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Old 21st January 2005, 05:56 AM   #1
nola000 is offline nola000  United States
diyAudio Member
Join Date: Jan 2005
Location: New Orleans
Default HELP! Need Amp Info

I recently purchased an amp off an ebay member, I can't find any information on this particular amp any where on the internet...not even a mention! I know its a long shot, but I was hoping someone on this forum would have some knowledge about this rarity.

Its a 4-channel amp, it says; JENNINGS RESEARCH INC., and THE AMP on the front. It has a push button power switch and two push button switches that say "Monitor" and "Remote". On the top it has an "operational schematic" (I'll draw it out if you think it would help) and the following figures:

POWER OUTPUT : 200 watts per channel into 8 ohms
FREQUENCY RESPONSE : +/-0.25db, 20Hz to 20kHz
DISTORTION : No More Than 0.25% THD or IM
NOISE LEVEL : -101db referred to rated output
INPUT IMPEDANCE : 25K ohm nominal
INPUT SENSITIVITY : 1.0 volt rms for rated output
CROSSTALK : 80db down at 1kHz

I was also hoping someone could tell me these 4 things(if needed I can open it up and tell you whats inside) :

1. I bought the amp for $60, was that a good deal?
2. Is this a good amp? Enough power for my 14x14 living room?
3. VERY IMPORTANT : How many watts would it put out at 4ohm?
4. What can I do to improve it? What areas is this amp weak in?
5. What is the power output in bridged mode?
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Old 19th September 2010, 10:58 PM   #2
nola000 is offline nola000  United States
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Join Date: Jan 2005
Location: New Orleans
I posted this forever ago, but I still have these amps and I have pics now. I have a bunch of questions that have never been answered about these mysterious amps and I thought that the smart people on this forum would be the best qualified to answer my queries. I hope someone can help me out on this, here goes...

1. What the hell are these and should, how and what result would I get from adjusting them. There are maybe 5 or so of these in identical positions in the circuit boards of both amps but the adjustments are different on them in both amps. A couple of them can be turned with a flat head screwdriver from the back of the amps without taking the covers off =

2. Can someone point to some components on these amps that I could or should replace to improve sound or output. I read about caps dying out. Which caps should I replace. Forgive my ignorance. Describe them for me using this picture. Im hoping to get a lesson in hi-fi circuitry modding. =

3. What exactly is meant by this? Ive always just left the "LINE" cord plugged into the wall and let the "CONTROL" cord hang free. Im assuming I could leave the "LINE" cord plugged into the wall and plug the "CONTROL" cord into the switched power outlet on the back of my preamp so I wouldnt have to manually turn my amp on and off. Is this correct? =

4. These amps make my speakers pop when I turn them on or off regardless of whether or not I turn off the preamp first or last, adjust the volume or unplug it from the wall. The order is - turn off amp - 3 second delay - suction pop from my woofers. When I turn it on the pop is instant but more audible than visual(and less scary). Anyone know what changes I can make to it to stop this behavior?

5. I have two of these exact amps. But there are subtle differences. I dont really know what Im looking at here so I was hoping that one of you really intelligent electrical engineer types could help a brotha out.

A. In this set the difference is this black rubbery stuff on top of what looks like big blue capacitors.

B. Whatever purpose this serves, its different between the two. Maybe its just a different brand.

C. The inputs are different. What the hell is up with that? That is the only noticeable difference from the outside without cracking open the tops(except the lack of a "CONTROL" cord on one).

D. I also noticed that in various places around the inside of the amp with the RCA inputs that certain lengths of wire are of a heavier gauge than the amp with the 1/4" jack inputs. Im wondering if this has something to do with the lack of the "CONTROL" cord on the amp with the 1/4" jack inputs. The amp with the skinny wire looks to be about 20+ gauge the heavier wire looks to be about 18 gauge. This is the best pic I could get. Look at the red wire next to the black with the female spade connector on it in both pics.

E. Those big blue caps appear to be different in each amp. They may be the same value just older/newer models. Both are Mallory brand.

F. The top white relays, at least they LOOK like relays, are of a different value. One say 120V the other is 24V. Again might have something to do with the lack of a "CONTROL" cord in the 1/4" jack input amp. I would like to modify that amp to have a "CONTROL" cord as well. How would I go about doing that?

Im really noobtacular when it comes to electrical components and I really would appreciate a hands-on, or "pictures-on" lesson in modifying acoustic electronics using my two amps as test dummies. If anybody lives in the New Orleans/Northshore area of Louisiana and wants to trade my carpentry services for a little 101 on this subject Id be game, if not then some responses from this forum for the above questions would be great as well.

Thanks -

Last edited by nola000; 19th September 2010 at 11:10 PM.
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Old 19th September 2010, 11:46 PM   #3
nola000 is offline nola000  United States
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Join Date: Jan 2005
Location: New Orleans
Almost forgot.

Anyone know what I should do about replacing this bulb in my Hegeman Hapi 2 power button?
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Old 19th September 2010, 11:54 PM   #4
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Join Date: Jun 2010
Hi! I'd like to start with, I'm not an expert that you speak of, but I might could help you anyway.

It looks like one of the amps has been worked on. There's one that looks cleaner and has spade connectors that have plastic crimps on them. That seems to have been played with. Maybe the guy took it on himself to replace some of that wiring, that's my best explanation.

As far as helping an amplifiers sound, Caps might do you some good. I would suggest following the rca inputs around and replacing caps that directly touch those, probably some of the very first caps the wires come in contact with on the board will be the most audible. I suggest Polypropylene caps of the same size as you can make out on the current caps.

The adjustments are most likely the bias adjustment and I wouldn't play with that until you understand what it does.

Next thing to do would be to replace the ceramic caps (big disc shaped ones) with poly's as well. Not having a schematic is really going to hurt you cuz it'll be hard for someone to differentiate from a picture exactly what to do. If I were gonna try to work on this amp, I would most likely try to draw a schematic from the board before I started so I knew exactly what I was changing.

Sorry I'm not much help, but I don't work on old stuff. I only know what I've read, and I've read similar things to what you want to do. Replace caps, replace carbon resistors with metal film. I don't have a feel for how much difference that actually makes though.
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Old 20th September 2010, 12:08 AM   #5
nola000 is offline nola000  United States
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Join Date: Jan 2005
Location: New Orleans
If I get few more posts on this topic then Ill take the time to try and map out the circuits.
Big disc shaped ones? Which ones are those?

Last edited by nola000; 20th September 2010 at 12:15 AM.
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Old 20th September 2010, 03:29 AM   #6
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Join Date: Jun 2010
Ceramic caps are the greens ones around the blue dial in one of your first pictures.
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