RCA to XLR Sonics

[lovinthehd]

Your QSC amps follow domestic specs closely. The input sensitivity is 1.2 volts and not 2.5 to 12 volts, and the input impedance is 20K Ohms and not 2.2 K Ohms.

The OP's rig will not perform well unless the large miss match he has is corrected.

Or chooses a more appropriate amp.....too bad VTV doesn't offer an option or do they?

 

[TLS Guy]

Or chooses a more appropriate amp.....too bad VTV doesn't offer an option or do they?

The amp he chose looks like a good amp. The fix I outlined is easy and not expensive. Actually the set up I outlined is the high road, and by far the best way to connect a receiver to a fully fledged power amp. The results will be superb, and sound by far the best.

 

[lovinthehd]

The amp he chose looks like a good amp. The fix I outlined is easy and not expensive. Actually the set up I outlined is the high road, and by far the best way to connect a receiver to a fully fledged power amp. The results will be superb, and sound by far the best.

I meant VTV offering unbalanced/rca inputs. Seems adding the ART box would work if needed, but I'd still try without too. The Denons can output more than 2V

 

[TLS Guy]

I meant VTV offering unbalanced/rca inputs. Seems adding the ART box would work if needed, but I'd still try without too. The Denons can output more than 2V

He will get better SQ if he uses an active solution. RCA outs will not perform properly into an input impedance less than 20K ohms. The impedance mismatch is the most critical one to address.

 

[lovinthehd]

He will get better SQ if he uses an active solution. RCA outs will not perform properly into an input impedance less than 20K ohms. The impedance mismatch is the most critical one to address.

How does that fit in with the output/input impedance thing of at least 10% between preamp/amp?

 

[TLS Guy]

How does that fit in with the output/input impedance thing of at least 10% between preamp/amp?

I think you mean X 10 and not 10%.

The issue is that connections between stages must be voltage driven and NOT power driven, until you get to the output.

So in going from a line out to a line in, you want the input impedance to be at least 10 times the output impedance of the driving line out.

A line output impedance of consumer goods is not generally specified. However most line out impedances are in the region of 600 ohms being typical. So you need an input impedance of at least 6K ohms, but higher is typical. You can reasonably expect an input line in impedance to be at least 20 K ohms and around 50k ohms is typical.

Balanced connections in general have both lower output and input impedances as a rule.

Certainly a 2.2 K Ohm impedance is too low, and the connection will be current driven to an extent and will significantly reduce SQ. That is why generally it is recommended for a line input impedance to be 20K ohms or higher so it is NOT in anyway current driven.

When considering adding power amplification to receiver preouts this is an important issue to consider.

 

[Verdinut]

Your QSC amps follow domestic specs closely. The input sensitivity is 1.2 volts and not 2.5 to 12 volts, and the input impedance is 20K Ohms and not 2.2 K Ohms.

The OP's rig will not perform well unless the large miss match he has is corrected.

Actually, the DCA 1222s only need 0.9 volt for full rated output for a 4 ohm load. They have an input impedance of 10K ohms unbalanced and 20K ohms balanced. IMO, they're a good substitute for the discontinued current dumping Quads which you own and expensive to purchase as used.

 

[lovinthehd]

Don't know why I was thinking Denon but seems he has the Yamaha 1060 which specs an output impedance of 470 ohm (and max preout voltage of 2.0V "or more"). Looking around the VTV site where are you getting 2.2 kohm from?

 

[TLS Guy]

Don't know why I was thinking Denon but seems he has the Yamaha 1060 which specs an output impedance of 470 ohm (and max preout voltage of 2.0V "or more"). Looking around the VTV site where are you getting 2.2 kohm from?

When I went through the spec sheet that was the stated input impedance, and not atypical for a balanced input.

 

[Verdinut]

When I went through the spec sheet that was the stated input impedance, and not atypical for a balanced input.

I guess you meant not typical, right?

 

[lovinthehd]

When I went through the spec sheet that was the stated input impedance, and not atypical for a balanced input.

I saw specs much higher here https://vtvamplifier.com/wp-content/uploads/2020/05/Purifi-Series-Manual-.pdf but not sure that's same amp/buffer etc

 

[TLS Guy]

I guess you meant not typical, right?

