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Old 20th October 2012, 03:14 PM   #131
Salas is offline Salas  Greece
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Or up? There is the input CCS that defines the load resistor's current...so it must be turning on the buffer harder. Comp caps needing also revision then?
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Old 20th October 2012, 03:16 PM   #132
sonnya is offline sonnya  Denmark
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When readjusting the bias for the mosfets, the Working is the same.
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Old 20th October 2012, 03:18 PM   #133
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When changing R7,R8 still the same workings?
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Old 20th October 2012, 03:19 PM   #134
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Or up? There is the input CCS that defines the load resistor's current...so it must be turning on the buffer harder. Comp caps needing also revision then?
No that is not necessary. The feedback network is still the same, and also the bandwitdh
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Old 20th October 2012, 03:21 PM   #135
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The overall current in each leg of the i/p cct has to stay more or less the same. With this mod we are changing the ratios of the where that current is supplied from - decreasing the current through R7 & R8 and increasing the current from the CCS - thus increasing the overall impedance between the rails and the inputs of the o/p stage and thereby increasing the OLG - hope that makes sense !
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Old 20th October 2012, 03:23 PM   #136
Salas is offline Salas  Greece
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Quote:
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No that is not necessary. The feedback network is still the same, and also the bandwitdh
OK. Got 47pF silver Mica 10pcs came in just a couple of days ago. Only thing I miss for the boards are 3266W trimmers. Hard to find locally and the post seem to had lost them...Jinx!
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Old 20th October 2012, 03:24 PM   #137
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The gain in the audioband is increased but the gain at VFH is not changed much so compensation was not changed but I did not retest square waves yet.
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Old 20th October 2012, 03:31 PM   #138
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Quote:
Originally Posted by mikelm View Post
The overall current in each leg of the i/p cct has to stay more or less the same. With this mod we are changing the ratios of the where that current is supplied from - decreasing the current through R7 & R8 and increasing the current from the CCS - thus increasing the overall impedance between the rails and the inputs of the o/p stage and thereby increasing the OLG - hope that makes sense !
Increasing the driving impedance has no side effect because we have driving emitter followers?
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Old 20th October 2012, 03:32 PM   #139
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You are right. i mean both of you. Both of the last two post.
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Old 21st October 2012, 01:48 PM   #140
mikelm is offline mikelm  England
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Feedback on the Mod:

Just to remind about my current TSSA1.6 configuration:

OLG 56db, CLG 27db, rails 25V, bias 1A, choke regulated supplies, about 32mF of capacitance after chokes.

Much of my following comment revolve around my dislike for the sound of cheap resistors ( particularly trimmers ) so if ur of the opinion that all resistors sound the same, the following could sound like complete nonsense.

When I first did this mod ( changing R7 & R8 from 1K to 3K3 ) I did not really like the sound - more authority but somehow a bit rough around the edges but I was aware that the CCS's, that were now injecting most of the current into the i/p circuit, were being regulated by a very sensitive adjustment of a 5K trimmer ( set to about 240R ! ) so having established the needed resistance I soldered some nice ( caddock MK132 ) 320R resistors across the R22 trimmer and then used the trimmer - now in parallel to the fixed resistor - to trim them down to the required value.

Now it is a very different story - The sound is much more refined and once again I can say that at present this is the best sound I have heard in my system ( or anywhere else ) I would recommend this mod . . . . In fact I would recommend doing this trimmer mod to all the trimmers even if you are not going to do the original mod so that most of the current is passing through a fixed value resistor - it makes a big difference and allows this design to sound even better.

In spice it now looks like 3rd HD is slightly higher that 2nd but I have heard nothing unpleasant about the actual sound so I guess that's OK.

I have other CFB designs in spice with the same open & closed loop gain that have much much lower 3rd - 10th HD - averaging 25db better and I'm hoping that with carefully built, regulated supplies I can match the clarity of TSSA and have the best of both worlds

What my current design is not doing that well at present is 3D imaging - adding the 22.000uF to the board smoothed out the sound a bit too much in that respect but I'm working on a new supply arrangement that I'm hoping will restore that soon.

I will compare to my ( recently revised ) DC linked fetzilla soon and let you now how it now compares.

mike
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