I have read the whole thread and I can find hardly anything regarding the THD measurements for a preamplicatorThank xrk971 for pointing me to this thread from https://www.diyaudio.com/forums/sol...mate-fidelity-amplifier-1315.html#post6337348
Yes i have a sound card in my MacBook Pro, i downloaded REW but i don't figure out how to connect the preamp output to my Mac. I read Half of this Thread, i did not find any Recommendation yet for the connection between the Preamp and the Mac. Could someone post a diagram or connection schematic.
I also calibrated the default Audio device and this is the result, what do you think?
Thanks i will try that....and keep looking for a schematic
Thanks xrk for your help, this is what i found, i need a lot more stuff than just a song card and PC.This is the schematic from Post 1:
Now replace the DUT with your preamp, and the 8ohm dummy load with something like 10kohm - or whatever load your preamp is supposed to be able to drive. Some preamps are designed to drive 600ohm loads. Some are more like headphone amps and can drive 32ohm loads.
The important thing is to make sure your load resistor is non inductive. Wire-wound and thick film metal oxide are terrible for low distortion.
Use metal thin film if you can. You may need to adjust your signal attenuator to match the range of your audio sound interface input. Also use quality metal thin film resistors here. Dale CMF55 are great for this.
The attenuator design by Voltwide is very handy. I just use one or two values that get me the 10:1 or 20:1 range I need. For a preamp, usually the input of the sound card can handle the full dynamic range unless it’s one of those monster preamps like the Aksa Lender capable of 60Vpp.
Here is the Voltwide attenuator - it’s AC coupled to the balanced inline input so also good for BTL amps:
Looks like this:
Make sure your grounding is good and you are not close to mains cables or have big laptop SMPS plugged into same outlet as you test equipment.
I have read the whole thread and I can find hardly anything regarding the THD measurements for a preamplicator
Also, based on the findings of some other people, the right (or B) channel is a little less noisy than the left.
EDIT: that's an old picture of the dummy load, just showing the load resistors. I added the attenuator resistors later and use both RCA jacks to feed the differential signal to the EMU.