Hi,
Can you lift one side of resistor 51 and see if the oscillation in the +15 goes out and the hum stop.
Can you lift one side of resistor 51 and see if the oscillation in the +15 goes out and the hum stop.
Lifted R51, no difference.
Replaced TR1,2,3 w/ 2N5089, 2N5088, MPSA06 respectively, no difference.
Not feeling defeated quite yet...I guess I'm now suspecting a noisy resistor in the preamp somewhere...
Replaced TR1,2,3 w/ 2N5089, 2N5088, MPSA06 respectively, no difference.
Not feeling defeated quite yet...I guess I'm now suspecting a noisy resistor in the preamp somewhere...
Hi,
Can you lift R56 and R54 ? This will isolate the preamp from the vibrator and from the reed. Also did you check the variable resistor for the vibrator control?
Can you lift R56 and R54 ? This will isolate the preamp from the vibrator and from the reed. Also did you check the variable resistor for the vibrator control?
Lifting R56/54 made no difference. The trimmer pot seems OK...I've cleaned it and it swings properly between one end to the other.
I've discovered that the noise is actually hum (60hz?) as well as hiss. I've grounded some things in the preamp...
Grounding the Base of TR 2 or 3 stops the noises entirely.
Grounding the Base or Emitter of TR1, or the trimmer pot on either end stops the hum, but not the hiss. The noises are of about the same volume so there is no really improvement. So somewhere between TR1 and 2?
I've discovered that the noise is actually hum (60hz?) as well as hiss. I've grounded some things in the preamp...
Grounding the Base of TR 2 or 3 stops the noises entirely.
Grounding the Base or Emitter of TR1, or the trimmer pot on either end stops the hum, but not the hiss. The noises are of about the same volume so there is no really improvement. So somewhere between TR1 and 2?
Hi,
With the R56/54 Lifted check the +15 volts with the scope. Make sure it is clean. Also short the reed input and the mic. If I remembered when you short the pin 5 and pin 1 of the volume the hum when away. Right?
With the R56/54 Lifted check the +15 volts with the scope. Make sure it is clean. Also short the reed input and the mic. If I remembered when you short the pin 5 and pin 1 of the volume the hum when away. Right?
With R54/56 lifted, the 15V looks the same...10mV oscillation...nothing big.
Shorting the inputs has no effect. Shorting the volume pot does make the hum go away.
Shorting the inputs has no effect. Shorting the volume pot does make the hum go away.
Hi,
Let see where the hum it is generated. Scope the base of TR1,TR2 and TR3. It will tell us where the hum start.
Let see where the hum it is generated. Scope the base of TR1,TR2 and TR3. It will tell us where the hum start.
Ok we're getting somewhere.
I was able to kill the hum by adding the a 3rd filter (.33uf) to the reed bar pickup as shown in later schematics. As for the hiss, the base of TR 1 and 2 are clean. The scope shows noise at the base of TR3.
Thank you so much for your help thus far, I appreciate it 🙂
I was able to kill the hum by adding the a 3rd filter (.33uf) to the reed bar pickup as shown in later schematics. As for the hiss, the base of TR 1 and 2 are clean. The scope shows noise at the base of TR3.
Thank you so much for your help thus far, I appreciate it 🙂
Hi,
Now that the hum it is going lets see where the hiss it is coming. Do you have the R54 back? If yes remove it and see if the hiss still there. Compare the TR2 base signal with the TR2 collector signal.
Now that the hum it is going lets see where the hiss it is coming. Do you have the R54 back? If yes remove it and see if the hiss still there. Compare the TR2 base signal with the TR2 collector signal.
I've removed R54 and measured again...TR2 base is clean, TR2 collector is noisy just like the TR3 base as before. When R54 is installed I can hear the hiss modulate slightly due to the vibrato circuit, even though the vibrato pot is full CCW. Removing R54 reduces the hiss by about 10%, if that.
Hi,
Let's do another test since by R54 the hiss dropped 10 % and the hum it is gone. Removed again R54 and R51 these will eliminate completely the vibrato from the circuit. If the hiss goes away then the noises it is coming from the vibrato but if still there then noises it is coming from the +15 volts. The TR2 base it is cleaned and collector it is noisy it is possible that the noises must come from the +15 volts.
Let's do another test since by R54 the hiss dropped 10 % and the hum it is gone. Removed again R54 and R51 these will eliminate completely the vibrato from the circuit. If the hiss goes away then the noises it is coming from the vibrato but if still there then noises it is coming from the +15 volts. The TR2 base it is cleaned and collector it is noisy it is possible that the noises must come from the +15 volts.
R54/51 removed and the noise remains. How can it be the 15V line if the collector of TR3 is clean?
- Status
- Not open for further replies.