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Ye Beta24 build

beta24

Re: Ye Beta24 build

Postby zhanqian » March 16th, 2018, 5:14 am

Thank you, Ti, Pieterh.

Pieterh, I remember read your post before, I did swap Q1 and Q3, and had measure the Idss(good match), but with no luck.
OK, try to swap Q2 and Q4 only, compare the component values between the two boards.
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Re: Ye Beta24 build

Postby zhanqian » March 26th, 2018, 9:05 am

After one week, finally fixed the setup problem, :P

Wrote down what I had tried, hope it may be useful.
First I tried swap Q1 and Q3 only, not work. And swap Q2 and Q4 only was not helpful too.
Tried replace the CRDs, all change to the ones have about 52mA regular current, not helpful.

Replace Q5,Q6,Q7,Q8,Q9,Q10,Q11,Q12,Q13,Q14,Q15,Q16 with new BC550C and BC560C, I can get R47 up to about 30mA(before is 5mV).Then as Ti suggest, turn VR1, make R7 about 4.5V, than I can get R47 up to about 35mA.If I set R7 to 5.0V, may be I can fix problem. But then I remembered I have bought some 2sk170bl and 2sj74 before, may be I should match them.

what I found out are:
Q1 = 7.55
Q3 = 7.48
Q2 = 7.59
Q4 = 8.00

Q41 = 7.79
Q43 = 7.70
Q42 = 7.62
Q44 = 7.81

thought the Q4 may be the problem, with the extra 2sk170bl I have, I manage to match them:
Q1 = 7.55
Q3 = 7.55 (new one)
Q2 = 7.59
Q4 = 7.62

Q41 = 7.79
Q43 = 7.74 (new one)
Q42 = 8.00
Q44 = 7.81

The setup went easy, at first R11 = 144.5mV, R13 = 105.1mV, I only have to adjust VR4 a little bit to make them both about 130mV.
At the end, Finally able to make R45 and R47 about 40mV, DC offset is -4.0mV to 4.0mV

I think the problem may be caused by I switched Q4 and Q42 by mistake, but I don't remember.

So glad to make two board setup OK now :D

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Re: Ye Beta24 build

Postby zhanqian » March 26th, 2018, 10:53 pm

Hi, Ti,

About the speaker turn on delay, I plan to use the Omron LY2NJ relay rated at 10A https://www.mouser.com/ProductDetail/Omron-Automation-and-Safety/LY2N-DC12?qs=sGAEpiMZZMtSzCF3XBhmW6a4uLc7Qu8rG36dg8eKOrI%3d.

I saw your post about the speaker current,
Postby amb » January 9th, 2018, 7:12 pm

The standard high power class AB version has a voltage gain of 20x (26dB), and a huge amount of current gain (determined by the speaker impedance and signal content).


Should I worry about max switching current of the Omron LY2NJ relay was not enough?
May be I should simply omit the speaker turn on delay for better sound quality?
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Re: Ye Beta24 build

Postby Pieterh » March 27th, 2018, 12:12 am

Congrats that you solved your problem and you have two working boards now.
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Re: Ye Beta24 build

Postby zhanqian » March 27th, 2018, 1:32 am

Thanks Pieterh.

Saw your Beta24 build, you have devoted much effort into it, once it born, must be an excellent one.

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Re: Ye Beta24 build

Postby amb » March 27th, 2018, 3:56 am

zhanqian wrote:Should I worry about max switching current of the Omron LY2NJ relay was not enough?

10A rating should be adequate, but higher current ratings usually mean bigger, lower resistance contacts, which are desirable.

May be I should simply omit the speaker turn on delay for better sound quality?

Any relay in the path of the speaker wires will add a small amount of contact resistance. In small signal situations (preamp or before) this resistance is usually too low to be of concern because of the low currents involved. On a speaker line, the resistance will add to the amp's output impedance and cause a small loss of damping factor. It is most likely not audible, but the relays are added complexity to the system. The β24 should normally start up with virtually no thump, so a relay for delay-muting purposes isn't necessary. If your relay circuit also contains DC offset protection, etc., then you have to decide whether that is worthwhile to add.

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Re: Ye Beta24 build

Postby zhanqian » March 27th, 2018, 4:45 am

OK, Ti.

Happy to omit the speaker turn on delay :D
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Re: Ye Beta24 build

Postby zhanqian » March 30th, 2018, 8:15 pm

Ti, after the amp warm up about 20 minutes, R45 and R47 of one board drop to about 31mv, the other board drop to about 34mv,
Do I have to adjust VR2,VR3 to make them about 40mv, and adjust VR4 to null the DC offset again?
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Re: Ye Beta24 build

Postby amb » March 30th, 2018, 8:58 pm

Yes, the target should be 200mA per bank while it’s warmed up. Since MOSFETs have a negative thermal coefficient, the current will read lower after warmup than when cold.
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Re: Ye Beta24 build

Postby zhanqian » April 1st, 2018, 12:44 am

After successfully made R45 and R47 about 40mV, put the heatsinks back to the chassis, they still drop to 32mV.
I think it may be caused by the enclosure I used is not well ventilated,the MOSFETs became much hotter when put back in the chassis.
Try drill some holes on the bottom plate, see if can solve the problem or not.
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