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DDDAC experts

djdstone

djdstone

pfm Member
Are there any DDDac experts that hang around in the DIY area of the forum? Had a power surge in my house last night - ever since my 3 board DDDac has distortion in the mid to HF range - the upper register of vocals are distorted for example. Seems to get worse as the sample rate gets lower? Where should I be looking to find the source. The output is via a pair of Cinemag transformers that have some 22k Mills resistors across the left and right channel to match the impedance of the pre amp I use. I measured the R load and one channel was 1530k and the other was 1860k. Could the surge have effected these?
 
not sure - just that everything tripped. The preamp was connected to the MA12s and the DACs analogue output was connected to the preamp amp.
 
I'm just trying to get to the bottom of what caused this so as to be better able to advise really... A surge in UK mains of sufficient to damage equipment is very rare indeed and you would probably have a claim with your supplier if it could be proved... therein lies the rub...

The more info you can provide as to what exactly happened the better... What precisely do you mean by "everything tripped"?
 
Thanks Jez - not sure really that's why I'm being vague. I was listening to music and then all the power when off. Initially I thought I'd damaged my speakers but the problem seems to be the DAC
 
I have a DDDAC board tester here in Hereford so if you want them tested individually I can do that for you. If you go over to diy audio forum, my posts are under Almeg69 you will be able to see what I have got up to with the DDDAC ...
 
djdstone said:
Hi Alex - do you think that might be causing the distortion?
Click to expand...

As Jez has said, it would be very unlikely that a mains power surge could cause the damage. The DDDAC power supply has a very wide tolerance to AC input voltage. The normal transformer is 15v AC but I have 25V AC because I wanted to use a higher resistance to give a bit more smoothing in the C R C section. I would try a different input to the Dac, so if you have trouble with the USB input, try the SPDIF or vice versa just in case your power surge has caused any damage to your source.
It would be worth checking the joints on the resistors as you may have a "dry" joint on one of them.
Another check would be the 40Mv constant current source trimmer as variations there will give different values on the output.
 
Hi Alex - I’ve tried the SPDIF input and the result was the same -distortion in the mid band and especially the HF range which lessens when the sample rate increases. I’ll try the resistors first - where is the 40Mv current source trimmer? Doede recommended that I used a value of 22k around the analogue output - when I measured them the values were lower.Could that cause the distortion? I have two of the standard power supplies - is it better to increase the value to the Dacs when you’re running more boards?
 
It's extremely unlikely to be anything other than blown silicon if it was indeed a surge (which seems very unlikely). If it was a surge and it turns out not to be an IC or similar then go and put the lottery on!

Careful with that 40Mv trimmer as it's likely to strike an arc from several yards away....:D
 
Thanks Jez - would that account for the distortion. It's hard to pin it down but it appears to be in the mid band?
 
It is very unusual for distortion to be only in the mid range. I doubt you will find a solution short of replacing the faulty board.

I presume you've ruled out everything but the DAC by substitution?
 
djdstone said:
Hi Alex - I’ve tried the SPDIF input and the result was the same -distortion in the mid band and especially the HF range which lessens when the sample rate increases. I’ll try the resistors first - where is the 40Mv current source trimmer? Doede recommended that I used a value of 22k around the analogue output - when I measured them the values were lower.Could that cause the distortion? I have two of the standard power supplies - is it better to increase the value to the Dacs when you’re running more boards?
Click to expand...

Have you got the latest Powered by tent boards. If you are they will have 2 multi turn variable resistors which will enable you to set the voltage across the 100R resistor to 40 millivolts.
 
Hi Alex - they aren’t the newer versions. I’ve removed the boards and have gone back to a single board and the distortion seems to have gone. Can I send them to you to test? PM your address and I’ll drop them in the post
 
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djdstone said:
Hi Alex - they aren’t the newer versions. I’ve removed the boards and have gone back to a single board and the distortion seems to have gone. Can I send them to you to test? PM your address and I’ll drop them in the post
Click to expand...

I am not sure how to do a PM but no problem because I will have it sent to my work address which is: Attn Alex, A H Fabrications, Unit 5G Ramsden Rd, Rotherwas Ind Est, Hereford, HR2 6LR.
I am always there through Monday to Friday. and no one is at my home address.
 
Thanks for your help Alex - sounding really sweet over the weekend. I’d recommend the DDDAC build to anyone.
 
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