Loss in audio quality when using RCA input selector box

[ClassicalSurroundFan]

I use a Rolls SS312 between my preamp and power amp as a 1 in, 2 out switch with an unusual y cable arrangement out of the Rolls and in to the power amp. I engage the potentiometer on one of the outputs. I use the SS312 to switch between the the two systems of SACD/DVD-A height channels in my collection (MDG and Chesky in stereo vs Telarc in mono).

Much heavier than the generic boxes on amazon, nice movement feel to the switch and potentiometer. I’m assuming the Rolls is correctly wired, as they are not known for screwing that up at least, and this is 3x the price of the generics.

Sometimes there is temporarily very low/distorted output on the y cabled output that goes away if I run it for 10-20 seconds. I wonder if this is a sudden change of impedance to the power amp that then sorts itself out.

 

[barfle]

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?

If you KNOW what’s in the box, then opening it up won’t tell you anything. But you don’t know, because there’s some issue that isn’t clear. Are there any other parts in the box like capacitors oe resistors? If they are wafer switches, are the contacts clean? Are the solder connections solid?

Questions that we can’t answer could be revealed.

 

[barfle]

One other thought. If you have any RCA barrel connectors (two female jacks back-to-back) bypass the box with them and see if the sound improves. If not, then it’s not the box.

 

[MidiMagic]

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.

Those are intended for line-level signals, not phono cartridge levels.

You can't use it backwards. It switches a number of sources to one amp input. You were trying to switch one source to many inputs. All of the phono inputs excep the one selected had no source connected (but had cables connected) so they made a loud hum.

Note that taking two signal paths off of one source might load it down, depending on the input and output impedances.

 

[par4ken]

Resistors are sometimes used break up ground loops. That is likely the case here. Instead of connecting the jacks directly to the box they connect via resistors but 10K seems rather high. The other boxes described are plastic and require no ground connection. The plastic boxes provide no shieling either but that should not be a problem with line level signals. IMHO a better way would be to leave the jacks insulated from the box and then run a separate ground wire from the box to the amp. Such a grounding scheme is a must with very low level signals like turntables.

 

[LuvMyQuad]

One other thought. If you have any RCA barrel connectors (two female jacks back-to-back) bypass the box with them and see if the sound improves. If not, then it’s not the box.

Great idea. I was going to suggest it myself.

 

[par4ken]

Great idea. I was going to suggest it myself.

I said it first

 

[LuvMyQuad]

I said it first

Then you get a gold star.

 

[Sal1950]

.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!

Have you ever put those cables to a blind listening session?
The only reason for any properly designed cable to sound different than the next is that one of them is of a poor design
and introducing a change in frequency response, too high resistance or capacitance. The average free-bee is plenty good
unless a cheap connector is causing a poor connection.

 

[par4ken]

There are some very poor cables out there. Those supplied with decent equipment should be fine.

Dollar store cables often have only few strands of wire for the center conductor and the same for the shield! I just fixed a microphone cable for my niece from a Karaoke unit that she got for Christmas, same thing only very few strands of hair like wire, no wonder it broke on the first day!

 

[gene_stl]

On the one hand , Asian manufacturer's,, starting with the Japanese (whom I have EXTREME respect for) raised it to an art form, the reduction in copper used in cables, expecially for low power applications. On the other hand this very action probably lowers the capacitance. After the Japanese did it others followed suit all over the far east.

The main application where cable capacitance matters is , naturally, the CD4 cartridge to phono preamp/demodulator.

there is a free program called REW which is for measuring room response and EQ. You need a suitable soundcard (which is probably most of them) and a microphone with decent high frequency response. This software will allow you to measure the actual high frequency losses. This software is one of the darlings over at Audio Science Review among all the DSP aficionados.

https://www.roomeqwizard.com/

 

[MidiMagic]

Resistors are sometimes used break up ground loops. That is likely the case here. Instead of connecting the jacks directly to the box they connect via resistors but 10K seems rather high. The other boxes described are plastic and require no ground connection. The plastic boxes provide no shieling either but that should not be a problem with line level signals. IMHO a better way would be to leave the jacks insulated from the box and then run a separate ground wire from the box to the amp. Such a grounding scheme is a must with very low level signals like turntables.

Resistors for ground loops are usually 10 ohms or under.