mfb speakers i have a few questions:
1.
When music off both speakers go into standby mode. When music is back only one speaker is awaking. The second one needs long time to wake up (about 20 minutes or more) or needs to bi hit 🙂 After hit speaker is waking up immediately. Do you have any idea what is wrong?
2.
Second question is: do i need to trim mfb circuit? I guess R57 is that trimmer but how to measure correct position?
3.
Is R58 trimmer offset correction? Shoud I trim it to get 0V between 0,33 ohm resistors?
Thanks to Zapper scheme is HERE.
Regards
ED
And a few photos:
@Edward wrote:
Hi!
After a few weeks of using Restek Optima mfb speakers i have a few questions:
1.
When music off both speakers go into standby mode. When music is back only one speaker is awaking. The second one needs long time to wake up (about 20 minutes or more) or needs to bi hit 🙂 After hit speaker is waking up immediately. Do you have any idea what is wrong?2.
Second question is: do i need to trim mfb circuit? I guess R57 is that trimmer but how to measure correct position?3.
Is R58 trimmer offset correction? Shoud I trim it to get 0V between 0,33 ohm resistors?Thanks to Zapper scheme is HERE.
Regards
ED
Edward, I am not absolutely sure but my guesses are :
Question 1) the circuit is not charging a capacitor fast enough, or the capacitor is decharged by an off-specs leak-current. This should be one of the capacitors around the 555. First check the solder joints... Then check the capacitors, or replace them. Also check the components around T14 (and the op-amp), for they also control the operation of the 555. Use the values measured in the proper working amp as a guideline (note them for future use!).
Question 2) R57 appears to control the feedbackcircuit. Since the type of feedback in a MFB circuit is verry delicate, you ought to be careful adjusting it. B.T.W. is there any reason why you want to correct the setting?
Question 3) R58 controls the Quiesentcurrent of the powertransistors. This quiesentcurrent determins a certain area in which the amp operates in Class A, to reduce cross-over distortion. In Class AB amps, like these, the quiesent current ranges usually from 20mA till 100 mA. I, however can't tell you the correct setting for this amplifier. IF you have a scope and a generator, you can determine the correct setting in an empirical way.
Good luck.
esgigt,
Thanks for answer.
is there any reason why you want to correct the setting?
Actually no 🙂 I just think that after many years it needs to be corrected but i can be wrong.
IF you have a scope and a generator
Yes, i have good digitizing scope and sine wave generator, but maybe better idea is to leave circuit as is.
A pair of 22AH587 is waiting for inspection too 🙂
Regards
ED
