142-2000 Direct Injection
Posted: Mon Aug 14, 2017 8:48 pm
Hello Goldfinger:
426 posted the following info in another forum and I have a question
Ok here is what I got from Goldfinger:
If you want to drive the modulator directly, you will need a 50-100 watt home audio amp between the line level source and the radio as the modulator doesn't have enough gain for line level to work. I use a 10uF 50 volt tantalum, + towards the circuit board where C174 was removed, with 2 - 1Kohm 1 watt in parallel going to ground to load the audio amp.
Note the blue electrolytic at the bottom of the picture? That is a 220uF 35 volt radial lead electrolytic going between PC ground and Chassis ground to allow the low frequencies a good ground return. I install this cap on either method of feed.
This is a 2000 but works with 142 also. the large cap is a .22uf 50v Teflon cap very hard to find but a Mylar will work also.
Thank you Goldfinger!!
Well since the Audio Amp is loaded by 500 ohms instead of 8 ohms, the watts drop way back. It's true it only takes 5-10 watts to drive the modulator, but my circuit is "voltage fed". If I would have loaded it with an 8 ohm 50 watt resistor it would be "current fed". Since it is voltage fed at a higher impedance, it takes more "volume" from the audio amp to drive it. Also using a 50-100 watt amp gives it some headroom without clipping. 4040 tried using a 35 watts per channel receiver for his amp and the clipping kept blowing the modulator. Prime is using an Art Audio 100 WPC pro audio amp on his and it works great. He just sets his brick wall limiter in Pro-tools at 115-120% mod on the Cobra and calls it good. The brick wall prevents the 100 watt amp from harming the radio in case there is a loud noise in the room.
The problem with using a smaller audio amp is having to use a 25-50 watt, 8 ohm load resistor. That is the advantage of using a voltage fed circuit.
A little more info again thanks to Goldfinger for this info!!!
My question is:
What happen when you use a 8 Ohm Resistor instead of the Teflon Cap for Current Fed ?
Do you still loading the input with the 2 1K Ohm Resistors in Parallel to Ground ?
This is the Resistor that I try to use along with a 30 Watts Audio Amp
Thank you in advance for your opinion and great help
Regards
A365
426 posted the following info in another forum and I have a question
Ok here is what I got from Goldfinger:
If you want to drive the modulator directly, you will need a 50-100 watt home audio amp between the line level source and the radio as the modulator doesn't have enough gain for line level to work. I use a 10uF 50 volt tantalum, + towards the circuit board where C174 was removed, with 2 - 1Kohm 1 watt in parallel going to ground to load the audio amp.
Note the blue electrolytic at the bottom of the picture? That is a 220uF 35 volt radial lead electrolytic going between PC ground and Chassis ground to allow the low frequencies a good ground return. I install this cap on either method of feed.
This is a 2000 but works with 142 also. the large cap is a .22uf 50v Teflon cap very hard to find but a Mylar will work also.
Thank you Goldfinger!!
Well since the Audio Amp is loaded by 500 ohms instead of 8 ohms, the watts drop way back. It's true it only takes 5-10 watts to drive the modulator, but my circuit is "voltage fed". If I would have loaded it with an 8 ohm 50 watt resistor it would be "current fed". Since it is voltage fed at a higher impedance, it takes more "volume" from the audio amp to drive it. Also using a 50-100 watt amp gives it some headroom without clipping. 4040 tried using a 35 watts per channel receiver for his amp and the clipping kept blowing the modulator. Prime is using an Art Audio 100 WPC pro audio amp on his and it works great. He just sets his brick wall limiter in Pro-tools at 115-120% mod on the Cobra and calls it good. The brick wall prevents the 100 watt amp from harming the radio in case there is a loud noise in the room.
The problem with using a smaller audio amp is having to use a 25-50 watt, 8 ohm load resistor. That is the advantage of using a voltage fed circuit.
A little more info again thanks to Goldfinger for this info!!!
My question is:
What happen when you use a 8 Ohm Resistor instead of the Teflon Cap for Current Fed ?
Do you still loading the input with the 2 1K Ohm Resistors in Parallel to Ground ?
This is the Resistor that I try to use along with a 30 Watts Audio Amp
Thank you in advance for your opinion and great help
Regards
A365