Conference napalm::guitar

    Active Electronics lists several kits and components that may be of
    interest in their catalog & carry most in the Westboro store.  I'm not
    certain about mixers, but I know they have kits for power & preamps. 
    They also have several encapsulated hybrid units that basically consist
    of the entire power or preamp section, heat sinks, etc molded in an
    epoxy block.  You add packaging, power supply, controls, and you're in
    business.  Not allthat cheap, but the specs look pretty impressive. 
    Their catalog is free, and the new one should be out by now.
    							joe

    This is not an anser, but a similar request.
    
    Me too I am interested in building a portable amplifier ao +/- 30
    watts.
    
    I live in Europe, comming over to the US from time to time.
    
    If you are requesting catalogues, would you mind to ask for two sets,
    and drop one in the mail for me?
                                  
    My address is Jean-Paul Bergmans @GMO F158
                                  
    Thanks in advance and regards.
         
         

    Re: Basenote
    
    Every audio component I've taken apart has a power supply as the first 
    element in the power distribution subsystem.  Using a mixer as an
    example, a power supply might convert 117VAC, 60Hz, to +12VDC, -12VDC,
    and maybe +5VDC.  I believe it should be possible to take a mixer, remove
    the power supply altogether and replace it with a DC-to-DC converter.
    The converter would accept +12VDC from car batteries and provide the 
    required voltages.
    
    Now, calculating the power required: Is it reasonable to take the 
    naameplate power requirement from the mixer and ratio the amperage
    by the ratio of voltages?  For example, if the mixer asks for 100w,
    then it's looking for slightly less than 1 amp (100w/117V = ~.8amps).
    That means the battery must put out something like 8 amps (100w/12V =
    ~8amps).  Batteries are rated in ampere-hours: a 60a-h battery can 
    deliver 60 amps at rated voltage for at least one hour.  So it appears
    you can run six mixers for an hour on one typical car battery.  In
    practice, I would guess you'll have at least 3X margin, because the
    equipment NEVER runs at nameplate power.
    
    Add up the namepkate power ratings for your preamps, mixers, power
    amps, laser light shows, SuperTroupers(tm), equipment lifts,... ;^)
    to figure out how many batteries.
    
    If a Pignose can scream with four D-cells, you guys oughta be the
    equivalent of the Who at Sullivan Stadium if you use a DieHard.
    
    Happy volting!
    
    Johnny Jupiter
    

	Re: .3

	We did some power checks before our last gig at Harvard Square,
	where we used an 8 ch Sunn feeding a pair of CervinVegas.  The
	Sunn drew close to an amp when we played a thumping bass riff
	thru it at the rental store (EUW, Framingham).

	Because our music is quite folky (two acoustic guitars and an
	electric piano are our only instruments), we figured we'd be
	drawing much less than that during actual use.  That was indeed
	the case, and our run-of-the-mill 12V battery performed fine
	as far as power draw went.

	The only bummer was our invertor that generated a lot of noise.
	Not surprising, since its rated output *is* a square wave.  Yuck.
	Also, I guess the Sunn didn't have a super filtering stage in its
	PSU.  That's what drove me to think about building an amp without
	a PSU (well, I'd still use a cleanup stage, but there would be
	no 60Hz buzz).

	I think it would be less expensive to build than buy a used amp
	and remove its PSU.  I might go the way of pre-build modules
	if the price is not too prohibitive.

	/ravi

	Re: .1

	Thanks for the tip, Joe!  Will check out Active Electronics
	today.

	/ravi

	Jean-Paul,

	I'll pick up duplicate catalogs for you from Active Electronics
	and other places I contact.

	/ravi

    See note 1279 entitled "Wild in the streets". This note discusses 
    
    portable PA, and instrument amps.
    
    The obvious choice for the power amp is to get a discreet automotive
    power amp, which is generally mounted under the seat or in the trunk
    of a car. These are available with anything from 15w/side upto 200+
    watts/side. Since they are designed for automotive applications, they
    are built to take much rougher handling than home stereo amps. They 
    usually have RCA type jacks and handle line level signals from car
    stereo slave units.
    
    Finding a mixing board that can run on dc shouldn't be too hard. 
    Some of the small Boss mixers do.
    
