[Hap]

Is there a way to install a phase (polarity) inverting switch to the analog outputs of a CD player.

I've done this many times with turntable outputs; used a 4PDT on/on switch and ran the wiring with one side correct and the other side reversed to the RCA's.

Tried installing this switching circuit into a Sherwood CDP, but ran into problems with getting the phase inverted side to play; no sound is produced when the switch is on the PI side.

Noticed the CDP analog outputs share a common ground line, so I don't know if that is the problem, or something in the D to A circuit that will not allow the output polarity to be reversed.

The problem is that my speakers will not allow for me to flip the speaker leads for phase correction; as something in the new circuit does not like this and trips the amps protection.

I don't have a lot of experience with digital circuits, so would appreciate any suggestions on whether a switching circuit like this is possible with a CDP.

Cheers.

[mgalusha]

If the CDP is single ended, which it almost certainly is since you mention RCA's then you can't do this. As you noted, there is no sound when you flip the switch. That's because it's shorting the output.

Depending on the DAC and how the analog stage is implemented it might be possible to swap the outputs from the DAC to the analog stage. This would only be possible if the DAC had balanced outputs (many do) but even then this is not very optimal as you then introduce long leads and a switch between the DAC's and the analog stages. And most things are surface mount these days, making this a very challenging option.

The easiest way is to use a transformer but good ones tend to be expensive.

mike

[*Scotty*]

Mike has outlined the problem rather succinctly and attempting major surgery on your CDP wouldn't be my first choice either.  Your problem with reversing phase at the speakers should be investigated further. More information about your amp and your loudspeakers would be helpful. Also I would advise you the contact the amplifier manufacturer and the speaker manufacturer about this situation.
Scotty
 

[Occam]

Iff'n your preamp has true balanced in, its achievable with some surgery on the cd players ground terminations impedance. Balanced interconnects do not require differential circuitry, rather, they need balanced source impedances. If you've a balanced input preamp, you could still use the dpdt switch and adjust the cd player like so -


with the phase reversal -

reversing lines 2&3 of the XLR output.

If your preamp doesn't have balanced inputs, nevermind.....

[Hap]

Thanks Paul and Mike for the insight into this issue.

Kinda figured this would not be an easy task, like it is with the TT outputs.

My preamp is a Conrad Johnson PV12, so no balanced inputs/outputs; the RCA outputs are phase inverting by design.
Speakers are Quad ESL63's that have new 3rd party (non quad) input spark arrestor circuit boards, which for whatever reasons will not allow flipping the speaker leads, as doing this causes the power amps to trip.
Hence my current situation...

There are no problems with the power amp(s), as I've duplicated this problem with 3 different amps.

Currently not using an external DAC
Are there any external DAC's that have a phase inverting switch option.

Cheers,
Hap

[Mike B.]

You can create a phase switch on the outputs by inserting a output transformer. It is possible to eliminate the gain stage and use a transformer for this as well. Check with Kevin at the K and K forum associated with the Audio Asylum

[BobM]

Not only is it a bit complicated, but feedback from those who have tried this on DAC's and CD players says it does cause degredation in the sound. The best place to do this in a player is in the digital realm, not as part of the output circuitry.

Bob

[jb]

Whether or not the job is complicated depends on your point of view. Doing the phase swap in the analog domain is usually less complicated because it doesn't involve PCB surgery and the processes needn't cause signal degradation if it is done right with quality components.

Here's what I did: Using a small component box, I spliced a Jensen input transformer and DPDT switch into the preamp-to-amp IC. The assembly plugs into the RCA jack on the amp.

[NewBuyer]

Whether or not the job is complicated depends on your point of view. Doing the phase swap in the analog domain is usually less complicated because it doesn't involve PCB surgery and the processes needn't cause signal degradation if it is done right with quality components.

Here's what I did: Using a small component box, I spliced a Jensen input transformer and DPDT switch into the preamp-to-amp IC. The assembly plugs into the RCA jack on the amp.

Wow - very nice!

Is there an RCA input on the other side?

[jb]

Is there an RCA input on the other side?

No. As I said, the box is spliced into the IC. The IC comes out of the box opposite the switch (visible at the upper right of the picture) and there is an RCA plug on the end of the IC. Obviously, I could have put a RCA input in the box but that would be an additional connection in the signal path.

In case anyone is interested: To do the phase swap in the digital domain all you need to do is cut one trace and splice in a 74xx1G86. Cut the data output trace from the S/PDIF receiver chip and connect it to one input of the ’86, connect the other ’86 input to a SPDT switch that switches between VCC and GND, and connect the output of the ’86 to other end of the cut data trace.

