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Thread: 2 Channel line amp - suggestions?

  1. #1
    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    2 Channel line amp - suggestions?

    Anyone have suggestions for a high-quality two-channel line-amp? I may not be naming it correctly, but...

    Everything into my system pre-amp is nicely gain matched, except the TV. I need to boost the TV feed before my system pre-amp to keep the gain structure normalized across all inputs (i.e., so I don't have to change the pre-amp output gain when changing sources).

    The L/R variable gain feed from TV is substantially padded - I've got everything wide open but it still is at-least -10dB below other sources into my system pre-amp (2.0, nothing fancy). So, when tubing, the pre-amp gain must be at 1 O'Clock, and when CD'ing, it is never above 9.30 O'Clock. I hate the risk of someone switching sources from TV to CD without knocking back the gain. Been lucky so far...

    Right now, I'm using a POS Mackie 1202, with TV L/R into two variable mic pre's, coming out the Main L/R outs. Works great, but it's a bit excessive. I recall reading where Earl has solved a similar condition with a similar solution.

    Ideas...?
    bo

    "Indeed, not!!"

  2. #2
    RIP 2010 scott fitlin's Avatar
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    Parts Express may have something for that. Not sure I will check.
    scottyj

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    Senior Member Audiobeer's Avatar
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    For about $300 (used) you can get a B&K PT5. What I liked about them was it had a remote and you could adjust the gain on each input and store it.

    http://www.bkcomp.com/pdf/PT_5_brochure.pdf

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    Senior Member SMKSoundPro's Avatar
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    I have the same thing happening here at the bar. Cable converters too low in output audio signal, bartender switches the sony receiver to hear another input and forgets to turn the volume knob down, first.


    Here is what I use here to send signals back and forth from the two dj booths to the main bar feed. I use one at each end with two balanced lines in between. Perfectly takes an rca signal from the sony at the bar and sends it into the mackie 1202 mixer in the small dj booth on stereo channel 5/6. Then an unbalanced tape out rca feed out of the 1202 feeds back in to be balanced to the other box and inputs one of the inputs on the sony. It sounds confusing as I write it, but really works well. Simple enough for bartenders. (sort of)
    http://www.partsexpress.com/pe/pshow...TOKEN=15999537

    In your application, Input your tv audio into channel one, jumper the xlr input and outputs together, and use the channel two rca out to your hifi preamp in. You'll end up with a knob for input and a knob for output. They work well.

    All your looking for is a line-driver.

    Scott.
    One step above: "Two Tin Cans and a String!"
    Longtime Alaskan Low-Fi Guy - E=MC² ±3db

  5. #5
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by boputnam View Post
    Anyone have suggestions for a high-quality two-channel line-amp?
    It's overkill but I can semi-permanently lend you my Adcom GFP 750. It'll do the trick if you have the rack space... I have the rack ears too.


    Widget

  6. #6
    Super Moderator Hofmannhp's Avatar
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    studio pro amp

    Quote Originally Posted by boputnam View Post
    Anyone have suggestions for a high-quality two-channel line-amp? I may not be naming it correctly, but...
    .....
    Ideas...?
    Hi Bo,

    I can offer you different pro studio two channel line amps from german broadcasting studios with transformer coupled balanced in and outs. amplification from -34dB to max level +22dBm.
    It's a PCB with VG-jacket 31pin. Needs a little soldering for the connections and a 24VDC supply.

    names: V372D, V472, V572D, V1072D, V972,...

    V = Verstärker (amplifier)
    3xx = number 3 f.e. is for the company which fabricated it
    x72= means "line amp"
    D= double

    HP
    Please help us save more info about the vintage systems. Let us register your speakers and drivers.

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    Senior Member Ian Mackenzie's Avatar
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    Bo,

    I would use small (tiny) mixer so you can adjust the gain accurately. Ideally it want to be at the TV end to boost from there to preseve the SN. I uses an Yenyk 802 (Behringer) and it works fine, only 6 inches square with 4 inputs.