    Radio Shack offers a couple of compact units with a mixer and
    power amp in one box. Some are AC/DC powered, and some are just DC.
    
    Another power source to consider is a motorcycle battery. They are
    about 1/3 the size and weight of a car battery and provide 12v, 6AH.
    
    Mark J
    

    re [.3] - it's not quite as simple as that.  While preamps, and mixers
    might be set up top run on +-12V, Power amps generally require much
    higher voltages, often necessitating expensive transformers.  This is
    especially true of tube amps, where the voltages may be in the range of
    400-600 volts.  Even the encapsulated MOSFET amps I mentioned in [.1]
    call for +- 48 volts.  This is not to say that it would not be possible
    to simply swap power supplies in an existing amp, however, it would
    probably require getting a transformer with 12V primaries and the same
    secondaries as the original, and that might be hard to find.

	How about an address or phone # for Active Electronics. I'd like to
	see what odds & ends are available also.
							Jens

    I personally, have never had much luck with Active Electronics, but I
    haven't dealt with them in quite a while. I recall they are mostly into
    computer hardware, and digital components.
    
    Another electronics supply shop in the area is Stark Electronics in 
    Worcester. They are geared more towards Radio/TV/satellite electronics.
    They are located on Franklin Street. If anyone is interested, I could
    provide directions. They are about 2 minutes from the UMASS medical
    center just off Rt 9. I have dealt with Stark for all kinds of audio
    and video connectors, coax cable, speaker wire, antenaes, etc.
    
    I still believe that you would be much better off using off-the-shelf 
    equipment than to try building your own. Unless you are a pro, I would 
    expect homemade equipment to be unreliable at best. You could probably 
    get a car power amp for around $100, and a decent little 6 channel mixer 
    for about $200, even cheaper if you go used. Even the radio shack self
    contained units would probably be better than home-made gear and their 
    best unit sells for under $150.
    
    Mark J.
    

	Re: .9,

	Active Electronics

	133 Flanders Road, Westborough, MA. 01581. 508/366-8899
	Mon-Fri  8:00am - 6:00pm
	Sat      9:00am - 5:00pm
	Sun      Closed

	11 Cummings Park, Woburn, MA. 01801. 617/932-4616
	Mon-Wed  8:00am - 6:00pm
	Thu      8:00am - 9:00pm
	Fri      8:00am - 6:00pm
	Sat      9:00am - 5:00pm

	/ravi

	Re: .10

	> ... recall they are mostly into computer hardware, and digital
	> components.

	I just picked up their catalog and did a very quick browse of
	their Westboro store.  They seem to keep a lot of digital stuff
	but have a decent stock of RCs, semiconductors, trannys, switches
	and other Shack type hardware, including cases and tools.

	I was impressed by their books - they have a good number of data
	books plus some (so-so) books on audio (home recording, how to
	make a demo tape, etc).

	> ... Stark Electronics ...

	Could you post directions to Stark?  Tnx!

	> ... better off using off-the-shelf equipment ...

	I'm not worried about building the gear - I've been doing that
	for some time.  The preamp poses no problem, it's the power amp
	that is cause for worry.

	What I worry about is reliability and power requirements - I could
	build a sturdier unit using ILP (or equiv) power modules as opposed
	to going off in 2N3055 land.  Powerwise, I agree with you - a used
	hi-power (30W RMS) car amp is probably the way to go.

	Tnx for your feedback (no pun intended)!

	/ravi

    	Stark Electronics Inc.
    	444 Franklin Street
    	Worcester, Ma. 
    	508-756-7136 or 508-756-6047
    
    	From 495, take route 9 west. Drive past Spags and continue up the
    hill until you are directly in front of the UMASS medical center.
    When you get in front of UMASS, get in the left lane, and take a left
    turn onto plantation street. Drive ~1/4 to 1/2 mile down Plantation st.
    and look for Franklin. Turn right onto Franklin and go about 1/4 mile.
    Stark is on your left. Look for satellite dishes out front in their
    parking lot. 
    
    They have about the best supply of switchcraft connectors in the area 
    as far as I know. 
    
