Phono stage output impedance question for the technically clever.

Hi

Can someone explain what the difference is between Ohms and volts when trying to understand how much output a phono stage has. Is it possible to compare different phono stages' outputs if some are stated in volts and others in ohm?

Here are some examples:

EAR 834p has a Max output of 30V

The EE Minimax has a Maximum Output of 20V

The DIY Hifi supply Cole is described as having an output impedance of 600 ohm (but there is no voltage figure).

Obviously, the EAR will have a greater output than the Minimax. But how about the Cole, where does it fit in?

 

Voltage and impedance are measuring different things.

Impedance is kind of like resistance. If phono stages are like CD players (I don’t know much about phonostages!) you should look for a low output impedance. The pre-amp (or poweramp if using a passive pre) should have a high input impedance.

The power transferred will be effected by the impedance of each, but most stages will probably be low enough to not worry about it when comparing the output voltage so I suspect the voltage will tell you what you need to know about which has a higher or lower output.

I'm sure Rob could clarify things more.

 

Hi,

Voltage and impedance are two entirely different things.

600 Ohms relates to the output impedance of the phono stage and the output impedance will influence it's ability to deliver full output into the load. Most solid state electronics will have a low output impedance of around <30 Ohms and should be able to swing full voltage into any reasonable load over 5K Ohms. Tube stages have much higher output impedances and need a much higher load to swing full output. As an absolute minimum standard, the load should be roughly X10 the output impedance or more, so your 600 Ohm phono stage should feed 6K Ohms minimum. There are other factors such as capacitance and inductance but would require a lengthy post


BTW I notice that you live about 2 miles from me - feel free to drop by for a fuller explanation

 

LOL -

You wanted an example of telepathic thought Simon - you got it!

 

Thanks for the explanations Simon and Rob. I need to get myself a book explaining basic electronic principles. Science was never of much interest at school!

Thorsten advised that I needed to find a phono stage ideally below 3kohm to partner with the ol' MF TVC. Obviously, the Cole is fine. Is it possible to get any kind of idea from the output voltage figure what the output impedance might be or do I need to consult the manufacturer on that?

Rob- Are you East or North?

 

My tube stage has an impedance of 1.5K and will not drive a TVC at all - just motorboats.

Valve stages tend to be able to swing far higher votages, so if the spec says 20 or 30 volts it's likely to be tube and the output impedance fairly high. IMO you need to tread very carefully if you plan to use anything with a tube output with a TVC. The TVC load is also quite inductive (the TVC is a transformer after all) and I'd personally keep them away from tube stages and poor, weedy OP amp outputs.

I'm North East - more East than North - Walthamstow, Just off the Lea Bridge Road.
PM if you fancy a short trip.

 

The maximum output voltage has nothing to do with the gain. If you are using a passive preamp you will need a high gain phono stage with an output at a similar level to a CD player, a gain of about 70-80dB for MC and 50-60dB for MM.

When driving a TVC you will need a low output impedance, the lower the better, i would guess less than 300 ohms to maintain a good bass performance.

HTH

Chris

 

Cheers Chris

I'm in contact with Harry at MF about it. As far as valve stages go, the 834p and Cole (600ohm) are meant to be a good match for the TVC. But Harry said that he wouldnt recommend I use the EE minimax with it, which is a bit dissapointing- was about to buy it.

I'm looking for a phono stage that has twin inputs, as my deck has 2 arms. It appears there are not many valve stages that match AND have twin inputs- only the Cole. That said, could always use 2 phono stages!

 

Neath London :rds2:

 

hi, cartridges very much depend on impidance matching , m.m. are not so fazzy but m.c.'s are, most A.T.'S work well at 100 ohms, but line level imputs vary on certain pre amps, voltage loading is very important with phono stages as some carts have very few micro volt's in their output, the thing to do in my opinion is to try different ohms inputs and see../

 

thanks nando.

 

Hi- thanks to everyone on ZG for your phono stage suggestions on my other thread- Finally bought one- an E E minimax for a very reasonable price and cheap enough not to worry about an audition- if there's a mismatch with the pre, could always sell it on. Touch wood, vinyl now sorted! (famous last words no doubt)

 

In what way Tenson ?