RCA to 1/4" mono: Is the signal as good as 1/4" to 1/4"?

T

Tom Overthere

Member
I have an old but very useful parametric equalizer from back in my Tascam analog days. It has RCA connectors, but my current PC interface (Presonus Firestudio Project) is all 1/4".

If I use an RCA-to-TRS conversion cable LIKE THIS, will I experience any signal loss compared to two units both having 1/4" connectors?

I'm trying to decide whether I should replace this EQ (RCA connectors) with a modern unit having 1/4" connectors. If there's no obvious difference in signal quality, I'll keep what I have.

Thanks,
Tom
 
If the presonis device has TS connections, it's all the same. The sound quality and noise level will be the same, regardless of you using RCA or 1/4" TS cables.

TRS cables may make a small difference, the shielding of the RCA-TRS cable will provide some RF shielding, so it may be worth it to go that route. Of course, the cable won't be completely "grounded." Some RCA-equipped devices have a ground screw; you might have some luck going from that to the cable shielding, but you will need to cut away a bit of the insulating jacket on your new cables.
I'd try it out, see if there is no or little noise.
 
stevieb said:
If the presonis device has TS connections, it's all the same. The sound quality and noise level will be the same, regardless of you using RCA or 1/4" TS cables.

TRS cables may make a small difference, the shielding of the RCA-TRS cable will provide some RF shielding, so it may be worth it to go that route. Of course, the cable won't be completely "grounded." Some RCA-equipped devices have a ground screw; you might have some luck going from that to the cable shielding, but you will need to cut away a bit of the insulating jacket on your new cables.
I'd try it out, see if there is no or little noise.
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regular RCA cables are shielded ..... so are regular 1/4 guitar type cables. I see no benefit is getting TRS cables, especially if you have to start cutting into them to ground them or make them work.
The OP is clearly a begginner or they wouldn't wonder if there's a signal loss from RCA to 1/4" so they don't need any additional complications.
 
Sound-on-Sound magazine did a connector shootout several years ago.
They found that XLR, 1/4" and RCA had very similar resistance and surface area.

The only difference between RCA and 1/4" is the shape of the plug/socket; it's 2 wires and a metal shell
TRS ans XLR just add a shield around them to help protect them from electromagnetic interference
(if you have no problems, dont worry about it.)

The only plug they found lacking was the 1/8" miniplug.
It has higher resistance and lower surface area, so you should use them as little as possible.
 
Just make sure your signals are calibrated properly. RCA is often a "consumer" device connection and consumer devices often are set up for a -10 dBv signal level. A lot of newer/pro/prosumer audio gear is set up to expect a +4dBu signal.
So long as you get everything calibrated this doesn't have to be a problem you just have to make sure the devices are getting the right levels to work properly within their specs
 
Bristol Posse said:
Just make sure your signals are calibrated properly. RCA is often a "consumer" device connection and consumer devices often are set up for a -10 dBv signal level. A lot of newer/pro/prosumer audio gear is set up to expect a +4dBu signal.
So long as you get everything calibrated this doesn't have to be a problem you just have to make sure the devices are getting the right levels to work properly within their specs
Click to expand...
Thanks, all. Very helpful.

The EQ in question is an SAE 180 with 16 dB boost/cut on each channel, impedance specs are as follows:
Input impedance..........100K Ohms I read that as 100,000 Ohms
Output impedance........500 Ohms

I'm comparing it to and considering the Presonus EQ3B with the following specs:
TRS Input Impedance ...................... 10k Ohms I read that as 10,000 Ohms
TRS Output Impedance .................... 51 Ohms

It appears to me the old SAE unit (RCA connectors) has impedance spec 10 TIMES that of the modern EQ unit. So can I expect the SAE output to be "very quite" by comparison?

The Presonus FireStudio Project has two 1/4" channel inserts. That's where I intend to patch in the EQ unit channels. I'm pretty sure they're the same as its Line inputs, which are:
Input Impedance (Balanced) ................ 10 KΩ I read that as 10,000 Ohms

There's no feature (that I can recall) for adjusting the Firestudio's Channel insert levels in its virtual mixer. So I'm not sure how or if I can calibrate as you suggest, BP... Please advise if I'm missing something obvious.


Not stupid, just been "Overthere" too long and need a "re-grounding" in the art of Impedance Matching. :D
 
Tom Overthere said:
Thanks, all. Very helpful.

