This is the one which I have, but mine has not got the USB sector populated. It is unmodified other than removing the opamps and wiring in a pair of UTC a-20 transformers to the chip outputs (a la Jensen). Another Scottish member sent me some Russian Teflon caps - for which I am very thankful - and they have made the sound more seriously good - and seem to be improving daily!
It is a good board.
Thanks for that, I'll get ordering
Hi
Just one last thing...I'm not planning to add an output transformer at this stage.
Can someone remember where the correct resistor values etc were discussed in this long thread?
I'm about to buy the bits to build a Lightspeed Attenuator and it would be nice to add the dac parts to this order.
Thanks
Richard
Just one last thing...I'm not planning to add an output transformer at this stage.
Can someone remember where the correct resistor values etc were discussed in this long thread?
I'm about to buy the bits to build a Lightspeed Attenuator and it would be nice to add the dac parts to this order.
Thanks
Richard
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Change of subject!
We often forget lessons learnt years ago!! In my case I simply reversed the mains polarity in my CD reader! Immediate and immense difference - for the better. I then checked the mains plug polarity and it was OK. I then did the same with the DAC power cable and - again - a big jump in sound quality.
Just an idea in case anyone who tries might just benefit.
Years ago when seting up a system I always tried polarity reversal....I just forgot all about it until I read something similar on a recent post concerning Keith Jarret and his ECM CD experiences!
We often forget lessons learnt years ago!! In my case I simply reversed the mains polarity in my CD reader! Immediate and immense difference - for the better. I then checked the mains plug polarity and it was OK. I then did the same with the DAC power cable and - again - a big jump in sound quality.
Just an idea in case anyone who tries might just benefit.
Years ago when seting up a system I always tried polarity reversal....I just forgot all about it until I read something similar on a recent post concerning Keith Jarret and his ECM CD experiences!
Thanks for posting that, it sounds like your leaving out the bit for adjusting offset?
Does reversing the power cord polarity (neutral/hot) is safe to practice or is it the polarity of the primary transformer that you refer to...? I'm kinda lost here for a simple thing....
I've been listening to the DAC with the A-20 transformers and am pretty impressed now they've been playing for over a week. When first using them they sounded pretty muffled and closed in. They've 'opened up' beautifully now. I'm using the Jensen recommended values on the primary, with just a 680R across secondary's.
The only problem I have is a hum on both channels (changes with volume level - not constant). I wired up according to the printouts on the front of the transformers, but - following advice on this board - did not connect the ground/screen terminal to anything. The DAC is also running without any earthing at present - could this be the problem?
Cheers,
- John
The only problem I have is a hum on both channels (changes with volume level - not constant). I wired up according to the printouts on the front of the transformers, but - following advice on this board - did not connect the ground/screen terminal to anything. The DAC is also running without any earthing at present - could this be the problem?
Cheers,
- John
Hi John, I've used mine with both balanced and unbalanced preamps and have always had dead silence. Assuming your RCAs are isolated from the chassis, the hum would have to originate from your DAC power trafo or some other stray magnetic field. Could they be physically too close to each other?
Things to try include bolting the A20s to the chassis if they are not, rotating them, tying the shields to the chassis, and last resort, tying the shields to the RCA ground lugs. Let us know what you end up with.
Oh, I'm also assuming your chassis is earth grounded.
Best, Bill
No problems this way.
Mine is all rca, and wired similarly to yours. It is a bread board on wood. The mains lead is two core and there is no earthing of anything. The A-20s are wired to the points marked on the underside of the pcb and I have wired the A-20s to the underside solder pads at the RCA -out plugs. Resistors and caps are soldered directly to the terminals of the A-20s.
It is absolutely silent.
I would check all joints.
Mine is all rca, and wired similarly to yours. It is a bread board on wood. The mains lead is two core and there is no earthing of anything. The A-20s are wired to the points marked on the underside of the pcb and I have wired the A-20s to the underside solder pads at the RCA -out plugs. Resistors and caps are soldered directly to the terminals of the A-20s.
It is absolutely silent.
I would check all joints.
You only need to change the switches if you use a higher sampling rate. If you are using a 24-bit 44.1 file no need to change switches
Hm, that's my question. I listen to both 44.1 and higher. Let's say I play some 24/192 classical from Linn Audio after listening to a regular cd/mp3, would I have to change the switches, or is there a setting that allows me to listen to both without switching?
Thanks for your replies
Soldering is perfectly fine - no problem there. It's in a chassis but no chassis earth attached at present until I've finished the rear panel and fitted the IEC socket and so on...
Power is supplied by a toroidal transformer, which is quite far away from the A20s at the opposite end of the chassis. As the chassis base-plate is pressed steel perhaps interference from the transformer is being induced into the metal body of the A20s? I'll try and isolate the A20s from the chassis and see if this helps. Will also try rotating them as you suggest Bill. RCAs are currently on a piece of paxolin board, and are not touching the chassis.
A20s are attached to the spot on the main circuit boards where the caps used to be (beside the DAC circuit board) marked L-/L+/R+/R-. Resistors and caps mounted directly to the A20 terminals (and I just double checked for any shorts etc).
- John
Soldering is perfectly fine - no problem there. It's in a chassis but no chassis earth attached at present until I've finished the rear panel and fitted the IEC socket and so on...
Power is supplied by a toroidal transformer, which is quite far away from the A20s at the opposite end of the chassis. As the chassis base-plate is pressed steel perhaps interference from the transformer is being induced into the metal body of the A20s? I'll try and isolate the A20s from the chassis and see if this helps. Will also try rotating them as you suggest Bill. RCAs are currently on a piece of paxolin board, and are not touching the chassis.
A20s are attached to the spot on the main circuit boards where the caps used to be (beside the DAC circuit board) marked L-/L+/R+/R-. Resistors and caps mounted directly to the A20 terminals (and I just double checked for any shorts etc).
- John
You'd have to change the switch I'm afraid.
However you could add some toggle switches to the front panel of your chassis, and run leads to where the original switches used to be on the DAC board. Would at least be easier to select sampling rate then.
I plan to do this too once I've got it all working properly and hum free.
Thought! (happens one in a while hahaha!).
COULD this hum be because I have attached the ('negative') A20 wires to the L- and R- points on the main circuit board (where those 4 caps used to be)... but as the caps are no longer there (and therefore no longer linking each pair of solder holes together per ex-cap position) the - return isn't going anywhere, so I have no earth?!?
- John
EDIT: Talking out my backside... this is how everyone else seems to have connected it up. Will try A20 orientation next.
COULD this hum be because I have attached the ('negative') A20 wires to the L- and R- points on the main circuit board (where those 4 caps used to be)... but as the caps are no longer there (and therefore no longer linking each pair of solder holes together per ex-cap position) the - return isn't going anywhere, so I have no earth?!?
- John
EDIT: Talking out my backside... this is how everyone else seems to have connected it up. Will try A20 orientation next.
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Mine is all rca, and wired similarly to yours. It is a bread board on wood. The mains lead is two core and there is no earthing of anything. The A-20s are wired to the points marked on the underside of the pcb and I have wired the A-20s to the underside solder pads at the RCA -out plugs. Resistors and caps are soldered directly to the terminals of the A-20s.
It is absolutely silent.
I would check all joints.
Brianco - did you connect the shield/CT to pins 3 & 4 and 9 & 10 on each of your A20s?
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