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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Salas hotrodded blue DCB1 build
Salas hotrodded blue DCB1 build
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Old 21st January 2018, 12:14 PM   #5731
stefanhgm is offline stefanhgm
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Okay, thank you very much for your detailed explanation I think I got it now. I will use it as you described.

Apart from the protection, the three wires on my attached picture are the right one to be plugged into the PCB. Yes or No?
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Old 21st January 2018, 12:50 PM   #5732
AndrewT is offline AndrewT  Scotland
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use the MBT to power ON the transformer alone (no rectifier, no smoothing capacitors, no amplifier).
Measure the two sets of secondary voltages.
Are they what you expect?

Power OFF.
Short together the two middle leads.
Power ON
Measure the three sets of output voltages.
Are they what you expect?
Power OFF.
report back.
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Old 29th January 2018, 06:51 PM   #5733
stefanhgm is offline stefanhgm
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Finally, I got my B1 up and runnig. AndrewT I followed you advise and nothing blew up ;-).

However, I wired it up with my power amps and a audio source and there is no sound. I followed Salas advice in "HOW TO KNOW IF THE CIRCUIT IS WORKING PROPERLY" to check whether it is working.

So, here are my results:
1. See that you have 2V+/-0.3V across R1 combinations. That says the shunts CCS currents are normal.
At my 10 Ohm resistors (hot-rodded version) I measure 1.62 and 1.60 volts.
2. Check that you hear the output relay clicking one time 3-4 seconds after power on.
It is definitely clicking, yes.
3. See that you have less than +/-5mV DC offset on the audio outputs.
Strangely my multimeter shows 0.000V.
4. See that you have +Vout a bit more than - Vout.
+Vout is 9.65 and -Vout is 9.86.

LEDs all seem to work.

I connected a mesmerize I-Select for input selection. I enabled the first input by shortwiring the according contacts. When it is powered on the input is going through to the inputs of the B1. So, this should not cause the problem.

Any advice?
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Old 29th January 2018, 10:41 PM   #5734
Salas is offline Salas  Greece
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Salas hotrodded blue DCB1 build
1. Still a high enough CCS result to go by without issues. Very good match though.
2. Good sign
3. Weird. Make sure you measure each channel's output pad at DCmV DMM scale VS the middle output (ground) pad.
4. +V>-V is expected in the Mezmerize. You have a Hypno so any mismatch could go either way due to IDSS & VF tolerances

If (3) is still 0mV try at the 220R resistors next to the relay VS ground. That's the signal path to the relay. So to know if offset or test signal exists. If yes, the relay blocks. If no life signs before the relay, check there is ~10V D-S voltage on each signal FET in the quartet and their correct orientation.

Play a strong 300HZ sinewave from a lab gen or a digital source with no power amp connected to the pre and trace it from RCA input through the modules until it vanishes so to find the bottleneck point. Use the DMM in ACV if you haven't got a scope. There could be some wrong wiring arrangement or a bad part. There are many website signal generators or free software gen applications for PC audio and mobile phones.
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Old 30th January 2018, 08:18 AM   #5735
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by stefanhgm View Post
..................
3. See that you have less than +/-5mV DC offset on the audio outputs.
Strangely my multimeter shows 0.000V...............
You cannot accurately measure 0, or 1, or 2mvdc output offset if you use a digital voltmeter that has a resolution of 1mVdc (0.001Vdc)
You should select a range that is ~ 10times more sensitive than the measurement you expect.
If you are trying to measure around 1mVdc, then use the 199.9mVdc voltmeter range. The LSD is 0.1mVdc (LSD = Least Significant Digit).
That will give reasonably accurate measurements of offsets down to <0.5mVdc and might be good enough down to 0.2mVdc

That is a general rule that applies to many measurements. Your resolution should be ~ 10% of the lowest reading you want to see.
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Old 31st January 2018, 09:49 PM   #5736
BigE is offline BigE  Canada
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Quote:
Originally Posted by AndrewT View Post
You cannot accurately measure 0, or 1, or 2mvdc output offset if you use a digital voltmeter that has a resolution of 1mVdc (0.001Vdc)
You should select a range that is ~ 10times more sensitive than the measurement you expect.
If you are trying to measure around 1mVdc, then use the 199.9mVdc voltmeter range. The LSD is 0.1mVdc (LSD = Least Significant Digit).
That will give reasonably accurate measurements of offsets down to <0.5mVdc and might be good enough down to 0.2mVdc

That is a general rule that applies to many measurements. Your resolution should be ~ 10% of the lowest reading you want to see.
are the fets in the right place?
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Old 9th February 2018, 04:31 PM   #5737
stefanhgm is offline stefanhgm
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Hey guys,

sorry for my late reply.
3. Weird. Make sure you measure each channel's output pad at DCmV DMM scale VS the middle output (ground) pad.
You were right of course, I measured 1-1.3 mV.
Play a strong 300HZ sinewave from a lab gen or a digital source with no power amp connected to the pre and trace it from RCA input through the modules until it vanishes so to find the bottleneck point. Use the DMM in ACV if you haven't got a scope. There could be some wrong wiring arrangement or a bad part. There are many website signal generators or free software gen applications for PC audio and mobile phones.
Very good advise as well. I did as you said and found a wrong wiring of the audio signal. Last project I worked on was a mono amp and that seemed to have confused me.

I have the DCB1 working now and I must say I am impressed. It sounds superb. I never expected a pre-amp to have such an effect. Everything sounds clearer and I can hear more details. Next step will be the case of the amp. Thanks for your help again!
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Old 9th February 2018, 05:32 PM   #5738
Salas is offline Salas  Greece
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Salas hotrodded blue DCB1 build
Congratulations. We will be happy to also see new pictures of your build when finished.
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Old 17th February 2018, 07:26 PM   #5739
TioFrancotirador is offline TioFrancotirador  Poland
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Hi Salas,

I got one DCB1 laying around that I want to use as -/+ 15V voltage regulator.
Is it ok to just add two red leds on both sides or I need to change some e.g.: resistor values additionally?
Is the performance of DCB1 used as voltage -/+ 15V regulator comparable to Salas BiB (in terms of noise)?

Regards,
Tio
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Old 17th February 2018, 09:01 PM   #5740
Salas is offline Salas  Greece
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Salas hotrodded blue DCB1 build
Yes you can add extra Leds to boost the Vrefs and also use an adequate voltage trafo. No resistors manipulation is needed when using only Leds as voltage setting elements.

I would use three Leds* in series on thumbnail sized matrix boards and wire the whole things end to end at one of the original five Leds pads on the main board per side. Leaving one empty if first populating or pull out one original Led from each side if its an already assembled board.

Noisewise its comparable to the BiB when using same Vref filter capacitors (at the Wimas area there is space and pads for film or electrolytic). Currentwise its more capable than an unmodified BiB due to its big MOSFETS.

*Maybe mixing some green with the reds also, depends on what brand of Leds are in hand. If its important to reach the 15V goal exactly or to match the other side well, it will take some iterations in Leds picking. There are the usual VF and IDSS tolerances at play here too. If its a Mezmerize board it will also need a small easy trick not to oppose your matching efforts of its voltage sides. Because its rigged to force a small asymmetry. In that case let me know to explain more. If its a Hypnotize board do nothing further.
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