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Messages - Jazz P Bass

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31
Your + & - 16 volt supplies are being pulled down.

32
Preamps and Effects / Re: Fender STC1 Chorus Pedal
« on: April 23, 2021, 11:22:41 AM »
Awesome 'gift'.
Thank you sir.

33
Preamps and Effects / Re: Fender STC1 Chorus Pedal
« on: April 22, 2021, 09:50:40 AM »
I had to make a pdf of this.:)

34
Preamps and Effects / Re: Fender STC1 Chorus Pedal
« on: April 22, 2021, 12:54:23 AM »
Nice run down on the BBD circuit, Mandu.
thanks.

35
The amplifier had a failure.
Take it to a tech.
Attached schematic.

36
Amplifier Discussion / Re: Fender Frontman 212R with distorted sound
« on: March 14, 2021, 01:17:25 PM »
When I listened to the mpg file my first thought was "that's a bad speaker".
But then I saw that you verified them as good.
Glad that you got it sorted out.

37
Amplifier Discussion / Re: Fender Frontman 212R with distorted sound
« on: March 14, 2021, 12:42:42 AM »
The dc voltages don't look bad at all.
You don't have access to a scope do you?

38
Amplifier Discussion / Re: Fender Frontman 212R with distorted sound
« on: March 13, 2021, 02:55:19 PM »
Next step is to measure the output transistor voltages.
The first stage opamp (pin #1 & #7), the driver bases & the output transistor bases. (the left leg of the component)
No signal. Volts dc.

39
Schematics and Layouts / Re: Gallien Krueger 100 MPL
« on: March 10, 2021, 12:32:28 AM »
That is one heck of of a circuit description write up!!!
You have not noted what is wrong with the unit but a good tech should be able to narrow it down with that excellent info.

40
Schematics and Layouts / Re: Fender Stage 112 SE - Transformer wiring
« on: March 09, 2021, 11:37:41 AM »
Where are you located ?
Are you wiring it for Domestic (110Vsc) or Export (220Vac)?

Here is the 'Domestic' layout.

Blk (CP8)and Wht (PS4) are the Primary leads from the Mains plug.
I can only surmise that the Wht wire (PS4) indicates Power Switch tab 4.

Red -Ylw- Red:  is the 45 Vac taps with Ylw being the Center Tap
CP1-CP2-CP3
Blu- Brwn- Blu is the low voltage Vac tap with Brwn being the Center Tap.
CP4-CP5-CP6

The tabs on the PCB should be clearly marked.

41
Amplifier Discussion / Re: Fender Frontman 212R with distorted sound
« on: March 07, 2021, 12:37:27 PM »
Please check the power supply voltages for stability, sameness & lack of ripple.
+ & - 42Vdc
+ & - 16Vdc

42
The Newcomer's Forum / Re: Yamaha G100II Broken, Help Wanted...
« on: March 01, 2021, 01:56:09 AM »
This may be the correct schematic:

43
Amplifier Discussion / Re: Fender M-80 Chorus Bias/Avalanche
« on: February 23, 2021, 11:39:19 AM »
Well you do have a working amp to compare voltage readings to.
First off, is R 165 cement resistor still good?

44
Amplifier Discussion / Re: Hohner 1250 Question
« on: February 23, 2021, 11:34:51 AM »
It appears to me that the diode string is what makes it a distortion circuit.
With the string removed you should have a clean signal.
If you do not, then you have other issues that need to be addressed first.

45
The output topology is Class A/B.
So with no current reading across the emitter resistors, the amp is in Class B.
Fellow member Enzo has an excellant old school method of setting the bias.
-Measure the current draw from the mains while turning the bias trim pot.
When you start to see more current being drawn, the amp is now entering the Class A part of A/B.
Turn the trim pot back down a tad and you are done.-
There is not a 'specific' current draw across the emitters that can be stated.


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