Hi. I am trying to figure out the best impedance match between a passive attenuator, and a unique old amp.
The amp in question is an Onkyo M-505. It has an input impedance of 100k. There was a matching preamp (P-303) with an output impedance of 600 Ohms.
The designer says that this is to ensure for the least amount of voltage loss.
I am not aware of any quality 1K audio pots, and I am not sure that one could build a stepped attenuator that could achieve or maintain this value.
I thought about trying a 10K pot, but this may skew the sound of this special amp.
https://audio-database.com/ONKYO/amp/integram-505-e.html
The amp in question is an Onkyo M-505. It has an input impedance of 100k. There was a matching preamp (P-303) with an output impedance of 600 Ohms.
The designer says that this is to ensure for the least amount of voltage loss.
I am not aware of any quality 1K audio pots, and I am not sure that one could build a stepped attenuator that could achieve or maintain this value.
I thought about trying a 10K pot, but this may skew the sound of this special amp.
https://audio-database.com/ONKYO/amp/integram-505-e.html
I guess no one cares to speculate on this. I have my eyes on a 10K TDK, but I am going to wait and see what the PS Audio preamp I scored has in it.
A 10k pot should be fine imo. 100k input impedance is high. The pot should always be fed from a low impedance if possible though which I guess in your case will be output impedance of your source components.
Capacitance at the power amp input can alter the response but 10k is low enough for that not to be an issue. The output impedance of a pot is a variable and highest at the 50:50 setting.
Capacitance at the power amp input can alter the response but 10k is low enough for that not to be an issue. The output impedance of a pot is a variable and highest at the 50:50 setting.
A 10k pot will be fine, this is the common standard of loading for solid state sources.
The preamp output coupling capacitor appears to be 1uF, which into 10k will be -3dB at 16Hz.
The preamp output coupling capacitor appears to be 1uF, which into 10k will be -3dB at 16Hz.
Is the typical output of 50K low enough?
I don't know enough about how pots work. At what point is the specced value measured?
The preamp bass rolloff with 600 ohm loading is acceptable, just not great.
Treble behavior depends on the volume control setting, the cable, and the particular amplifier circuit.
Treble behavior depends on the volume control setting, the cable, and the particular amplifier circuit.
I mostly use custom made Mogami 2549 cables, with Neutrik Rean RCA's.
I would think that a short run of it would have low enough capacitance not to affect the frequency response.
I would think that a short run of it would have low enough capacitance not to affect the frequency response.
In cases like this I like to invoke the "rule of tens"...the load should be at least ten times the output impedance of the driving device. So with an output of 600 ohms a 10k pot resistance is fine. The other end has a different constraint, the capacitance of the cable comes into play weather one likes it or not, and can attenuate the higher frequencies if it's not properly implemented. Short, low capacitance cables are a must if high fidelity is the goal.
It's also important to allow enough strain relief on the wire connections and plugs.
There are those sellers out there that would make up an attenuator to your needs. It reminds that Glassware Audio has a two knob solution for this which you are also allowed to choose the resistors in the path. It combines a ladder design in step with a shunt design. Well worth checking out.
The stated output of 600 Ohms is with a preamp I don't own. The output impedance of the PS Audio is unknown.
I am trying to figure out a passive solution.
I am trying to figure out a passive solution.
What Onkyo was referring to was the lowest driving impedance in a lot of datasheets back then. So that would have been 1.5V signal @ 600 ohms.
So 100K wouldn't need anything on it, and the voltage will be higher, like almost 5V, and guaranteed specs would be 50K and higher if using other manufacturer's amps. I used to sell/repair them at one point in time.
The designer of the amp says that a high impedance source sent directly to the amp would cause numerous problems with the amplifiers performance.
The typical source component has an output of 50K, which the designer said is too high.
https://www.audiokarma.org/forums/i...may-be-as-good-as-ew-700c.105181/post-1479389
The typical source component has an output of 50K, which the designer said is too high.
https://www.audiokarma.org/forums/i...may-be-as-good-as-ew-700c.105181/post-1479389
Tom says: "The P303 was designed to work specifically with the Onkyo M505 power amplifier."
I said:" 100K wouldn't need anything on it, guaranteed specs would be 50K and higher if using other manufacturer's amps."
He was referring to input voltages when connecting a CD player directly to the amp without a preamp.
I think you don't understand that 600 ohm/1.5V is a power rating and not an operating impedance