RCA cable fitment

My first encounter with the input jacks on an original Dynaco ST-70 found me shaving the plastic off of the RCA cable shells to get them to fit next to each other. I later replaced the input jack board with one that spaced the jacks out. Now I have a PAS-3X and see the same problem with the input and output RCA jacks on the back. A site offers replacement jack boards that stagger the jacks, but are bit pricey. Here's my solution: FOS RCA cables. The shells are narrow enough to plug in side by side.

Oh, I have a new set of gold plated jack boards to replace the originals and they have the narrow spacing also.

Make your own cables using the Switchcraft 3502 connectors. They are are narrow and fit between the ST70 panel jacks just fine. Use either Belden 8412 or Mogami W2549 microphone cables. These are two wires with an outer shield. The toughest part is grounding one end of the shield after connecting both the inner conductors. I made many sets of these up years ago and they sound and work great. Stop buying large modern styles that cost a bundle. Then have to change the amp.  The 3502 series also has options like nickle vs gold plating and different barrel colors. Search a little and you will find so
me you like.

Beautiful, but may not be practical for most users.  The Switchcraft 3502 connectors can run you $15 (4 pack, nickel plated) and the Belden 8412 is about $2.00 a foot for a spool of 50 feet.  So a set of your 3 foot cables could cost about $27 compared to the FOSPOWER at $11.  And then you have to have the time and skills to assemble and test them.  I used to make these and XLR cables in my broadcast engineering days, but then the boss was buying the materials and paying my salary to do it.  Oh, and the reviews on the FOSPOWER cables aren't too shabby.

I happen to be making up cables today with Mogami W2549 terminated with Amphenol RCA . May as well post pics here of how I isolate the copper shield , on one end only .

Thanks for the info regarding affordable Fospower interconnects , good to know.

fredeb wrote:I happen to be making up cables today with Mogami W2549 terminated with Amphenol RCA . May as well post pics here of how I isolate the copper shield , on one end only .

It's important to mark the cables for direction. The connected shield end is the source and the lifted shield is the load.

See An Overview of Audio System Grounding and Interfacing for more on system interfacing

Seamus wrote:

fredeb wrote:I happen to be making up cables today with Mogami W2549 terminated with Amphenol RCA . May as well post pics here of how I isolate the copper shield , on one end only .

It's important to mark the cables for direction. The connected shield end is the source and the lifted shield is the load.

See An Overview of Audio System Grounding and Interfacing for more on system interfacing

Yes Seamus , I add slither of heatshrink to the cable on Grounded side

Unfortunately RCA connectors don't have much in the way of standards.  Some shells fit the jack so loosely they barely make contact, others are so tight you risk damage pulling them out.  Today's "audiophile grade" cables tend to be fat.  Such things didn't exist in the Dynaco heyday.  Also, Dave Haffler didn't believe components affected sound whereas modern audiophiles ascribe magical properties to interconnects and connectors.  Personally, I believe the truth is somewhere in between.

Yes, building your own cables is a good option.  I think I have used Switchcraft RCA's (from Parts Express) and I have definitely used Switchcraft XLR's, which are my favorite.  If you're handy enough to have built a Dynaco or Tubes4HiFi kit building cables should be no problem.

Seamus wrote:

fredeb wrote:I happen to be making up cables today with Mogami W2549 terminated with Amphenol RCA . May as well post pics here of how I isolate the copper shield , on one end only .

It's important to mark the cables for direction. The connected shield end is the source and the lifted shield is the load.

See An Overview of Audio System Grounding and Interfacing for more on system interfacing

Yes, but it's about grounding, not "direction". And if the shield is grounded at one end only, which end is best is system dependent.

Wotan wrote:Yes, but it's about grounding, not "direction".  And if the shield is grounded at one end only, which end is best is system dependent.

Grounding at the receiver affects CMMR. Always ground the screen at the driver.

See p27 UNDERSTANDING, FINDING, & ELIMINATING GROUND LOOPS by Bill Whitlock of Jensen Transformers revised 2008

If you have RCA cables that have a shielding jacket (braid or foil) around the the two main elements (signal and ground) the shield should be attached to the ground at ONE end only, It doesn't matter which physical end of the cable it is, but that grounded end should always be attached to the source (ie, cd player, dac, tuner, TT) The ungrounded end would plug into the component RECEIVING the signal. This is what makes the cable directional and the cable should be marked appropriately. The purpose of this is that any RF noise being picked up by the cable will be blocked and drained back to the source component instead of being passed on to your preamp.

Cables outgoing from your preamp (ie, to the amplifiers) will have the grounded end at the preamp. Again, so that any RF noise being picked up on the cable will be drained by the shield back to the preamp and not passed to the amplifier for amplification.

All this assumes that your individual components are properly grounded and that you do not have any existing ground loops.

Enjoy the Music...

As a follow-up to my post, I did look up some info on the FosPower cables. They seem to be well constructed cables with a dual layer of shielding against RF and EMI noise using both a foil and a braided shield. I could NOT find anywhere any information in their videos or descriptions or any pictures showing that they were directional. In order to make the directional, you would have to slide back the barrel and disconnect / isolate both the foil and braid from one end of the cable. Make sure it is NOT touching the barrel at that end.

If you do use these cables throughout your system (I support the notion that is a good practice to use the same quality cables throughout your system to keep impedances matched on each input - with the exception of the turntable where you should have the best cable you choose to use) any RF/EMI noise picked up by any component or cable will be theoretically be drained to the component with the lowest impedance path to ground.

I normally use all directional cables of good quality. Having worked in the hi-fi industry all my life, I have collected a good collection and use Monster M1000 series RCA cables. Not the best, but as good as most Very good construction, clear definition in the mids and highs and good solid bass, The only exception are the phono cables from the turntable to the SUT and from the SUT to the preamp - These are Audioquest Leopard directional cables.

All ground connections for the RCA's in the pre-amp have been lifted from the main circuit board and wired directly to the ground terminal of that exits through the back of preamp and is also connected to the ground lug of the IEC power cord.

Enjoy the Music

I'm probably the least expert person to add something to this thread. But if the interconnect solution for the ST-70's close proximity, female RCA connection is salient to this thread, here is my bit:

My recipe is for a thin cable and minimal mass RCA connectors — ie: no audiophile jewelry each weighing as much as three silver US dollars. Cheaper, low mass connectors are usually slim enough to not interfere with each other on old Dynaco stuff like the ST-70.

I've got all kinds of cable. A lot of it is homemade using various designs and brands of cable. But what I've come to make as a house standard is cheap, flexible and easy to make. I use CAT4 or CAT 5 LAN wire. I cut open the cable strand and choose a twisted pair — for example solid green, and white / green stripe. So there are two runs of decent, solid core, insulated, twisted copper that is somewhat resistant to RF. I use quality boot lacing as a cover.

Termination:I find that some of the least expensive RCA connectors in any electronics supply often make the best connections — not too tight and not too loose. And if they are not gripping enough, you can easily create more bite with a bit of pressure using some pliers. With tinny cheap connectors you can customize any grip you want. Low mass means you can solder the conductors with just a touch of the iron. The insulation on the wire and the RCA pin remains pretty much unaffected by heat.

I realize that this might cause many enthusiasts to gasp in horror or induce ridicule. OK, but its light, cheap, electrically sound and looks good enough. These days you can choose from all sorts of colored, thin, round boot lace for covers. This makes the usual octopus tangle easier to to keep track of. And to my ears, they sound just fine. And I've got some pretty expensive kit around here to compare.