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daveinpoway
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join:2006-07-03
Poway, CA

daveinpoway

Premium Member

Audio Alchemy Digital Decoding Engine, v1.1

When applying a coaxial SPDIF signal, the front-panel "Locked" light will come on and there is analog audio out on both channels, but it is extremely weak (you need to turn the preamp volume to almost full to hear anything).

I believe that the mute circuit is always on, but I cannot say for sure. I have seen requests online for a schematic for this model, but I have not seen anyone state that they found one.

There are two green LED's (D10 and D11) in the analog output section and neither of them light up, no matter what digital input and output phase I select; are these supposed to light when the unit comes out of mute?

Since it has a multi-layer PCB, tracing the signal path is not easy, so I am not sure which transistors comprise the mute circuit. If the above-mentioned LED's are supposed to light in the no-mute condition, this would tell me that the circuitry near them is associated with the muting.

This is an old DAC, but it was well-regarded in its day.

Sly
Premium Member
join:2004-02-20
Tennessee

Sly

Premium Member

I haven't found any documentation that states this DAC has a mute feature, but I did find this:

That tiny fascia contains two switches and three LEDs. The first switch chooses between digital coaxial and TOSlink optical inputs. A red LED indicates 'locked', to show the successful reception of a signal, and two green LEDs marked 'analog' and 'digital' indicate 'power on' status for the separate power supply regulators within. »hometheaterreview.com/au ··· eviewed/

If neither of the LEDs are lit, then you may have an internal power supply problem.

[edit]Here's a post stating that the power supplies were unreliable: »forum.tz-uk.com/showthre ··· in-a-Box
Sly

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Click for full size
I haven't found a schematic but I did find this picture. I would look for a bad cap or maybe the transistors on the right side...
»www.hifido.co.jp/KW/G040 ··· 8127-00/
daveinpoway
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join:2006-07-03
Poway, CA

daveinpoway to Sly

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Thanks for your response.

The article you located refers to the v1.0; on the v1.1, the front-panel power status LED's are red and they are both lit on my unit.

When I am trying to get analog sound out of the unit, the front-panel Input 2 (Coaxial), Digital Power, Analog Power, Locked and either 0 or 180 degrees phase LED's are all lit. Changing the phase has no effect on the music volume.

Not sure if they all have it, but I believe that most DAC's have a mute feature, to block clicks/pops/other unpleasant noises from reaching the speakers.

I assume that the LED's on the PCB are supposed to come on under some circumstances.

If anyone here has a (properly-working) DDE v1.1, could you please remove the top cover (2 screws on the outside edges of the back panel, plus an additional screw supporting the Toslink connector) and tell me if LED's D10 and D11 light up and under what circumstances does this happen. The LED's are green in my unit; no idea if other colors were used in other production runs.

Sly
Premium Member
join:2004-02-20
Tennessee

1 edit

Sly

Premium Member

Came across this:

Output muting is accomplished by tying the front-panel lock indicator to the Bitstream chip, muting the output until the unit has locked to the incoming digital signal. »www.stereophile.com/cont ··· gine-v10

It seems that if it doesn't see a digital signal it recognizes, it may stay muted. What source are you using to feed it? Maybe you're using the wrong bitrate?

Even though this is for the 1.0, it may apply to yours as well. Chances are you need to feed it 16bit 44.1kHz sampling rate PCM data...
daveinpoway
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join:2006-07-03
Poway, CA

daveinpoway to Sly

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Thanks for posting this; I believe that the problem is on the left side (the analog output section). The volume is the same for both the left and right channels, so the issue is something common to the 2 channels (most likely power supply or muting).

If you move forward from the 2 RCA jacks at the left-rear of the PCB, the 2 green LED's I mentioned are plainly visible. They were possibly incorporated to give a service technician an indication of what is happening, so that he/she can quickly isolate where a problem is located.
daveinpoway

daveinpoway to Sly

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The output settings for my Mac were set for 44.1 KHz/16 bits. Since the (very soft) music coming out is correct for the CD, the unit is obviously performing D-to-A conversion, but something is preventing the proper amount of signals from reading the analog output jacks.

