Even semiconductor manufacturers get things wrong. I copied the errors from ON Semi without looking at them:

 

If the speaker is 4 ohms (common for a car speaker)

This is what is used now, 4 ohms. But when the Mindblower was in use the commonly used speakers in a car were 8 ohm, I know this as fact, from putting in many back in the day. you also keep talking about "distortion" in this thread, you don't seem to understand that when these Mindblowers were in use, distortion wasn't even a thought in peoples minds at the time. This stuff was never intended as being "audiophile".

 

Your right shortbus. I don't even know how to explain to someone what it was like buying them, installing them, and then cranking them up!
and yes I used an exclamation mark in there.

 

You have to have been around AG for years to understand. He is an audio purist, doesn't like distortion and can hear the slightest amount of it.

 

If I decide to change up components can something like this be used?
https://www.mouser.com/Search/Refin...MI67e7g-P73AIVjbrACh2vggFtEAAYASAAEgI48_D_BwE

It says 100W

 

You have to have been around AG for years to understand. He is an audio purist, doesn't like distortion and can hear the slightest amount of it.

To be fair, regardless of your opinions on distortion, there's the issue of misleading descriptions, inaccurate specs, whatever you want to call it.

If someone suggests an amplifier design and claims 100W output, but it's clearly only capable of 15, it's fair to point that out, repeatedly if necessary.

No one would question this behavior if we were discussing, for example, power supplies. If someone posted plans for 12V, 10A power supply, but it was clear from the schematic that it could never deliver more than 11V and 5A, they'd get called out every time.

Why should it be any different with audio?

Don't get me wrong, I know you can crank a stereo up until there's audible distortion and a large number of people will be glad to have the volume, with no regard for the distortion. Buy/build whatever you want, and use/abuse it however you want - those are personal choices. But as soon as you start putting numeric specs on things, then those numbers have real meanings. I applaud AG for trying to keep the numbers honest.

My personal experience with these confusing, misleading wattage claims from manufacturers was 20+ years ago shopping for a home stereo receiver while I was in college. Circuit City had a dozen or more "100W" receivers around a certain price point, all of which sounded "fine," coming from Sony, Pioneer, JVC, etc. At nearly the same price point, they had a Harman Kardon. It sounded noticeably cleaner, crisper, more gutsy, more powerful. The sound didn't change noticeably as you turned it up, like on the other receivers. So that was my obvious choice. I still have, and love, that receiver. The twist is that it only claimed 35W power.

How could it be so much more powerful, but have specs indicating it was so much less powerful? Misleading distortion specs. I don't remember the exact values anymore, but it was something vaguely like this: 100W at 1-2%THD is actually a weaker amp than 35W at 0.1%THD. Any power rating is only meaningful if you know what distortion level it corresponds to. A more honest manufacturer may deliver significantly more power while claiming much less, because they're quoting clean power, not heavily distorted "power."

 

Picking parts at random gets you more problems.
The first listing on the datasheet for the TDA7293 amplifier IC says, "Minimum supply is +/- 12V (24V)". Where will you get 24V in a car or truck?
Powered from 24V the output power is about 14W into 4 ohms.

The output is 100 Whats (severely distorted) with an 80V (!) supply and an 8 ohm speaker. You need 6 motorcycle batteries to produce the 80V and 8 ohm car speakers are rare or not available anymore.

 

I think what shortbus and I are saying is that some people just don't pay attention as much to it ebeowulf.
I to applaud AG for being honest about wattage and even teaching me what RMS is.
https://whatis.techtarget.com/definition/root-mean-square-RMS
Still don't fully understand the math and how to calculate it correctly though.
I also have known for years that what is on the box is a lie. manufacturers inflate wattage to sell a product and get your attention in an ad and on the box. I to still own a (old school) pioneer 500W house system. It only has 4 speakers to it and I would put it up against some small bar sound systems in a minute. It's so loud it shakes the house. Bet if they rated it nowadays it would easily be mistaken for 1500W, 2000W system. Bought a RCA RT2911 a few years ago because it had three HDMI inputs on it for my bedroom. My 55" Hitachi TV is almost as loud as it is and the RCA said 1000W. The pioneer puts it to shame. I VALUE and APPRECIATE everyone on here for even taking the time to answer my post, much less put up with my inexperience and total lack of knowledge of electronics. AG, shortbus, MrChips and ebeowulf and everyone else I would still be looking at my project in total confusion if not for you all. AG is a little rough on me but I do understand why. As he pointed out and I do listen or rather read: You need to learn the math, you need to understand how components work, you need to read the tutorials, OHM's law. and everything in between and work hard at it. I'm trying AG, just don't give up on me and keep pushing. I truly want to learn.

 

The first listing on the datasheet for the TDA7293 amplifier IC says, "Minimum supply is +/- 12V (24V)". Where will you get 24V in a car or truck?

https://www.amazon.com/ELECTRONIX-E...7008&sr=8-10&keywords=12+to+24+volt+converter

Powered from 24V the output power is about 14W into 4 ohms.

