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Get familiar with the reaction system: Introducing the Reaction System
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Totally. I was doing fine until I thought I would be clever and turn my laptop into a desktop by plugging in one of those multiport powered USB-C hubs.
It added a terrible high pitched squeal. I couldn’t be bothered tracking it down; just unplugged it.
Boo! Well at least you found it.
These sort of issues motivated me to migrate to 100% balanced interconnects, balanced DACs, and amps with balanced inputs. I have had ZERO issues ever since doing that about 6 years ago. There are just too many potential noise sources with any and all computer and networking related equipment, which are not designed with audio in mind. Radiated electronic noise can also be demodulated by non-linearities in the input stages of amplifiers. Since I have been doing DSP in software on mini PCs for over 10 years, I experienced a host of problems with unbalanced equipment.
Pro audio electronics (DACs and amplifiers) with balanced inputs are designed to reject all of this noise. I got started off with a Behringer UMC1820 audio interface and I have had good luck picking up used install amps from Crestron on Ebay for CHEAP, like $200 (e.g. AMP-2210T, AMP-3210T) which are 1U class-D fanless amps that deliver 100W@8Ohms, 200W@4Ohms.
Thanks for the feedback, Charlie - Sounds Like this could get more expensive going forward but for now I have a very clean sounding system at my DAW position.
Turning down the MiniDSP 4x10HD output and raising the PC output volume thru the Scarlett 8i6 SPdif has also helped reduce the noise floor - now I have to put my ear up next to the speakers to hear the D/A chip chatter.
Balanced input on the amp and balanced cabling is all that's really needed. Balanced output from the DAC is "nice to have", but not strictly necessary. The balanced output increases signal level, which helps SNR some but that's it. Noise immunity comes from the balanced input and cabling. Proper shielded twisted pair cabling works perfectly well whether both ends have balanced connector, or if the source end has RCA. It's easy to test noise/hum pickup from cabling with REW RTA, I compared some of my cables, laid them parallel to an AC lamp cord and even the cheapest crappiest balanced cable I can find outperformed every RCA I have by a mile.
Setup at my computer uses this low cost monoprice cable from DAC to amp, sits next to AC cords and my monitor power supply, there is absolutely no noise. None.
In my listening room everything I have is consumer grade RCA outputs except for my amps that all have balanced XLR inputs. I concur with dcibel that those types of cables are very effective.
The key is the cabling - twisted pair of wires with an outer shield. Sadly my supplier no longer carries them.
In my home lab I use a mono test amp that's based on the LM3886 chip. It has a Neutrik combo-socket (XLR/jack).
I wonder if one can accidentally buy one that uses unshielded cabling.
@dcibel - Which model of monoprice cable did you buy?
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I have had good luck picking up used install amps from Crestron on Ebay for CHEAP, like $200 (e.g. AMP-2210T, AMP-3210T) which are 1U class-D fanless amps that deliver 100W@8Ohms, 200W@4Ohms.
Charlie - Do you have the part numbers for the Phoenix connectors that fit ^ these amps?
I can't find part number for them in the literature and all the amps available are missing them - kind-of a deal breaker for me . . .
https://www.amazon.ca/Monoprice-Connectors-Shielded-Oxygen-Free-Conductors/dp/B009GURYL8?pd_rd_w=1RQVG&content-id=amzn1.sym.692b7330-b0b8-46a6-a467-efe1241a0906&pf_rd_p=692b7330-b0b8-46a6-a467-efe1241a0906&pf_rd_r=CAGM1HH5D0Z8BZNDNWBR&pd_rd_wg=6nVMT&pd_rd_r=e2984b08-4845-4689-97fd-c42c54c0adc8&pd_rd_i=B009GURYL8&psc=1&ref_=pd_bap_d_grid_rp_0_6_t
The monoprice cable is well constructed, and cheaper than what I could get if purchasing wire and ends and assembling myself.
I've inspected several cheap balanced cables, some the pair of wires is just run parallel, untwisted, and with basic loose strand shield, and possibly with thin 24AWG wire despite a thick insulation to make it look beefy/premium. This bargain bin cable without real shield still outperformed any RCA cable I have on hand for noise/hum pickup:
With that conclusion, I decided to not stress too much over balanced cable, get what is a good deal with quality connectors and if you really want a premium cable then just get Mogami and be done with it.
