VISONIK V800HC rebuild /upgrade

[amprepairman 10+ year member]

the purpose of this thread is to let everyone see what can be done with a high power class AB amplifier.The amp we're starting with is really nice and I am pretty impressed with the factory build and I told my customer that this amp would be perfect to modify because it has so many possibilities.I am going to go through step by step and perform the actual repair to the amp and then the mods we have agreed on as well with a description of what each one will achieve as we go..With this amp we are going to do simple upgrades-parts swap outs with just one circuit board mod to make sure the new op amps have enough current to run...These mods can be expensive because even though were replacing parts that aren't even bad we are still replacing parts and its the same thing time wise as fixing many different parts of the amp plus...those parts obviously cost money too.I'm gonna be giving basic descriptions of the parts we're adding and what the benefits are but not exact part numbers...

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[amprepairman 10+ year member]

mod pics

 

[amprepairman 10+ year member]

here's the starting pics I took of this amp..for some reason they didn't all take in one post...If you look at them carefully there are a few obvious things..Its built pretty tough right from the factory..it has 2 output resisters per output which I like a lot... its very clean...and its blown up pretty bad in one channel...Its a funny thing too..Myself and other techs are always talking about using matched batch parts when fixing or upgrading a amp..this one left the factory with mixed batch parts in one of the channels and all over the power supply..of course..the mixed batch channel is the one that blew up..go figure..A note to all the guys who send me pics and ask me for a estimate..this amp is a perfect example as to why I cant do that..there isn't a human being out there who could have looked at this amp and been able to tell what was wrong with it based on a pic..it looked brand new when I opened it up yet it has several blown outputs in it.

 

[Jh8909 10+ year member]

wow. Its crazy seeing my my amp completely torn apart. Thanks alot Louis. can't wait to see the finished product. //content.invisioncic.com/y282845/emoticons/thumbsupwink.gif.129404938effda6ad9cca39e7f4b58a3.gif

 

[x1le 10+ year member]

Very interested in the build up and will hopefully be able to learn a thing or 2!

 

[Jh8909 10+ year member]

Just from him talking to me and explaining what parts help with what functions of the amp, I have learned so much from him. He's a great guy.

 

[amprepairman 10+ year member]

for some reason the pics didn't all take in one post

 

[Jh8909 10+ year member]

you should get a photo bucket account. you can list alot in one post that way and the pictures will be bigger.

 

[amprepairman 10+ year member]

I've got people coming and going right now..the weekend is always nuts here..before the nights over I'm gonna strip down and start on the power supply...

 

[Jh8909 10+ year member]

Very cool. pics of the process of the power supply rebuild as well?

 

[amprepairman 10+ year member]

heres is the board..power supply parts stripped and the old and new parts were working with

 

[amprepairman 10+ year member]

OK in the parts pic are the old and new parts going in the amp..The fets..OLD:55volt 49 amp at 25c 35 amp at 100 c 94 watt 160 amp max pulse drain...NEW:60 volt 54 amp at 25c 40 amp at 100 c 120 watt 200 amp max pulse drain...(c= Celsius and it is referring to the fets current(amperage) ability at 2 different temperatures of 25 and 100 Celsius)they don't look much different until you look at the pulse drain max which is 40 amps higher on the new ones and the wattage jumped as well..I have gotten different specs from different sheets..which didn't make sense to me but they were all consistently higher on the new ones by the same amounts.I am mainly concerned with the max pulse drain current and its much better with the new ones..there are many fet options available but this power supply is well built right from the factory so we're doing great with these just adding the 40 amps max pulse we gained with each fet..and there are 16 of them so you do the math. I'm also replacing the filter caps with the Rubycons in the pic( I stock Rubycon and Elna caps in my shop and will be selling them on my website when it comes online-we'll get to the Elna's later in the build)..they are just a much better cap same UF and voltage I'm going to have to move 2 resisters under the board to make them fit but its worth it... I have had excellent results with all the Rubycon caps and I use them mainly in power supply applications..Down in the lower left is 4 small case parts and 4 larger case parts..they are the diodes and I am putting the much larger ones in because the smaller ones I have seen go bad over and over and also if you can see I put a couple upside down so you can see the surface that is usually up against the heat sink..it is plastic..they are totally encased in plastic and that makes them very bad at transferring heat away from the part to the heat sink..I'm doubling the current capability of the rectifiers and I'm going with a standard tab type to improve heat transfer by going back to a metal tab and adding a silicone insulator..also these are called a soft recovery diode which will improver the sound of the amp because they make the job of the filter caps a little easier..there are several versions available and in the high end home audio world its a very important part of sound quality improvements so we are making a improvement in three different ways with just the diode's being changed..Many old school home audio guys have a specific brand of diodes they prefer and pay a lot of money to get the right ones This circuit board happened to already be drilled for the bigger diodes ..Finally there is the TL494 Pulse Width Modulator chip..I'm really picky about this I.C. I prefer the real one made by Texas instruments..many many companies make this same IC and I have replaced so many of them its just sickening.Whenever I work on a power supply I always replace this IC and I always put a TI part in it its worth the time for reliability.. In Closing..None of the mods I'm doing to this power supply will make it actually put out more power..it puts out what the amp requires to run..and that s all it's ever going to do..however..the fets are stronger so they will add reliability..the diodes as we discussed are going to help by not cooking under a intense load and with SQ as well and the caps are a much better quality than the factory ones and the ti 494 chip makes me feel better as far as reliability goes too so we have done alot in the reliability department..and IF the amp asks for more power..by removing all the weak links it is now capable of giving it without a problem...I'll put the power supply together tomorrow and post pics on how it looks complete and a pic of the relocated parts to get the caps on the board as well but its now 2:30 am and I have been up working since about 8 am this morning so I'm quitting for tonight

