Finding pre-amp output in mini system

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chuck55

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Joined 2003
I got my Denon UD-M31 apart again and found 5 wires to the chip-amp board:
Red / Orange / Black / Blue / White
(There are also 7 smaller white wires but I think these are for some control function).
I got the schematic from Denon but it is no help as to explaining the colored wires that go to the amp board.

So I would appreciate some help with:
1) Can I measure the voltages of these wires to find out if they are, indeed, the preamp outputs and, if so, for which channel?
2) What happens if I get, say, the (+) for the right channel and the (-) for the left channel? How would I know if I found found both which go to the same channel?
3) Would the voltage go up and down as I adjust the volume level?
4) Can I tap off these wires as to retain the original amp function of the Denon and route the tapped-off wires to separate RCA outputs to hook up a gainclone amp? The Denon has 4 RCA's for tape input/output so I would probably just cut those wires and solder the pre-amp wires to those 4 RCA's. (Note that I would not be running both amps at the same time).
5) I'm thinking the 5th wire may be some system ground. Any way to verify that?

Thanks
 
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Minion

Member
Joined 2006
Well if you are trying to find the output of the pre-amp (input to the power amp) and it uses a chip amp then look at the chips datasheet and trace the input to the wire from the preamp output , the datasheet will tell you what pin on the chip is the input which will also help you find the wire that leads to the input...


Cheers

Once you found the wire you can tap off it.....
 
M

Minion

Member
Joined 2006
Im not talking about the schematic , the datasheet for the chip amp will tell you what pin on the IC is the input pin , now you find the input pin and follow the copper trace on the PCB back to were the signal comes from the preamp to the power amp ... should be fairly simple as long as the PCB doesn"t have more than 2 layers .....

Just find out (by visual examination) what type of chip is used in the amp and then do a datasheet search on the net...
 
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Enzo

Member
Joined 2004
You look on the schematic and see that the chip amp is some number - for example LM3886 - and then you enter that part number into google. Google will then present you with a variety of sources of the data sheet for that IC. Not only that, but if you look up the part in Mouser, for almost all parts they sell, there is a link to a data sheet on the page.

www.mouser.com
 
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pacificblue

Member
Joined 2008
Those are both voltage regulators. Look for something bigger with more pins. If you have built a gainclone you should know, how a power amp IC looks.

Start your search at the speaker terminals. The wires or traces that end there start at the power amplifier section. If they lead you to transistors instead of a chipamp, you will have to send the schematic to somebody for help. Don't post it, because that might bring you into trouble with Denon.
 
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chuck55

Member
Joined 2003
"The chips (if indeed it is a chip amp) will be bolted to a big piece of metal called a heatsink ....."

Yup, the other two I found were bolted to a little piece of metal.
I finally found it. Amazing how they get these things together... and for so cheap.

It's not that great. Here it is:
SANYO STK 402-050

I see channel 1 and 2 but with all that other balony going on, can I really tap off those four wires without messing something else up? And if the amp is this average, how much better can the pre-amp be? Quiet enough for a LM3875 chipamp?
 
jaycee

jaycee

Member
Joined 2004
To be honest I gutted a Denon microsystem, a DC30. They're nothing brilliant. The circuit was full of 4558 style opamps running on single voltage, and full of capacitors in the signal path, and plenty of BU4066 quad analog switches. The only good part was a motorised ALPS pot :)

What kind of preamp do you need? They're not that hard to make to be honest.
 
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chuck55

Member
Joined 2003
Hi Jaycee,
Well I'm disappointed but not too surprised. Ideally would like one with tone control at 100 / 10,000 hz and a remote control. A Djangos AVC sounds impressive too. Just don't want to go the confusing audiophile route like Adcom, Bel Canto, Placette, and on and on.....
Then there is this:
Pro-ject pre

It will have to work with this:

LM3875 gainclone

Looked into a bunch of passive pre kits with remote last year.
 
jaycee

jaycee

Member
Joined 2004
They look like typical overpriced audiophile hoodoo to me. I would argue a transformer based attenuator is going to be way more nonlinear than any pot, even a very bad one with gross channel imbalance. Sorry, but for $1K i can't help feeling you would be wasting your money.

If you don't need any gain for your sources, a good 50K Log ALPS "Blue Velvet" type pot will do, or indeed any good quality pot. A 4-way input selector can be made from any good quality 2-pole 4-way rotary switch.

If you wanted extra refinement, you could get some good quality DPDT signal relays and wire them up so that a 4-way rotary switch picks which relay to feed +12V to.

The only sore point here is that you want a remote. That means a microcontroller, which is going to be whats stopping you making one. I do belive though, there are a couple of kits about that are designed to control the motor of an ALPS motorised type pot that would do the job for you. I'm damn sure i've seen one on here that will do that, and even control some relays for source select.

Perhaps I should make one!
 
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chuck55

Member
Joined 2003
I hear you about the overpriced, audiophile stuff. Until you make one I found a few remotes preamps.
They question I have is will they drive the LM3875 chip amp. From what I've read the sound is thin and lacks dynamics. Even Peter Daniels uses a TVC for his Patek.


DIY Club:
http://eshop.diyclub.biz/product_info.php?products_id=195

Decibel Audio K7:
http://www.decibelhifi.com.au/category4_1.htm

Dantimax.com has a Remote 1:
http://electronics.dantimax.dk/Kits/index.html

and Remote3 & 4:
http://electronics.dantimax.dk/Kits/Preamps_-_poweramps/index.html

AudioElectronics Supply has "overpriced" stuff:

http://www.audioelectronicsupply.co...t=detail&dept_id=5&aisle_id=51&prod_num=RVC_2

Altronics:
http://www.altronics.com.au/index.asp?area=item&id=K5026

So I've been searching, just not sure which to buy / if I want to make a kit.
 
jaycee

jaycee

Member
Joined 2004
Again to be honest, hoodoo. The LM chip amps are easily driven by any preamp or source directly. If memory serves they have an input impedance of 22K. There is no black magic to a gainclone really. My self built one certainly has no problems.

The Remote1 kit looks good. Be aware that it's just a controller for a motorised pot, not a preamp. Control1 also looks good if you want to switch some relays for an input selector. It's a pity they dont do an integrated unit that has the features of both.

Control1 full kit for 37EUR isnt a bad price... be aware that you would have to buy the ALPS motorised pot, though.
 
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