car amp repair man.....

[amprepairman 10+ year member]

I think hes talkin about me...

I didnt read the rules..so I'm not sure what I did yet...but i would guess I did something...

 

[MakeshiftAudio 10+ year member]

I think it's an advertising rule that was broken.

I guess that I was just worrying about unimportant things like gate charge and switching delay/rise/fall and whatnot. //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif

 

[amprepairman 10+ year member]

stop man....I really dont wanna get into a fetfight with you.....I understand what your saying and I agree...I just didnt think it was important to post in the context of the given conversation thats all...the conversation was more about cost and how someone can end up with a less than perfect part based on the needs of the manufacturer and in the case of the KIA part for the IR part swap...its a direct replacement that the original manufacturer could have used but went cheap... in a industrial or a computer power supply I think what your saying is very very important but your average car amp power supply doesnt run anywhere close to the operating limits of a power mosfet as far as speed goes...duty cycle is another story though...thats what blows fets up and causes your board to melt down...to long of a duty cycle on a heavy load makes for a very unhappy fet.Fets in standard car amp power supply use totem pole switching and are diode clamped and if the surrounding curcuitry would allow it....could run faster.. Because of the nature of AC voltage and the effects of the transformer and the caps on the other curcuitry things can only happen so fast.. ..but its not running anywhere near as fast as either the pulse width modulator or the fets are capable of...the rest of the supply is what cant keep up.......this is as I said before is only in reference to a simple car amp dc to dc switching power supply which are cheaply built and inefficient by design....

 

[MakeshiftAudio 10+ year member]

I am not wanting to fight with you, I am just saying I do not think things are exactly right. I do not intend my messages to come off as offensive or harsh, though it seems like you're saying I don't know what I'm talking about. If anything, it's more in a manner of a jokingly critical statement. More of a false harassment in order to initiate a semi-technical conversation/debate. I love modifying my own amplifiers, and that is the context I am taking this. Slightly serious modifications, read below. This post may be kind of felt to be cut up.

Not onto your post.

I partially agree.

I never had an issue with the KIA replacement thing. I read something like "I will upgrade the amplifier by utilizing the best fet for the application." or something like that, and I'm thinking "Oh boy, let's just pop a monster IXYS fet on there and be done with it." It might have been a misunderstanding from me, but whatever.

You were also talking about board layouts... You just said that the speeds are not high enough to matter, though board layouts really start to matter in RF designs where stray inductance becomes a serious issue. Make up your mind! //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif

I decided to leave a large fraction of technical talk out of my post, as I do not need to prove my point here under these conditions.

PS: I do pick technical points to harass about because I do design industrial power inverters that use the parts to their full potential without straining them(too much). You're absolutely right, car amp smps typically have horrible efficiencies.

I think I'll mention this: it is a halfbridge that drives each leg of the transformer in a car smps, not a totem pole such as the configuration of the transistors immedately before the gate resistors and after the driver. The diodes you're talking about are also in what's called a flyback configuration.

As a personal taste, I think the 494/KA7500 is kinda bleh compared to some of the ICs I use/have used in my designs. Simple to use, old fashioned chips are always good though.

 

[amprepairman 10+ year member]

I am not wanting to fight with you, I am just saying I do not think things are exactly right. I do not intend my messages to come off as offensive or harsh, though it seems like you're saying I don't know what I'm talking about. If anything, it's more in a manner of a jokingly critical statement. More of a false harassment in order to initiate a semi-technical conversation/debate. I love modifying my own amplifiers, and that is the context I am taking this. Slightly serious modifications, read below. This post may be kind of felt to be cut up.
Not onto your post.

I partially agree.

I never had an issue with the KIA replacement thing. I read something like "I will upgrade the amplifier by utilizing the best fet for the application." or something like that, and I'm thinking "Oh boy, let's just pop a monster IXYS fet on there and be done with it." It might have been a misunderstanding from me, but whatever.

You were also talking about board layouts... You just said that the speeds are not high enough to matter, though board layouts really start to matter in RF designs where stray inductance becomes a serious issue. Make up your mind! //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif

I decided to leave a large fraction of technical talk out of my post, as I do not need to prove my point here under these conditions.

