[JJ15k]

Hello,
I would like a preamp with remote for the convenience. however I am worried about the distortions introduced by another component in the audio chain. I don t need active amplification, just input/volume switching with remote.
If possible I d rather not spend a fortune so I was wondering if maybe some kind of passive pream could do the trick?
It would be used with an aqvox or lavry source and K1000, so quality needs to be on par.
Thanks

 

[Ferbose]

PreSonus Central Station is the passive pre-amp I use in my K1000 system.
It has a remote control, but a cabled one, which is for studio use.
If you mean wireless remote control, you may have to look somewhere else.

 

[JJ15k]

Well, what s one more wire in my room

Wireless would be better but feel free to suggest preamps with wired remote
PS: I noticed the central station also works as a DAC, It really adds to the price while I don t need it, is there a stripped down model?

 

[rocktboy]

adcom gfp-750. highly praised since the mid 90's.
http://www.adcom.com/preamplifiers/gfp750.htm

or Welborne labs zephyr
http://www.welbornelabs.com/zephyr.htm

Both should fit very well with your associated equipment. Both are solid pieces of engineeering at affordable prices.

 

[chadh]

Placette makes a single input passive unit that comes with remote. You can often find them on audiogon for around $600 or $700, or else new for around $1000. The attentuator is stepped, I believe, with an obscene number of steps for extremely fine control of volume. By all reports it is quite outstanding.

This is the three input version: http://cls.audiogon.com/cgi-bin/cls....ran&1145694437 . But you can usually find a single input version (the RVC). This one just sold: http://cls.audiogon.com/cgi-bin/cls....ran&1146075310

The Bent NOH is no longer produced. It was a transformer volume control - a passive unit that has the advantage of not impeding dynamics as it uses a transformer rather than resistors to accomplish the attenuation. It came with optional remote. These have been extremely hard to come by as they were apparently just soooo good, but as the new Bent units are soon to be available, things may change. In fact, this one seemed to be slow to move (it may still be available): http://www.audiocircle.com/circles/v...ic.php?t=26010

Of course, you could always wait for the new Bent units to be available. I think they might even have DIY options, if you're interested.

The Sonic Euphoria passive line stage is similar to the Bent, except it uses an autoformer rather than transformer. It's more pricey, though - probably around $1500 with a remote control.

At the lower end of the price spectrum, there's the Creek OBH-10 or OBH-12. By all reports, it's a good little passive unit and comes with remote. This one recently sold on audiogon for $190: http://cls.audiogon.com/cgi-bin/cls....ran&1146600453
I think the OBH-12 is an updated version of the OBH-10.

Finally, if you're into DIY, a passive line stage is a pretty easy project (even I made one!). You could spend a couple of hundred for a DACT attenuator and another couple of hundred for their remote control unit and make a fine unit yourself for less than $500.

Chad

 

[Ferbose]

Quote:

Originally Posted by JJ15k PS: I noticed the central station also works as a DAC, It really adds to the price while I don t need it, is there a stripped down model?

The price is really low anyway here in US, and Musician's Friend has a sale for $400. The pre-amp section is totally transparent as far as I can tell, in agreement with all the pro-audio review. I prefer using it as a pre-amp than using DAC1's internal volume control.

The headphone section is very good as well, just like the DAC. This baby is an unbeatable value. See my review of Central Station: http://www6.head-fi.org/forums/showthread.php?t=155336

 

[Ferbose]

I am not an expert on passive pre-amp, but I believe many of passive pre-amp designs have obvious issues.

For all those based on a variable resistor, be it a potentiometer or stepped attenuator, it is impossible to keep imput impedance high and output impedance low simultaneously. You have to find a compromise point in-between and many people think this causes a lost in dynamics.

Transformer based designs, there is no impedance matching problem, but transformers are not totally linear. It seems that transfomers can create higher distortions than active pre-amps.

Nowadays you can make a passive preamp with resistors and switches. And based on volume setting use DSP to calculate which resistors should be in the signal path. This way, impedance can be optimized at each attenuation setting. This is exactly what PreSonus does. Although it has a volume knob, it is used to tell the DSP chip what volume seting is desired. The DSP then controls the mechnical relays to swap various resostors in or out of the signal path. Central Station has 34 mechanical relays, and the signal path only goes through a few fixed-value resistors and relays, but no potentiometer. So it is actually a potentiometer-free, digitally-controlled passive analog attenuation.

I know that Lavry black DAC has a preamp section based on digitally-controlled resistor networks, similar to Central Station. But the switches appear to be semiconductor switches instead of mechanical relays. Since semiconductor switch is still an active device, I would prefer to see mechanical relays which are truly passive.

I have described the types of passive preamps that I know of, are there any more ways to build a passive pre-amp?

 

[JJ15k]

Ferbose, you seem really impressed by the central station, a DAC as good as DAC1 and on the level of lavry/aqvox?That alone justifies the price, however I was wondering if you would give some of your impressions once again since you have had the device for longer.
your help is much appreciated.
Btw: how is it going with the k1000 "ambience recovery"?

 

[Ferbose]

Quote:

Originally Posted by JJ15k Ferbose, you seem really impressed by the central station, a DAC as good as DAC1 and on the level of lavry/aqvox?That alone justifies the price, however I was wondering if you would give some of your impressions once again since you have had the device for longer. your help is much appreciated. Btw: how is it going with the k1000 "ambience recovery"?

