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-   -   help with aleph- x amp (http://www.diyaudio.com/forums/pass-labs/77623-help-aleph-x-amp.html)

elviukai 12th April 2006 06:14 PM

help with aleph- x amp
 
am using Kristijan boards, but slightly modified-thicker traces.

http://www.kk-pcb.com/alephx.html

questions
1. I have excelent vishay dale carbon 1% tolerance 10w resistors. 1ohm. if conect 2 in paralel I get 0.50ohm, this is more, original schematic uses 0,47ohm x4 5w is paralel. can I use 8x 10w 1ohm instead originals.


2. bias Left, right and bias q?what values I should use, can i put resitors there, or pot is needed to achieve some voltage points(like in zen v4) if I put pots from waht position start amp? I am sure I will fire first if set pot to incorect value..
what rssitors is the most critical? I used 1% tolerance 0,6w , but they are not the same. irf 240 and irf9610 are mached at 0,01V

my transformers is 18V secondaries.

also Iwant to use one amp on speakers which has 2 ohm impedanse at 70 and 30hzhz . what modification I shopuld do, to make amp that controls loww region well enought.
note I am speaker designer and not a expert on amps, variac, bias etc .

will wait any input..






__________________
adding 47Ohm resistors in series to tweeter improoves low frequency response!!

Nelson Pass 12th April 2006 09:07 PM

Because the Alephs use the pn junction voltage to set the bias
on the output stage current source, they tend to put about
.65 volts across the output resistors, unless you add or drain
current from the Base of the npn transistor that sets the bias.

This gives you about 1.3A for each device, and at 25V rails,
the dissipation per device is about 32 watts.

The only pot adjustment is for the front end bias, and you set it
for low DC offset at the output.

Want to drive 2 ohms? Double the # of devices.

:cool:

elviukai 13th April 2006 09:30 PM

2 Attachment(s)
Thanks again Mr. Nelson for clearing clouds :)

why there in scematic 3 potentiometers not one? :confused:

Zen Mod 14th April 2006 12:16 AM

Quote:

Originally posted by elviukai
Thanks again Mr. Nelson for clearing clouds :)

why there in scematic 3 potentiometers not one? :confused:


left 50K pot is for fine setting Iq of left half
right 50K is for fine setting Iq of right half
200E pot is for fine setting of input CCS (LTP) current and-as consequence- DC offset on amp's output

elviukai 14th April 2006 11:54 AM

what is Iq and in what points I should measure voltage an what values I must get? :confused:

Zen Mod 14th April 2006 11:20 PM

Quote:

Originally posted by elviukai
what is Iq and in what points I should measure voltage an what values I must get? :confused:

Iq means quiescent current
you measure it with voltmeter probes across one 0E39 resistor on left and across one 0E39 resistor on right side,respectively........
when you set Iq in amount you wish,then try to fiddle with pot in CCS for input LTP ,to achieve smallest offset between two hots in output.
I dunno what values you must get,just because I'm so familiar with X-es.......1A per mosfet?

anyway-choose (first search here) Iq value,then use golden equation U=RI to know what voltage you'll measure across 0E39


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