PS: I do pick technical points to harass about because I do design industrial power inverters that use the parts to their full potential without straining them(too much). You're absolutely right, car amp smps typically have horrible efficiencies.

I think I'll mention this: it is a halfbridge that drives each leg of the transformer in a car smps, not a totem pole such as the configuration of the transistors immedately before the gate resistors and after the driver. The diodes you're talking about are also in what's called a flyback configuration.

As a personal taste, I think the 494/KA7500 is kinda bleh compared to some of the ICs I use/have used in my designs. Simple to use, old fashioned chips are always good though.

when I mentioned the totem ploles..I was refering to the gate driver transister set up not as in totem pole topology and with the addition of diode clamping...the PWM and the the fets are capable of switching much faster than the rest of the power supply..allso in a car amp..the board layout does matter I posted on that earlier...but when I was talking about layout I was mainly reffering to noise in the audio end...due to poor layout on the amplifer side...cross talk and those kinds of issues..When I said the switching speeds didnt matter I was refering to the point that I dont think theres a fet out there that couldnt switch twice as fast as is possible once you install it in a car amp due to the bad design of car amp power supplies ..so in picking a fet..I'm not overly concerned about switching speed as Ill never approach the limits of even a bad fet as long as Im putting it in a car amp( I might be pushing it with the "bad fet" thing).....I will say I might be wrong on that one Ive seen some parts that a mechanical relay could **** near keep up with.....but the parts I have put in amps so far are running at a fraction of there capabilities in the switching department...again..as a result of the poor design of the rest of the supply...

As a side note..I allso work on drives and industrial power supplies(I cant even begin to design one) but the supplies are for treaters in the plastics industry...and they use those IGBT.! we call them ozone generators because as Im sure you know that anything creating a corona is gonna make some oxone...I do some work for a company that also actually does pressure vessel ozone manufacturing for water treament...I love amps but just got laid off from my industrial electronics job....They are allso into cell stack technology and I repair all thier cell stack power supplies....low voltage with tons of extremely controllable currrent...I do it for the same reasons as you do.....I love power electronics....as far as the TI494..were stuck with it forever...it justs fits in and every power supply guy in the car audio world know how to build around it...I remember when everyone was still running off 555's!

Dude...Im not saying your stupid...I just felt last night thats what your comment was indicating about me..I dont know everything...but I am pretty solid when it comes to making it work again..any usually keeping it that way......I understant the conversations get heated...I never had it any other way..Im a tech who has been surrounded by engineers for years...and we all know how those realtaionships work out...

More than once I have been inclined to eat a valium before a meeting with the enginnering department over a project assigned to me that in the process of builing a prototype I have found problems and the designs not gonna wrk without some changes....As a rule somewhere in one of the commandmant is says"techs dont make recommendations to engineers"

needless to say..I havent beed to chuch lately...but some church bought me a dukane 70 volt amp today and gave me the super sad face with the "without this amplifier christmas eve mass will be a real mess"....great..Im gonna get smoted...I swear its lookin at me from across the room....

Lively conversation...I'm sure its not done yet...anyway..thanks for your responce...maybe...just maybe..your engineering skills might come in handy..Im working on a class A home audio projet based on a early levinson design...I allso am about done hagling witha guy over a 4 channel Macintosh car amp that Im gonna do some tricks too...I expect it to be alot of fun...

I'll brob keep it though...

 

[lucas569 10+ year member]

speaking of mac amps i heard they really arent that great? true or false?

also the pos wire on one my amps came loose after hitting one of our infamous new england pot holes.

it caused my left speaker to blow and now i get static sound from all the channels, rough idea on what i smoked?

 

[MakeshiftAudio 10+ year member]

Yeah, you're pretty much on the spot unless you get into using hexfets with anything... The darned things practically need a special driver for themselves due to their fall time...

Ah, yes! The high voltage stuff. IGBTs are better suited for the higher voltage stuff anyways. It's not often that you see a high voltage fet that's decently cheap. I know of some IGBTs that are rated for 3.4kV.

