- Joined
- Jan 9, 2013
- Messages
- 25,823
If the higher quality cables sound better .... there's your culprit!
Loss in audio quality when using RCA input selector box
- Thread starter Lance7489
- Start date
Help Support QuadraphonicQuad:
As suggested, open the box and lets see inside it.
I honestly believe you may be chasing ghosts here.
The mind can be a real enemy, if it first believes something it's hard
to change. Also as suggested make some measurement or use Audacity
to look at the signal. A few pieces of wire and a switch should not cause any
change in frequency response unless that wire is seriously badly engineered to
introduce a large amount of resistance into the path..
You have to break this down and try to isolate the problem.
1) Disconnect all the program sources. 2) Connect one only to the Parasound. Make sure it works right. Then insert the switch box with that only one program source (the same one) and see if it makes a difference. 3) Now start trying combinations of two and then three and finally four sources.
See if you can discern where the difference occurs.
A second series of tests is to hook the thing up and select a program source and run some music. But while running the music put a disc in two , three or four sources and hit play. Before you do any of these turn the Parasound volume all the way down for speaker safety. Then after hitting play on both items and the timer displays show they are running bring the Parasound volume up. If you hear more than one program the thing is wired wrong. This is unlikely if the thing has only printed circuit boards but if there is point to point wiring it possible that some kind of error was made in building it or even as mentioned above a design flaw. If you hear more than one program then I would throw the thing away. Can you return it? Open a case with Amazon? If you hear more than one program each source is driving not only the input impedance of the Parasound but also the output stage of the other devices. This should not be but if it is it is likely the problem.
How long are the cables. High frequency loss due to too long cables is possible, but should be unlikely. The speakers in my avatar were driven by
by cables that ran from the living room to the power amps downstairs in the basement using RCA cables I made that were very long maybe 30 40 feet.
Of course I had shelving controls for the high frequency amps. If the unit passes the above test, try to get the shortest cables that will work. The capacitance of cabling is often a direct function of length. Capacitance in parallel with the output COULD roll off high frequencies (but like Sal I consider this rather unlikely.)
See if you can find out 1) the input impedance of the Parasound. Being solid state it may be very low. (ie 500 or 600 ohms) and 2) the output impedance of your various program sources which if they don't have enough buffer amplification might not be able to drive the Parasound if it is too low. This all should be unlikely but you may have equipment that just is a little bit incompatible.
Are you only using one of the two outputs the unit has? Does it do the same thing when you use both outputs? The one I sent you the link to only has one output which would probably be a better way to configure all this. (Edit: just reread how you are using this.)
It looks like the way this opens is that four screws on the front and four on the back allow the respective panels to come off. One panel probably has a circuit board and the other some wiring from the panel do said board. So becareful taking them apart so you don't pull the one with wiring apart. It hopefully is soldered and there should be enough slack to get a look.
You can buy a volt ohm milliameter at Harbor Fright for less than ten dollars and with this you could do some probing to see if there is conductivity where it does not belong. Amazon too for even less money.
https://www.harborfreight.com/7-function-digital-multimeter-63759.html
You can get a sound test CD that will turn you players into a test generator.
https://audiophilestyle.com/ca/ca-academy/drzs-test-cd-free-download-r780/There are many others. Notably from Stereophile , Denon that can be found.
Some of these can use your sound card as Sal suggested as a measuring tool. There are lots of such tools including Adobe Audition which is out there in a version for free. Audacity which is free and many others.
You can also get a radio shack style sound level meter to measure the output and it may have enough high frequency response to tell if there is a roll off.
https://pages.uoregon.edu/baker/tools/toollibrary/RS (Sound Level Meter).pdf
1) Disconnect all the program sources. 2) Connect one only to the Parasound. Make sure it works right. Then insert the switch box with that only one program source (the same one) and see if it makes a difference. 3) Now start trying combinations of two and then three and finally four sources.
See if you can discern where the difference occurs.
A second series of tests is to hook the thing up and select a program source and run some music. But while running the music put a disc in two , three or four sources and hit play. Before you do any of these turn the Parasound volume all the way down for speaker safety. Then after hitting play on both items and the timer displays show they are running bring the Parasound volume up. If you hear more than one program the thing is wired wrong. This is unlikely if the thing has only printed circuit boards but if there is point to point wiring it possible that some kind of error was made in building it or even as mentioned above a design flaw. If you hear more than one program then I would throw the thing away. Can you return it? Open a case with Amazon? If you hear more than one program each source is driving not only the input impedance of the Parasound but also the output stage of the other devices. This should not be but if it is it is likely the problem.
How long are the cables. High frequency loss due to too long cables is possible, but should be unlikely. The speakers in my avatar were driven by
by cables that ran from the living room to the power amps downstairs in the basement using RCA cables I made that were very long maybe 30 40 feet.
