[recca]

DAC-AH might be old news with all of the new tech coming out these days but thought I would post some pics of my dac-ah finally running with battery power. For the mod I used a Pacific Valve modded dac-ah. First I removed the power transformer and the bridge rectifiers. From there I added a connector for an Audiomagus Powercenter battery power supply which has dual outs (the other output is for my Trends TA10.1). All you have to do is connect the + and - from the 12V connector to the corresponding ins on the board.

The other mods are the standard resistor mod and passive output mod. I kept the 6V regulators and changed the resistors to Riken Ohm Carbons 150ohm. For the passive output stage I used Jupiter Beeswax caps 2.2uF.

With Trends and dac-ah on battery power the system sounds pretty nice. Its been a while since I've had the stock dac-ah. I ripped the guts out a while ago but only recently finished the project so I can't remember what it sounded like before but I can say that everything is quiet which really makes it easy to hear the details. BTW - I'm not using it with headphones, just speakers (Aperion Audio Intimus 4).

BTW - Yeah I know the soldering sucks. I'm still a hack but at least it all works!

 

[compuryan]

cool man. go you. i had a heavily modded dac-ah a couple years ago and it kicked ass. I'm sure yours will too!

 

[jsplice]

This is very interesting. I actually have a Yulong DAH1 that I've wanted to convert to battery power, but I'm not sure how effective it would be, considering the power is used by not only the DAC, but a built-in headphone amp and a backlit LCD display (which may possible to disable if necessary). I suppose I could also disable the headphone amp, but not exactly sure how. I know the transformer has 2 x 15v output windings, so I'm not sure how I'd get 15 volts of DC from a battery because that doesn't seem like a standard voltage.

How did you get this to work if the dac itself is designed to run on AC?

 

[recca]

The stock dac-ah board had three sections, digital receiver, DAC chips and output stage. The output stage required +-15V dc which would have been very complicated to supply with a battery. Once I switched to the passive output stage it was no longer necessary to supply this voltage. The digital receiver and DAC chips required a standard 10v supply so I just connected up the battery to the spot after the bridge rectifiers converted AC to DC (I think thats what they do...I'm still learning). This supplies the voltage regulators with the required DC to power the DAC. I may be providing too much voltage to the rectifiers but hopefully they an handle it.

 

[Budgie]

Check the temperature with your finger. Warm is fine but hot will shorten the life span of the regulators. My guess is the regulators will be fine.

 

[Bosk]

Awesome mod.

I'm planning on copying you and putting my DAC-AH on battery power once I've performed the passive mod.

Just one question, does it specify on the board which of the holes under the bridge rectifiers are positve & negative? It's a little difficult to tell from those pics which wire should be soldered where.

Again, congrats on a great mod. How does it sound now incidentally?

 

[recca]

Thanks for the comments bosk. It actually sounds really nice. Maybe not the tightest bass but it could be my sub, I'm not sure. Other than that it is quiet, with a nice midrange and slightly rolled off top end. For a computer system it works out well because I don't need a ton of output and the treble is not super hot so its relatively easy to listen to. Having an all battery (except sub) system is great since there is absolutely no noise coming from all of the computer gear I have around my desk. Also the battery I have will last over 5 hours on a full charge. I rarely listen for that long continuously.

After you remove the rectifiers you'll see that pos and neg holes are marked. I sort of went out on a limb and assumed it would work. I'm not an electrical engineer by any means so I just went on faith. Luckily it worked out and nothing blew up.

BTW - I posted on your thread in the DIY forum regarding the passive out mod. Good luck.

 

[Bosk]

Cheers recca!

I'm going to mod mine in exactly the same way next week once I have some caps for the bypass mod. (I'm planning on using Obbligatos from DIY hifi supply)

I recently put the Trends t-amp that I'm using with my Dac-AH in my computer system on battery power and found that compared with the stock external power supply bass impact was slightly lowered, and overall there was less "attack" to the sound.
But on the other hand, music is now far less fatiguing to listen too, imaging is more solid, and detail is increased. Overall I prefer the change.