As a hobby earlier on in my electrical love life I messed with high voltage. IE solid state tesla coils, RF power supplies, and whatnot. Ozone is usually a thing that HV tinkerers love to smell... Before it, you know, damages things so that you can't smell it anymore sort of thing. A 5kW CW RF supply openly discharging through the air with a 2' discharge fills the house with ozone quickly I might add. I've also worked on class C armstrongs and E transmitters. Interesting stuff... Tubes are fun to mess with too, though most forget about them. Haha. *Drags out the forced water cooled 80kW RF triode.*

Yeah... Techs vs Engineers... Yeah... Not fun grounds for the techs...

Maybe? Just maybe? Anytime, just ask if you want to.

After a minute or so of google work, I hope this helps, I know a good old schematic sets the ground beneath my feet in a tricky situation:

http://oak.cats.ohiou.edu/~postr/bapix/Duk1a475.gif

 

[dB-r 10+ year member]

Someone new here. Not necessarily a bad thing. You guys squabble about tech vs engineer all you want. LOL. Mosfet Smosfet... Good luck amprepairman, these forums can be brutal if you don't do a good repair job on someone's amp, so be sure you do them right, if not, believe me, you will pay for it all over the internet.... Remember people take pictures of "funny looking repairs" and post them on forums for guys like myself and MakeshiftAudio to pick apart and warn others to not send stuff there anymore, so just do a good job and you will be fine. Good luck!

 

[chardy85 10+ year member]

Someone new here. Not necessarily a bad thing. You guys squabble about tech vs engineer all you want. LOL. Mosfet Smosfet... Good luck amprepairman, these forums can be brutal if you don't do a good repair job on someone's amp, so be sure you do them right, if not, believe me, you will pay for it all over the internet.... Remember people take pictures of "funny looking repairs" and post them on forums for guys like myself and MakeshiftAudio to pick apart and warn others to not send stuff there anymore, so just do a good job and you will be fine. Good luck!

Thanks for welcoming him and letting him know the important stuff db-r.

The main reason I told him to come to the site is because I sometimes saw you saying you were backed up and didn't have time to take in some business.

You do a great job btw!

A While back my stepdad sent you an old RF 1000a1 to rebuild for him and it is still rocking 3 12's like nobody's business!

Curtis

 

[dB-r 10+ year member]

No problem Curtis. Glad to hear that amp is still going strong.

 

[amprepairman 10+ year member]

DB-r...Ive been wanting to meet you...I have heard nothing but stellar things about you....I have given all these things lots of thought...I'm very concerned about the repair quality and the opinion of the people who I work for....allmost to the point of fear....I seriously feel like as Im new...Id replace a amp before Id send it back mesed up....U cant put a value on your name when the whole world has acsess to it....Im looking forward to working off the internet...Ive been at it local forever and the internet as far as a service portal is a new thing for me...thanks for your reply....

 

[lucas569 10+ year member]

speaking of mac amps i heard they really arent that great? true or false?
also the pos wire on one my amps came loose after hitting one of our infamous new england pot holes.

it caused my left speaker to blow and now i get static sound from all the channels, rough idea on what i smoked?

bueller? id like to get this amp repaired nonetheless....

 

[amprepairman 10+ year member]

Im not sure about the mac car amps...but we all know the mac home components are seriously tough stuff....Im trying to get one and find out though!..If it can be damaged I'll surely be the one do do it....

 

[amprepairman 10+ year member]

the first two of three amps I bought off ebay have showed up...I ss750 autotec and a100.4 memphis...Im waiting on another ss750 and Ill prob build the two ss750's as a set....I'll post pics before I start on them

 

[amprepairman 10+ year member]

merry christmas everyone..I managed to talk someone out of a 4 channel mac Im not even sure what the model number is. The guy sent me a pic of it and weve been hagling over price for about 2 months... I was a tech at a mac dealer here in town for years but we didnt sell mobile mac...So this will be the first one Ive ever owned...for it being I think 100 or 125 a channel its got a monster heat sink...cant wait to get my hands on it...