No, I think balanced inputs generally to have lower input and output impedances in the pro world, or at least used to. It has been my practice to buffer when going from line to balanced. And is the case here in the two lines that are line to balanced. That is the high road and will avoid issues.

It is easy, and the added cost to a high end system is insignificant. I do know that good pros buffer in this situation.

 

[Verdinut]

No, I think balanced inputs generally to have lower input and output impedances in the pro world, or at least used to. It has been my practice to buffer when going from line to balanced. And is the case here in the two lines that are line to balanced. That is the high road and will avoid issues.

It is easy, and the added cost to a high end system is insignificant. I do know that good pros buffer in this situation.

My DCA 1222s have a higher balanced input impedance of 20K ohms compared to 10K ohms for an unbalanced input. These amps are used in Cineplex theaters across North America.

 

[TLS Guy]

My DCA 1222s have a higher balanced input impedance of 20K ohms compared to 10K ohms for an unbalanced input. These amps are used in Cineplex theaters across North America.

There are lots of issues here. QSC are good amps. A high input impedance is of no consequence. However pro line spec for input voltage is 2.2 to 2.5 Volts not including head room. I know many manufacturers try to bridge the divide so to speak. That can come at the expense of S/N. Standard practice is however line out at 1.2. to 1.5 volt range, and balanced 2.2 and up generally 2.2 to 2.5 volts full modulation.

A floating passive interconnection in my view is inferior to an active buffered solution. Generally line outs are best feeding amps in the 0.5 to 1 Volt range. I think 0.5 to 0.75 volts is optimal for a line input sensitivity. That way you do not stress equipment with a line output and will leave headroom.

By the way, I hope my Quads see me out. I know those current dumping amps well and have parts and adequate service test equipment. I have always used Quad amps exclusively for over 50 years now. I just find the whole design concept of them so elegant and intellectually satisfying. So it is all about what you know, and how to get the best from what you have.

 

[highfigh]

Balanced connections are commonly used for live audio and in recording studios for microphones with long cables. Long cables (30 feet or more) carrying microphone (low voltage, 1-3 mV) or guitar pick-up signals can pick up noise from EMI or RFI. Balanced connections along with the differential circuits required inside the electronic gear can cancel out this noise. Read about it here: http://en.wikipedia.org/wiki/Balanced_audio

In pro audio, balanced interconnect cables, with XLR plugs, have become standard for all situations. Having both balanced and unbalanced cables would just create unnecessary expense and confusion. In home audio, RCA plugs on unbalanced connections have long been the norm. RCA plugs are smaller, taking less space on crowded rear panels of electronic gear. In most homes, much shorter interconnect cables are used, and there is typically much less EMI or RFI noise. In home audio, the only signal sources with very low voltages (similar to microphones) are phonograph pick-ups. They are single-ended sources, unbalanced, and use shielded cables with RCA plugs. In most cases, they do not suffer from EMI/RFI noise.

It seems that balanced connections have become fashionable for preamp-to-amp connections. Many products offer these as a highly sought-after feature, usually at higher prices. The voltage levels between preamps and amps are much higher than microphone level, roughly 100 times higher. Interconnects at this level are much less prone to induced EMI or RFI noise, especially if they are less than 30 feet long. Standard RCA interconnects between a preamp and amp are fine, unless you have an unusually noisy environment with high levels of EMI or RFI. Its not worth paying a premium price just to have an amp with pro-style balanced inputs.

Very few guitar rigs use balanced connections. They should, but they don't. Les Paul was using LoZ in the early-'50s and nobody liked it because it was too clean. Well, other guitar players didn't like it- he sold millions of records. Also, manufacturers & cork sniffer guitar effects pedal builders wouldn't have anything to hang their hats on WRT (said in a whiny dork voice) "Your pedals aren't true bypass". Another reason is that if a guitar player is going to be extremely far from their pedals and amp(s), they'll use a wireless system because long cables are hard to manage.

The majority of amplifier manufacturers that aren't in the pro/commercial market add XLR jacks because it's a trend that far too many follow for the wrong reasons. Most aren't true complimentary balanced circuits, even in brands that are known for making very good equipment.