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Old 3rd December 2012, 05:02 PM   #3181
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Quote:
Originally Posted by Nelson Pass View Post
At the moment I do not have plans to sell those boards.

Thanks Mr. Pass. Best
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Old 3rd December 2012, 05:33 PM   #3182
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Quote:
Originally Posted by buzzforb View Post
Do we hav eto worry abou tproximity to toroid considering use of xformer? In my rats nest, i ha dto keep some diatance from toroid to prevent little hum. Most likely rats nest, bu tthough ti would ask. Also, i notice that Nelson shoves his all the way in the back, away from the main doughnut.
buzzforb: The last picture in the sixmoons article showed with good clarity the inside of Mr. Pass's F6. It is a goldmine of info for the DIYer. Suppose that he used an industry standard enclosure. The long side of the PCBs is along its known depth dimension. One can calculate/estimate the minimum distance between the center of the power toroid and the edges of the JENSEN closest to it for no hum. One can also calculate/estimate the center to center distance between the power JFETs for optimal heat distribution on the heat sinks.

There are 5 power resistors [ big and light grey] on each PCB. By comparison, the schematic showed only 2; and here I speculate they belong to the feedback loop. I'll gaze more at the PCBs and understand what's it mean if anything.
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Old 3rd December 2012, 06:48 PM   #3183
lhquam is offline lhquam  United States
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Based on their location it looks like there are two 3 watt source resistors per JFET and one 3 watt resistor for each feeback loop. I suspect that the 2 resistors in parallel per JFET are in order to tune the resistance. Papa probably has two sets of resistances on rotary switches for adjusting a channel, and then solders resistors into the board to match. Anyway, that is how I would do it for production.

Quote:
Originally Posted by Antoinel View Post
buzzforb: The last picture in the sixmoons article showed with good clarity the inside of Mr. Pass's F6. It is a goldmine of info for the DIYer. Suppose that he used an industry standard enclosure. The long side of the PCBs is along its known depth dimension. One can calculate/estimate the minimum distance between the center of the power toroid and the edges of the JENSEN closest to it for no hum. One can also calculate/estimate the center to center distance between the power JFETs for optimal heat distribution on the heat sinks.

There are 5 power resistors [ big and light grey] on each PCB. By comparison, the schematic showed only 2; and here I speculate they belong to the feedback loop. I'll gaze more at the PCBs and understand what's it mean if anything.
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Old 3rd December 2012, 07:29 PM   #3184
lhquam is offline lhquam  United States
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Here are some interesting plots based on Spice simulations with combinations of Rs1 and the Rs2, the upper and lower source resistors respectively. In all cases the F6 is driving an 8 ohm load at 1 watt. The plots are of the harmonics H2, H3 and H2/H3.
Attached Images
File Type: jpg H2-sweeps.jpg (160.0 KB, 460 views)
File Type: jpg H3-sweeps.jpg (160.0 KB, 448 views)
File Type: jpg RS1-RS2-sweeps.jpg (164.6 KB, 438 views)
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Old 3rd December 2012, 07:38 PM   #3185
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Quote:
Originally Posted by lhquam View Post
Based on their location it looks like there are two 3 watt source resistors per JFET and one 3 watt resistor for each feeback loop. I suspect that the 2 resistors in parallel per JFET are in order to tune the resistance. Papa probably has two sets of resistances on rotary switches for adjusting a channel, and then solders resistors into the board to match. Anyway, that is how I would do it for production.
Thanks lhquam. I am still missing the 100 Ohm/5W for the feedback loop. One clearly sees the 20 Ohmer to ground. One also sees two electrolytic capacitors [of similar physical size] per JFET. Maybe two 470 uF in parallel adding up to the prescribed 1,000 uF of the schematic? The low wattage resistor between each pair of these electrolytics is the 10K resistor connected to the wiper of the 5K bias pot.
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Old 3rd December 2012, 07:41 PM   #3186
lhquam is offline lhquam  United States
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Default Simulation vs Measurements

For those of you who are sceptical about the utility of Spice simulations, particularly when transformers are involved, here are two plots that show a reasonable degree of agreement between simulation and measurement.
The plots show THD, H2, H2, H2phase, and H3 phase. The upper plot is from simulation; the lower plot from actual measurement of the Teaser-6 left channel.
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File Type: jpg F6-sim-vs-measured.jpg (160.8 KB, 379 views)
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Old 3rd December 2012, 07:42 PM   #3187
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Quote:
Originally Posted by lhquam View Post
Based on their location it looks like there are two 3 watt source resistors per JFET and one 3 watt resistor for each feeback loop. I suspect that the 2 resistors in parallel per JFET are in order to tune the resistance. Papa probably has two sets of resistances on rotary switches for adjusting a channel, and then solders resistors into the board to match. Anyway, that is how I would do it for production.
It confirms the obivious that Nelson tunes his amplifier to ear and measurement, and not a given schematic, much like Ilquam has done with all his work . No magic, just measuring, listening, and adjusting.
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Old 3rd December 2012, 07:46 PM   #3188
Rush is offline Rush  United States
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Quote:
Originally Posted by lhquam View Post
Here are some interesting plots based on Spice simulations with combinations of Rs1 and the Rs2, the upper and lower source resistors respectively. In all cases the F6 is driving an 8 ohm load at 1 watt. The plots are of the harmonics H2, H3 and H2/H3.
Could you explain the 3rd simulation, H2/H3. The scale starts at 1% and goes off the chart?

Rush
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Old 3rd December 2012, 07:52 PM   #3189
lhquam is offline lhquam  United States
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The scale is not %, but the ratio of H2 to H3. Yes, one of the plots goes off the chart - I just got overzealous in windowing the graph.

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Originally Posted by Rush View Post
Could you explain the 3rd simulation, H2/H3. The scale starts at 1% and goes off the chart?

Rush
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Old 4th December 2012, 04:38 AM   #3190
lhquam is offline lhquam  United States
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I measured the hum & noise on my Teaser-6 with a Fluke meter. Outputs connected to 8 ohm loads. Inputs connected to M-Audio AP-192 sound card with no signal.

left channel: 0.6mV AC RMS
right channel: 0.2mV AC RMS

As shown in post #1519 F6 Amplifier, the left channel is much closer to the toroid. However, not all the difference is due to the coupling to the Jensen transformers. I saw similar (but smaller) differences with a pair of F5 channels using the same heatsink and chassis.
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