I think getting as many components as possible "off the grid" makes sense. I've even toyed with the idea of using some kind of UPS for the PC itself for critical listening sessions.
Given that I'm using a Toslink from the PC to the DAC this is probably a silly idea, but I'd like to connect them via coax at some point in future having read that shielded coax is generally a better solution.

Anyway, thanks again for your pics and advice I can't wait to emulate your work.

 

[recca]

Keep updating this thread. I'd love to hear how things turn out for you.

 

[Bosk]

Unfortunately things have not gone at all well.

I found that my local Dick Smith store (Aussie equivalent to Radioshack) sold cheap film caps so I bought a couple of 2.2uf caps and decided to do both your battery power mod, and the bypass mod at the same time.

Both mods seemed to go fine, although removing the transformer and desoldering the rectifiers was tricky.

I decided to solder the cable from the SLA battery directly to the DAC's board, not while plugged into the battery of course - figuring I would rig up some kind of power outlet at the rear of the DAC once I'd verified that everything was working.


To cut a long story shot I fired up the DAC and heard silence. I checked all the work and found nothing wrong.

Eventually I got so desperate that all I could think of was that I'd got the polarity on the SLA battery's cable wrong. So I reversed polarity on the cable (dumb idea, I know..) as I was moving the hot wire's bulldog clip towards the SLA battery I saw a whole bunch of yellow sparks between the bulldog clip & battery terminal (yikes!) but didn't notice any smoke or noises coming from the DAC...

It was only AFTERWARDS I realised that the Toslink from the PC wasn't plugged into the DAC...

Anyway I fired it up with the battery cable reversed back to normal and sure enough the DAC works.

Problem is..... I'm getting huge amounts of distortion in anything but ultra quiet passages of music - it sounds a bit like when a radio station isn't properly tuned in and most of what you hear is noise.


I'm due to get my 2.2uf Obbligato's in the mail this week so I'll swap those in place of the cheap film caps I used for the bypass (could the caps be the problem?) but I have a nasty feeling that I may have killed my DAC..

Is there any way I can use my multimeter to diagnose what could be causing the distortion perhaps?

 

[recca]

Good old unplugged cable trick does it again. I think we've all done that one a few times. Seriously though I think you're okay. What you have to do is adjust the trim pots to a 3.3 reference. There's some discussion in the really long thread about how to do this. You need a multimeter to do this accurately. You should do this after you confirm that the resistors are the right value. If they are, then do this adjustment after a half hour of warm up.

 

[Bosk]

Quote:

Originally Posted by recca /img/forum/go_quote.gif Good old unplugged cable trick does it again. I think we've all done that one a few times. Seriously though I think you're okay. What you have to do is adjust the trim pots to a 3.3 reference. There's some discussion in the really long thread about how to do this. You need a multimeter to do this accurately. You should do this after you confirm that the resistors are the right value. If they are, then do this adjustment after a half hour of warm up.

Cheers recca!

Quick question - where are the trim pots and how do I go about adjusting them?

 

[recca]

Here's a quote from the original Dac-Ah circuit error thread:

From Kim Hardee:

The trimpot is located near the output jacks on top of the PC board. Mine is a blue rectangular shape with the trim screw on top, scured with some sort of white goop. Just turn it with a screwdriver and the goop will break free.

You can measure the DAC output voltages on one side of R35, R36 (the other side is ground, or you can measure on the DAC chips directly. I believe it's pins 5 and 7. I would suggest trying 3.85V and 4.3V and see if you hear a difference, especially on very loud complex sections of music.

The only thing I would suggest is to use a value of 3.3V instead of the 3.85V or 4.3V.

Here's the thread. Tons of information on the first page alone although its worth reading most of it.

http://www.head-fi.org/forums/f7/cir...sy-fix-198589/

 

[recca]

BTW - Did you replace the Resistors at R35 and R36? This is critical and may be the cause of the distortion.

 

[Bosk]

Quote:

Originally Posted by recca /img/forum/go_quote.gif BTW - Did you replace the Resistors at R35 and R36? This is critical and may be the cause of the distortion.

Nope, I haven't replaced them yet - which value resistors should I replace them with?