Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Messages - Loudthud

Pages: [1] 2 3 ... 18
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.

Amplifier Discussion / Re: newbie question about cranked amp overdrive
« on: December 24, 2021, 04:40:44 PM »
Huh ? Those schematics look like wireless transmitters.

Schematics and Layouts / Re: Sunn Beta PCB
« on: November 05, 2021, 04:37:43 PM »
Here's where DiscoVlad stole the idea for the MC14506 replacement.

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.

Amplifier Discussion / Re: Sunn SL260 Help Needed With Pot Orientation
« on: October 10, 2021, 04:08:27 PM »
Pin 3 of your pot symbol appears to be the clockwise terminal, therefore, the Mid, Treble and Bass controls are backwards.

Amplifier Discussion / Re: Fender M80 Issues
« on: September 25, 2021, 10:06:31 AM »
Back in the days of fixing vacuum tube TV sets, the diagnosis was No Picture, No Sound.

Amplifier Discussion / Re: 200 watt amplifier board.
« on: May 22, 2021, 07:17:50 PM »
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.

Amplifier Discussion / Re: Power amp transistor choices??
« on: May 08, 2021, 11:40:04 PM »
Look for something with a bigger Safe Operating Area (SOA).

Amplifier Discussion / Re: Thunderfunk with Dead Power Amp Board
« on: May 03, 2021, 06:25:06 PM »
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 :(

Preamps and Effects / Re: pre-amp suggestions
« on: April 27, 2021, 06:03:57 AM »
4069s can definitely sound buzzy. There are conflicting characteristics that you need to balance. As the rail Voltage goes down, the gain goes up and the clipping gets sharper, less rounding at the top and bottom of the waveform. Also, bandwidth goes down as the Voltage goes down. Loading is one way to control bandwidth. A cap to ground on the output or from input to output should do the job.

The preamp I posted over at MEF really doesn't sound very good. I've got something I want to try but just haven't had the time to get it done. The layout sketch I did is difficult to follow, I used mostly 1/8W axial resistors on 0.1 inch centers. I call it hairpin lead dress like those old transistor portable radios from the 60's.

Preamps and Effects / Re: pre-amp suggestions
« on: April 24, 2021, 07:44:16 AM »

Preamps and Effects / Re: pre-amp suggestions
« on: April 22, 2021, 05:33:27 AM »
You can connect the MOSFETs in a CD4007U to be NAND and NOR gates. The 3 input NOR with a gain of about 2 is the most like a tube. Run the gates on 8 to 10V.

Amplifier Discussion / Re: The Sunn Solos II
« on: April 15, 2021, 06:33:44 PM »
Man, it's been so long since I posted that schematic, I forgot about it. That's a pretty rare amp.

Amplifier Discussion / Re: Acoustic 370 Output Level Issue
« on: March 31, 2021, 09:48:30 PM »
Read my lips:

Looks like Q301 is bad.

Amplifier Discussion / Re: Acoustic 370 Output Level Issue
« on: March 31, 2021, 08:28:43 PM »
Q301 should be OFF because it's Base Emitter junction is reverse biased. However, Q301 is feeding current to R308-R307 and thus turning Q303 ON. The low Voltage on Q303's collector is fed back to the Base of Q302, but Q302 is unable to turn Q301 OFF. Looks like Q301 is bad.

Pages: [1] 2 3 ... 18