The EQ in question is an SAE 180 with 16 dB boost/cut on each channel, impedance specs are as follows:
Input impedance..........100K Ohms I read that as 100,000 Ohms
Output impedance........500 Ohms

I'm comparing it to and considering the Presonus EQ3B with the following specs:
TRS Input Impedance ...................... 10k Ohms I read that as 10,000 Ohms
TRS Output Impedance .................... 51 Ohms

It appears to me the old SAE unit (RCA connectors) has impedance spec 10 TIMES that of the modern EQ unit. So can I expect the SAE output to be "very quite" by comparison?

The Presonus FireStudio Project has two 1/4" channel inserts. That's where I intend to patch in the EQ unit channels. I'm pretty sure they're the same as its Line inputs, which are:
Input Impedance (Balanced) ................ 10 KΩ I read that as 10,000 Ohms

There's no feature (that I can recall) for adjusting the Firestudio's Channel insert levels in its virtual mixer. So I'm not sure how or if I can calibrate as you suggest, BP... Please advise if I'm missing something obvious.


Not stupid, just been "Overthere" too long and need a "re-grounding" in the art of Impedance Matching. :D
Click to expand...

I think that impedance wise you should be OK. If memory serves you are looking at impedance bridging where the load impedance is much bigger than the source impedance and so you get maximum voltage transfer, although school was a long time ago so I may have that backwards.

What I was referring to in my original post was the voltage reference for line level. Since RCA connections for audio signals were/are often used on "consumer" devices it might be an indication that this device is going to be expecting to send and receive "consumer" line level signals which are -10 dBv which is approx 0.32 volts. Most pro and prosumer audio gear runs at +4 dBV line level which is approx 1.29 volts. in audio terms -10 dBv line levels are around 12 dBu lower than + 4dBu levels.

So to conclude a rather longwinded post if the EQ is expecting consumer line levels and you send +4bDu you are going to be running it exteremely hot levels. If the EQ has tons of head room this may be OK if it doesn't you could end up with a lot of clipping and distortion and depending on the sensitivity of the electronics damage or shorten the life of the EQ if you know this is the case just lower the level of the signal you send by around -12dBFS in your DAW and you should be sending approriate signals. If the device is +4dBU then you are fine

Differently, if the EQ is outputting -10dBv into a +4dBV there won't be a problem of over load but your line level will be 12 dBFS below the rest of your recordings. Generally +4dBu line level comes out as around -18dBFS so adding a -10 dBv signal will register at around -30 dBFS on your DAW meters. If the EQ adds noise to the signal and you now have to add 12dB of gain to bring the levels up to match the rest of the tracks, you will be introducing a lot of noise to your mix

Did any of that make sense at all?
 
Bristol Posse said:
Did any of that make sense at all?
Click to expand...

It makes perfect sense, and thank you for once again "going to the mat" to provide truly useful and helpful information.

I'm going to sell my 1980s demo gear, maybe as an intact "vintage collection" and based on your comments I think the venerable SAE 180 will have to be sold with the lot. It worked extremely well with the RCA channel inserts and main outs on my Tascam PortaStudio 244.
 
Just plug it in and see if it works. You certainly won't break anything. If you get acceptable results, everything is fine. If you don't...
 
Farview said:
Just plug it in and see if it works. You certainly won't break anything. If you get acceptable results, everything is fine. If you don't...
Click to expand...
ditto ..... don't just assume anything. It might work just fine. If it doesn't [then dump it.
 
You guys are right, and I would have done that first except I don't have the conversion cables (the point of this thread). I could add a 1/4" adapter to the end of a standard RCA cable, but after not being able to locate any from my "collection", I came here to ask :DBTUSE QUESTI:DNS as Plan B.

I don't want to spend $10 on specialty cables if the unit isn't up to the job. I'd rather spend that $ on an appropriate EQ. I'll scrounge some more per your good advice, and will test if I find an adapter. I used to have several but you know how that goes... Thanks
 
Tom Overthere said:
You guys are right, and I would have done that first except I don't have the conversion cables (the point of this thread). I could add a 1/4" adapter to the end of a standard RCA cable, but after not being able to locate any from my "collection", I came here to ask :DBTUSE QUESTI:DNS as Plan B.

I don't want to spend $10 on specialty cables if the unit isn't up to the job. I'd rather spend that $ on an appropriate EQ. I'll scrounge some more per your good advice, and will test if I find an adapter. I used to have several but you know how that goes... Thanks
Click to expand...
tons of those at Radio Shack. They're not much ..... I think a pair of the adapters is 3 or 4 bucks.
 
Lt. Bob said:
tons of those at Radio Shack. They're not much ..... I think a pair of the adapters is 3 or 4 bucks.
Click to expand...
True but my RCA Days are over, and if I do buy more you know the new one's will just end up wherever the hell the rest of 'em are... :D

I'll try to do some more looking around later today...
 
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