Thanks Kevin.
This has got me thinking whether a case can be made for pots with different calibration: P1 with fewer turns to set bias and P2 with finer adjustment for offset. Might make the two steps forward one step back dance simpler?
As you rightly said, I'll see 🙂
Cheers!
I'm getting my Focusrite 2i2 out of the box. Old laptop having problems, now replaced. Just need to download REW or ARTA and put connection wires together.
Russellc
That's not how it works, both pots set bias and offset and both need to be the same.
Just a suggestion:
1. Once you completed the loopback spectra to test that the connections are working properly, try connecting a 10K load (if it's a preamp and 8/16 ohm if its an amp) at the output of the device under test, say BA-3.
2. Use an attenuator after the load to limit the input to the Focusrite to avoid clipping.
3. Set output of the generator to get 1Vrms at the 10k load, and then adjust the attenuator to limit the input voltage to the FocusRite to prevent clipping.
I found out that using the connection I describe above, it is much easier to see the changes in amplitude of the harmonics as you adjust P3, then P1 and P2.
@Russellc
For attenuation I highly recommend either Peter Millet's Sound Card Interface or Jan Didden's (Linear Audio) Autoranger. Both work great and are fun projects in their own right. It's worth the investment if your going to be testing other amplifiers, setting P3, etc.
For attenuation I highly recommend either Peter Millet's Sound Card Interface or Jan Didden's (Linear Audio) Autoranger. Both work great and are fun projects in their own right. It's worth the investment if your going to be testing other amplifiers, setting P3, etc.
Another option for attenuator between device under test (DUT) output and sound card input:
https://www.akitika.com/documents/BuildingTheAttenuatorRev4.pdf
This is what I use for signal attenuation.
https://www.akitika.com/documents/BuildingTheAttenuatorRev4.pdf
This is what I use for signal attenuation.
Me too! It's the circuit inside the gray box in post # 2126 The BA-3 as preamp build guide 6dB to 36 dB.
Nice. I am re reading all the threads from this conversation started with 2i2 (and others) and P3 adjustment.
Russellc
Will operator error strikes again. There was nothing wrong with my build. I just need to read the guide a little more closely and be patient adjusting the bias. I adjusted P1 and P2 to zero ohms and fired the amp up and started making my adjustments. Everything came into place and I was able to get it to bias at about 1v and offset was fairly close to 0. I will probably go back and check everything again later, but it is playing music.
Here are some pictures of my not fancy build. I wanted something that was more like the tube amps I have build in the past.
Here are some pictures of my not fancy build. I wanted something that was more like the tube amps I have build in the past.
Attachments
Nice build BRN. I would drill some holes where the heat sinks are to help with ventilation. Otherwise the hot air can get trapped in there.
Which output caps are those?
Which output caps are those?
Ventilation is a good call. The base does have feet to allow air to flow under it, but adding vent to the top will only help.
The caps are Panasonic EZP-E 10uF that I purchase for another build, but never used. So far they sound good, but at the moment my hearing is jacked up. I had a procedure on my left ear and can't heat s#!t out of it.