DIY passive preamp

Printable View

  • 03-05-2008, 08:18 AM
    Bigmoney
    DIY passive preamp
    Hello, I have been reading a few posts on this forum from years back about the benefits and monitary savings of usin a passive preamp. I have a rotel 1080 and marantz 3002 dvd player. From what I have read a good passiv preamp will beat out an active preamp if driven properly. My cd puts out 2 volts and my 1080 accepts 1.5-5 volts. Therefore my dvd can power the amp, correct? Does anyone know of inexpensive preamps, under 250. Or possibly a DIY preamp that would be better. I figured with the money I had saved I could purchase a good DAC and go coax from my dvd. This seems like the most cost/benefit plan I can think of. Plus without a phono I have no reason to need* an active preamp amp I assume.
  • 03-05-2008, 09:29 AM
    Feanor
    Passive issues
    Quote:
    Originally Posted by Bigmoney
    Hello, I have been reading a few posts on this forum from years back about the benefits and monitary savings of usin a passive preamp. I have a rotel 1080 and marantz 3002 dvd player. From what I have read a good passiv preamp will beat out an active preamp if driven properly. My cd puts out 2 volts and my 1080 accepts 1.5-5 volts. Therefore my dvd can power the amp, correct? Does anyone know of inexpensive preamps, under 250. Or possibly a DIY preamp that would be better. I figured with the money I had saved I could purchase a good DAC and go coax from my dvd. This seems like the most cost/benefit plan I can think of. Plus without a phono I have no reason to need* an active preamp amp I assume.
    From what I've heard and read, the key factor in the passives is input and output impedance. The general rule is the higher the input impedance of a component, (active or passive), and the lower the output impedance, the better. The minimum ratio, output : input is 1:10, with 1:100+ being ideal. Keeping interconnect lengths short is also desirable with passives.

    As you have figured, output voltage and input sensitivity are also issues, but most amps can be driven to full output by 2 volts.

    I used an Adcom GFP750 in passive mode with excellent results -- even with 7-foot interconnects. GFP750's output impedance was 1200 ohms from the balanced outputs as I recall, while my Monarchy amps had an input impedance of 100,000 ohms and a sensitivity of 1V for full output, so no problem.
  • 03-05-2008, 09:55 AM
    Bigmoney
    How do I know what the input and output impedances are?
  • 03-05-2008, 12:04 PM
    Feanor
    Ryfm
    Quote:
    Originally Posted by Bigmoney
    How do I know what the input and output impedances are?
    I'm afraid that a non-electrical engineer (like me) can only find out by reading the manual or contacting the manufacturer. Input and output impedances are often, but not always, amongst the listed specifications.
  • 03-05-2008, 01:24 PM
    Glen B
    Quote:
    Originally Posted by Bigmoney
    Does anyone know of inexpensive preamps, under 250.
    The Channel Islands VPC-3 passive is $299.00. That's about the closest to your budget. Anything less and you may end up with something of inferior quality with poor channel tracking and compromised sonics, likely negating any benefits of going passive. A product like the DACT Stepped Attenuator for example which uses a ladder of individual high quality resistors for each channel instead of a potentiometer, forms the heart of a good quality passive unit. That alone will run you in excess of 2 bills.

    http://www.musicdirect.com/product/73299

    http://www.audiyo.com/product_desc2....&cat=2&cat2=18
  • 03-05-2008, 05:01 PM
    Feanor
    Creek, etc.
    Quote:
    Originally Posted by Bigmoney
    ... Does anyone know of inexpensive preamps, under 250.
    The Creek OBH22 passive with remote control has a pretty good reputation and can be found quite often on eBay or Audiogon.

    Or you might grab this Monolithic PA-1 passive (no remote) on eBay. Monolithic is affilated with Channel Island previously mentioned.

    Or you might check ot this B&K Pro MT that has a passive mode; a lttlle more money though. Also on Audiogon presently are a few low cost passives -- to the home page and enter "passive" in the search box.
  • 03-05-2008, 08:05 PM
    E-Stat
    Quote:
    Originally Posted by Bigmoney
    Or possibly a DIY preamp that would be better.
    If you can do simple soldering, you can make a basic one using Radio Shack parts for $20. Don't underestimate what one of these can do. Mine outperformed the line stage on an Audio Research preamp. I later built another using better parts, including DACT stepped attenuators, Cardas connectors, and JPS Labs wire for the main system. Since I no longer use the first one, drop me a line if you want it. BTW, Marantz doesn't specify the output impedance of the player but it is most likely op amp based which typically is pretty low. Ideally, you'll need some low capacitance cables like what Blue Jeans sells.

    Quote:
    Originally Posted by Bigmoney
    I figured with the money I had saved I could purchase a good DAC and go coax from my dvd. This seems like the most cost/benefit plan I can think of. Plus without a phono I have no reason to need* an active preamp amp I assume.
    That is a good plan. I bought a used Manley DAC with tube output for the vintage system that was far better than the one onboard the Pioneer player. It had gain controls so I use it to drive a Threshold power amp directly.

    rw