Hi,
The 100 ohm resistors are used to protect the circuit from damage in the event of faults or bias mis-adjustment. Until the amplifier is working correctly, I strongly suggest you fit these in place of the fuses.
It may not be a bad idea to start by connecting one pair of output transistors instead of five as you have done. Just don't operate the amplifier at high output with a low-impedance load at this stage.
What did you have connected to the input and output to determine that you have distorted sound?
Could you take some DC voltage measurements please:
1) -ve probe on 0V, +ve at top end of R28
2) -ve probe on 0V, +ve at lower end of R28
3) voltage across R6
4) voltage across R7
5) voltage across R17
6) voltage across R20
7) The output to 0V (offset)
Thanks,
currentflow
Thanks for helping me.
What did you have connected to the input and output to determine that you have distorted sound? I connected my mp3 player at low volume and the sound was distorted, incresed the volume, sound gets more distorted, not clean at all.
Now I changed the R24 1.2k to 680oh. bias adjusted but sound still not clean.
R5 is a resister, no jumper wire.
I added two 100oh on the + and - Rail.
I mesure some Rail voltage on -+ Rail:
+Amp side volt Rail-v1-100oh--25.48 V (V1 = 22.49v )
-Amp side volt Rail-v2-100oh--25.46 V (V2 =22.33v )
) -ve probe on 0V, +ve at top end of R28 = 0.964V
2) -ve probe on 0V, +ve at lower end of R28 = 0.253V
3) voltage across R6 = 123mv
4) voltage across R7 = 144mv
5) voltage across R17 = 69mv
6) voltage across R20 = 301mv
7) The output to 0V (offset) = 0.046v
Across R39 = 1mv
Across R44 = 5mv
Regards
Michael
What did you have connected to the input and output to determine that you have distorted sound? I connected my mp3 player at low volume and the sound was distorted, incresed the volume, sound gets more distorted, not clean at all.
Now I changed the R24 1.2k to 680oh. bias adjusted but sound still not clean.
R5 is a resister, no jumper wire.
I added two 100oh on the + and - Rail.
I mesure some Rail voltage on -+ Rail:
+Amp side volt Rail-v1-100oh--25.48 V (V1 = 22.49v )
-Amp side volt Rail-v2-100oh--25.46 V (V2 =22.33v )
) -ve probe on 0V, +ve at top end of R28 = 0.964V
2) -ve probe on 0V, +ve at lower end of R28 = 0.253V
3) voltage across R6 = 123mv
4) voltage across R7 = 144mv
5) voltage across R17 = 69mv
6) voltage across R20 = 301mv
7) The output to 0V (offset) = 0.046v
Across R39 = 1mv
Across R44 = 5mv
Regards
Michael
Please verify R5 is actually 10 ohms.
Changing the value of R24 will only modify the adjustment range for the bias. If the correct bias is achieved, this resistor will have no other effect on the sound.
Thank you for your readings. The CCS (T5, T6), differential input pair (T1, T2) and current mirror (T3, T4) all appear to be working normally in their steady-state condition. T5 collector is passing 2.7mA which agrees with the calculated value. Similarly, the current through the VAS (T8) & T9 seems to be as per that expected.
Temporarily increase the bias current to give 10mV across R39 and see if this resolves the distortion. This will give a quiescent current of 21mA through T12. We should be able to identify whether this is crossover distortion or instability.
Incorrect values for C9 and C7 might also lead to instability / oscillation and hence distortion. Worth checking.
Are you monitoring the output sound quality with a speaker attached?
Regards,
currentflow
You didn't say how you are listening to the output. Is a loudspeaker or some other load connected and, if so, what is its impedance?
Regards,
currentflow
That speaker load should be fine. Is the speaker possibly damaged? (sorry to ask!) Are the transistors you've fitted exactly those as specified? If not, do the ones fitted have the same pinouts?
Try using a different pair of output transistors after disconnecting the originals, then re-adjust the bias setting.
The lower end of R5 isn't open-circuit to ground by any chance?
As BMW850 suggests, you may have one or more fake transistors...
Regards,
currentflow
Your transistor substitutes as listed should work fine. Other areas to investigate include PCB track breaks and/or shorts and faulty components. Do you have an oscilloscope?
Regards,
currentflow
Have a video made of the amplifier with my mobile phone.
Hopefully I have the music not too loud, no talking about distortion sounds
Here you can also see my acoustics ceiling treatment.
You also see my jumper/wire over the 1uF, it sound much better without the 1uF.
Special Note about the 1uF cap, you can do this only if you use a preamplifier, NOT with a passive volume control.
I'm not going in discussion why not, some things come not from myself.
You have chance you get than a problem, because you are going to hear the steps of the passive volume control.
You also select a piece of DC along with your passive volume control
My Fettle Preamp (and 99% of other preamps) has a output capacitor, which stops the DC, and also before the pre.
Video now uploading (748mb):
http://www.youtube.com/watch?v=X0pkmtH0058
Regards,
Rudy
Hopefully I have the music not too loud, no talking about distortion sounds
Here you can also see my acoustics ceiling treatment.
You also see my jumper/wire over the 1uF, it sound much better without the 1uF.
Special Note about the 1uF cap, you can do this only if you use a preamplifier, NOT with a passive volume control.
I'm not going in discussion why not, some things come not from myself.
You have chance you get than a problem, because you are going to hear the steps of the passive volume control.
You also select a piece of DC along with your passive volume control
My Fettle Preamp (and 99% of other preamps) has a output capacitor, which stops the DC, and also before the pre.
Video now uploading (748mb):
http://www.youtube.com/watch?v=X0pkmtH0058
Regards,
Rudy
Last edited:
Video may contain content that is in possession of or administered by these entities:
• Entity: WMG and UMG content type: audio recording.
Therefore, your video is blocked in the following locations:
American Samoa, Guam, Northern Mariana Islands, Puerto Rico, United States, United States Minor Outlying Islands, United States Virgin Islands.
Nowadays one can download music anywhere in the highest bitrate and a simple video is blocked by youtube
• Entity: WMG and UMG content type: audio recording.
Therefore, your video is blocked in the following locations:
American Samoa, Guam, Northern Mariana Islands, Puerto Rico, United States, United States Minor Outlying Islands, United States Virgin Islands.
Nowadays one can download music anywhere in the highest bitrate and a simple video is blocked by youtube
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