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Messages - Jazz P Bass

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1
Amplifier Discussion / Re: Dean Markley Spectra 225A Solid state amp made a loud pop and then didn’t work
« on: March 22, 2021, 06:57:41 PM »
The amplifier had a failure.
Take it to a tech.
Attached schematic.

2
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.

3
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?

4
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.

5
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.

6
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.

7
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

8
The Newcomer's Forum / Re: Yamaha G100II Broken, Help Wanted...
« on: March 01, 2021, 01:56:09 AM »
This may be the correct schematic:

9
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?

10
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.

11
Amplifier Discussion / Re: 1967 Mosrite BG-500 Output Transistor Bias Question
« on: February 22, 2021, 11:55:14 AM »
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.


12
Amplifier Discussion / Re: Help - Roland JC 120 no chorus
« on: February 14, 2021, 01:37:09 AM »
There are many different schematics on this amp model.
here is the '1982'.
See if it is close.
You need to troubleshoot the circuit.

13
Amplifier Discussion / Re: Amp Input Jacks
« on: February 04, 2021, 11:22:34 AM »
Here is a pic of the jack and the Harvard wiring.
The numbering scheme that you used depends on how you are looking at it.
Use the jack drawing and you will get it right.

14
Amplifier Discussion / Re: Rocktron Rampage R80 - No Sound problem
« on: January 29, 2021, 11:40:49 AM »
Nice work!

15
Tubes and Hybrids / Re: Reduce signal from preamp.
« on: January 20, 2021, 10:38:32 AM »
Not too sure what you want to do.
The input sensitivity of the module is listed as 80mv's.
If your input signal is too hot, knock it down with a voltage divider.
2 resistors. 1 in series. 1 to ground.

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