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Old 10th May 2012, 05:40 PM   #2871
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Thanks so much that was extremely informative. This is kind of a new direction for me.

For a couple of years I tinkered with meshplate 2A3's from bottlehead with magnequest cobalts output trafos on Talon khorus that werwe tweaked a bit. I worked for Talon for a while in sales. I don't have the access or money to do this hobby the way I used too.
It was Srjaen Ebaen's review of the patek that got me interested in gainclones. His tastes are very similar to mine so here goes.

I am going to be running these amps directly from a buffalo dac into transmision line loaded Fostex FE 206EN in a John Swenson bazooka enclosure.

Thanks for the refrences and any other suggestions you might have.

jgwtriode
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Old 17th May 2012, 02:38 AM   #2872
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Default Trouble shooting DAC problems

Hi

I've finally finished assembling the NOS DAC and am waiting on the Hammond transformer to start her up. Unfortunately the transformer will be a couple of weeks away so I decided to use what I've got in the meantime to see if it works.

These are two multi-tapped transformers (using two as I read it's good to keep analogue and digital on separate windings). The transformers didn't have the correct V output taps so the DAC is connected to the 15V and 24V windings on one to give me 9Vac (for the AN8009) and between 24V and 30V on the other transformer to give me 6Vac (for the AN8005). I think this is OK to do this.

I connected it to the mains using the bulb tester - no bright light from the tester indicating problems but I did notice the bulb was faintly glowing but thought this was OK.
I removed the bulb tester and connected directly to the mains and measured voltages across R1,R2 and across R3,R4 to make sure my transformer connections were correct. Voltage across R1,R2 (feeding AN8008) was good at 9.82Vdc but the problem is with the voltage across R3,R4 (feeding the AN8005's) which is only measuring 3.3Vdc.

Doing some testing, I decided to take the AN8005 regulators out of the circuit: I un-soldered one end of both 20R dales (R3,R4) and measured the voltage - this was 8.4Vdc (unloaded) which is OK. I still wasn't sure whether my method of getting the desired voltage between taps was correct so I disconnected the wires from the DAC at the transformer and soldered a 10R (10W) resistor directly across the transformer windings and measured 6.5Vac across the resistor so I proved the transformer OK.

I've checked the components - they all seem to be correctly placed and can't see any shorts etc on the cct board, so not sure what is causing this low reading, but I'm presuming the 3.3Vdc is caused by a higher than normal current draw somewhere dragging down the voltage.
This would be the causing the bulb testers to glow faintly when first testing, but shouldn't I be seeing something getting hot or smoke if the current is high enough to drag the voltage this low or am I totally off the mark in understanding what's happening?

I haven't connected up the DAC to my stereo as I don't want to keep it connected to the mains, fearing damage.
Should I be trying to isolate the problem by disconnecting each of the 8005's in turn to find the problem? Can I do further voltage measurements (at the chips) with the bulb tester in place or do I have to remove the bulb tester to get accurate voltage readings?

I have attached a couple of photo's just in case anyone can see any problems. Sorry for the long-winded explanation above - appreciate any help given!

cheers
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Old 17th May 2012, 09:49 AM   #2873
AndrewT is offline AndrewT  Scotland
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What is the mains voltage before and after the bulb tester?
That will give a clue to whether the "system" is affected by low supply voltage.

That very low secondary voltage indicates high current flow.
What current do you expect here?
Add in a series resistor that you expect would drop 1V across it.
Now read off the actual volts drop to compare expected current to actual current.

There seems to be a problem, these checks should confirm one way or the other.
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Old 18th May 2012, 10:34 AM   #2874
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Thanks Andrew,

In post #68 of this thread, Peter wrote:
"For the DAC.....the current draw can be calculated: I have series 20R resistors on both rail and ground feed for each section (4 total ). With DAC the drop is 1.14V and for receiver it is 0.95V"

The voltage drop across my 20R resistor (at R3 to receiver) is 1.38Vdc. I also inserted am ammeter at R3 and measured the current draw at 68mA but (if I've calculated correctly) from Peter's post above the current draw should be only 48mA, so mine is drawing around 20mA more.
I still don't get why I'm only getting 3.3Vdc across R3 and R4 - it shouldn't work at this voltage but...the good news is that I connected the DAC up to my computer speakers and it worked!
I then connected it to my stereo and it sounds very good indeed so I'm happy, but would still like to know what is causing the higher than normal current draw and whether it may cause any future problems.

The circuit schematic attached file can be foumd here at post #165
AudioSector-chip amp kits, dacs, chassis


Quote:
Originally Posted by AndrewT View Post
What is the mains voltage before and after the bulb tester?
That will give a clue to whether the "system" is affected by low supply voltage.

That very low secondary voltage indicates high current flow.
What current do you expect here?
Add in a series resistor that you expect would drop 1V across it.
Now read off the actual volts drop to compare expected current to actual current.

There seems to be a problem, these checks should confirm one way or the other.
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Old 1st August 2012, 07:22 PM   #2875
endia is offline endia  Turkey
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Default transformer for AudioSector nos dac

hi,
recently i bought a second hand dac without transformer..
while i was searching for a r-core transformer on the net i remembered that i have this transformer in my parts bin.. is it suitable for the dac or should i look a r-core?
thanks..
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Old 5th August 2012, 03:19 PM   #2876
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This transformer is fine.
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Old 14th August 2012, 02:28 PM   #2877
slungu is offline slungu  Germany
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Peter, looking to your 4780 kit I noticed that it was build for balanced input. Why did you choose this configuration instead of going by the "normal" unbalanced topology as described in the TI data sheet. I liked the idea of double power in my 8Ohm load, but since all sources I have are unbalanced, as I would guess many people have, I was just wondering how this particular configuration was choosen.

Regards, Stefan
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Old 14th August 2012, 03:22 PM   #2878
sangram is offline sangram  India
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^^I can assure you the board works fine in SE mode as well.

Here is somebody who has done just that and has pictures. I have too, but my SE board blew up before I owned a camera

LM4780 Monoblock Amplifiers : DIY by Tim Jarsky

I use two of the 4780 dual mono kits for one of my amps in a balanced configuration.
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Old 29th August 2012, 08:27 PM   #2879
endia is offline endia  Turkey
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Quote:
Originally Posted by Peter Daniel View Post
This transformer is fine.
thank you Peter,
this is what i'm planning to wire green dac board to the mains.. there should be no problem, right? just, i want to be sure before soldering..
thanks..
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Old 31st August 2012, 02:41 AM   #2880
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Yes, that would be correct connection.

Quote:
Originally Posted by slungu View Post
Peter, looking to your 4780 kit I noticed that it was build for balanced input. Why did you choose this configuration instead of going by the "normal" unbalanced topology as described in the TI data sheet. I liked the idea of double power in my 8Ohm load, but since all sources I have are unbalanced, as I would guess many people have, I was just wondering how this particular configuration was choosen.

Regards, Stefan
The LM4780 kit is not specifically built for balanced setup. It can be used any other way as described here: AudioSector-chip amp kits, dacs, chassis
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