    Of course, there is also "You-Do-It" which is right off rt 128 in 
    Needham ??
    
    Mark

    
    	Yes, a little late in the conversation, but what the hey!
    
    	I know that RS has an amp that's one of the best buy's as far
    as "bang for the buck" - it's a 50WPC stereo, runs off +12, with
    a switch mode powersupply. It's $100 I believe. I'd like to get
    one someday, to replace my Proton 222.
    
    	One silly idea I've had was to build a "self contained FM Stereo
    radio station", with a 6 channel mixer, compressor, EQ, etc. Then
    you could just "park the van nearby" with a good car stereo system
    in it and just transmit over _to_ it. (Point the speakers out the
    back doors - you wouldnt even have to unload!) Or, have a bunch of 
    people show up with their "boom boxes" all tuned to *you*. (A little sign 
    says "88.1 FM"...) I bet the sound level would add up quickly -
    you'd just be kinda stuck if there was a "mass exodus" ;')

    	Joe Jasniewski
    

	Re: .14

	> ... RS has an amp that's one of the best buy's as far
	> as "bang for the buck" - it's a 50WPC stereo, runs off +12, with
	> a switch mode powersupply. It's $100 I believe.

	I think I'm going to end up buying their 40+40 amp ($ 79).  The
	power rating is probably peak music power, so it's probably 30WRMS
	per channel, which is more than enough for us.

	> ... have a bunch of people show up with their "boom boxes" ...
	> ... you'd just be kinda stuck if there was a "mass exodus"

	Can you say "Disturbing the Peace" ? :-)

	/ravi

RE < Note 1694.14 by ELESYS::JASNIEWSKI "This time forever!" >

	What's the difference between this kind of amp and the kind for Pro 
Audio applications?  If I supplied the proper DC power, would it perform the
same?  Would it be a cheaper alternative to buying a small rack-mount "pro"
amp for, say, a small monitor system on stage?

	Dan

    
    	Hi Dan,
    
    	Well, the key here is *if* you supply the proper DC power. The
    50 watt stereo amp from RS is going to draw, oh, 10-20 amps from
    the +12 volt power source! Do you happen to have a 20 amp 12 volt
    regulated power supply?
    
    	I would say that the main difference between this kind of amp
    and one for Pro Audio applications is in the construction and the
    materials used. I mean, at $1 / watt, they really have to be printing 
    them out like postage stamps! I imagine that they do exactly what's 
    claimed for them; it's just that they (have to) do it ... cheaply.
    	
    	Personally, I would trust something like the RS amp if I were 
    doing a performance in Harvard Square, or a beach party, or around
    a campfire - where the +12 volt power attribute of that amp makes it 
    the most suitable. If I was getting up on stage where there was
    plenty of AC power available, I'd feel better about using something
    like a Phase Linear 100, than one of the RS amps with a big 12 V power
    supply.
    
    	Joe Jasniewski

    
    	Regarding my last entry;
    
    	That they are "printing them out like postage stamps" may actually
    be a "good thing" in terms of the reliability of the RS amplifier.
    A lot of that is due to the manufacturing process and the technology
    used to build it - large scale integration, surface mount components,
    automated construction processes, etc.
    
    	For example, a 100 watt computer power supply built by some
    far east manufacturer has a reliability (or average time till it
    breaks...) measured in the hundreds of thousand-hours of operation.
    100K hours is something like 10 *years* of continuous operation.
    They also print these things out like postage stamps, they *have*
    to be very cheap, so that the computer they power can be competitively
    priced.
    
    	It is feasable that you could use these RS amps for doing sound
    reinforcement work, and have a very reliable setup. The big problem
    is as I mentioned earlier, the mega-amps of current these amplifiers
    can take, at 12 volts DC power. To run two of 'em, the powersupply
    will be as big as a 100W stereo amplifier -
    
    	Joe

Thanks, Joe, for the comments.  I take it, then, that a 20 amp 12 volt power 
supply is not something most people can find around the house...  I do have a
+/- 12 power supply at home with screw-on terminals, but its probably not that
big.  I was just wonderin'.

	Dan

    Thanks Ravi, I got the "Active" catalogue today.
    
    Jean-Paul