Of course I had shelving controls for the high frequency amps. If the unit passes the above test, try to get the shortest cables that will work. The capacitance of cabling is often a direct function of length. Capacitance in parallel with the output COULD roll off high frequencies (but like Sal I consider this rather unlikely.)
See if you can find out 1) the input impedance of the Parasound. Being solid state it may be very low. (ie 500 or 600 ohms) and 2) the output impedance of your various program sources which if they don't have enough buffer amplification might not be able to drive the Parasound if it is too low. This all should be unlikely but you may have equipment that just is a little bit incompatible.
Are you only using one of the two outputs the unit has? Does it do the same thing when you use both outputs? The one I sent you the link to only has one output which would probably be a better way to configure all this. (Edit: just reread how you are using this.)
It looks like the way this opens is that four screws on the front and four on the back allow the respective panels to come off. One panel probably has a circuit board and the other some wiring from the panel do said board. So becareful taking them apart so you don't pull the one with wiring apart. It hopefully is soldered and there should be enough slack to get a look.
You can buy a volt ohm milliameter at Harbor Fright for less than ten dollars and with this you could do some probing to see if there is conductivity where it does not belong. Amazon too for even less money.
https://www.harborfreight.com/7-function-digital-multimeter-63759.html
You can get a sound test CD that will turn you players into a test generator.
https://audiophilestyle.com/ca/ca-academy/drzs-test-cd-free-download-r780/There are many others. Notably from Stereophile , Denon that can be found.
Some of these can use your sound card as Sal suggested as a measuring tool. There are lots of such tools including Adobe Audition which is out there in a version for free. Audacity which is free and many others.
You can also get a radio shack style sound level meter to measure the output and it may have enough high frequency response to tell if there is a roll off.
https://pages.uoregon.edu/baker/tools/toollibrary/RS (Sound Level Meter).pdf
Last edited:
A switch box being purly a passive device should not cause any signal quality loss. That being said poor switch contacts could cause problems, that box has two sets of switch contacts. Try differant input output combinations to see if it can be traced to a switch contact.
As others have said possibly cables. While you don't need ultra high end (expensive) cables very cheap ones can cause problems.
As a test connect one component to the amplifier bypassing the switch box by joining the box's input and output cables with an RCA female to female adapter to verify that it's the box not the cables.
Much less likly there could be leakage from one input to another, some switchboxs short the unused inputs when not selected to prevent that possibility. If it sounds OK with one input connected try adding the other components one by one to see it anything changes.
As others have said possibly cables. While you don't need ultra high end (expensive) cables very cheap ones can cause problems.
As a test connect one component to the amplifier bypassing the switch box by joining the box's input and output cables with an RCA female to female adapter to verify that it's the box not the cables.
Much less likly there could be leakage from one input to another, some switchboxs short the unused inputs when not selected to prevent that possibility. If it sounds OK with one input connected try adding the other components one by one to see it anything changes.
Last edited:
Yes, let us see what’s inside the box. Also, I believe that you have two P7 preamps IIRC. Maybe you can try daisy chaining them together and see if you still get quality losses.
As for the cables being the culprits, the differences between the cheap and expensive cables should be subtle, not of the magnitude that you are noticing.
BUT…how long are the cheap cables? If they are long, you might experience losses.
As for the cables being the culprits, the differences between the cheap and expensive cables should be subtle, not of the magnitude that you are noticing.
BUT…how long are the cheap cables? If they are long, you might experience losses.
Regarding the cables, keep in mind that if they are all the same length, the signal path triples in length with the box in the circuit. I am not a cable believer, but if you are using some esoteric cable design that has a high capacitance (in an effort to stand out and sound different) it may result in a noticeable HF loss.
As has been noted earlier, let's see what's in the box. There don't seem to be any power supply connections, so no active circuitry, but maybe there's some sort of static bypass or other parts inside that are causing your problems.
MidiMagic
2K Club - QQ Super Nova
- Joined
- Jul 5, 2010
- Messages
- 2,256
If the selector is a totally passive switch, there is no way the amp could know it is there.
One possibility is that the video portion of such a selector switch has filters in it. If so, don't run the audio through a video switch.
Note that connecting two line outputs together will cause attenuation of the signal.
Another (rare) possibility is that the amp has a lower input impedance than the output impedance of the source.
Coleman 7.1SW switcher. Per Stereophile s Kal Robinson and me!
Lance7489
Well-known Member
I don't understand the purpose of having someone else switch the cables around or opening the box up. What will seeing 2 wafer style switches mean in relationship to the problem I'm describing?
