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Old 20th September 2017, 01:31 PM   #1
tommas is offline tommas  Sweden
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Default Looking for a way to add phono to an opus dual mono DAC...

Hey!

Ten years ago I was looking for a kit to give me balanced output from USB, and someone pointed me at the OPUS and I had a great time soldering it together and got a dual mono balanced DAC that has been humming happily away for a decade. So, cheers for that! I am actually going to make a second one for a raspberry pi, the onboard sound on those things is disgusting.

Anyway... I recently started to play some more vinyl, I have so far been just kludging together something awful with a Behringer USB RIAA card to get the audio to the speakers. However it sounds terrible and makes me sad.

So then I came to the twisted pear website and saw they have a lovely RIAA stage. I have two questions I hope someone can help me with,

1. High or low impedance? I am using a Grado cartridge, which all seem to be MI, which is more like a MM cartridge. Is the low impedance better for MM then?!

2. I suppose the Retro will have two balanced outputs, that I will solder onto XLR plugs and then plug the OPUS out when I want phono and back in when I want USB. But is there some kind of machine that Twisted pear audio makes that would allow me to input a pair of balanced inputs and then press a button or twist a knob or something that would send one of the inputs to the balanced outputs?

I understand I am describing a preamp, and I think vaguely that the Joshu tree thing is a preamp, but when I read the description it feels like a big volume controller, and I am not good at electronics. I just like nice sound

Any help with either of these questions would be very appreciated!

Thanks!
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Old 20th September 2017, 03:13 PM   #2
pixelpusher is offline pixelpusher  United States
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1. The high impedance Retro is recommended for MM cartridges.
2. How do you control volume? You could just rig a selector switch to change the signal to the output.
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Old 22nd September 2017, 01:04 PM   #3
tommas is offline tommas  Sweden
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I guess there is no 'kit' for that right? It would just be a selector switch with 6 poles? Or can the grounds be shared for the balanced outputs?

Is there any specific type of selector switch that would be suitable for this? Or can this affect the audio much?
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Old 22nd September 2017, 04:06 PM   #4
pixelpusher is offline pixelpusher  United States
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The grounds on a balanced output should go directly to the chassis so you would need 4 poles. If you only have two sources it could be as simple as a 4 pole toggle switch.
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Old 26th September 2017, 10:23 PM   #5
tommas is offline tommas  Sweden
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Cool! I will pick up a 4 pole then!

I have one last small question, I need a Low Current Dual Supply for the OPUS (dual balanced mono) and then a Low Current Bipolar Supply for the RIAA stage, these are not in any way redundant are they?

Plus if I do add in a volume control, is there any specific one that is going to be easier to set up with a dual XLR output?

If I put the USB -> Opus and the RIAA, and have those going into a 4 pole switch, and then coming out of that is the dual balanced outputs, is the only TA option the Joshua Tree Balanced Complete Kit?

And that needs 7-24VAC, does that need another separate power supply? Are there suitable ones from TA?
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Old 1st October 2017, 04:58 PM   #6
pixelpusher is offline pixelpusher  United States
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You can use the same power supply (assuming it is 15v bipolar). I used mine that way for a while but had trouble with hum and buzz. I ended up using Jan Didden's SilentSwitcher power supply which is now available in the DIY audio store. This really cleaned things up.

The addition of a volume control in a balanced circuit really complicates things. I tried several options without much success. You might as well go with a full preamp.

I could recommend Bruno Putsey's Balanced preamp. I am very happy with it. There are several threads here discussing it.
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Old 4th October 2017, 04:23 PM   #7
BrianDonegan is offline BrianDonegan  United States
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Looking for a way to add phono to an opus dual mono DAC...
Quote:
Originally Posted by tommas View Post
Cool! I will pick up a 4 pole then!

I have one last small question, I need a Low Current Dual Supply for the OPUS (dual balanced mono) and then a Low Current Bipolar Supply for the RIAA stage, these are not in any way redundant are they?

Plus if I do add in a volume control, is there any specific one that is going to be easier to set up with a dual XLR output?

If I put the USB -> Opus and the RIAA, and have those going into a 4 pole switch, and then coming out of that is the dual balanced outputs, is the only TA option the Joshua Tree Balanced Complete Kit?

And that needs 7-24VAC, does that need another separate power supply? Are there suitable ones from TA?
The JT can use AC or DC. You can just use the same transformer you are powering the DAC with.
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