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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
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Old 29th January 2019, 10:13 AM   #3061
Mleod is offline Mleod  Italy
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Greetings to all,

the BB with low impedance loads, 1-3 ohms, how does it behave? ... distortion, power supply, etc. but not the last sound and harmonic aspect.
Thank you. HELLO

Mleod
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Old 29th January 2019, 09:10 PM   #3062
AKSA is offline AKSA  Australia
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These loads are below the designed parameters. I designed if for 4R loads, to go no lower than 3R. Your figures are so low that indicate a ribbon speaker with pure resistive loading.

HD
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Old 30th January 2019, 01:05 AM   #3063
xrk971 is offline xrk971  United States
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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Add a 2ohm resistor?
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Old 12th February 2019, 01:39 AM   #3064
drpro is offline drpro  United States
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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
X, I have a question regarding the BB. I have my boards and supplies completed. Fired everything up, found a builder error, so no sound yet. I have repaired my error and before applying power again, I doubled checked to make sure the CPU cooler was not connected to the boards by the bolts.
In my checking I discovered both the V+ and V- tabs appear to be connected to the vias that are right above them. I am using an ohm meter to check. This is true of both boards I have constructed.
Is this normal?
Thanks
David
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Old 12th February 2019, 02:17 AM   #3065
wtl is offline wtl  Australia
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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Dave,
I checked my BB boards (unpopulated) and yes they are connected to the vias above them.

Steve.
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Old 12th February 2019, 03:32 AM   #3066
drpro is offline drpro  United States
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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Thanks Steve. That is reassuring, not losing my mind here!!
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Old 12th February 2019, 05:36 AM   #3067
drpro is offline drpro  United States
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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Hugh, I found and corrected my build error. I powered one of the boards and was able to play some music through it, however at a very low level. I am guessing due to my construction error and powering the board I burnt out the two KSA992 transistors (V101 & V105)
Would I be correct in understanding the circuit that these two transistors supply the initial amplification?
Thanks
David
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Old 12th February 2019, 08:22 AM   #3068
xrk971 is offline xrk971  United States
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Hi DrPro,
Sorry to hear your BB had some shorts due to vias. I think I mentioned that in the thread that CPU coolers needed insulating washers to prevent a short. I used felt washers. Always a good idea to check for shorts between a heatsink and rails with DMM before adding power. Was that your build error? If so, normally just blows fuses on the PSU. The amp normally survives that as current is shunted straight to ground - or from positive to negative rail and doesn’t flow through components.

Click the image to open in full size.

Main thing to check: are you getting the usual 3A of bias current through the MOSFETs? Measure voltage across R145/6/7 - should have 3A and they will be warm. MOSFETs will be warm.

If weak sound, then maybe input connection is bad or reversed in polarity?

Next is check if you have about 2mA bias current through the LTP. Measure acrosss R104.

If both above are good, you should have sound.

Other possible thing to check is V111, sometimes that can get damaged or is wrong sex. Then you won’t have bias current and DC offset is huge(24V) in one direction but MOSFETs not hot.
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Last edited by xrk971; 12th February 2019 at 08:24 AM.
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Old 12th February 2019, 02:28 PM   #3069
drpro is offline drpro  United States
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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Thanks X for the insights. I will check all after work today.
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Old 12th February 2019, 05:33 PM   #3070
drpro is offline drpro  United States
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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Had a moment X.

Measured from the outs of the Cap MX. Adjusted based on Hugh's suggestion.
+V = 37.3
-V = 40.2

Across the R145/6/7 combo
.6vdc
with about 2.75a bias

Across R104
11.5vdc
with about 3.5ma bias

No other observed issues, so I will check V111 when I get home.

Thanks
David
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