- Joined
- Jan 9, 2013
- Messages
- 25,823
Since most reputable companies [including Amazon and Music Direct] offer generous time periods in which to return merchandise, I would try upgrading the cables as a possible culprit ....... and see if that does make a difference .......I once tried a less expensive set of RCA cables for my tank like Marantz SA11S3 Stereo SACD player and I didn't like what I heard so I returned them and upgraded to a more expensive pair and the difference was NOT subtle ... the more expensive Shunyata Research cables were actually SUPERIOR! I have two Parasound P7 pre amps and although mine have proven to be finicky ... the sound is exceptional and they deserve MUCH better RCA cables than the bargain basement variety!
I also play everything at FLAT response and never engage the P7's tone controls ....... NEVER felt a need .........
@MidiMagic
The push button A/V selector I linked to has identical signal paths with no components whatsoever , only push button switches. I have one like it and opened it to make sure. The only difference for the video path is a yellow RCA. I don't not claim that applies to all , only to this particular flavor of chinese switch box. I was concerned that the video path could differ from the audios but it appears not to. Even though they claim various impedances there are no components in there to effect that. Probably quoting expected output impedance of the driving circuitry. Circuit traces the same size.
The push button A/V selector I linked to has identical signal paths with no components whatsoever , only push button switches. I have one like it and opened it to make sure. The only difference for the video path is a yellow RCA. I don't not claim that applies to all , only to this particular flavor of chinese switch box. I was concerned that the video path could differ from the audios but it appears not to. Even though they claim various impedances there are no components in there to effect that. Probably quoting expected output impedance of the driving circuitry. Circuit traces the same size.
Last edited:
HiFiMan
Active Member
This may or may not help someone in this discussion. I tried several of these type switches (some slight cosmetic differences, but all wired the same internally, and all probably made by the same company) between a turntable and several amps. They all gave me the same problem (can't remember exactly, hum or feedback?????), but what it boiled down to was they use a common ground for all the pairs of channels. I never could find one where each set of channels were completely isolated from each other. I even tried to find just the switch to build my own; NO luck.
RCA cables. I have tested perhaps 15 to 20 brands (primarily for capacitance). Some very inexpensive "comes in the box" cables actually have very good (low) capacitance, and some very expensive brands very high capacitance. The brand I finally settled on for reasonably low capacitance at a reasonable price are made by Hosa (ex; CRA-202AU 2m). Not critically important for line level applications, but especially important for phono signals. Low capacitance plays an important role in preserving those higher frequencies. Think CD-4 carrier signals too.
RCA cables. I have tested perhaps 15 to 20 brands (primarily for capacitance). Some very inexpensive "comes in the box" cables actually have very good (low) capacitance, and some very expensive brands very high capacitance. The brand I finally settled on for reasonably low capacitance at a reasonable price are made by Hosa (ex; CRA-202AU 2m). Not critically important for line level applications, but especially important for phono signals. Low capacitance plays an important role in preserving those higher frequencies. Think CD-4 carrier signals too.
Lance7489
Well-known Member
I appear to be missing something. Everyone is telling me to open up the box & see what's there.......What am I looking to see or not see?? .....What am I going to see that could be causing the problem??
Lance7489
Well-known Member
Also, this isn't a "mind thing" that some have suggested. When going through the switch box, I had the treble set from 6 to 8 (10 is the highest on the P7) to be satisfactory to me. I've had these switch boxes hooked up for almost a year & always wondered why the phono input had so much high end (the turntable is the only thing not going through the boxes) & everything else was pretty blah sounding. Recently, just for the hell of it, I plugged the CD player directly into the P7 & WOW!!!.........The difference blew me away. My wife even noticed it. I now have my treble either flat or maybe 2.
Lance7489
Well-known Member
I actually have a bunch of these. I use them with my other system (which is in the garage, used during the Summer). The only thing I don't like about these is they're push button. They're so light that when you push a button, you have to hold the unit with your other hand, otherwise they slide back into your audio cabinet. I have to pull the unit back into position & by doing this, sometimes a RCA cable will pop out.........That's why I went to the rotary type selector.
Lance7489
Well-known Member
They probably need to be fastened together and anchored. They are very inexpensive.
What I was interested in seeing in the open box was if there was point to point wiring which there is not.
So now you have to figure out if they just made a bad design and have more than one device feeding the output or something like that.
If it doesn't happen with the push button ones then you need to return the rotary switch one. I don't see any other alternative.
What I was interested in seeing in the open box was if there was point to point wiring which there is not.
So now you have to figure out if they just made a bad design and have more than one device feeding the output or something like that.
If it doesn't happen with the push button ones then you need to return the rotary switch one. I don't see any other alternative.
Last edited:
Lance7489
Well-known Member
Yeah, I know. I think they're about $17 each. They're resistors although I think they're going to cabinet ground. Are there any resistors in the pushbutton ones?
