Balanced input phono stage for MC?
- Thread starter alanbeeb
- Start date
Analogue Andy
Active Member
I currently use a CEC PH53 which has this option, but am connecting my MC cartridge via a step-up transformer into the MM input of the CEC via single ended i/cs.
CEC strongly recommend using the balanced input as the circuitry is so designed for best performance. As far as I understand it, there is no need to match impedance as the balanced connection automatically does this. (I may have misunderstood this point)
The performance is so good as it is I feel reluctant to change, but the temptation is becoming very strong.
I guess the answer to your question depends on the design of your phono stage.
CEC strongly recommend using the balanced input as the circuitry is so designed for best performance. As far as I understand it, there is no need to match impedance as the balanced connection automatically does this. (I may have misunderstood this point)
The performance is so good as it is I feel reluctant to change, but the temptation is becoming very strong.
I guess the answer to your question depends on the design of your phono stage.
I may be a mile off the mark here but according to my understanding of balanced inuts, these are to reduce noise. By feeding an "in phase" and an "out of phase" signal down a length of cable at the same time any noise generated in the cable gets cancelled out once the signal is returned to "normal" by a transformer or input circuit receiving the signal. Of caourse additionally a transformer is in itself normally is an impedence matching device.
i_should_coco
I am weasel
No, you still have to load the cartridge with the correct impedance.
Analogue Andy
Active Member
Thanks for the clarification! The CEC is a very unassuming unit, but it can't half do some very magical things with my vinyl. It's the finest phono stage I've had in my system which includes some far pricier solid state and valve designs.
As far as I know, no use of any balanced input on a pre phono for the simple reason that the cartridge outputs a + and a - on each channel, so RCA is the standard.
You may output on balanced to go to the preamp, then the phono amp needs to be equipped with balanced output if it is built in balanced mode. Makes sense ?
Look at ARC REFERENCE Phono 2 rear plate. It has only RCA inputs but XLR and RCA outputs
Purité Audio
Trade: Purite Audio
We are just taking delivery of the new Trinity Audio balanced phono, it should be spectacular,
Keith.
Keith.
sergeauckland
pfm Member
No, all MC cartridges are inherently balanced, and so are most MM cartridges. Therefore, a balanced differential phono input is the ideal configuration. By the way, balanced and differential are not synonymous, one can have a differential input that's not balanced, but a balanced input is differential.
There's no significant difference between a microphone input and a phono input, so there's no reason not to balance phono inputs.
It's one of the recurring ironies of HiFi, which shows how far from technical reality it's got, that balanced power amps are commonplace, balanced output and line input pre-amps are not unusual but the one input that could really benefit from balancing, i.e. the phono input, is very rarely balanced.
S.
Werner
pfm Member
The automatic impedance matching is a rumour, spread by manufacturers. In fact, no such thing exists, not even in the mind of the most freaky 70s Japanese high-end manufacturers.
The CEC circuit is broadly identical to the Aqvox's, reviewed here http://www.tnt-audio.com/ampli/aqvox_phono2ci_part1_e.html, http://www.tnt-audio.com/ampli/aqvox_phono2ci_part2_e.html.
It is a common-base input, meaning that contrary to standard practice it presents the cartridge with a very low impedance (a near short), and then steals its current to flow into and through the input stage transtors. That's the CEC/Aqvox's unique selling point, but sadly this technique is incompatible with MM. They support MM, but in a way that negates their own circuit's uniqueness. Hence their advise to use the balanced inputs for MC.
Should you compare on the CEC they know that it is apples and oranges, as the cartridge loading and indeed the very circuit operation itself differ significantly between bal and unbal here.
A balanced link and receiver reject common mode noise, that is noise and disturbances picked up commonly by the link's two wires. In a domestic system this amounts perhaps to hum (if badly grounded or laid out), but not much more. The broad swath of non-common noise in the system is left unaffected.
In fact, when no transformers are used a circuit with balanced input requires two input stages, which appear in series with respect to the output signal. Thus these stages sum their (thermal) noise, and end up 3dB noisier than the equivalent unbalanced system. Perhaps that's why balanced MC inputs are not very fashionable: the cost of two front-ends and the noise penalty.
sergeauckland
pfm Member
Although there are plenty of very quiet op-amps which have differential inputs as standard, so just need equal impedances round the circuit to become properly balanced. I think the reluctance to balance phono inputs is commercial in that it needs different connectors, (usually XLRs), most people's phono cables are RCA terminated, so the punter would have to mess around with adapters (in which case the benefit of balancing is lost), or rewire their phono cables. Furthermore many arms aren't wired balanced past the socket at the bottom of the arm, so the manufacturer of a properly balanced phono amplifier would just get a lot of grief from punters who get it wrong. I also wonder how many dealers understand balancing, and the difference between a balanced circuit and a differential circuit.
S.
Indeed. Before having the Ref Phono 2, I did own the Ayre Phono P5Xe, very good gear for its price. And it had balanced inputs righly so.
A very good phono btw.