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Chip Amps Amplifiers based on integrated circuits

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Old 10th March 2007, 11:05 PM   #1
male is offline male  United States
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Join Date: Oct 2006
Default (not that you care, but...) Introducing the Quadularity

In a previous post I mentioned building a quadraphonic chip amp from my junkpile. The chips I ended up using were four HA1384's (1ch-BTL). I actually found two TDA7377's (2ch-BTL) that I would have liked to have used (much external smaller part count) but I clumsily broke the pins off one trying to remove it (from a through-hole board). I got the second one off with a blow-torch--perhaps I'll find a use for it in another project. (note to self: always use blow-torch to remove parts from multi-layer PCBs!). In any case, the HA1384's are perfectly suitable. It took me longer to construct the chassis than to actually build the circuit.

The top of the chassis is a curved piece of 1/8th inch thick aluminum from an discarded phone-booth (remember those?). The sides are walnut-veneer facing from an old RCA console stereo and Pentium II slot-1 heat sinks. Mounted to each heatsink are two HA1384s and their associated circuits (on perfboard). Four tri-color jumbo LEDs on the front panel indicate the power status, mode (quad/stereo) and the signal level--a separate circuit drives the four level LEDs and is tapped into the speaker outputs. One knob controls the master volume for all four channels; this was achieved by gluing two stereo ganged open-backed audio-taper pots together in a mating posture. Another knob reduces the level of the rear channels (fader). There is no balance control. Two switched phone jacks permit the use of my Pioneer SE-Q404 quadraphonic headphones (when headphones are connected the amps are run in single-ended mode). An ON-OFF-ON DPDT switch controls the mode: QUAD-OFF-STEREO. In STEREO mode the two outer-most LEDs remain off and power to the rear-amplifiers remains disconnected.

The circuit itself is relatively uninteresting. As with all chip-amps, the datasheet application note is hard to improve upon. I did, however, use fairly large capacitors in the power supply to compensate for the somewhat underrated power transformer.

I've been listening to the finished amp for a few weeks now and I'm quite pleased with its performance. The noise level is completely inaudible compared to my previous system--important for my application. My speaker configuration is near-field (for mixing/mastering) and I hardly need 300 Watt amp when the front speakers are arms-length away from my ears. The amp inputs are being driven by an M-Audio Delta 66 computer interface at +4dBu (the inputs of which are themselves connected to an AKAI 1730D-SS Quad open-reel tape deck). The (pictured) Sansui RA-500 stereo spring reverb unit is used primarily to provide zero-latency reverb'd monitoring with the Delta 66--and it also looks pretty.

A still photograph can't really do the Quadularity's flickering magic-eye-like level indicators justice, but I've included some nonetheless.

Oh, I almost forgot to mention. Every part of the Quadularity is recycled except for the solder and the heat-sink compound. Let's see if memory serves... The knobs and rear-panel aluminum sheet are from an H.H. Scott. The two stereo pots ganged together for the master volume are from a nameless Karaoke machine. The power/mode switch is from the crossover network of some huge vintage EPIcure omnidirectional floor-standers. The HA1384 chips themselves are from a Jaguar car-stereo. The side panels and heatsinks have already been covered. The switched headphone jacks are from two different GE stereo systems. The power transformer is from another Karaoke machine. The bridge diode block is from a 12V battery charger. The jumbo LEDs are from a ghastly Christmas lawn ornament. The IEC jack is from a computer power-supply. The input RCA jacks and speaker terminals are from an AIWA 5.1ch receiver. The various wires, resistors and capacitors are from the bottom of my junk-pile. And, of course, the 1/8" aluminum sheet for the chassis top and bottom are from an old phone-booth. Total cost: $0.

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Old 11th March 2007, 12:31 AM   #2
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Join Date: Mar 2004
Location: Arkansas
Hey Hippie!

Seeing this thread, I started having an In-A-Gadda-Da-Vida,
Sock-It-To-Me, Psychedelified, Flacid-Acid-Flashback Man!
Ya dig ?

All because I too used to have one of those Super-8itchen'
Sansui ReReReverb'berbs brought back from the Vietnam PX!!!

The Funkydellic-Rainbow, Acid-Trippin' display was like Totally Far-
Out-Man.
Outta-Sight, In-The-Groove and On-The-Move, compared to them
PunTang-Twang sounding pioneer reverbinators, which were
kinda BOSS too, but I just couldn't Dig the Mellow-Yellow Bongwater
Green Screen Man.

I also had some very similar Pioneer SE-50 headphones.
That was a tough act to drive because of their low 8 ohm
impedence. Still have my Pioneer SX-2500.

Peace, Love, Dope!
- head_spaz

You can carry a bucket,
___You can carry a grudge,
______But you can't carry on,
_________'Cause here come da judge,
_____________Here come da judge...


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Old 11th March 2007, 12:59 AM   #3
male is offline male  United States
diyAudio Member
 
Join Date: Oct 2006
Quote:
Originally posted by head_spaz
[B]Hey Hippie!

Seeing this thread, I started having an In-A-Gadda-Da-Vida,
Sock-It-To-Me, Psychedelified, Flacid-Acid-Flashback Man!
Ya dig ?

All because I too used to have one of those Super-8itchen'
Sansui ReReReverb'berbs brought back from the Vietnam PX!!!
I dig. I used to have an RA-700 reverb (pretty much identical, but with a slightly different display) but I got rid of it. Very good discrete spring reverbs. All plain ol' C945's inside, if I recall, but they still sound very clean. A ghetto Quad trick is to Y the front channel inputs and send them through the RA into the rear inputs. Not quite Pro-logic, but it's effectively what the majority of pop/rock quad mixes are at bottom.

Quote:
I also had some very similar Pioneer SE-50 headphones.
That was a tough act to drive because of their low 8 ohm
impedence. Still have my Pioneer SX-2500.
Ah, those are the white ones, right? AFAIK the SE-Q404's are 32 ohm--that's what I designed my circuit for, and they sound perfect with it.
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