Sly
Premium Member
join:2004-02-20
Tennessee

Sly

Premium Member

From what I've read, the 1.1 does not have a mute feature, only the v3. The 1.1 will mute the audio until it has a lock, but you are getting a lock and you are getting some audio.

My next question: Are you sure that your receiver/amp is not muted? Have you tried hooking up the DAC to a different input on the receiver? Have you tried a different source such as a cd player to the receiver's input to be sure the input is working correctly?
daveinpoway
Premium Member
join:2006-07-03
Poway, CA

daveinpoway

Premium Member

I have put my fingers on the bare RCA plugs of the interconnects (after unplugging them from the DAC) and I heard a buzz over the speakers (with the preamp volume turned up), so I know that the preamp input is active and the interconnects are not defective.
daveinpoway

daveinpoway

Premium Member

It occurs to me that having the DDE's front-panel "Locked" light turned on may not be sufficient for turning off the mute:

On my M-Audio SUPER DAC 2496, the "Data Valid" light does not turn on unless I am actually playing audio content (CD, stored iTunes music or online video). The DDE v1.1 turns on the "Locked" light anytime that my Mac is running (even if no audio is being played). So, it is quite possible that there is another lockup function (not monitored by the DDE's front panel) which takes effect only when audio is being played and this is what disables the muting.

Something (perhaps mute-disable) must turn on the two PCB LED's; otherwise, it would make no sense for them to be there. The fact that the LED's never light could be a clue as to what is wrong, but I do not know where they are situated in the circuit (due to lack of a schematic/block diagram/service manual).

Sly
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join:2004-02-20
Tennessee

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A buzzing sound doesn't necessarily mean that the input is not muted. When you touch the RCAs, you are introducing noise through the grounding system, bypassing some of the control circuitry. You could still hear a pop or a buzzing even if it's muted. I would try hooking in another source such as the dvd player you mentioned on another thread.
Sly

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When your Mac is on, it is sending a PCM clock signal even if no audio is playing. If you unplug the coax line, does the "lock" indicator go off? You should get a lock on the PCM audio even if the Mac is "playing" silence.
daveinpoway
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join:2006-07-03
Poway, CA

daveinpoway

Premium Member

The preamp is completely manual (no microprocessor), so there is no control circuitry. The preamp "Mute" switch is a toggle switch and that is set to "Play"- I know this switch is set correctly, since the SUPER DAC would not be able to play through its input connectors if the switch was set to "Mute". The input selection is done by a manual rotary switch (no relays).

If I set the DDE to Input 1 (Toslink), the "Locked" LED goes out, since there is no Toslink cable connected. Even though the Mac is always sending out a PCM clock signal, this is not sufficient for the SUPER DAC to light its "Data Valid" LED and turn off its muting circuitry- perhaps it is also not sufficient for the DDE to unmute.

It would be great if I had another (properly-working) DDE v1.1 to compare this one to (especially in regards to when that one lights the PCB LED's), but I do not know anybody who owns one. Someone is selling an Audio Alchemy setup in the local Craigslist, but his DAC is a later-version DDE, so it is probably totally different inside.
daveinpoway

1 recommendation

daveinpoway

Premium Member

It works! It works! It works!

This morning, I dug out a meter and made some measurements- even though the Analog power light has been lit, there was no -8 V coming out of the power supply section.

I never had the original power supply, so I had made an adapter using two coaxial power sockets (salvaged from some scrap PCB's) wired to a 1/8" stereo mini plug; two 12.5 V power supplies plug into the salvaged sockets. Due to a stupid wiring mistake, there was no -12.5 V being sent to the mini plug.

Initial impressions is that it is not as good as the SUPER DAC, but I am using some random cables with this DAC, whereas I have spent time optimizing the cables for the SD.
daveinpoway

daveinpoway

Premium Member

Have contacted someone who is selling an Audio Alchemy package (will not split it up) in Craigslist to ask if he has any extra AA power supplies lying around. Doubtful that he does, but I will never know if I do not ask.

Sly
Premium Member
join:2004-02-20
Tennessee

Sly

Premium Member

Do the LEDs inside the cover do anything now?
daveinpoway
Premium Member
join:2006-07-03
Poway, CA

daveinpoway

Premium Member

That's a good point- once the music started coming out, I put the top cover back on and completely forgot about checking the LED's.