I have a Technics SA-R210 receiver with preamp outputs. I was going to use this to power external amps. I checked the output impedance and it is 38k, that just seems super high.
I checked it by putting in a 1khz sine wave and adjusting the volume to get 2vac at the preamp output with no load, except the dvm. Putting a 38k load drops it to 1vac.
Is this typical for these receivers?
I checked it by putting in a 1khz sine wave and adjusting the volume to get 2vac at the preamp output with no load, except the dvm. Putting a 38k load drops it to 1vac.
Is this typical for these receivers?
Pretty bad, you'd need a buffer on that. It isn't a serious feature. At least that spec is accurate.
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From the schematic there's only a 330 ohm resistor in series on that path, but if you were injecting your signal via the AUX input there's no active circuitry between that and the TAPE OUT, so you're likely seeing your signal generator's impedance.
I agree, something seems out of order, no way a preamp has 38k output Z, it would hardly work with realistic loads.
What does the manual say?
Jan
What does the manual say?
Jan
I was injecting the signal at the CD input, no AUX on this. I was measuring the voltage at the pre-out, not the tape out.
I couldn't find the schematic for this, only the older SA-210.
I couldn't find the schematic for this, only the older SA-210.
LMGTFY.
It looks to me that you may have grossly overloaded the input with 2V?
There's no CD input here so where did you inject the signal?
BTW This is from the SA120.
Jan
It looks to me that you may have grossly overloaded the input with 2V?
There's no CD input here so where did you inject the signal?
BTW This is from the SA120.
Jan
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It does have a CD input, you looking at the wrong receiver. As I said in the original post it is an SA-R210.
I did not inject 2v, I injected about 0.5v and used the volume control to bring the preamp output to 2v.
I did it several ways with a potentiometer and resistors and got the same reading, a square wave going through it is wacked also. I suspect there is something wrong with it. I always verify resistance with a dvm, don't just go by the color code.
Yes I noticed that also, I couldn't find anything on the SA R210, in my Google search. Only the SA210 popped up, which is a totally different receiver.
Thanks for the attitude....
Post 12 : does it mean you verified 38k load ?
Would you care to show the "wacked" square wave ?
Would you care to show the "wacked" square wave ?
NO WAY a SS preamp has such high output impedance.
Perfect for an unbuffered 12AX7 triode stage (100k load resistance in parallel with internal 68k or so) but it´s clearly not the case.
In my own Guitar amps I *add* a 4k7 resistor in series with preamp out, so 2 100W heads can be used together onstage simply by paralelling their preamp outs with a plain Guitar cable with no further complications (the resistors act as mixing resistors and both preamps are combined and driving both power amps at the same time) but notice I have to add it on purpose.
And even so I have 4k7 output impedance, which is very reasonable.
38k reminds me of 60´s Ampeg and Fender amps, which could so be combined, but nothing "modern" and certainly not SS.
If having enough time and patience, the OP might trace path backwards to last Op Amp or Transistor found, also measuring any resistor in the path.
Just thinking aloud: any Electrolytic in the path might be drier than the Sahara Desert.
Perfect for an unbuffered 12AX7 triode stage (100k load resistance in parallel with internal 68k or so) but it´s clearly not the case.
In my own Guitar amps I *add* a 4k7 resistor in series with preamp out, so 2 100W heads can be used together onstage simply by paralelling their preamp outs with a plain Guitar cable with no further complications (the resistors act as mixing resistors and both preamps are combined and driving both power amps at the same time) but notice I have to add it on purpose.
And even so I have 4k7 output impedance, which is very reasonable.
38k reminds me of 60´s Ampeg and Fender amps, which could so be combined, but nothing "modern" and certainly not SS.
If having enough time and patience, the OP might trace path backwards to last Op Amp or Transistor found, also measuring any resistor in the path.
Just thinking aloud: any Electrolytic in the path might be drier than the Sahara Desert.