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Old 27th August 2012, 07:25 PM   #1211
lhquam is offline lhquam  United States
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Quote:
Originally Posted by Zen Mod View Post
with those RC constants in bias nets , not possible in powering on

for plugging-unplugging - it's not easy to make fool-proof amp , and it's certainly impossible to make it idiot-proof ;
I was repairing one channel/section of radio mixing console - live , during airing,I was frequently plugging/unplugging XLR's ......... but only when I was in idiot-mode , I made the same with RCA's ........

but I think it's not problem even with that
You are probably right. I think with the larger caps suggested by Nelson the problem will be eliminated or at least minimized, particularly if the input is frequency limited to above a few Hz.

I got worried when my build with 22uf caps and 20k resistors occasionally got into an oscillation. I first encountered it when running low frequency square wave response tests. I later discovered that relatively low levels of <1Hz sine wave signals would do it.
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Old 27th August 2012, 07:36 PM   #1212
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Quote:
Originally Posted by lhquam View Post
I haven't tried a classical (aka. linear) PSU yet. I want current limiting while debugging.

No, I think the problem is transformer impedance related.

I just performed measurements using a signal generator at .2V p-p output and the schematic shown here. Here are the resulting measurements:

Freq(Hz) Y(V) dB Primary Impedance (Ohms)
1000 .19 -.4 9400
100 .175 -1.2 3760
10 .115 -4.8 1106
1 .03 -16.5 552


Note that the primary impedance calculated includes the DC coil resistance.

Compare the tabulated dB numbers to the Spice Bode plot.


Compare these with
Sorry, i am not able to read this.

I just remember of one culprit PSU producing motorboating.

Some pumping due to current limiting?

Forgive to insist.
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Old 27th August 2012, 07:58 PM   #1213
lhquam is offline lhquam  United States
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Originally Posted by bobodioulasso View Post
Sorry, i am not able to read this.

I just remember of one culprit PSU producing motorboating.

Some pumping due to current limiting?

Forgive to insist.
Sorry about the table in the previous post. I couldn't figure out how to get white space characters to be retained. Here is the table as an image, and an update of the schematic to include the coil DC resistances.
Attached Images
File Type: jpg JT-123-FLPCH-test-table.jpg (6.8 KB, 329 views)
File Type: jpg JT-123-FLPCH-test.jpg (135.0 KB, 328 views)
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Old 27th August 2012, 08:24 PM   #1214
lhquam is offline lhquam  United States
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Default Updated schematic

Here is the update schematic and THD vs Frequency plot
Attached Images
File Type: jpg F6-R100-v6-cleaned.jpg (83.9 KB, 333 views)
File Type: jpg F6-R100-v6-470uf-10k-1pole-nocap.jpg (123.7 KB, 259 views)
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Old 27th August 2012, 09:00 PM   #1215
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Originally Posted by lhquam View Post
Here is the update schematic and THD vs Frequency plot
And hopefully it does not motorboat or sing. Will you listen to this clone of F6? Best regards

Last edited by Antoinel; 27th August 2012 at 09:03 PM.
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Old 27th August 2012, 10:21 PM   #1216
lhquam is offline lhquam  United States
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Originally Posted by Antoinel View Post
And hopefully it does not motorboat or sing. Will you listen to this clone of F6? Best regards
I listened to this single channel in my workshop, a room which is not nearly as lively at my normal listening room. My first impression was that the high end was missing, but this is mostly due to the differences in room acoustics. I measured the hi freq rolloff. 20kHz -.446dB, 40kHz -1.4dB.

I plan to build a second channel and use both with an F5 power supply that is currently unused. Then I can do some serious listening.
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Old 27th August 2012, 10:56 PM   #1217
Zen Mod is offline Zen Mod  Serbia
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half a db on 20k is nothing to write home about

you can try to tighten freq. extremes with little extra loading on secs (resistor in parallel) but , from my experience with decent repeaters - not necessary if you are already there .

vividness is what we are looking for ,when introducing xformers in chain

.... and happily ever after .....

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Old 27th August 2012, 10:56 PM   #1218
lhquam is offline lhquam  United States
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I welcome suggested changes to the F6 circuit shown in post #1214. I plan to send off PCB design files for fabrication soon and would like to avoid having to make major changes to resulting boards.

BTW: I have been thinking about making boards that conform to the "Universal Mounting Spec" {UMS), but I have a couple of reservations.
  • I currently use ExpressPCB for fabrication. They provide a very nice board layout editor, fast turn-around times, and good prices, particularly for 2.5"x3.8" prototype boards. The UMS boards would approximately double to costs for prototypes. Can someone suggest another vendor that would be less expensive for prototyping the larger boards? The F6 will nicely fit on the 2.5"x3.8" board, but it does not conform to the UMS.
  • I suggest an extension to the UMS for power and I/O connections. I find that hex standoffs are extremely convenient for DIY projects and allow assembly/disassembly of boards to heatsinks without soldering and unsoldering. I adopted the practice from the FX5 layout: thanks EUVL. Similarly, gold-plated .1 inch spacing headers are nice for input connections to the board. Boards can be swapped out and in in just a few minutes with such connections.

Last edited by lhquam; 27th August 2012 at 11:00 PM.
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Old 27th August 2012, 11:07 PM   #1219
Rush is offline Rush  United States
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Quote:
Originally Posted by lhquam View Post
I welcome suggested changes to the F6 circuit shown in post #1214. I plan to send off PCB design files for fabrication soon and would like to avoid having to make major changes to resulting boards.

BTW: I have been thinking about making boards that conform to the "Universal Mounting Spec" {UMS), but I have a couple of reservations.
  • I currently use ExpressPCB for fabrication. They provide a very nice board layout editor, fast turn-around times, and good prices, particularly for 2.5"x3.8" prototype boards. The UMS boards would approximately double to costs for prototypes. Can someone suggest another vendor that would be less expensive for prototyping the larger boards? The F6 will nicely fit on the 2.5"x3.8" board, but it does not conform to the UMS.
  • I suggest an extension to the UMS for power and I/O connections. I find that hex standoffs are extremely convenient for DIY projects and allow assembly/disassembly of boards to heatsinks without soldering and unsoldering. I adopted the practice from the FX5 layout: thanks EUVL. Similarly, gold-plated .1 inch spacing headers are nice for input connections to the board. Boards can be swapped out and in in just a few minutes with such connections.
I would be interested in joining you in a pair of boards. I have some old ADC transformers that would mount off the board and have the SemiSouth already. I will split the cost down the middle or however you would like.

Rush
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Old 27th August 2012, 11:39 PM   #1220
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Originally Posted by Rush View Post
I would be interested in joining you in a pair of boards. I have some old ADC transformers that would mount off the board and have the SemiSouth already. I will split the cost down the middle or however you would like.

Rush
Rush and lhquam. Would you say that you now have a functioning clone of F6 which is relatively 90% [or better] developed?
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