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Messages - mandu

The Newcomer's Forum / Re: Shorted IEC line filter
January 28, 2023, 06:40:50 AM
These line filters live for many years.
Probably, the ac supply voltage exceeded more than the rating of some component for too long.

Amplifier Discussion / Re: Fender 112 Deluxe Plus
September 01, 2022, 10:40:08 AM
The diodes may be producing some RF induced hum. Try connecting 0.01 uF capacitors across each of the diodes to see if it reduces the hum.
An interview with Bob Galien by sweetwater where he explains some designs of his amlifiers.
(30 minutes)
For those interested.


One schematic with 3886 output with +/- 31 volts supply has 130 ohms in the PSU circuit.
The other schematic with 2050 output with +/- 22 volts supply has 10 ohms in PSU circuit
No mention about the output power in both the schematics.

Is this the resistor attached to the 12 volt regulators?
Quote from: Tassieviking on June 19, 2022, 08:58:36 AMThanks guys for the answers, I think I will not keep the Electrolytic caps since I don't know the age of them.
Better be safe then sorry.

I would suggest you experiment with those old electrolytic capacitors before throwing out to learn something and acquire some knowledge out of it. Regards.
I had a pair of new 6800mf/80 volts caps in shelf for 10 years. With capacitance meter both measured good above 6800 mf. To clear doubt I connected a 40 volts DC supply and left for 30 minutes. The capacitors became very hot and I have to throw them away.
Either the capacitor becomes dry (lower capacitance) or have lower dielectrics (high leakage current).
You can connect a DC power supply to it and check if they survive as I did.
If the physical look is bulged, then throw them away.
Can you check if C7 (2.2 mF) in poweramp is OK?
May be no heatsink compound on the power transistors. Only mica washers?
If you reverse the phase and neutral, does the hum goes away? If it works, you still have to rewire the on/off switch correctly that it disconnects the live end for continued safety.
Rod designs are good and proven. But one big bottle neck is some board designs do not have mounting holes. The board is supported by either the power transistors clamping bolts or by the potentiometers. To me they are not that much flexible to use when using TO3 transistors or separate potentiometers. Just my view. There are many who have successfully used his boards. Regards.   
Preamps and Effects / Re: Fender STC1 Chorus Pedal
April 23, 2021, 09:37:14 PM
Great information in one place.
Philips produced TDA1022 and TDA1097 BBD chips
And there was SAD512 chip from some other manufacturer
These were originally developed for telephony applications.
Thank you very much.
Preamps and Effects / Re: Fender STC1 Chorus Pedal
April 22, 2021, 07:46:57 AM
Just a small explanation of the name bucket brigade delay.
Imagine a line of 10 fire fighters. One side is fire and the other side is water. Buckets of water has to be moved from the water source by buckets to the other to kill the fire.
Since the fire fighters are in a line, when they receive a bucket of water, they can't deliver to the next person. Similarly when they deliver water to the next person, they can't receive water.
A BBD chip in similar, has tiny line of capacitors (say 511) inside representing the buckets. Electronic switches (say 512) are in between each capacitor and the  switches represent the fire fighters.
The odd numbered switches and even numbered switches are turned On and OFF alternatively from the square wave signals.
When the odd numbered switches are turned on, they transfer the charge from the left side capacitors (input side) to the right side capacitor. When the even numbered switches are turned on, they transfer the charged capacitor value to the next and so on.
At the output, switches 511 and 512 outputs are connected together so there is a continuous signal flow. Now there is signal at the output but chopped at the same frequency as the square wave.
Since this chopped frequency is 30 Khz or more, a low pass filter of 20 Khz is inserted at the output to filter out all higher frequency above audible range. If the portion of signal is fed back to the input to create a flanging or echo, another low pass filter is required at the input before the BBD.
Since the stages work similar to the bucket brigade fire fighters, hence the name bucket brigade delay line.
To prevent loss of signal (leakage of capacitors) during modulating frequency transition, the driver chip is interlocked internally cmos or ttl gates so the rise and fall of the wave forms never cross each other.

Preamps and Effects / Re: Fender STC1 Chorus Pedal
April 21, 2021, 08:42:19 PM
All those early chorus pedals used a BBD chip (bucket brigade delay line chip) and are obsolete now.
If you want to service, :
The BBD chip has variants. Some with 512 stages, some with 1024 or 4096 stages. 4096 stages usually for producing longer delays (echo).

All the circuits using the BBD chip have these common components.
Signal path : An input buffer > low pass filter (20KHz) > BBD chip > low pass filter (20KHZ)> output buffer, mixer
Modulation path : A Low frequency oscillator (0.5 Hz to 10 Hz) > A square wave oscillator with 2 outputs with 180 deg opposing phase

The square wave oscillator IC drives the BBD chip. (one for odd numbered stages and other even numbered stages). This frequency determines the delay time. This square wave oscillator frequency is varied (modulated) with a very low frequency oscillator triangle wave (LFO), thus the delay time is also varied.
The instrument signal is buffered and passed to a low pass filter (around 20 KHz), then to the BBD chip. The output from BBD is passed through another low pass filter (around 20KHz). This signal is mixed with the original and buffered to output.   

Depending on the delay time, feedback and mixing methods, same circuit does the chorus, flanger, delay, echo etc.

Hope this is of little help.
Year 2001 application note from ON semi regarding mounting considerations for power semiconductors. Regards.