Zen Mod said:
It appears the Goldpoint can fairly easily be configured that way - the fourth set of RCAs can be internally set with jumpers to act as a third input, a second attenuated output, a tape output, or an output that has bypassed the selector switch. Some rewiring of the jumper board should allow a buffered/unbuffered setup.
-j
Re: Output impedance
I'm using 100 ohms on the output of mine, with no measured issues when installed. I believe it needs to be hooked up, and then hit with a square wave to check for problems. Probably want the amp off though. I did some brief tests, and with 100 ohms on the output, the -3dB point was about 10MHz when driving a 50 ohm 1M BNC cable to my scope.
I know op-amp circuits with lots of feedback need to be careful driving capacitance, for phase margin and stability reasons. I can't say why it's needed here on the output. Probably if you don't have a scope to check, the larger recommended value is safer.
thanh1973 said:
I'm using 100 ohms on the output of mine, with no measured issues when installed. I believe it needs to be hooked up, and then hit with a square wave to check for problems. Probably want the amp off though. I did some brief tests, and with 100 ohms on the output, the -3dB point was about 10MHz when driving a 50 ohm 1M BNC cable to my scope.
I know op-amp circuits with lots of feedback need to be careful driving capacitance, for phase margin and stability reasons. I can't say why it's needed here on the output. Probably if you don't have a scope to check, the larger recommended value is safer.
Today I hooked up a CRO to a CD player to see what affect there would be using different input impedances.
The CD player was an ordinary Sony CD player about 1 year old (I don't know what the output impedance is). The music was Weather Report's track called Barbary Coast from the Black Market album.
When conected to a 1Megaohm impedance I got sound peaks of 3.75V when I connected it to a 50k impedance I got peaks of 3.6V and when I connected it to a 10k impedance I got peaks of 3.0V.
My question is, does this reduction in peak output voltage with reducing input impedance occur linearly across all amplitudes or are the peak amplitudes reduced more than smaller amplitudes?
Eg With a 10k impedance (preamp input impedance) the peak output of a cd player is reduced to about 3V which is about 20% reduction (to keep the maths easy) compared to 3.6V for a 50k input impedance.
So would 1V seen on 50k input impedance be reduced to 0.8V (ie 20% reduction) on a 10K input impedance or would the reuction be less (eg 5% reduction) at lower amplitudes compared to the higher amplitudes?
I hope this makes sense.
The CD player was an ordinary Sony CD player about 1 year old (I don't know what the output impedance is). The music was Weather Report's track called Barbary Coast from the Black Market album.
When conected to a 1Megaohm impedance I got sound peaks of 3.75V when I connected it to a 50k impedance I got peaks of 3.6V and when I connected it to a 10k impedance I got peaks of 3.0V.
My question is, does this reduction in peak output voltage with reducing input impedance occur linearly across all amplitudes or are the peak amplitudes reduced more than smaller amplitudes?
Eg With a 10k impedance (preamp input impedance) the peak output of a cd player is reduced to about 3V which is about 20% reduction (to keep the maths easy) compared to 3.6V for a 50k input impedance.
So would 1V seen on 50k input impedance be reduced to 0.8V (ie 20% reduction) on a 10K input impedance or would the reuction be less (eg 5% reduction) at lower amplitudes compared to the higher amplitudes?
I hope this makes sense.
I'm not so sure the reduction you describe will be totally linear. especially at the extremes. In the typical operating range it should be however. You might want to be asking if it is purely resistive? It is due to source impeadance. That is, output impeadance of your CD Player. Usually, when the level is cut in 1/2 (6db), you are driving a load equal to your source impeadance. When driving a load 10X or more the source impeadance, you are considered to be getting the max output and source impeadance will be causing very little or no ill effects.
But, as I say, if you are driving something into clipping etc. then all bets are off. That would not be a linear operating area you want to be working in.
But, as I say, if you are driving something into clipping etc. then all bets are off. That would not be a linear operating area you want to be working in.
if you could repeat the test measurements while playing a constant amplitude test signal at just below 0dBfs, you can calculate your CD player's output impedance.
The measurements you have at the moment indicate an enormous output impedance and I think your peak voltages are being mis-read.
The measurements you have at the moment indicate an enormous output impedance and I think your peak voltages are being mis-read.
Thanks everyone.
I have access to a lot of good measuring gear, and a friend that can show me how to use it.
So I thought I would start learning how to use some of the equipment and do real measurements.
I hope to do some more real measurements, next on the list will be the B1.
I just have to wire and case it up to finish it, so it might be another week or two.
To do the measrements discussed above, I used something called persistance which basicly captures and freezes everthing on the screen untill the sound fills the screen and you end up with a rectangle.
I then just read the peak voltage off the y axis, so there could be errors of +/- 0.1V.
I have access to a lot of good measuring gear, and a friend that can show me how to use it.
So I thought I would start learning how to use some of the equipment and do real measurements.
I hope to do some more real measurements, next on the list will be the B1.
I just have to wire and case it up to finish it, so it might be another week or two.
To do the measrements discussed above, I used something called persistance which basicly captures and freezes everthing on the screen untill the sound fills the screen and you end up with a rectangle.
I then just read the peak voltage off the y axis, so there could be errors of +/- 0.1V.
Pot Values
I am electing to use a dual gang/ stereo pot for the B1 instead of the pair for the ease of use. My local Radio Shack has a 100K pot, but not the prescribed 25K pot. Would this value work and how would it effect the overall function?
RS 100K Potentiometer
I am electing to use a dual gang/ stereo pot for the B1 instead of the pair for the ease of use. My local Radio Shack has a 100K pot, but not the prescribed 25K pot. Would this value work and how would it effect the overall function?
RS 100K Potentiometer
Re: Pot Values
I have used those pots for various "chip amp" gift implementations and they are good for the money / ease of access BUT...
I would never think about that in a "premium" system. I would spend a tad bit more for an eBay special or the like.
As for the specification of 100K versus 25K I think that has been covered earlier.
zcables said:
I have used those pots for various "chip amp" gift implementations and they are good for the money / ease of access BUT...
I would never think about that in a "premium" system. I would spend a tad bit more for an eBay special or the like.
As for the specification of 100K versus 25K I think that has been covered earlier.