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Active Speakers, Cable Runs & Passive Pre-Amps

Blumlein 88

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The easy way to do this is put the passive very close to the speakers. The cable feeding the passive hardly matters. What matters is the cable between passive output and speaker input. Best would be right next to each speaker. Not convenient. In any case, assuming the phono output has low enough impedance 10k is going to be the way to go. 25 feet between passive volume and speakers is going to be iffy.
 
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Blumlein 88

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A traditional good quality preamp of low gain would be good in this case. It would be better quality than your AVR. Another option if you don't need remote control would be a basic microphone preamp. You only need line level and most of those also function as a good line level pre and control.

Again if you put a single passive control, preferably switched for matching channels, within 6 feet of each speaker your cable problems pretty much disappear.
 

Speedskater

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My phono stage has an output of 8v and increases gain adequately to the listening volume I need. What I'm trying to figure out is how to impedance match a passive pre-amp if used to attenuate the phono stage connected directly to my active speakers.
If your powered phono stage has a volume control before it's output stage. What you need is a fixed attenuator at the input to the active speakers.
 

LTig

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This where my knowledge hits a wall.

The phono stage is a Musical Fidelity MX VNYL:

The cables are 25' Mogami W2534, which I assume add to the impedance of the MX VNYL:
I see that the phono pre has a volume pot. Why not just feeding the ATCs directly from XLR out, and connect the AVR from RCA out?
The speakers are ATC monitors which are expecting an impedance of >10K.
I don't think so. Have a look in the manual, I'm quite sure that their input impedance ist > 10 kOhm which means that according to the 1:10 "law" the output impedance of the source feeding the ATC should not be higher than 1 kOhm.
What would you say was the ideal impedance of the passive pre-amp sitting between the speakers and phono stage?
The specs of the phono pre do not state the output impedance, so difficult to say. If in doubt use 5k. If in real doubt go active.t
 

LTig

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If your powered phono stage has a volume control before it's output stage. What you need is a fixed attenuator at the input to the active speakers.
Only if the ATCs have no means to change the input sensitivity. Could this be true? Even the cheap JBL LSR2023P have a volume control. Anyway, a fixed attenuator is not expensive to build.
 

Blumlein 88

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I see that the phono pre has a volume pot. Why not just feeding the ATCs directly from XLR out, and connect the AVR from RCA out?

I don't think so. Have a look in the manual, I'm quite sure that their input impedance ist > 10 kOhm which means that according to the 1:10 "law" the output impedance of the source feeding the ATC should not be higher than 1 kOhm.

The specs of the phono pre do not state the output impedance, so difficult to say. If in doubt use 5k. If in real doubt go active.t
That is not a volume pot. It is used to set cartridge loading.
 

Blumlein 88

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I would suggest something like the SMSL HO200. Headphone amp and balanced preamp. Measurements are pretty much SOTA. It isn't going to color the sound. Has 3 gain settings and in your case low will likely do the job. (assuming the pre out follows the headphone out which is not clearly specified). Cost little more than some of the passive's you are considering.

The other thing to consider is they don't specify a max input. Might wish to write and ask before purchasing one.


1679960523271.png
 

LTig

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The specs of the phono pre do not state the output impedance, so difficult to say. If in doubt use 5k. If in real doubt go active.t
I found a german review and they state an output impedance of 45/90 Ohm - the latter presumably for the XLR output. So a 1k pot in the passive preamp would work.
 

MRC01

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Those speakers only say "> 10 kOhm" so assume it's only 10 kOhm. That's fairly low input impedance for a solid state device; they're usually 20k oHm or more. That's not well suited for a passive attenuator; it means you want no more than a 5k attenuator (max output impedance of 1250 ohm).

That phono stage doesn't publish an output impedance. You'll have to write them and ask. The cables say 34 pF per foot, which isn't too bad.
If all of your source devices have an output impedance of < 500 ohms, then a 5k attenuator could work.

OR, get a high quality traditional active preamp. Plug and play, you don't have to worry about impedance matching. Another good preamp option, in addition to ones mentioned above, is the Schiit Freya, which gives you both passive & active options. And is reviewed here.
 
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NicS

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Those speakers only say "> 10 kOhm" so assume it's only 10 kOhm. That's fairly low input impedance for a solid state device; they're usually 20k oHm or more. That's not well suited for a passive attenuator; it means you want no more than a 5k attenuator (max output impedance of 1250 ohm).

That phono stage doesn't publish an output impedance. You'll have to write them and ask. The cables say 34 pF per foot, which isn't too bad.
If all of your source devices have an output impedance of < 500 ohms, then a 5k attenuator could work.

OR, get a high quality traditional active preamp. Plug and play, you don't have to worry about impedance matching. Another good preamp option, in addition to ones mentioned above, is the Schiit Freya, which gives you both passive & active options. And is reviewed here.
Thanks for this....
 

robwpdx

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Along with the many good answers, what you ar looking for is an O-Pad. It is 4 resistors, 2 of which can be variable. It can be designed for your choice of input and output impedance. You can look up the resistor values for an O-Pad. The missing piece of information is what impedance does the Musical Fidelity want to see on its output? And what voltage can it put out into various impedances? It is similar to the discussions we have on headphone load to headphone amp matching without the headphone reactance.

If it can put out 8V into high impedance, it has more than enough drive for the speaker line level input.

It would be great if you could take the cover off the Musical Fidelity and photograph the inside, purely for curiosity sake.
 
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NicS

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I rewired the power plug on the unit. It was one of those crappy coaxial power plugs that never fits properly. If I jiggled it, i could see the power light flicker. So I swapped it out for a locking dual pin plug hooked up to a linear power supply. Cheap upgrade.
 

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robwpdx

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I rewired the power plug on the unit. It was one of those crappy coaxial power plugs that never fits properly. If I jiggled it, i could see the power light flicker. So I swapped it out for a locking dual pin plug hooked up to a linear power supply. Cheap upgrade.
What are the transistor/FET/metal can part numbers? Same for the black mult-leg chips. They may use a little more power, but linear supplies are potentially quieter - so good for that! It looks like the front panel uses the chips to switch mechanical relays for resistors and such, which is a good plan.
 
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NicS

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What are the transistor/FET/metal can part numbers? Same for the black mult-leg chips. They may use a little more power, but linear supplies are potentially quieter - so good for that!

I find it curios when I open some electronic boxes that it seems well designed and performs well but the power supplies are relatively crappy wall-warts and the connectors fail easily. It seem a false economy to cheap out on something like that.

I bought this phono sage because it is a relatively cheap, fully balanced unit. If connected to the tonearm wired for a balanced signal, it's chalk and cheese over the RCA unbalanced configuration. Signal to noise ration is audibly better. Improved again by adding the linear power supply. So is channel separation and as a consequence the "image" which I know if a fluffy term. The jazz records I listen to seem to sound much more focussed per instrument. Maybe there isn't as great channel separation with the RCA inputs. Maybe it's confirmation bias. Who knows?
 
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