Thats right, and I was expecting this to be a bridged unit. I even talked about that as I was opening the case. Note that was cut out as I had to eat a little crow when I saw the layout.

@@12voltvids I want to ask. Is it ok if I download my favorite videos of yours soley for my personal viewing? I never intend on posting them anywhere online.

None!

Yes i know. We all had them at one point. And the home speakers in the back seat. That one untill a kid crashed his car and an unsecured speaker flew out if the car and into the car that hit him just missing hitting a baby in the back seat. Then the police started issuing tickets for unsecured home speakers in the back of cars. I put 2 8" woofers in a wood box and secured it in the trunk behind the back seat. They did the job intended.

​@12voltvids how would they even enforce this have a road block checking for speakers 😆

That link to the old catalogs is a trip down memory lane.. I used to love flipping through those catalogs.

I repaired one of these a while ago. It’s just output transformers and no switching power supply. I also own those other amp you mentioned and they do have switching power supplies and no output transformers.

Car speakers back in the 1970's were over 90 db/1W...often closer to 100! You could get painfully loud audio from 4 speakers and a BTL (bridged) car amp, which provide about 12W RMS (like this booster).

See the top right corner of page 64 of the 1987 Radio Shack catalog. This unit was made in 1987, not 1977. It also sold for $79.95 back then.

I had the audiovox 60wpc amp and it was a true 60 that could be bridged to 120 mono. Ussd a dc-dc converter. Got that one in 1980 i believe.

Well i never worry about a dead battery I just plug my car it.

This served me well in my first old car. Got this when I was probably 18. Took it out when I upgraded to something better. Looking through old boxes stuck in storage locker.

@@12voltvids my father had a really nice top of the line Alpine alpine head unit and infinity speakers in his truck from a high-end car stereo dealer that he did tax accounting for. In turn, he got to pick out a really nice system as payment. Awesome head unit, but only 4 watts per channel. I installed one of these boosters in the truck everybody is like NO! Realistic with your dad’s alpine setup? Then I turned it on...best sounding stereo system in the entire high school parking lot :). What a day of joy. So many fond memories of that system, I still have the old Alpine head unit.

@@danielknepper6884 yea too much $$

No way one of those boosters could keep up with what you had. You outsmarted them all.

It does get smoking hot.

These things were often installed under the dash on the passenger side. I wonder how many people had their legs burned.

@@FluxCondenser they didn't get that hot. The heat sink was inside the case the hit air exits the top and up under the dash.

12voltvids Ah, so the outer case must do a good job insulating the heat if it gets as hot as you say. Having the heat sinks exposed to the outside would have helped cool things better and not doing so probably led to the high numbers of failures reported with these boosters. They may have made the trade-off to protect people from the high heat given that the typical way these were mounted made it more likely for there to be skin contact.

@@FluxCondenser Well back when these were around cars were a little bigger so your legs wouldn't be anywhere near the unit. You want to talk hot, try riding a Harley in stop and go traffic on a hot day. The engine about 450' right between your legs.

No car audio back in the day was. Not until they started using smps to get the voltage up.

Right. The 20 watt used 2 10 watt ic amplifier chips driven out of phase one for the + lead and the other for - speaker lead. BTL output.

Imaginary power handling specs - most common in car stereo world, boom boxes and HT world. Sony AVR receiver, or something similar, with 7x100W @0.01THD stickers - sure in the wildest wet dreams.

I opened one of the JBL cheap car amps - they made better ones 40yrs ago. But generally most car amps were built to survive the heat not to sound good. I bet if someone would put the 3886 IC modules into a box with decent switching car power supply the thing would better than many car amps. Imagine a real separate hi-end home amp, even something like Parasound, Bryston, NAD inside car amp - it would be all car audio reviewers favorite amp.

a lot of older auto sound gear was rated in Peak output, instead of RMS, which resulted in highly inflated output figures.

Yes that would also work however I believe they went with this design as if allowed the 2 outputs to operate as a more of a class A design to reduce distortion.

No i don't sorry.

Yes they work similar to how tube amps used the output except the tube amp was the opposite. Voltage to current. The tube side high impidence the speaker low. The output transformer was a center tapped primary. This has separate primary winding for each output.

Yes an unusual way to do it. Audiovox also did it like this in their early stuff.

@@12voltvids I had an Audiovox that could have been this things cousin. Bought it with head unit and speakers in the Navy Exchange on board ship. We needed something to spend money on while at sea, stuff for your car back in port was always cool, or a stereo for the home, cameras, drum sets cheap and good. Lots of that Vietnam-era gear came home from Army/Navy Exchanges all over the Far East and Europe too!! We were so spoiled!

The problem with that is I forget to turn it off silent mode and have missed important messages. Viberating mode is no good because I never feel it when it goes off in my pocket. I turned my work phone to silent during a meeting, and forgot to switch it back for 2 days. The boss was pretty pissed when he was trying to get hold of me and my phone was going to voicemail Of course I wasn't getting those notifications either.