    Ian

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    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Hey, guys...

    Thanks kindly for the "input"...

    The Mackie 1202 is working really great, I gotta say, and just like you mention Ian, I do the boost at the TV outputs (rather than back by the pre-amp). Don't know if the little distance matters, but I was thinking alike...

    Scott - that device might be the ticket. Rolls has similar gadgets - do these sound good? I mean, are they acceptible quality for this application? One reason I went the Mackie route is the pre's on their mic inputs are not terribly bad...

    And, Widget, I'll take the GFP-750 for a case o' Guiness, minimum!
    bo

    "Indeed, not!!"

  9. #9
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by boputnam View Post
    And, Widget, I'll take the GFP-750 for a case o' Guiness, minimum!
    Hmmm... now a keg in one of those handy bar sized fridges with a Guinness tap would be cool.


    Widget

  10. #10
    Senior Member Ian Mackenzie's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    Hmmm... now a keg in one of those handy bar sized fridges with a Guinness tap would be cool.


    Widget
    Hmmm,

    That sounds like a nice deal!!

  11. #11
    Senior Member SMKSoundPro's Avatar
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    Bo,

    Yes, it does sound great for your application! I used them upstairs above the bar to send a stereo signal from from hifi in my office down the snake into the Big room where my table saw and shop area are. And the beauty is use can send a signal back the other way! No feedback loop!

    No ground loop problems. I was able to tie my office hifi into the larger hifi out in the big room. It works like a champ. Quiet and simple! I found mine on ebay, but partsexpress price is the same.

    Widget,

    I have all sorts of taps, handles, tubing and CO2 regulators in my office to make you one of thos little fridges, or you can use the parts and mount the tap handle on a regular size fridge of your choice. Mount the tap through a hole drilled in the front of the door, like the rednecks do.
    I also maintain all of the refrigeration stuff here at the bar. I'll look to see if I have an extra Guiness handle. We have boxes of old tap handles. All different brands.

    Doesn't bother me. Been on the wagon since '90. 1dayatatime.

    Good luck all!

    Scott.
    One step above: "Two Tin Cans and a String!"
    Longtime Alaskan Low-Fi Guy - E=MC² ±3db

  12. #12
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    There is a company called Radio Design Labs that makes all kind of compact audio interface units. They have a couple of different two channel line amps available.
    Here is their weblink http://www.rdlnet.com/


    Mike Caldwell

  13. #13
    Senior Member jim campbell's Avatar
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    Quote Originally Posted by boputnam View Post
    I hate the risk of someone switching sources from TV to CD without knocking back the gain. Been lucky so far...



    Ideas...?
    im not sure that switching functions without turning down the gain or muting is a good idea even with properly matched components.id insure that anyone with the keys to your system be properly licensed and trained

  14. #14
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    what is your tv audio source? What sounds good depends an awful lot on that. If its no better than the quality of a television speaker output (I'm assuming stereo) you could pad down the speaker output to a line input and have head to spare. If your current audio source is real high end then that's not a good option. You could probably find a PAT 4 cheap on ebay or at a swap meet and they're clean enough that MAC stopped their clinics over them.

    Or you could throw something together with an op amp. When you get it adjusted where you want it stick it in a paper cup and pour epoxy on it. Power it with a wall wart. should be bullet proof.

  15. #15
    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    The winner is...

    Quote Originally Posted by SMKSoundPro View Post
    Here is what I use...
    And it works, great. The ART CleanBOX device did the trick, and without introducing a Ground Loop! Commonly, devices with a AC/DC power converter and two-prong AC plug don't interface well with pro gear, but this one did. Ch1 is RCA in, XLRf out; CH2 is XLRm in, RCA out. I only needed Ch1.

    I was familiar with ART's higher-end tube mic pre-amps - they are frequently used in FOH applications. They sound nice. It seems their attention to quality persists to their consumer solutions, as well.

    Thanks for all the input and to Scott for the final solution...
    Attached Images Attached Images  
    bo

    "Indeed, not!!"

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