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Messages - Loudthud

#16
Quote from: Enzo on April 11, 2022, 12:54:41 PMIt is like an electrical appliance in your home.  If double insulated, no need for earth.   Just my opinion.
All you need is a double insulated guitar and you're set. Without the safety ground, you can get hum and mild shocks when you touch microphones or other guitar players :(
#17
The clipping LEDs make the amp a little more bedroom friendly. When operated with the Master Volume turned down so as not to allow the power amp chip to clip, the LEDs give the effect of more preamp gain and allow the Master Volume to be turned up a little farther past the point where the volume jumps from nothing to too loud.
#18
The Newcomer's Forum / Re: Modding a Frontman 15
March 29, 2022, 01:38:06 AM
A low cost amp such as this is probably not capable of driving an additional speaker. The power transformer and power output chip are carefully chosen for low cost. It may be possible to drive two speakers, but they would need to be twice the impedance of the stock speaker.
#19
Quote from: Jazz P Bass on March 04, 2022, 01:12:43 AM
Did you search the web?
I found this.
Not sure of the particulars.
In the upper right Notes section it says PCB: JMP27A
#20
Quote from: phatt on February 25, 2022, 06:33:06 AM
Mean time all the older analog stuff (SS or Valve) which are mostly simple designs will still be repairable.

That assumes you can find someone to repair it and they can find the parts. If you can find somebody, they may be half way across the globe.
#21
Amplifier Discussion / Re: Panasonic AN17827A chipamp?
January 23, 2022, 02:43:47 AM
I think the big limitation will be that the package will limit the power dissipation. Apparently the chip comes in a 16 pin dip and there are no options.
#22
That resistor looks like 1/8W. At 180K it would take 150V to reach 1/8W. If it is 18K ( multiplier looks like orange to me ) it would take 47V. E=Square root (P*R)

Is there that much Voltage in that circuit ? If it were me, I'd unsolder one end of the resistor on the good board and measure it.
#23
Huh ? Those schematics look like wireless transmitters.
#24
Schematics and Layouts / Re: Sunn Beta PCB
November 05, 2021, 04:37:43 PM
Here's where DiscoVlad stole the idea for the MC14506 replacement.

https://forum.sunnstillshines.online/index.php?topic=6864.msg29374#msg29374
#25
The link you posted does not download completely for me. From what I can see, the death cap is C2, .02uF 600V. One side goes to ground, the other to one side of the power switch.
#26
Pin 3 of your pot symbol appears to be the clockwise terminal, therefore, the Mid, Treble and Bass controls are backwards.
#27
Amplifier Discussion / Re: Fender M80 Issues
September 25, 2021, 10:06:31 AM
Back in the days of fixing vacuum tube TV sets, the diagnosis was No Picture, No Sound.
#28
What impedance speaker load do you intend to use ? If 4 Ohms, you will need a rail to rail Voltage of about 100V. For 8 Ohms, about 140V.

The good news is that  the capacitors used as local bypass of the rails on the board are marked as 220uF @ 100V so you are good there. But, only 4 output devices is on the light weight side for a musical instrument amplifier of 200 Watts. Better to have six or eight. Also, those standup 0.22 Ohm emitter resistors might be hard to find.
#29
Look for something with a bigger Safe Operating Area (SOA).
#30
Like most of these modules, the output is balanced. That means you can't ground one side, and you shouldn't use phone type plugs because there will be dangerous Voltages on the metal shells.

There is no good way to drop Voltages to what you need. You can burn several hundred watts via analog means, or build a switching regulator :(