[NewBuyer]

Ah yes there it is - I do now see the wire opposite the switch.

It seems you've perhaps tried both solutions for phase reversal (digital and analog), and you are confident with both methods.

Have you found one approach (digital vs. analog) to be preferable sonically in any way, or have you found them to actually be equivalent to your ears?

[jb]

It seems you've perhaps tried both solutions for phase reversal (digital and analog), and you are confident with both methods.

I am quite confident both methods invert the phase.

With the digital approach, both channels are either inverted or not and I would have to butcher the PCB of every one of the nine DACs I own and possibly diminish their resale value.

With the analog approach I can invert the phase of one or both channels of every source I might use, DAC, phono, tape, tuner, etc. and I can use it with any amp I have or might get in the future. As I said, if done right with quality components there is no signal degradation. Jensen transformers are very, very good, will last a lifetime, and will probably outperform any component you can buy.

[Hap]

Could anyone share more direction on how to do this:
In case anyone is interested: To do the phase swap in the digital domain all you need to do is cut one trace and splice in a 74xx1G86. Cut the data output trace from the S/PDIF receiver chip and connect it to one input of the ’86, connect the other ’86 input to a SPDT switch that switches between VCC and GND, and connect the output of the ’86 to other end of the cut data trace.

My CDP is a Sherwood CD7080R, and would like to add this switching circuit to the CDP if possible.

Doing the phase inversion with the transformer to RCA line will be difficult as my system uses two pairs of outputs from the preamp, then another two pairs of outputs from an electronic crossover.

Don't have too much knowledge about the '86 lines or 74xx1G86 or digital circuit works; but could probably get it done if someone tells me what parts to get and where to put it.

Apprecaite any help all could share on this.

Cheers.
Hap

[jb]

Doing the phase inversion with the transformer to RCA line will be difficult as my system uses two pairs of outputs from the preamp, then another two pairs of outputs from an electronic crossover.

If you don't want to deal with multiple pairs of outputs then add the xformer and switch to the analog output of the DAC/CDP. It doesn't matter where you put it, e.g., between the DAC/CDP and the pre or between the pre and the amp, except that if you use an input transformer, like I did, then you put it at the 'output' end of the IC. If you use an output transformer, then you put it at the input end of the IC.

Don't have too much knowledge about the '86 lines or 74xx1G86 or digital circuit works; but could probably get it done if someone tells me what parts to get and where to put it.

What more do you need to know? I already identified the parts you need and where to put them. If you don’t understand the directions I gave than this project is probably beyond your capability.

In addition to being portable and not requiring PCB surgery, the analog approach, done right, does less damage to the signal. In spite of what you may have been told, inverting the signal in the digital domain adds distortion. Although nobody seems to notice it, it is still there. Perhaps it is because there is already so much added noise and distortion in the digital audio signal that a little more is not noticed or because the hearing ability of most audiophiles is not as good as they would like to think. To understand how this distortion comes about requires a very good understanding of binary numbers and digital audio fundamentals. I don’t think highjacking this thread for such a discussion is appropriate at this time.

[NewBuyer]

...With the digital approach, both channels are either inverted or not and I would have to butcher the PCB of every one of the nine DACs I own... With the analog approach I can invert the phase of one or both channels... if done right with quality components there is no signal degradation....

Good points - I am going to try a variant of your analog approach. Thanks very much for sharing this!


Hap, I hope you will find any help you need for your digital-side project interest...

[jb]

As an alternative to the mono phase-switch boxes I made you could start with a Jensen Iso-Max, shown below, topless. All you have to do is squeeze in a couple sub-miniature DPDT switches or remount the PCB and switches in a larger box and your done. You can get the Iso-Max from Markertek. They have pretty good prices, too.

[Hap]

jb,

Thanks for that info.
That gives me a couple options for doing this project.
Agree it may be best for a dummy like me to do the phase inversion at the outputs rather than messing with the digital circuit.

Many thanks to Occam for sharing insight into doing this.

Was also looking at the DAC project on Lukasz Fikus' website, so may go that route and add the jensen transformers with a 4PDT on/on switch to do the phase inversion at the output side.

Cheers,
Hap

[art]

There is no SPDIF RX chip in a CD player. In older players, you can insert the XOR gate between the decoder and the filter chip, or the filter and the DAC. Newer ones could have the filter and DAC rolled into one chip. Usually, the decoder is separate.

You just have to find the trace that carries the data, and not some other signal.

Pat