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UGS-UP-Mini: A 25W SUSY Amp
UGS-UP-Mini: A 25W SUSY Amp
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Old 9th August 2018, 06:33 PM   #21
Itsmee is offline Itsmee  England
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Quote:
Originally Posted by needtubes View Post
Well, I have several boards left over from my initial run, if you are interested
Thank you, I'll let aspringv have first dibbs, I'm currently hacking two BA3 boards at the moment, but boards are always handy for future projects.
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Old 10th August 2018, 12:49 AM   #22
aspringv is offline aspringv  Australia
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UGS-UP-Mini: A 25W SUSY Amp
Oh hey, I had no intention of jumping in ahead there. Happy to wait as well - I'm thinking I can try a latfets in there with some leads to the board and do a lower bias version easily enough.

I've plenty of the k246 matching j parts, so it'll be a somewhat franken-build of your original build, but hopefully fun nonetheless.
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Old 13th August 2018, 05:39 PM   #23
needtubes is offline needtubes  United States
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I have about 10 boards that I can spare, so no shortage yet. I've been down and out with a nasty cold, and still can't hear out of my right ear because of the sinus pressure, but will PM both of you shortly for shipping details. Sorry for disappearing.

Before the sinus pressure became unbearable, I did have a listen to the amp with a 10k resistor loading only the positive phase of the front end (R33 installed). The effect was to alleviate the forwardness of the original presentation and push the soundstage back a foot or two so that it is more suspended between the two speakers. Ears were fuzzy from the cold, so I can't say more yet. But, those effects were noticeable.
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Old 14th August 2018, 12:26 AM   #24
aspringv is offline aspringv  Australia
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Originally Posted by needtubes View Post
I have about 10 boards that I can spare, so no shortage yet. I've been down and out with a nasty cold, and still can't hear out of my right ear because of the sinus pressure, but will PM both of you shortly for shipping details. Sorry for disappearing.

Before the sinus pressure became unbearable, I did have a listen to the amp with a 10k resistor loading only the positive phase of the front end (R33 installed). The effect was to alleviate the forwardness of the original presentation and push the soundstage back a foot or two so that it is more suspended between the two speakers. Ears were fuzzy from the cold, so I can't say more yet. But, those effects were noticeable.
A hearing related illness, with this sort of hobby is doubly unkind. I wish you a speedy recovery.

Id assume that the above gives you some second harmonic (positive or negative?) and that sense is the end result. Is there a difference in terms of offset changing or gain on that side?

...and is the susy attempting to correct for that distortion? I guess I need to reread the susy paper.
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Old 14th August 2018, 01:20 AM   #25
needtubes is offline needtubes  United States
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Yes, the added load on the positive phase affects the relative amount of second harmonic to third harmonic. With no load (and assuming perfectly matched halves of the bridge), we have only odd harmonics (basically just third at low output levels). Increasing the load yields higher levels of 2nd harmonic. With relatively high values for R33 (larger than ~22k), SPICE predicts third dominates second. Below that, second dominates. With R33 at 10k, SPICE says I should have ~6dB more second harmonic than third, and that the second harmonic should be of negative phase. Generg did some experiments with the second-to-third harmonic ratio over in the F4 Beast thread. I'll have to re-read his comments about the differences in sound.

Adding R33 into the mix did not affect offset very much. Actually, I haven't yet bothered to zero the offset entirely since I had planned to test some different configurations out. I ballparked the relative and absolute offset to <10mV and called it good. Gain is a touch lower on the positive phase with R33 in place (according to SPICE).

I hope to finally be mobile tomorrow so that I can get some padded envelopes and a shipping quote for you and Itsmee.
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Old 14th August 2018, 06:30 AM   #26
Luke is offline Luke  New Zealand
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hi Needtubes, I'm interested in a couple of boards if you can spare them.
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Old 15th August 2018, 11:59 PM   #27
aspringv is offline aspringv  Australia
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Originally Posted by needtubes View Post
Yes, the added load on the positive phase affects the relative amount of second harmonic to third harmonic. With no load (and assuming perfectly matched halves of the bridge), we have only odd harmonics (basically just third at low output levels). Increasing the load yields higher levels of 2nd harmonic. With relatively high values for R33 (larger than ~22k), SPICE predicts third dominates second. Below that, second dominates. With R33 at 10k, SPICE says I should have ~6dB more second harmonic than third, and that the second harmonic should be of negative phase. Generg did some experiments with the second-to-third harmonic ratio over in the F4 Beast thread. I'll have to re-read his comments about the differences in sound.

Adding R33 into the mix did not affect offset very much. Actually, I haven't yet bothered to zero the offset entirely since I had planned to test some different configurations out. I ballparked the relative and absolute offset to <10mV and called it good. Gain is a touch lower on the positive phase with R33 in place (according to SPICE).

I hope to finally be mobile tomorrow so that I can get some padded envelopes and a shipping quote for you and Itsmee.
OK, thanks for the explanation! Why the choice of negative second harmonic distortion? I seem to recall that Pass talks about single ended amplification as an intrinsically single ended medium and I took the impression away that it was a positive distortion (although, that is an impression, I'll have to re read)

At the end of the day though, if it sounds good, then happy days!

Cheers again.
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Old 16th August 2018, 02:30 AM   #28
aspringv is offline aspringv  Australia
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Hmm, words are hard.

I meant 'air is an intrinsically single ended medium' and I'm wondering if that equates to positive or negative second harmonics being introduced.
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Old 18th August 2018, 06:24 PM   #29
needtubes is offline needtubes  United States
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Why the choice of negative second harmonic distortion?
This, again, stems from some discussions have taken place in the XA.8 Current Source thread, F4 Beast thread, and elsewhere. This interview at Stereophile with Mr. Pass sums everything up nicely:

Quote:
Originally Posted by Nelson Pass
There was a consistent subjective observation that there was a difference not only with the level of second harmonic, but phase also. Negative-phase second harmonic tends to expand the perception of front-to-back space in the soundstage, separating instruments a bit. Positive phase does the opposite, putting things subjectively closer and "in your face." I have heard this sort of comment from people who were not in a position to have expectation bias, so I treat it seriously.
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Old 18th August 2018, 06:35 PM   #30
needtubes is offline needtubes  United States
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The trick is to figure out how to get the negative phase second harmonic to appear. Many ideas have been tossed around in the threads I mentioned in the previous post. It looks like Pass Labs uses single-ended bias to get the job done (and Mr. Pass has stated that he prefers to get his second harmonics from the output stage), but I found in simulations that R33 has a similar effect. I may play around with SE bias on a future build with larger heatsinks to compare the sound.
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