Isn't that about what the Mindblower actually put out?
Just reading on how other people done it AG:
https://xtronic.org/circuit/amplifi...93-200-watts-rms-total-includes-power-supply/
I would only need one side of this.

 

The cheap Chinese voltage booster is made for a golf cart and appliances like lights, not to power an audio amplifier. It oscillates to boost the voltage and the oscillating frequency might produce a whining sound in the amplifier output.

Someone said the MindBlower maximum output power was 30W but maybe 15W of audio and another 15W for distortion since they did not say how much distortion.
ALL ordinary car radios today produce 14W or 15W per channel (at low distortion) because the amplifiers are bridged.
The stereo TDA7293 amplifier product is powered from AC electricity like any home stereo system. Do you have a really long AC extension cord that you can drag behind your truck?

 

If I came to where you work and bought a 100W single channel amp and bolted it on the bottom of a speaker then slapped a Mindblower label on it would that be OK?... … …

 

Work? What is that? Oh yeah, I worked before I retired a long time ago. Now I do whatever I want whenever I want.

 

To be fair, regardless of your opinions on distortion, there's the issue of misleading descriptions, inaccurate specs, whatever you want to call it.

If someone suggests an amplifier design and claims 100W output, but it's clearly only capable of 15, it's fair to point that out, repeatedly if necessary.

No one would question this behavior if we were discussing, for example, power supplies. If someone posted plans for 12V, 10A power supply, but it was clear from the schematic that it could never deliver more than 11V and 5A, they'd get called out every time.

Why should it be any different with audio?

It's not, plain and simple. But it's still done today both with stereo and power supplies, sorry to say.

But one thing being forgotten in this is that when the Mindblower was sold, very few cars had 'stereo' or FM for that matter. And the cars weren't as quiet in the interiors as today. Even home audio wasn't very sophisticated like today. And most people couldn't tell distortion from the normally expected sound.

And instead of trying to help Berzerker, we're trying to change his mind. He didn't ask, "how can I make this sound modern?" He asked, "how can I reproduce this?" As a car guy, I know some guys only want things in their cars that duplicate or mimic what was available when the car was made or popular. This is why at some of the bigger car events you see guys with the add on air conditioners, that are mounted on one of the side windows, little more than a portable 'swamp cooler'. Practical? No, but what was available at that period of time.

 

It's OK shortbus, I am a grown man. I just had to poke fun at AG. Can I ask AG? Do you collect things? You know like some people collect hats or shoes, or it could be anything. It's kinda like that? I don't care that it's only 30W or 15W (whatever). It was like an obsession to me. All my life I was in machining but this stayed on my mind so much I've kept a pair of them all these years. I'll find a 30W-50W tut or schematic somewhere and I'll start there. Yes I know it won't actually be that much wattage but it will give me knowledge of how it works. Yes I would love to be able to make one that has 100W (My own design) but I think that's a little while away.

 

It's not, plain and simple. But it's still done today both with stereo and power supplies, sorry to say.

But one thing being forgotten in this is that when the Mindblower was sold, very few cars had 'stereo' or FM for that matter. And the cars weren't as quiet in the interiors as today. Even home audio wasn't very sophisticated like today. And most people couldn't tell distortion from the normally expected sound.

And instead of trying to help Berzerker, we're trying to change his mind. He didn't ask, "how can I make this sound modern?" He asked, "how can I reproduce this?" As a car guy, I know some guys only want things in their cars that duplicate or mimic what was available when the car was made or popular. This is why at some of the bigger car events you see guys with the add on air conditioners, that are mounted on one of the side windows, little more than a portable 'swamp cooler'. Practical? No, but what was available at that period of time.

Totally understand.

Sorry, didn't mean to steer Berzerker away from anything. I'm all for having a good time recreating a circuit that brings you joy.

I was only trying to make a point about terminology, measurements, lingo, specs, etc, not say what circuits or methods should or shouldn't be used.

As for learning, copying, and recreating this circuit, I personally think this is a big leap for a first protect. It's jumping straight in with a novel, rare set up that's poorly documented. It's hard enough to learn traditional, well documented, standard amplifier architectures for which parts are readily available. Learning, copying, optimizing, and building this unusual setup, which will require custom made parts, as a first project seems like an exercise in frustration for everyone involved.

I actually think the circuit seems pretty clever and interesting. It's not that I think it shouldn't be explored, it's just that I think some significant intermediate steps are in order.

I would strongly recommend going through some standard tutorials, building and/or simulating at least one dual supply audio amplifier, and one single supply audio amplifier (different biasing methods and requirements) in order to get familiar with the basic methods and terminology. It'll be much easier to understand the oddities of this circuit from a foundation of basic amplifier knowledge. I'm not saying you have to put piles of money into multiple high power amps - these could be headphone amps, line converters, buffer amps, etc.

I hope I don't sound negative or discouraging; that's not my intent. I'm just trying to encourage a recipe for success. No-one expects to learn calculus before they learn arithmetic. Similarly, no-one should expect to understand this circuit before understanding the basics of AC signals, bias, active transistor regions, and other fundamental audio amp concepts. Learn those first, then apply that knowledge to this project.

