VOX VT80+

[km6xz]

Anyone have a schematic of the VOX VT80+? Seems to be a dreaded output section problem which looks very difficult to replace if the bottom of the power IC is bonded to the ground-plane.
Regardless of what is wrong, I need a schematic to verify the rest of the unit.
Thanks in advance if anyone can provide a print for this unit.

[mozwell]

KM6, all i have is the VT50, maybe this will be close enough...

[Jazz P Bass]

KM6, all i have is the VT50, maybe this will be close enough...

Page 4 & 5 are blank.
Which is the schematic.

[km6xz]

Thank you JPBass and Mozwell. A kind sole sent it by email last night. The power amp is a Class D with two out of phase output channels that work like bridging with the speaker between the two phases and an artificial ground. One of the sides is DC and no PWM pulses. I was afraid of that chip being bad due it being a PowerPad plastic Quad flatpacks where the bottom chip heatsink is bonded to the ground plane of the pc board. A bitch to change. It runs 160 watts with hardly a heatsink. I do not imagine too many shops are equipped for ball grid arrays or PowerPad replacement. Both sides of the board need to be preheated to remove it, which can be done soldering a replacement so as to get the proper thermal bond on the entire bottom of the chip is the hard part. I hate to have to buy a $350 board pre-heater just to replace it bu that is the future of moderate sizes power amps so it is good to be ready.

[Jazz P Bass]

Can you post the schematic?
I would like to see this output.
Bonded flatpacks.
BGA's.
I quit!

[mozwell]

page 4 & 5 of VT50, i cna see them fine in the fine i attached before, but here are just those two pages
Output stage is a STK404-100S on the VT50

[vintagekiki]

Page 4 & 5 are blank.
Which is the schematic.

Download and install Adobe Reader XI Font Packs - Asian and Extended Language Pack

http://www.adobe.com/support/downloads/detail.jsp?ftpID=5508

[km6xz]

Vox VT80Plus
vt80plus_schematic.pdf

[Jazz P Bass]

Thanks. Moz.

[blindboybenton]

Hi.
Ive got the same amp in with a cooked output ic. Did you replace yours. Im in the same situation with equipment.

BBB

[Jazz P Bass]

Quote: "I was afraid of that chip being bad due it being a PowerPad plastic Quad flatpacks where the bottom chip heatsink is bonded to the ground plane of the pc board. A bitch to change. "

Not having seen this amp, I cannot say whether or not the heatsink bonding is actually to the PCB.

There where a number of versions of this ic.
Some had the heatsink pad on the top.

If the thermal pad is on the top, normal smd remounting will suffice.(hint: there will be a heatsink attached to the top of the ic)

If it is the 'thermally bonded to the pcb' type, you will most probably require a preheater.
Also, in this case, the remounting can be a real challenge, as the most critical item is the thermal pad soldering.
And how do you tell if it is sufficient without an x ray machine?

[J M Fahey]

Let the Truth sink into your age hardened brains

These amps are not meant to be repaired at component level.

Nor by board swapping, hence the $350 tag.
If they were interested, they would offer a replacement board for $50 or $100 ... with an actual OEM Factory cost of about $30 .

These amps are disposable, as disposable as, say, a DVD player.

Do you know anybody who traces signal or voltages of any kind through them, finds the bad parts, desolders and replaces them?

Only difference is that DVD players have zero value hardware attached to them, say thin sheet metal useless cabinets and a power cord (which *might* be used somewhere else) , while these amps have bulky, heavy and relatively expensive cabinets and speakers attached to them and it's a pity junking that.

FWIW I am seeing more and more (in Argentina, maybe in USA not even that is worth doing) plastic powered cabinets (EON and all their kind) with unrepairable (here and for a reasonable price) guts removed , the empty heat sink left there just to cover the hole (or in a couple cases, just a plain makeshift plywood rectangle), a couple speakons added and them driven by a cheap external power amp (think Pyramid, the cheapest Behringers, etc) which is cheaper than repairing the Electronics.

And which in case of failure is disposable itself.

[Jazz P Bass]

Hah!
I just finished up a 'gutting' of a powered subwoofer.(which no longer did)

Removed the amp, power supply board & switches, gooped up the heatsink holes & added a neutrix connector.

[J M Fahey]

Just checked who the "Kimanson" guys are.

Boy, did a veil lift from my eyes

They are not even Korg which I suspected, but much more.

To begin with, they are OEM with manufacturing plants in Korea and Vietnam.

Found lists of customers, containers shipped, landing and discharging ports, etc.

One data page was mostly blocked, unless I open an account.
No thanks but what I found is chilling enough:

1) 4 results matching kimanson instruments as suppliers

a) Kimanson Instruments Co., Ltd. South Korea
Customer 1 : Fishman Transducers Inc.
Customer 2: Fender Musical Instruments Corp (Musical Instrument parts)
Customer 3: Kpbo, Duckjean, Kimanson Seoul-teukbyeolsi, South Korea (what we used to know as Dean Markley).
End customer: Kaman Music Corporation
this is the free sample, there are 166 shipments offered out of 267 total registered.

2) 23 results as buyers who claim to be kismanson customers:
* Us Music Corp Buffalo Grove, Illinois, United States (100 registered shipments)
* Korg U.S.A. Inc. (112 registered shipments)
* Fmic Distribution Center (51 shipments)
* Loud Technologies Inc. (42 shipments)
* PT Oz Guitar
* Watson E.P. Industries (Dongguan) Co., Ltd.
and so on and on and on, 23 main customers and 2,692 shipments total .
Including Samick, Pearl, Marshall Amplification PLC , Eurotec and hundreds others.

Have I found Santa's Factory, which makes all toys in the World?
Or its Musical Instrument equivalent .

Is there any real Factory left outside Asia?

CHILLING.

Just to confirm what's mentioned above, they also offer a loading and unloading ports list:

Port of Lading

Hong Kong (1)
Vung Tau (1)

Just in USA:

Port of Unlading

Long Beach, CA (1)
Tacoma, WA (1)
Boston, MA
Los Angeles, CA
Miami, FL

Show more…


Oh well, I guess I'll buy 24 sheep and sell wool (unwashed) , fresh milk and tangy cheese.

At least I'll have some future before me.

Or move to South Korea, where the Future lives, and open a Restaurant such as:

http://youtu.be/cBYrG0daiHs?t=1m12s

[teemuk]

I guess that in today's global world it's either this or going belly up quickly because your products cost way too much to be competitive with practically similar, but cheaper, products.


The prices of most of these amps aren't really -that- high anyway, so you can't really compare cost effectiveness of their repair to, say, repairing a car, which easily costs at least ten times more than a Valvetronix amp to begin with. Or any other similar utility, which -really- is moderately expensive, like a house's built-in air conditioner or heat echanger. So yes, disposability is pretty much what you pay for when you shop for inexpensive items. Truth is, by the time most of these need repair one can pretty much update to some newer similar belt and whistle with not much more costs than repairing the old item, and this is undoubtedly also one design aspect for such products. Needless to say, these things CAN be repaired but there's always a cost to any service...

I think despite all critique most Valvetronix series amps are very good and innovative products from Korg with very few similar competitors, if any. This comes with a price an ordinary Joe can afford. I don't see too much bad in this. I don't know if I wanted to go back to old days when even decent products were scarce and had ridiculous price tags.