 

[Jh8909 10+ year member]

nice work Louis. Looks great so far.

 

[amprepairman 10+ year member]

so far today...

 

[amprepairman 10+ year member]

in the first pic you can see a green resister to the left of the circle where the cap used to go..I have moved it just a little to make room for the new caps and to keep the heat it puts off from melting the plastic on the cap and the new location can be seen in the third pic I soldered it directly to the top of the board as it doesn't make a connection to anything on the bottom side of the amp anyway..Also there are small caps in the middle of the circles that I relocated under the board as they don't get hot. NEVER relocate a heat producing part under the board though as it will put that heat right back into the board and we don't want that-lots of amps are designed so that when you mount them in your car the board is actually upside down and the heat the parts put off is being radiated directly back at the board-this one is not built that way..another design feature I like.The middle pic is the end result with the new caps installed and the board cleaned up.If you look at the second pic you can see the large black wire running up the board..that is the speaker ground wire coming off the power supply secondary ground going to the speaker output terminals..(When working on a car power supply there are 2 sides to consider..Primary-being the 12 volt input side of it and Secondary-which is the output side of the power supply and it is what powers your amp) What the power supply does in simple terms is it takes the input DC voltage converts it to AC and runs it through the transformers and steps up the voltage and then the rectifiers or diodes convert it back to DC and the filter caps reduce left over ripple to get the cleanest DC voltage possible..left over AC signal in your DC output to your amp will introduce noise into the amp and we don't want that..we call it a dirty rail and it can cause all kinds of trouble including destroying your amp...also the secondary output of the supply has its own ground plane and when you hook a meter up(and use the output ground plane as a ground) you will get a positive and a negative output like 40 volts+ and 40volts- and these are called rail voltages and supply the output transistors with power along with everything else in the amp..Most of the time all the stuff going on in the Primary side of the power supply runs on primary(12 volt) power and everything going on in the secondary side of the power supply usually runs off the rails or secondary side of the power supply... Having a secondary ground plane is one of the reasons why there are warnings all over the place about never grounding a speaker wire to your car chassis even if it is called a "speaker ground".It gets a little complex but the secondary ground has been created inside the amp and works as a ground on the secondary side of the power supply including the speaker grounds as the amplifier section is on the secondary side of the power supply.All I have left to do is put in the TL494 PWM IC which is the IC thats actually does the switching to in effect create the ac voltage that feeds the transformers and is located on the primary side of the power supply.It gets a signal when running- from the secondary supply and monitors the rail voltages..when the rails start to drop from a load being on them either from turning up your volume control or from bass peaks the TL494 makes changes to compensate for the differences and keeps the secondary rail voltages stable and this is why I said earlier in the thread that the power supply is only going to supply more power IF the amp asks for it...the changes we have made just make sure the power is available when the amp needs it.