Hey all,
Got a Forte FT1 5 channel amp that has a monster turn on thump that drops 30VDC/20VDC to the right/left speakers when turned on. After the thump it drops to less than 20mv DC offset on both channels.
I put in a Soft Start that slows inrush and delays the cap charge, but doesn't really help a lot. Just seems to delay the thump a little.
When turned off it races to 3V, and has a little turn off thump. I looked for bleeder resistors and there was none, so I put 5k ohm/5 Watt across each rail (there are dual primaries and dual secondaries , so two pairs of resistors or four total) and seems to help a little...
Amp sounds just fine after the annoying thumps. Previous owner just left it on all the time.
There is NO info on this amp online. Anyone have any experience with this amp? Its annoying as hell, and my speakers cant take much more...
Got a Forte FT1 5 channel amp that has a monster turn on thump that drops 30VDC/20VDC to the right/left speakers when turned on. After the thump it drops to less than 20mv DC offset on both channels.
I put in a Soft Start that slows inrush and delays the cap charge, but doesn't really help a lot. Just seems to delay the thump a little.
When turned off it races to 3V, and has a little turn off thump. I looked for bleeder resistors and there was none, so I put 5k ohm/5 Watt across each rail (there are dual primaries and dual secondaries , so two pairs of resistors or four total) and seems to help a little...
Amp sounds just fine after the annoying thumps. Previous owner just left it on all the time.
There is NO info on this amp online. Anyone have any experience with this amp? Its annoying as hell, and my speakers cant take much more...
The speaker delay circuit would not really be feasible, as there are five channels, and not much room in the chassis.
It would be nice to find out if the caps are shot before I disassemble the amp to replace them...there are four 1000uf/63V on power supply.
If the PS caps were bad, wouldn't I see some nasty DC offset, or hum, or other audio issues along with the thump? It works perfectly fine after the monster thump on and slight thump off.
It would be nice to find out if the caps are shot before I disassemble the amp to replace them...there are four 1000uf/63V on power supply.
If the PS caps were bad, wouldn't I see some nasty DC offset, or hum, or other audio issues along with the thump? It works perfectly fine after the monster thump on and slight thump off.
I do notice when shutting down one channel continues playing for 3 or so seconds longer that the other channel....maybe there are cap issues after all...
NOTE - Actually, there are two separate power supplies, one for the front and center (125 wpc each) and one for the rear channels (55 wpc each) and I had the center speaker and one of the rear channels connected, so thats why the different draw downs...
When fronts or center speaker outs are connected, no difference in draw down, and same in the rears...
NOTE - Actually, there are two separate power supplies, one for the front and center (125 wpc each) and one for the rear channels (55 wpc each) and I had the center speaker and one of the rear channels connected, so thats why the different draw downs...
When fronts or center speaker outs are connected, no difference in draw down, and same in the rears...
john65b said:
It's a poor design. It should have relays. What happens if one of the output transistors short out ?? Could even cause a fire in the speakers
But then again the unit could be faulty.What you could do is to build an outboard speaker protection and dethump unit and use the 12 volt trigger from the HT unit to switch it on and off.
regards
trev
OK, so I am convinced that the previous owner before my friend had the amp disabled the mute circuit. He did a pretty sloppy job replacing the caps (under the board) and ran a separate wire from the PS rails to the main channel output devices.
What is annoying is there is NO INFO on this amp anywhere. If anyone has a schematic it would be nice to send it to me...
Anyway, here is a pic (extra high res) of the circuit.
I have circled what appears to be a resistor or component missing that disables the mute circuit. The switch that disables signal-less channels leading to the circuit in the middle also does not function and may be a part of the mute circuit.
Anyway, any advice? I am contemplating just soldering up a timer relay an speaker outs, but would like to see if I could get the amp back to original first...like I said, the DC offset s perfectly low and stable after 5 seconds on all 5 channels, just pops like a SOB when turned on (30VDC spike)...All 5 channels all have this turn on thump.
What is annoying is there is NO INFO on this amp anywhere. If anyone has a schematic it would be nice to send it to me...
Anyway, here is a pic (extra high res) of the circuit.
I have circled what appears to be a resistor or component missing that disables the mute circuit. The switch that disables signal-less channels leading to the circuit in the middle also does not function and may be a part of the mute circuit.
Anyway, any advice? I am contemplating just soldering up a timer relay an speaker outs, but would like to see if I could get the amp back to original first...like I said, the DC offset s perfectly low and stable after 5 seconds on all 5 channels, just pops like a SOB when turned on (30VDC spike)...All 5 channels all have this turn on thump.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I do not remember the devices in mine...
I would open the the top - you will see all five amp sections - to the right is the two L / R, and the left is the three other channels - look for some fried caps or resistors in the bad section. Each amp section will have a LED. If all is good, the LED should be lit...
Sorry can't help much, my amp was traded off a long while ago, and my memory sucks eggs...
I would open the the top - you will see all five amp sections - to the right is the two L / R, and the left is the three other channels - look for some fried caps or resistors in the bad section. Each amp section will have a LED. If all is good, the LED should be lit...
Sorry can't help much, my amp was traded off a long while ago, and my memory sucks eggs...
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