This was just a basic comparison, running loopback measurement of noise floor (no signal), with the cable run parallel to an AC cord with an LED lamp connected at the end, turned on. The yellow TRS above is the green trace, and a half decent RCA is the red trace. Sorry, y axis scale should not be SPL but you get the idea.
To those that don't know, TRS 1/4" plugs are balanced connections running one-channel in prosound configurations. I found this out some 13 years ago now, but I came from consumer electronics and not a prosound background. Just an FYI....
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TRS = "TIP, RING, SLEEVE" and are used as INSERT Cables for side-chaining Effects loops in mixers, Stereo output to headphones, signal splitters, etc but they are just a PLUG standard and not a cable standard. There are multiple uses for them depending upon how they are wired/configured.
I will have to respectfully disagree with much of what you have written above.
Firstly, balanced interfaces do not require balanced signal levels. That is not at all what the "balanced" in balanced interconnects is all about (more on this later).
Certain wiring physical configurations like twisted pair, using copper braided shielding, etc. DO help to reject noise and hum pickup, but this does not improve immunity by more than 10dB or 20dB at best and does nothing against ground loops.
You are lucky that your current setup does not have any noise problems. It sometimes just takes one piece of gear that injects DC and or is subject to noise pickup and there goes the S/N for the rest of your playback chain.
So, what IS a balanced interconnect and how does it work? The trick is to balance the IMPEDANCE of each of the two lines/wires that connect the equipment, and to design the input network to reject other sources of noise. All balanced inputs do is subtract one signal from the other (one line has been inverted by the source already). One of the lines can remain "undriven", that is sitting at ground potential (but not actually connected to ground) and many manufacturers do just that. The magic arises when the total impedance from source to sink in each line is exactly the same - both lines will pick up the exact same amount of noise and interference. Noise rejection via shielding is NOT REQUIRED at all. At the receiver end, the input network subtracts one signal from the other, and when the noise level is the same on both lines and the subtraction is performed correctly, there can be as much as 80 dB or more of rejection. Also, because there is no connection to ground for either line of a balanced connection they are immune to ground loops. Instead of returning via the ground, signal current simply flows back on the "other" line in the pair, much like an amplifier in BTL mode. This is strictly true for transformer based balanced inputs, and less perfectly but still very good for IC based inputs like those from THAT Corporation (e.g. 1200 series). These offer up to 90dB of rejection, even at DC.
As the impedance balancing becomes less and less accurate, the amount of noise pickup on each line will become slightly different and subtraction leaves a little in the signal.
There is a good writeup about balanced audio interconnects on Rod Elliots' web site:
https://sound-au.com/articles/balanced-2.htm#s1
He presents in Figure 5 how the accuracy of the impedance balancing effects the maximum possibly common mode noise rejection.
You can get all the necessary connectors from Ebay or Amazon. They are not a special part. The input connectors are 3-pin 3.5mm pin spacing and the output connectors are 4-pin 7.62mm spacing. See page 9 of this manual at Crestron:
https://www.crestron.com/getmedia/ede3864b-b708-4f5d-a74a-0d8609b0486d/mg_io_amp-2210t_amp-3210t_amp-2210ht_1
I have been using these amps for the last 2-3 years and I really like them.
I purchase a decent quality TRS-TRS (or whatever connector type you need) balanced cable from Amazon, cut it in half and strip back the jacket and wires, and then you just screw them into the connector obeying the proper polarity. It's easy.
I don't actually see much here that is in disagreement with what I've said, perhaps you've misunderstood my comments. My comments were about noise pickup, and 10-20dB improvement is not insignificant, in fact quite large. Intent was to provide what is an obvious improvement over single ended signal and cabling. As an upgrade path, start with the amp end and move backwards, not the other way around.
I would not say that I am "lucky" that my setup works, I have an education and profession in electronics so it should be no surprise that it works, as I am able to troubleshoot noise, hum, DC problems on my own.
