Help needed: Firing up the Aleph-X100 - diyAudio
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Old 1st February 2004, 02:06 PM   #1
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Default Help needed: Firing up the Aleph-X100

...so the first channel is build and I am trying to fire it up (sorry, don#t have a digital camera (yet)). The setting is done for 100W with 8 devices per channel. I use hifizen's boards with some minor adjustments as discussed here in the board.

I use a variac to test it and so far I have only +-7,8 Volts put on it (with 22Volt the target voltage). Now, something very strange happens: Side A (within the same channel) works nicely and quiet while the other side (B) buzzes like hell.

When doing some measurements, I have 0,04Volt over the 0,33R resistor in the current source of A and only 0,004 Volt on side B, so side B does not draw the intended current. Before I now destruct the whole thing and check each transistor, I would like to get some hints from the group on that.

The input and output is without any load. So no input caps as I will have a balanced preamp with output caps and nothing at the output yet.
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Old 1st February 2004, 02:41 PM   #2
Netlist is offline Netlist  Belgium
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I would try to raise the voltage a little more say 11 or 12V.

/Hugo
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Old 1st February 2004, 03:13 PM   #3
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OK, did that, buzzes is becoming exremly loud, sounds like if you have something mechanical buzzing.. I measured as well the voltage across R37 / the 1k resistor next to the MPSA18 (in my case a BC550C): Side A (which is OK): 0,07V, Side B: 0,0134 V.

I have exchange already both bipolars Q8/Q9, but without an effect.
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Old 1st February 2004, 03:25 PM   #4
Netlist is offline Netlist  Belgium
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What voltages do you measure at R31 and R32.
As you say no output is connected, where does the buzz come from? The toroid?
I assume we both have the original AlephX circuit in mind when talking about device numbers?

/Hugo
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Old 1st February 2004, 03:26 PM   #5
grataku is offline grataku  United States
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What do you mean by "side" we are talking about 1 channel, right? Why would 1 channel have 2 sides?
Please describe what you are doing in detail.

I ask too where is the buzz coming from?
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Old 1st February 2004, 03:46 PM   #6
Netlist is offline Netlist  Belgium
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Quote:
Originally posted by grataku
Why would 1 channel have 2 sides?
The half around Q1/Q2, the other half around Q10/Q11

/Hugo
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Old 1st February 2004, 04:42 PM   #7
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Yes, I mean with side exatly what Netlist describes: In Hofizen's schematic Q1/Q2 build one side and Q10/11 the oher side within one chammel.

No, the buzzing does not come from the toroid, it is absultely quiet. It come from the Mosfets on the heatsink, but only from those on one side

Over R31 I measure 0,025V on side B(buzzing) and over the same resistor R14 I measure on side A (quiet) 0,115 V.

Over the two 1K Resistors (R32/R15) I don't have a voltage on either side.
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Old 1st February 2004, 05:24 PM   #8
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Default firing up

Please check the pinning for the bipolairs.

MPSA 18 is ebc, BC550 is cbe. Verify this in the datasheets before changing anything!
I have looked at Fairchild's MPSA18 en Philips BC550.

Regards
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Old 1st February 2004, 05:25 PM   #9
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Hi there,

Did you check the insulation between the heatsink and mosfets?

Regards,
Remco Blankesteijn
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Old 1st February 2004, 05:44 PM   #10
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I saw that the pinning of the BC550 is different when assembling it, so that should be OK. I will now check for the insulation as suggested.
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