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Old 26th May 2008, 12:02 AM   #21
ttan98 is offline ttan98  Australia
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Quote:
Originally posted by Elkaid
Hello !

Thanks for the reply



You're right... I can even reach values around +/- 2V. However, I measured a voltage difference between T2 and T3 base of about 200mV.

I don't know if that's an issue (yet)

Thank you for your help !

I am not sure what you mean, say base of T2=1.2V and T3 about -1.2V, then voltage between bases of T2 & T3 should be 2.4V.
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Old 30th May 2008, 02:36 AM   #22
Elkaid is offline Elkaid  Canada
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Hello guys,

Here's a little update on my issue:

If you take a look at the attached schematic, I replaced Rb2 from 2.2k to 3k as suggested by the guys from chip-pcb.cn. (BTW, Rb1 is set to 300ohms)

Great ! Now I can adjust Bias correctly using Rp until I read 22mV across Re. (Which is supposed to give 100mA)

Going over 22mV, and the mosfets begin to heat up pretty quickly.

Now that I can adjust bias is one gig step but I'm still plagued with the very low volume output level.

Is there anyone having a clue ?

Thank you very much guys !
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Old 30th May 2008, 03:01 AM   #23
ttan98 is offline ttan98  Australia
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Quote:
Originally posted by Elkaid

Now that I can adjust bias is one gig step but I'm still plagued with the very low volume output level.

Is there anyone having a clue ?

Thank you very much guys !
I have the Bipolar version it works fine and sounds good too better than LM3886.

Please try these:

1. Check the feedback resistors, ie correct order, 33K and 1.2k.
2. with i/p shorted o/p offset should be 1-10mV if less then I think feedback resistors are incorrect soldered(ie reversed), as per 1.


Also, an obvious question, is your mosfet tightly screwed on the heat sink, I use computer cpu heatsink, at Iq=100mA and slow fan(9v instead of 12V) on, it is running cool(to touch).

hope you have some success.
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Old 30th May 2008, 08:09 AM   #24
AndrewT is offline AndrewT  Scotland
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Hi,
have you fitted gate resistors to the output FETs? 150r to 470r?

220uF (Ci) limits the bandwidth of the amp.
The 10uF Cin should limit the bandwidth.
Increase 220uF to 470uF to reduce the audio voltage appearing across this cap. Maybe add a 2u2F film cap in parallel to maximise the HF sound quality.
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Old 30th May 2008, 10:06 AM   #25
mhtplsh is offline mhtplsh  India
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tta 98
Quote:
I have the Bipolar version it works fine and sounds good too better than LM3886
Can u give schematics & pcb details?
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Old 30th May 2008, 10:39 AM   #26
ttan98 is offline ttan98  Australia
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Quote:
Originally posted by mhtplsh
tta 98


Can u give schematics & pcb details?
I cannot give you it is proprietry, let me tell you it is straight forward, nothing new.

I suggest if you want to build one buy from the seller it is cheap, if you buy all the components yourself, the total cost will exceed what you pay to the seller ie US$26 per channel(you need to solder yourself) includes all parts excl. heatsink and power supply, cheaper than some gainclones.

Search for Monkey, the seller here if you are interested and go to his website.
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