1. I have this universal amp that accepts Tuner, pickup tape, radio and microphone inputs. This is a pretty old circuit but has a very warm & mellow sound. I plan to use this in line with ipod feeding it. ( Please see preamp1.jpg)
Can someone tell me which resistor values i need to change so that it accepts the ipod inputs. I have tried using the inputs ( as it is ) and it sounds crap. I believe that is due to too much gain that overloads the power amp.
I was thinking changing R5 to 150K & R6 to 50k. and feed that too the preamp. Would that work?
2. Please see Poweramp.jpg
Is is possible i skip the entire preamp stage altogether and directly power this amp through my ipod. Right now the amp works well when the ipod is at 80-90% volume. So i guess an input gain of 3-4 db is what this amp needs to work properly. Suppose i change R1, R2 and R3 values would this help ?
Can someone tell me which resistor values i need to change so that it accepts the ipod inputs. I have tried using the inputs ( as it is ) and it sounds crap. I believe that is due to too much gain that overloads the power amp.
I was thinking changing R5 to 150K & R6 to 50k. and feed that too the preamp. Would that work?
2. Please see Poweramp.jpg
Is is possible i skip the entire preamp stage altogether and directly power this amp through my ipod. Right now the amp works well when the ipod is at 80-90% volume. So i guess an input gain of 3-4 db is what this amp needs to work properly. Suppose i change R1, R2 and R3 values would this help ?
Attachments
Yes sir !
I have the original pcb layout, schematic and literature. PM me your email and I will send it over.
The higher the R5, the smaller the amount of signal from TAPE that makes it into the input of the pre-amplifier. So, 150 kΩ + 50 kΩ would be a bad idea. Wrong direction.
One important idea (which is at least trivial!) is to hook a 2 MΩ pot in series with R₅. At least with that (and using care), you can find the value that works. Then remove it and substitute the nearest fixed value film resistor.
ANOTHER important idea is that using high value resistors for R5 also increases the input impedance that the iPod sees. Is this good, or bad?
Well, in one way it might be "not good", in that the iPod is expecting a load of anywhere from 8 Ω to 100 Ω for whatever headphone arrangement is attached. The way to address this is simple enough: put a pair (left, right) of 36 Ω resistors in parallel to the "tape" input pins and ground. This does NOT necessarily resolve the need for a higher R5. But it could clear up distortion. Give the ipod something to drive.
It could make all the difference in the world…
Really.
GoatGuy
One important idea (which is at least trivial!) is to hook a 2 MΩ pot in series with R₅. At least with that (and using care), you can find the value that works. Then remove it and substitute the nearest fixed value film resistor.
ANOTHER important idea is that using high value resistors for R5 also increases the input impedance that the iPod sees. Is this good, or bad?
Well, in one way it might be "not good", in that the iPod is expecting a load of anywhere from 8 Ω to 100 Ω for whatever headphone arrangement is attached. The way to address this is simple enough: put a pair (left, right) of 36 Ω resistors in parallel to the "tape" input pins and ground. This does NOT necessarily resolve the need for a higher R5. But it could clear up distortion. Give the ipod something to drive.
It could make all the difference in the world…
Really.
GoatGuy
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