I have not used Central Station's DAC for some time. It is only ever slightly inferior to DAC1, but you won't see me quitting up DAC1 anytime soon. I won't let go of something that Bob Katz considers a benchmark and Doug Sax bought seven.
So I am now reconnecting optical cable to Central Staion, and put on a familiar violin concerto recording with a violin sound I know is too lean. You know how lean violin sound can really challenge weaker digital sources. Not a problem with Central Station as it is hardly distinguishable from DAC1. Defintely more accurate and transparent than my Sony SACD/DVD player that was a $1000 flagship in 2001.

The K1000 ambience recovery thing is a real revelation. I hardly listen to K1000 by itself nowadays. Not that K1000 has any problem with ambience: it has superb ambience. It is stereo recording that has fundamental issues with with ambience (early reflection and reverberation), a fact that was recognized in the 1930's. For all these years, it has been impractical to go beyond two channels in audio, and it still largely is. The real sound is like 30% direct and 70% reflected, and stereo recordings only captures something like 70% direct and 30% reflected (adding more reflected sound would reduce clarity). This big (say 40%

) discrepancy keeps stereo from sounding totally natural. What I am doing accidentally addresses the ambience problem really well, to the point the timbre of violins and pianos start to sound like what they would sound in a poor concert halls (like our school's). The other day I was in the home of a reviewer for a respected online audio mag, and on that $50k system violin and piano timbres are quite out-of-tune, despite all the wonderful things it does. It made me realize how far I have traveled in my hi-fi journey. Of course I can't reproduce the spacious feeling of a real hall, especially not on a pair of headphones. But timbre is really the primary concern of a classical lover like me.

Back to Central Station, its DAC relfectes the pure tones of Claudio Arrau's piano as I am typing. With a decent power conditioner (in my case a Furman), Central Station has a relaxedness in its DAC and amp that is surprising for inexpensive SS gears. Highly recommended for both uses.

 

[sejarzo]

Quote:

Originally Posted by Ferbose For all those based on a variable resistor, be it a potentiometer or stepped attenuator, it is impossible to keep imput impedance high and output impedance low simultaneously. You have to find a compromise point in-between and many people think this causes a lost in dynamics........... ............Nowadays you can make a passive preamp with resistors and switches. And based on volume setting use DSP to calculate which resistors should be in the signal path. This way, impedance can be optimized at each attenuation setting. This is exactly what PreSonus does. Although it has a volume knob, it is used to tell the DSP chip what volume seting is desired. The DSP then controls the mechnical relays to swap various resostors in or out of the signal path. Central Station has 34 mechanical relays, and the signal path only goes through a few fixed-value resistors and relays, but no potentiometer. So it is actually a potentiometer-free, digitally-controlled passive analog attenuation.................. I have described the types of passive preamps that I know of, are there any more ways to build a passive pre-amp?

The big question regarding impedances in passives is what is "high enough" for your signal source but "low enough" for your amp input. FWIW, I'm pretty sure that for many years, most of the passives that used pots were built with 50 kohm pots--and it's pretty tough to hit a decent compromise with such a high impedance pot.

If you look at the Creek specs for their newest passive, the input impedance is simply shown as "<20 kohm" with the output impedance as "0 to 20 kohm". Given that many power amps have input impedances of 22 kohm or less, the high end of the Creek output impedance range still looks like it would create some matching issues--with compromised high frequency response or dynamics as a result.

I built one with 1.5 kohm Caddock TF020 "series resistors" followed by a 10 kohm Noble stereo pot as a variable shunt to ground. In conjunction with a 22 kohm input impedance on the inputs of my monoblocks, it presents a load of 2200 to 3000 ohms to the source. My main source has an output impedance of 47 ohms, so at typical listening levels, the ratio of load impedance to the source impedance is about 50.

"Looking back" at the source and preamp from the monoblock inputs, the monoblocks see 300 to 900 ohms net output impedance from the source and preamp.....so the ratio of load to source impedances ranges from 25 to 70 over typical listening levels.

I detect no problems whatsoever with dynamics with this set up. The -3 dB corner point for HF roll-off with my setup (including the capacitance of the cabling between the passive and the monoblocks) is around 150 kHz.......so I don't think there can be any real audible effect from that. It's definitely more transparent than my active preamp (a Stereophile Class B unit.)

One can build a mechanical stepped attenuator in the "ladder" configuration that works just like the switched network in the PreSonus. Goldpoint sells such units, but they are more expensive than a standard series attenuator or one built in the "fixed series attenutation/variable shunt to ground" configuration. There is only one resistor in series between the signal to the source and one shunting to ground between that "series resistor" and the load.

 

[Ferbose]

sejarzo,
Central Staion lists input impedance as 2k-5k.
The output impedance is not specified (something to hide?). Is there a way I can easily measure output impedance with an ordinary multimeter?

 

[JJ15k]

I may misread the specs, but on the site they list the output impedance of the main and cue outputs at 51 ohms.

 

[Ferbose]

Quote:

Originally Posted by JJ15k I may misread the specs, but on the site they list the output impedance of the main and cue outputs at 51 ohms.

The number quoted is for active outputs, I believe.
But I don't see a number for passive outputs.

 

[JJ15k]

oh, i also thought something was wrong, i didn t think you would miss it.
Maybe I ll shoot them a mail and see what they say.

 

[stryker]

Channel Islands has a passive pre that I'm looking at. I find their stuff to be well-built and very good for the money. I think one of the inputs can be adjusted internally. With the exchange rate of the Euro, you can't go wrong.