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Old 16th October 2007, 11:13 AM   #1221
MRupp is offline MRupp  Germany
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Quote:
ummmm... ya, so 5mA isn't in the the middle of the BL range, which is 6.0-12mA
Yes it is ! You mix up the Idss rating of a device with the actual bias current ...

Quote:
but during the matching process should I look towards the bottom of the BL range and try to get 5mA values, or try and find some GR grades.
Any BL device will do. If you want to match, match the N to the P channel device, this is more important.
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Old 16th October 2007, 01:10 PM   #1222
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Default Re: Re: Re: hdphn amp

Quote:
Originally posted by luvdunhill

see post #228

Thanks for the reference.

Papa said: "They run 5 ma, which makes them BL."
This means that the 5 ma is no need to be must, IMHO.

From Papa's curcuit, I understand that the jfets are mainly
to provide high input impedance and to make the input ac
voltages slip into the next mosfet stage. If so, I would not
hesitate in applying even 2 ma--i.e. GR, if available.

I'm too optimistic . . . ?



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Old 16th October 2007, 08:27 PM   #1223
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Quote:
Originally posted by MRupp


Yes it is ! You mix up the Idss rating of a device with the actual bias current ...



Any BL device will do. If you want to match, match the N to the P channel device, this is more important.

ah.... I assume there is a relationship between the two? i.e. if I know that the bias current was 5mA then that corresponds something in a certain Idss range?
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Old 16th October 2007, 09:19 PM   #1224
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Whoa! Put on the brakes! Everybody stop what you're doing and take a deep breath.
Next on today's to-do list--everyone pull out their handy-jim-dandy Toshiba datasheet. From the datasheet, we read that the GR grade part has from 2.6mA to 6.5mA and the BL from 6mA to 12mA. A bit of thought reveals that there is a smidgen of overlap between the GR and BL grades, and that (assuming that you were willing to play with the Source resistor values) you could use a top of the range GR in this application and still get 5mA out of it. The BL will give a bit of variation, depending on where in the 6-12mA range it happens to fall.
If you've got GR devices, consider using smaller value Source resistors so as to run them harder, assuming that 5mA is your goal.
(Hint: Resistance= noise, if you want to rationalize messing with the published values)
It all depends on what you're shooting for. You can slant the front end towards gain or noise or distortion or bandwidth or...like everything else, it's a question of tradeoffs. Where, exactly, do you want to go with this.
If I've said it once, I've said it a thousand times...don't obsess over Nelson's values. Get creative. Express yourself. This isn't homework that you're getting graded on, it's a circuit to make music to make you happy.
Someone pointed out that 5mA isn't within the BL grade. Correct. But, once you put the Source resistor under a 2SK170, you're going to pull back on the reins, thus lowering the current you observe through the device. To hit 5mA with a GR, you'd have to pick a device from the top of the range and use a smaller value Source resistor. To use a V, you'd use a larger Source resistor to hit the same bias current. It's the nature of the beast.

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Old 17th October 2007, 11:10 AM   #1225
Variac is offline Variac  United States
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Yipes! I'm running out of time with my F4!!

I have questions:

The negative terminals of the speakers go to ground, right? Should I attach them to the grounds of the power supply? ie the two wires that aren't the Plus and Minus, and connect to create the "ground" labeled on the power supply schematic.

I am tempted to run the two power supply grounds individually back to the star ground and tie the speaker grounds in there too..so that they all connect at one point.

OK?
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Old 17th October 2007, 01:54 PM   #1226
lykkedk is offline lykkedk  Denmark
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Don't know if i am right or wrong, Variac, but i had connected the gnd directly to isolated (- or gnd) out on speaker terminal's. I used veteran's board(modified a bit).

On veteran's board the gnd from psu, are on the same spot, as (- or gnd) on speakerterminal's.

I have absolutly no problem's with mine F4's connected like that... So i think your'e on the right track... BTW happy burningamp this weekend

Jesper.
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Old 17th October 2007, 02:25 PM   #1227
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I am tempted to run the two power supply grounds individually back to the star ground and tie the speaker grounds in there too..so that they all connect at one point.
That's the way to go.
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Old 17th October 2007, 04:07 PM   #1228
gl is offline gl  United States
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Yes that's the way to go.

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Old 17th October 2007, 05:38 PM   #1229
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Quote:
Originally posted by Variac

I am tempted to run the two power supply grounds individually back to the star ground and tie the speaker grounds in there too..so that they all connect at one point.

OK?

I usually connect the power supply grounds to the start point of the bridge rectifier ground wire or the grounding point of the first PSU capacitors.

So far so works . . .


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Old 17th October 2007, 05:44 PM   #1230
Jaac is offline Jaac  Netherlands
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Making ground at your first cap is better, because of the big transiŽnt currents going from your bridge rectifier to the caps.
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