I am planning to build this H2 next as a preamp, with selectable inputs, volume pot and dual outputs. However, this phase inverting business is very confusing to me. The most common way to correct the inverted phase is to swop the speaker wires. Now, swapping the speaker wires after the power amp is nothing else than swapping the output polarity to the speakers. But clearly swapping polarity of the input signal to the amp is not the same as inverting the phase of the signal, if I understand correctly. Which boggles my brain. Otherwise one could simply swap the output wires of the H2 on the output RCA connectors to invert the phase before the power amp. Looks like some folk here use an opamp to invert the phase before going to the power amp. I would be interested on how to implement this. Schematic perhaps?
One of the reasons why this inverted phase is problematic in my case is because I run full range speakers with a BSC soldered at the end of my speaker wires. If I swap them at the speakers, the BSC will be at the negative pole of the speaker. I suppose the solution to this is to swap the speaker wires at the amp outputs. That way the BSC remains connected to the positive speaker pole.
Some clarity will be appreciated, thanks.
One of the reasons why this inverted phase is problematic in my case is because I run full range speakers with a BSC soldered at the end of my speaker wires. If I swap them at the speakers, the BSC will be at the negative pole of the speaker. I suppose the solution to this is to swap the speaker wires at the amp outputs. That way the BSC remains connected to the positive speaker pole.
Some clarity will be appreciated, thanks.
Unless you have some odd speakers that you run DC to and your BSC uses polarized electrolytics
then your BSC will have no polarity to worry about. It is strictly dealing with AC and does not care about + or -. So don't worry about it. It will still work fine even if the pre-level is inverted and you swap your + and - speaker connections to negate that effect.
Can someone confirm if this would work.
Accessing my speakers binding posts is a real pain so if the above is possible that would be great.
Thanks! I will try this once the H2 is in my system. But good to know nothing will explode when I forget to swop the cables.Unless you have some odd speakers that you run DC to and your BSC uses polarized electrolytics
You could use a line output transformer, set up for no gain, to invert the line level to the RCA outputs. The transformer will have a lead maker or color for positive output; to reverse just use this as the negative output and use the other output lead for positive (attach to the RCA center contact).
No, why would you remove them, given their function? You may need to modify R5 to meet the loading of the transformer (if you use a Jensen transformer, the data sheet shows the recommended primary load, as I recall).
I have now passed on my H2 to another fellow. In the conversation we had I showed him how I used my H2 pre with two plots that I thought I had already shared here... but actually I didn't. So here they come.
I have a class AB pro amp with low THD (< 0.02% at 1 KHz, first plot) with level controls. By playing with the H2 volume and the amp level controls you can change the level of distortion as you wish. The two plots below are before and after adding the H2 at an arbitrary volume level and reducing the amp level controls to get the same 1 W on a 8 Ohm resistor load. There you have it a 0.44% THD level across the spectrum of pure second order harmonic. Play with the levels and you can change the THD to be higher or lower.
The real game here is that you set the levels based on your listening impressions and then measure what it looks like in terms of THD. I don't remember if this was the case for me. It was a while ago...
I have a class AB pro amp with low THD (< 0.02% at 1 KHz, first plot) with level controls. By playing with the H2 volume and the amp level controls you can change the level of distortion as you wish. The two plots below are before and after adding the H2 at an arbitrary volume level and reducing the amp level controls to get the same 1 W on a 8 Ohm resistor load. There you have it a 0.44% THD level across the spectrum of pure second order harmonic. Play with the levels and you can change the THD to be higher or lower.
The real game here is that you set the levels based on your listening impressions and then measure what it looks like in terms of THD. I don't remember if this was the case for me. It was a while ago...
Attachments
Finished my H2 kit and boxed it up in a cheap mdf enclosure. Using an old HP wall-wart, stepdown converter and CLC filter for 12V supply. Quiet as a dead mouse. I built it as a preamp with dual inputs, volume pot and dual outputs (for bi-amping). This H2 preamp with 9dB gain is absolutely the perfect match for my TDA8932 Class D (dual mono kits from Abraxalito) amp, driving full range speakers. Big and wide soundstage. Very musical combination. This is now my main daily listening setup and I am very happy with the sound.
Thank you Nelson and team for a simple but great sounding preamp!
Thank you Nelson and team for a simple but great sounding preamp!
