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Old 24th April 2011, 07:09 PM   #2221
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Hello Salas,

Thanks for your explanation, learned something again. Downloaded a 1kHz mp3 0 dB. It shows 1,98V. Maybe too low for the combi then. The values in the A-18 scheme I don't have at hand anymore, it's old.... Guess I will see if the dcb1/f5 combi plays what the verdict will be. I will let you know when it's finished, but already thanks for all your effort.

Joffrey
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Old 24th April 2011, 07:18 PM   #2222
Salas is offline Salas  Greece
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15W from that source with 15dB gain of F5. 2.21dBW less than nominal 25W max.
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Old 27th April 2011, 03:52 AM   #2223
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Default Finally Working - Yeah!

My DCB1 is working now with switch, fuses, and everything. My wiring mistakes on the inputs and outputs (the ground is not connected - now I soldered directly to the PCB) cost me a pair of tweeters and the shipping charge for Emotiva XPA-2 - not too bad considering what I've learned from the mistake.

The Emotiva is back. The repair report says it was over driven and the resistors on one of the output filter were burned. Right now I hook up with the Class D amp to my Scan Revelators.

Thanks Salas, Tea Bag, and everyone helped.
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Old 27th April 2011, 10:52 AM   #2224
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Good for you. Lesson learned the smoke way, is be careful from now on, don't haste when building.
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Old 27th April 2011, 02:09 PM   #2225
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Default Grounding DCB1

Salas,

Another observation I want to share is that the DCB1 is quite even in a cardboard box. My original B1 will create big hum without metal enclosure in the same environment.

I did not "Ground" the DCB1 yet. Should I connect the Ground pin from the IEC to somewhere on the PCB? I want to build a MDF box with wood veneer for it but want to know what could go wrong first and what's the right way to do a chassis ground on this design.

I currently use two 25K mono pots. I will add the LightSpeed volume control this weekend.

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Good for you. Lesson learned the smoke way, is be careful from now on, don't haste when building.
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Old 27th April 2011, 02:43 PM   #2226
Salas is offline Salas  Greece
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You will add a metal floor at least to your wooden box and there you will tie your mains ground with a short 1.5mm2 cable next to the IEC receptacle. You will insulate all nude mains prongs and cable ends also. IF there will be hum, you will run a short cable from where the board reads G (at the end of the regs before the audio portion) to the metal panel. You will also ground the pots bodies same way if they are encased in metal. You will place the transformer to the farthest diagonal distance in respect to the RCAs. Stay away from the IEC and the board GND for now, don't experiment.
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Old 27th April 2011, 08:26 PM   #2227
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Quote:
Originally Posted by parodielin View Post
Salas,

Another observation I want to share is that the DCB1 is quite even in a cardboard box. My original B1 will create big hum without metal enclosure in the same environment.

I did not "Ground" the DCB1 yet. Should I connect the Ground pin from the IEC to somewhere on the PCB? I want to build a MDF box with wood veneer for it but want to know what could go wrong first and what's the right way to do a chassis ground on this design.

I currently use two 25K mono pots. I will add the LightSpeed volume control this weekend.
The safest and most advisable thing to do is to tie the IEC earth yellow-green cable to the chassis with a bolt. Then tie the main ground from the board to the same bolt.

If using a wooden box, just join the IEC earth to the board ground.


Is there a better advice safetywise?
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Old 27th April 2011, 09:19 PM   #2228
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As usual my (arguable) point of view on these matters: if you like to keep your audio circuits clean please do not connect the boards GND directly to the IEC receptacle. Better use a heavy wattage resistor 10 Ohm or a Thermistor like Nelson Pass uses in some of his designs.There are various threads on this subject here. It has no use polluting your audio by connecting audio-GND straight to a non clean PE. It will also give more chances to have ground loops. Safety-wise there are some other angles. One of them is that PE is more or less a very good "earth" (which it is not in practice). I have had numerous occasions where PE connection caused more problems than it solved in terms of pollution. I very well realize I am on thin ice here when safety regulations are concerned as not every reader is capable of deciding which solution is according these regulations so "just connect GND to PE" is often the easiest solution when safety is concerned. Again, that is not the case for optimal results of your self built audio gear in many cases (only if it is mechanically and electrically well designed/well built of course

Example: I would not doubt a second to connect tube gears audio GND directly to PE !!!!

Another example: when a plastic case is used with a metal subchassis I would connect the subchassis directly to PE but I would not connect GND to PE at all as risks of touching live metal covers is non existent.

PE is for safety but it is also the sewer for getting rid of EMC/RF from switching power supplies, mains pollution, overvoltage protection circuits etc, etc. Stuff you don't want to creep in your gear via PE -> GND...
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Last edited by jean-paul; 27th April 2011 at 09:48 PM.
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Old 28th April 2011, 02:49 AM   #2229
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Default LightSpeed Volume Control

So I cheated on my schedule. I installed the LightSpeed tonight. It's working on my Lepai Class T $20 amplifier. No hum or anything - very quite. I'll let it run for a while and move them to the "real" speakers.

This time I checked everything before putting everything together. My Emotiva still in the box. It's way too heavy.

DCB1 has more dynamics and details than the B1. Now with LightSpeed - don't know what I should expect. Perhaps I should build another one with Hot Rod?
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Old 29th April 2011, 03:54 PM   #2230
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I agree with you regarding the DCB1 against the B1; the Salas unit is absolutely brilliant. I'm interested to hear what you think of the Optivol and DCB1 together having built both but not yet got around to trying them together myself.
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