A friend of mine askd me to revise his phono amp.. I Reverse-engineered the entire thing, and resoldered it on a new board. Somewhere, something went wrong, because It won't work anymore 🙁
I get a very faint signal, which seems to be unequalised by the RIAA stage. In fact, when I bridge the RIAA stage, I get the same result. Who can tell me where I made a mistake in reverse-engineering the thing?
This is the schematic as I think it would be.
I get a very faint signal, which seems to be unequalised by the RIAA stage. In fact, when I bridge the RIAA stage, I get the same result. Who can tell me where I made a mistake in reverse-engineering the thing?
This is the schematic as I think it would be.
An externally hosted image should be here but it was not working when we last tested it.
I thought that as well ... So I tried a 4.7k and a 1k resistor there, but with no results... 😡 Perhaps those were wrong values?
To make it a bit more difficult: All components that were in the original design are drawn here. I could have made an error in the wiring (misplaced a component). 😕
Bouke
Great you posted such a quick reply, thnx!
To make it a bit more difficult: All components that were in the original design are drawn here. I could have made an error in the wiring (misplaced a component). 😕
Bouke
Great you posted such a quick reply, thnx!
Circuit Fault
Hi Bakmeel,
Nothing on TV so I took a moment to check the circuit.
I think your schematic is correct. The second amplifier is almost exactly as in the book Audio IC Op-Amp Applications by Walt Jung. The first amplifier is a 1x buffer. Amplifier with voltage gain =1. Did you check the powersupply voltages and are the IC's not defective?😉
I see the light
OPA2604 is a dual opamp with V+ connected to pin 8 and V- connected to pin 4! See further the datasheet at www.ti.com 🙂 Your schematic is for a single opamp like OPA604.😉
Hi Bakmeel,
Nothing on TV so I took a moment to check the circuit.
I think your schematic is correct. The second amplifier is almost exactly as in the book Audio IC Op-Amp Applications by Walt Jung. The first amplifier is a 1x buffer. Amplifier with voltage gain =1. Did you check the powersupply voltages and are the IC's not defective?😉
I see the light
OPA2604 is a dual opamp with V+ connected to pin 8 and V- connected to pin 4! See further the datasheet at www.ti.com 🙂 Your schematic is for a single opamp like OPA604.😉
Thanx Elso
I reconnected the entire thing again and listened to what is going wrong.
Everything seems to be fine. All voltages check out ok: + and - 11,5 Volts. It's not very high, but it should do. Pinouts are also ok. The schematic above is just for reference. The OPA2604 are connected as they should be.
But here's the thing: In order to get "easy-listening-level" audio, I need to turn up the volume to, say, 10 o'clock. The music I then hear lacks bass and is rich in high tones...
Clearly, the RIAA feedback is not working.. But I keep checking my soldering over and over again, but I just can't find it!!
Could I have switched the 79,6k resistor with the 7,97k resistor?
Bouke
I reconnected the entire thing again and listened to what is going wrong.
Everything seems to be fine. All voltages check out ok: + and - 11,5 Volts. It's not very high, but it should do. Pinouts are also ok. The schematic above is just for reference. The OPA2604 are connected as they should be.
But here's the thing: In order to get "easy-listening-level" audio, I need to turn up the volume to, say, 10 o'clock. The music I then hear lacks bass and is rich in high tones...
Clearly, the RIAA feedback is not working.. But I keep checking my soldering over and over again, but I just can't find it!!
Could I have switched the 79,6k resistor with the 7,97k resistor? Bouke
here is the schematic with the right values...
http://www.tubecad.com/articles_2002/RIAA_Preamps_Part_1/page6.html
http://www.tubecad.com/articles_2002/RIAA_Preamps_Part_1/page6.html
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