I don't need an education lesson on how balanced cables and signals work, but for anyone who wants the basics, a nice youtube video here:
Steve, for your original post l, I bet the noise is from the power supply more than the hub itself. You may be able to use the hub as a passive devise if nothing on the hub needs 5v. If you need the 5v power supply you could consider a better power supply. There is a chance that the device is so poorly made that it lacks basic signal integrity but that is unlikely.
OK, I did not get that from what you wrote, but that I likely my fault. Also, I tend to wax pedantic when I post, but this is not in any way meant to be an intellectual smackdown or whatever, just that the post remains as a resource for anyone who cares to read and learn about the topic. Too many times I have seen very learned and astute posters in other forums just curtly answer a long post full of questions with a few words and no explanation, and I find that to be rather useless, because the "why" is just as important as the "what". See I am already being pedantic again... sigh. It's my nature, unfortunately.
No problem. Difference is providing a post with some useful tidbit vs writing an article, manual or textbook. My point was only that you don't need a balanced source to benefit from balanced cabling, if the receiving equipment includes balanced input an cable is manufactured properly with 2 conductors right down to the RCA end. Impedance balance is one factor, but generally you will have low source impedance, high input impedance, typical impedance mismatch from RCA to XLR cable can be 1% or less. Assumption here is 10-100 ohm output impedance and 10K or greater input impedance. Balanced end to end is ideal of course, perhaps one day consumer audio will abandon RCA/unbalanced connections altogether, but I think not in my lifetime.
Not that it matters much for this discussion, but I did crack open my Outlaw 5000x, it uses a THAT IC based balanced input.
The equipment I use the RCA to XLR cable is Topping DX3 to Boxem nCore.
Hey Ken - thanks for your thoughts - it was a cheap HOSA 4 port USB powered Hub causing the trouble.
Removing it stopped the high pitched squeal completely from the Compression drivers - I originally was blaming the Focusrite 8i6 and the downstream amp until I started removing parts from the signal chain and bypassing them.
The system is so quiet now that it sounds like listening in an anechoic chamber down here in my little dungeon.
(I worked in a rather large anechoic chamber in my past where aircraft radar signatures were recorded so I kinda have a clue about how that sounds)
Terrific information, Charlie - thanks for this!
Snagged 2 Crestron 2210T amps in nice shape off of eBay for $80 a piece by making an offer below the asking price.
This should have me set along with Charlies old Control-4 8 channel unit . . .
(I love it when a plan comes together).
Let us know what you think of them!
Oh, yeah . . . .
I want to get in on this Creston action!
What’s the SNR like? Good enough eg. 80-90?
And load (in)dependance causing HF fluctuations?
I’m not expecting Hypex UcD performance, but I’ve had pro amps before but the transformer hum or loud fans drove me batty. At least now that’s mostly gone with class D…
From the manual that Charlie linked-too ^
S/N Ratio >103 dB, A-weighted
Crosstalk >70 dB @ 1 kHz
Gain 23 dB with INPUT LEVEL control set at 12 o’clock nominal position
Input Sensitivity 2.22 Vrms for rated output power with INPUT LEVEL control set at 12 o’clock nominal position
That Musway DSP unit I have coming from Germany is rated at 95db SNR on the output and that is plenty good for me. This should be a good match using the Crestron amps for subs and midwoofers.
https://www.ebay.com/itm/314535925064?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=rjyvrmapqrs&sssrc=4429486&ssuid=NtMdzbxQRTm&var=&widget_ver=artemis&media=COPY
Found this one on eBay. Looks like a good price. No affiliation.
That looks like a 70V application amp.
It is configurable as both 4/8 Ohm load and 70V as most of the Crestron amps-are.
https://www.crestron.com/Products/Audio/Amplifiers/Modular-Amplifiers/AMP-2100
👍🏼
Um, no, it isn't! That particular one is 70V only. Note that the model number ends in "-70". Pay close attention to the different versions of the 2100 amp listed here:
https://www.crestron.com/Products/Audio/Amplifiers/Modular-Amplifiers/AMP-2100-70
You have to click on "SPECIFICATIONS" to get the details for each sub-model. There is a version that is 4/8 Ohm compatible, but not the "-70" version in the Ebay listing.
You really want to look for:
AMP-2210xx
AMP-3210xx
where xx can be T,S, or HT. All of those are 4/8 Ohm compatible and are 1U full rack width size.