 

And instead of trying to help Berzerker, we're trying to change his mind. He didn't ask, "how can I make this sound modern?" He asked, "how can I reproduce this?"

He wants to re-manufacture this old thing. Then he want to sell lots of them. To Who?

A custom-made input transformer and a custom-made center-tapped speaker or a custom-made output transformer would make a VERY expensive lousy sounding sound system

It must be understood that modern ordinary car radios are MUCH louder today, maybe louder that the old MindBlower.
Modern amplifiers have much less distortion and a flatter frequency response than the old ones because they have lots of negative feedback and do not use transformers.
The MIndBlower amplifier had no negative feedback and had one or two transformers to mess up the sound.
Modern speakers sound better than the old crap too.

 

Fleetwood Mac was on TV last night. It said 1982. They sounded much better than long ago so I called my wife. She said look at them, it is not Fleetwood Mac, it is a modern band playing the old songs really well. The TV guide said 2018.
Why did they sound so good?
My amplifier and speakers are modern. Not lousy old stuff.
The recording equipment is modern. Not lousy old stuff.

 

I would strongly recommend going through some standard tutorials, building and/or simulating at least one dual supply audio amplifier, and one single supply audio amplifier (different biasing methods and requirements) in order to get familiar with the basic methods and terminology. It'll be much easier to understand the oddities of this circuit from a foundation of basic amplifier knowledge. I'm not saying you have to put piles of money into multiple high power amps - these could be headphone amps, line converters, buffer amps, etc.

Yea I thought about buying one of those DIY kits you see all over the internet. You can get one for like $10 - $20 bucks to learn. I am still reading tuts and watching videos, here and other places as I stated before. I don't think anyone here learned what they know over night.

Fleetwood Mac was on TV last night.

I watched ELO the other night (Live on stage) didn't catch when it was from. Had everything in my room cranked up and loved it.
And ebeowulf I didn't think it would be quite that hard to replicate. I mean it's already been designed. I figured I would just have to change a few parts for newer ones (?). And yall haven't discouraged me, just made me give it a second look and try to figure something else out.

 

Yea I thought about buying one of those DIY kits you see all over the internet. You can get one for like $10 - $20 bucks to learn. I am still reading tuts and watching videos, here and other places as I stated before. I don't think anyone here learned what they know over night.

I watched ELO the other night (Live on stage) didn't catch when it was from. Had everything in my room cranked up and loved it.
And ebeowulf I didn't think it would be quite that hard to replicate. I mean it's already been designed. I figured I would just have to change a few parts for newer ones (?). And yall haven't discouraged me, just made me give it a second look and try to figure something else out.

The devil is in the details... especially when some parts won't be direct substitutes. I think you're going to have to understand the circuit a little better in order to do a reboot.

If every part were currently available, it might be possible to copy without understanding, but it doesn't look like that'll be the case.

Just as well, you'll be ten times happier after you've recreated it and understood it than if you just slapped some parts together without knowing how they worked. Learning is half the fun!

 

This discussion certainly has had a lot of talk. And a whole lot of blather and foam about how much better things are today. Yes, they do offer much lower distortion and more power, but indeed that was not the question. The transformers are not that hard to copy, I have wound transistor output transformers "close enough" to work well and sound OK. And if he wants to make a bunch of them there are companies that can produce as many as he can pay for within 15 miles of my house. Osborne is one of them. Building from a drawing is not that bad, the design,prototype and develop does add a lot of cost. But consumer quality audio transformers are not that bad. Circuit boards of that era were not so fine-line and complex. Making a copy to send to a China board house and for a hundred single sided boards probably $5 each or less, if no solder mask and no plated through holes, maybe $3 each. The resistors can be metered and the circuits traced out to verify that the values make sense. Germanium power transistors would be a challenge, so the circuit values will need to be adjusted, which will take several hours and studying data sheets a bit. So there is nothing really hard about copying the design and producing similar performing devices. A production run of 100 units would run just a few thousand dollars. Then comes what I see would be the really big problem: Nobody would want them. At least I wouldn't buy one because I already built one, or at least something fairly similar. It is very loud, and good enough that folks can tell it is my voice. It makes a great PA amplifier for yelling at people, but for music it is sort of lacking.It is easy to get 25 watts of audio from a 12 volt push-pull transformer output amplifier if you use good transistors and drive them with a decent (copied) driver transformer. The output transistors do need lots of base drive, but efficiency was not a goal for me, so "Oh Well."

I have a much louder one that does use an oscillator power supply to give plus and minus 40 volts or so, with not a trace of ripple, and the thing is rated at 250 watts at about 0.1% total distortion. It cost somebody a lot of money new, it cost me $2 at a garage sale the third day. And it worked after I downloaded the manual on how to connect it. Nobody else wanted it because the case is about 8 by 8 by 3 inches. And it does draw a lot of amps when it delivers full power.
So the whole thing gets down to just exactly what one wants to achieve. If somebody can find buyers for a product without telling any lies, great.