@@12voltvids that indeed remains a problem...

Oh they were bad.

Worth at least 80 bucks then. Word your advert right and the idiots will pay.

Ever see Dave's take on replacing a box fan capacitor. Try kzfaq.info/get/bejne/pb6hbNlmsdG9ZJ8.html.

Not a bad amp, hard to get the replacement parts. Interesting circuit - what I remember from faith memory.

I was pleasantly surprised when I opened it and saw the 2 output transformers. This one might be one to do a deep dive on if I can locate a full schematic for it. You are correct with the distortion more closely resembling a tube amp when it clips and all that other magic that happens in the audio output transformer.

@@12voltvids I'm sure that the output transformer circuit design was there way of increasing the output power of a solid state amplifier as opposed to fitting a noisy dynamo to get the required voltage in older vacuum tube car radio's way back when! I know that when the transistors were first being used in the early solid state amplifiers, engineer's were still using transformers on the outputs because they were so used to using them in vacuum tube designs. Apparently those early solid state Amplifiers also sound amazing but I have never heard one due to them being extremely rare! While transformers are expensive in comparison to capacitors, over the long run, if a capacitor coupled output amplifier had it's capacitors fail, it took your speakers with them adding to the cost! While transformers on the other hand are initially expensive, would never require replacement of it or the speakers it's driving! Kinda cheaper in the long run! More up time to enjoy that beautiful transformery sound LoL. On another note, I wonder what the impedance is on both sides of those output transformers?

@@PeterMilanovski Correct. Before car audio went with the smps / dc-dc converter / chopper design the voltage was limited to 12 volts. By using a dual primary transformer as in this setup you effectively give yourself 24 volts to play with. How, well if we refer to the diagram one winding is run directly to the 12 volt rail, with the transistor between the other side of the winding and ground. The other winding, which is 180' out of phase with the first is wound between ground and the collector of the transistor with the emitter going to the B+ rail. On the positive half of the audio signal, one transistor conducts and applies a positive voltage through the transformer resulting in a "North" magnetic field being created. When the audio waveform goes to the negative side, the other transistor goes into conduction. Remember that the other primary is connected to B+ and the other end of it is going to the collector of the negative transistor collector which has it's emitter grounded, so as the transistor goes into conduction it will pull the voltage down on the transformer winding introducing a "south" magnetic field in the core. When there is no sound both transistors are slightly driven on, so there will be a little current in the primary, but since one primary will be producing a north field, and the other a south field, the 2 will cancel each other out. The secondary has many more turns of wire so a higher voltage lower current is output. What might be an interesting experiment to do on camera is to see how much open coil voltage will be produced in the secondary. Of course that is always hazardous to the transformer, because these high voltages of they get too high can arc through the insulation and blow the transformer.

@@12voltvids that would be a great experiment! But instead of doing it at the rated voltage, you can get away with it at a lower voltage from your bench lab power supply! Then with simple mathematics you can just double the figure for example if you only fed 6.5 volts in to get the proper rated output voltage. Also, it would great to put on a 4 ohm dummy load and measure the output voltage of a 1khz input signal to work out it's actual power output before clipping and maybe just into clipping as well because it's transformer coupled and it should technically still sound very good so that we can see how close the output power printed on the face of the unit comes to actual measured values! Maybe the advertised output rating is for 4 speakers being driven? Which probably means that the output of each channel are paralleld and bring the output impedance down to 2 ohm's... Usually vacuum tube amplifiers have separate taps on the transformer output for different impedance speakers, I wonder what effect it has on it's output and transformers? Hmmm there's a lot more to this graphic equaliser booster than what meets the eye! Well if you do decide to do a follow up video, I will be watching with anticipation... It's almost like taking a peek into the minds of the people who were working to design something that would perform to the budget that they had to work to.. I love this kind of stuff, some people just don't understand how much can be learned from a product, even if it was not as good as what they had. This unit actually had some pretty good engineering put into it. They could have used a transformer to step up the voltage in the power supply like every other car amplifier on the market today but instead chose to go with the transformer at the output stage, that way, they can consume more current through the transistors to get the higher output levels. I get what they were thinking, the transformer at the power supply stage would need high frequency switching which can induce noise like distributer wine (remember that abomination lol), while at the output stage, they are only dealing with AF Signal.. much quieter. Kind smart if you think about it. You can even replace the power amplifier with something more modern and still keep the output transformers if you really wanted to. But I like it as it is 👌.

No because the transformer will remove the sharp edges that blow the speakers. So these may not be the best sounding but they are relatively safe to speakers.

Service Manuel

I drove a pair of 6x9 3-way speakers and a DVC 8" sub with passive crossover coils using this booster in my 1984 Olds Delta 88 and got very decent sound for the time and for my very limited budget

I still own this booster

Volume is not up, but the mic is sensitive.

No, it isn't true that the sound goes in through those transformers. If you watch and listen to the video, he explains how it works.

12-1959

12-1959