Stephen1966 wrote: ↑Tue Apr 19, 2022 7:22 pm
Many thanks Erwin. I looked at the Ox Box but I'm afraid it's well out of my price range. If I might suggest though, there is (possibly) another way to finding the balance which is really non-scientific but which does seem to yield positive results.
I have been using a 1 kHz sine at the input and with the volume and master to something like ordinary playing levels, I simply listened for the oscillation in the OT! I find that the extremes of the trimmer induce an audible oscillation of the OT whereas (in mine) in the 12 o'clock position the OT goes quiet. It's very rough at that point but after playing with it a bit, you get the picture that the balance is somewhere between 11 and 1 o'clock. It's handy to have a few samples on a looper because then you replace the dummy load with the speaker and just try fractionally moving the trimmer until you hear something like the sweet spot. At this point, I've been disabused of the notion that note bloom comes from the PI - at least not entirely - and the "sweet spot" is just a suggestion of a deeper harmonic structure to the notes. Mine, is currently around the 4 minutes to midnight position and at the right gain levels, the notes just take off. And great sustain especially in the higher mid range.
I would welcome any feedback on this idea because this is entirely hypothetical on my part but after spending many hours with a scope and FFT I can say, that this down and dirty method yields results that I can "more measurably" hear. It's subtle, to be sure, but once you tune your ear into it, the note structure is distinct and audible. Seriously, I'm surprised no-one else seems to have mentioned this before. I might be way off but if the sound makes me happy (which it does) there is possibly something more to this. I wouldn't ditch the scope - it's helped me track down quite a number of issues - but in this case, all I really needed was my ears.
Stephen
Hi Stephen. I was curious to see what your voltage difference was between the pins of the trimmer when you found the sweet spot. Was it anywhere close to 6V?
Cheers
Guy
Hi Guy,
Really depends on the tube I think. I first used a balanced 12AX7 which gave me a ~1v difference between the plates. The tube in there now, has 289V on the input side and 280V on the follower side - a 9V difference between the plates with the trimmer set more or less the same. Go figure Sounds great though.
Stephen1966 wrote: ↑Tue Apr 19, 2022 7:22 pm
Many thanks Erwin. I looked at the Ox Box but I'm afraid it's well out of my price range. If I might suggest though, there is (possibly) another way to finding the balance which is really non-scientific but which does seem to yield positive results.
I have been using a 1 kHz sine at the input and with the volume and master to something like ordinary playing levels, I simply listened for the oscillation in the OT! I find that the extremes of the trimmer induce an audible oscillation of the OT whereas (in mine) in the 12 o'clock position the OT goes quiet. It's very rough at that point but after playing with it a bit, you get the picture that the balance is somewhere between 11 and 1 o'clock. It's handy to have a few samples on a looper because then you replace the dummy load with the speaker and just try fractionally moving the trimmer until you hear something like the sweet spot. At this point, I've been disabused of the notion that note bloom comes from the PI - at least not entirely - and the "sweet spot" is just a suggestion of a deeper harmonic structure to the notes. Mine, is currently around the 4 minutes to midnight position and at the right gain levels, the notes just take off. And great sustain especially in the higher mid range.
I would welcome any feedback on this idea because this is entirely hypothetical on my part but after spending many hours with a scope and FFT I can say, that this down and dirty method yields results that I can "more measurably" hear. It's subtle, to be sure, but once you tune your ear into it, the note structure is distinct and audible. Seriously, I'm surprised no-one else seems to have mentioned this before. I might be way off but if the sound makes me happy (which it does) there is possibly something more to this. I wouldn't ditch the scope - it's helped me track down quite a number of issues - but in this case, all I really needed was my ears.
Stephen
Hi Stephen, I think it's funny you balance your amp this way, but if it works for you and got good results...
I know for sure that not every OT have this ringing like you had.
Stephen1966 wrote: ↑Tue Apr 19, 2022 7:22 pm
Many thanks Erwin. I looked at the Ox Box but I'm afraid it's well out of my price range. If I might suggest though, there is (possibly) another way to finding the balance which is really non-scientific but which does seem to yield positive results.
I have been using a 1 kHz sine at the input and with the volume and master to something like ordinary playing levels, I simply listened for the oscillation in the OT! I find that the extremes of the trimmer induce an audible oscillation of the OT whereas (in mine) in the 12 o'clock position the OT goes quiet. It's very rough at that point but after playing with it a bit, you get the picture that the balance is somewhere between 11 and 1 o'clock. It's handy to have a few samples on a looper because then you replace the dummy load with the speaker and just try fractionally moving the trimmer until you hear something like the sweet spot. At this point, I've been disabused of the notion that note bloom comes from the PI - at least not entirely - and the "sweet spot" is just a suggestion of a deeper harmonic structure to the notes. Mine, is currently around the 4 minutes to midnight position and at the right gain levels, the notes just take off. And great sustain especially in the higher mid range.
I would welcome any feedback on this idea because this is entirely hypothetical on my part but after spending many hours with a scope and FFT I can say, that this down and dirty method yields results that I can "more measurably" hear. It's subtle, to be sure, but once you tune your ear into it, the note structure is distinct and audible. Seriously, I'm surprised no-one else seems to have mentioned this before. I might be way off but if the sound makes me happy (which it does) there is possibly something more to this. I wouldn't ditch the scope - it's helped me track down quite a number of issues - but in this case, all I really needed was my ears.
Stephen
Hi Stephen, I think it's funny you balance your amp this way, but if it works for you and got good results...
I know for sure that not every OT have this ringing like you had.
I think of it more as supplemental method, I have gotten used to using the Ampeg procedure Martin outlined measuring the output with the scope at the cathodes of the power tubes as my main method. This non-scientific approach generally confirms the tuning. I take your word that not all OTs will produce this audible oscillation though. Still, if it does, and a builder hasn't got kitted out with a scope yet, it might prove useful.
I'll second that. I have also noticed that when balancing the PI, the OT is the quietest when the PI is balanced. I'm sure there are transformers without this ringing, but all of my builds have done this.
Sounds great though.
