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undertone 18th October 2007 11:04 PM

Hacking the Logitech Z5500
Like others on the net, I had something wrong with my Z5500 so they asked me to send back the controller and I ended up with an operational system and a "headless" one.

I now need a sub for a small system, and I figured I could somehow hack my Z5500 amp/sub for the purpose. After reading someone's post on how easy it was to access ins/outs and power switching on a 680 kit, since the connections had identifiable names on the PC board (FR, FL, RR, RL, etc...), I decided to take a look at the innards of the 5500.

After poking around in both the sub and the controller, I have to admit that there's a good reason Logitech asks for only the controller back: they've done everything possible to make it difficult for the DIYer to hack this speaker! Some of this stuff includes:

-No recognizable identification of any of the wire connections.
-Use of hot glue on the pcbs over many connection areas.
-Sanding of chip tops to prevent identification (mind you, the chinese subcontractor did a lousy job of this on my unit ;) )
-The volume wheel on the controller seems impossible to take off. It feels glued (!). You can't clearly see the other side without removing it.

There's two main boards in the sub unit, possibly multi-layered: a preamp (5*4850's there) and the amp board with 8 heat sinked chips (7 chip amps + probably a regulator), but there's also some logic switching on the preamp board, probably responsible for turning on the amp. It doesn't look like it's a simple "switch-to-ground-to-turn-on" deal.

So in brief, it's not at all clear how to handle this. I may have to disassemble the amp board to see what chips are used, and just plug a diy preamp into the sub amp chips, bypassing everything else. I'll keep digging.

BTW, does anyone know a good way of removing this type of glue without damaging pcb and components?

I'm curious to hear from anyone else attempting/considering this.

Bob25 19th October 2007 04:50 AM

I just started looking at my "headless" one too. The preamp board looks like it uses an 'HCT139 (marked on the chip) 2-to-4 line decoder as switching logic. This is a dual and one pair of input pins are wired to the controller connector. I can confirm the 4580's, none of my parts have the chip ID's sanded off.

The power board has two regulators in the middle of the board, looks like a 79M18 and a 78M18, neg and pos 18 volt regulators respectively. I haven't pulled off the heatsink bar to see what the amplifiers are yet. One side appears to have a three terminal (?) to-220 in addition to the amps.

This looks like it shouldn't be too hard to figure out if we can get the amplifier PN.

undertone 19th October 2007 07:52 AM


Originally posted by Bob25
The preamp board looks like it uses an 'HCT139 (marked on the chip) 2-to-4 line decoder as switching logic. This is a dual and one pair of input pins are wired to the controller connector.
Hi Bob,

I saw that too. Do you think this section is responsible for turning on the amp?


Originally posted by Bob25
...none of my parts have the chip ID's sanded off.
That would be in the controller not the sub.

I'm doing this as a part time DIY, and it's clear that more circuit tracing is in order. I have a feeling looking at the topside of the amp board might be revealing so I'll be taking that apart next week and I'll have the amp part numbers then (if they're not sanded off).

Thanks for chiming in!


undertone 20th October 2007 05:05 PM

Took off the bar holding the chipamps against the heatsinks today (had to know!) and found TDA7294 's.

The sub uses two bridged. This chip has standby and mute functions which may be what the switching-logic section is handling.

To be continued...

tashing 22nd October 2007 01:01 AM

Does this help?

I am also interested in doing this, unfortunately I am not very knowledgeable about electronics.


lakata 22nd October 2007 01:01 AM

Pin-out for the Logitech Z-5500 amp
Here is the pin out as I reverse engineered it. My goal was to take a discarded Z-5500 unit (no pod) and get it to work as an iPod amp.

DB15 connector:
1 - Right Rear in
2 - Sub In
3 - Left Rear in
4 - Center in
5 - Left Front in
6 - enable in
7 - enable in
8 - enable in
9 - Right Front in
10 - +8V logic supply out
11 - ?
12 - ?
13 - ground
14 - +18 V supply out
15 - -18 V supply out

I connected a 1/8" stereo jack as follows:

tip (left) to pins 3 and 5
ring (right) to pins 1 and 9
ground (sleeve) to pin 13

Also, I used a 10K pot to limit the sub, although this didn't work as I expected. I connected the left audio channel to pin 3 of the pot, pin 1 of the pot to ground, and pin 2 of the pot (middle pin) to pin 2 of the DB15.

And finally, ground pins 6,7 & 8 to ground (pin 13).

The center channel is unused. Tweak the pot until the bass sounds right. Note that the sub will suck power out of one of the channels and I haven't bothered to figure out why.

When you are done soldering (I did all of this inside the sub box, drilling 1/4" and 3/8" holes for the audio jack and pot), hot glue everything so that the sub woofer doesn't shake it loose.

I do not know what pins 11 and 12 are. They have 100 ohm impedence to ground and a DC offset of 0.140 mV.

Good luck! I was given a "bad" set by a friend that was going to trash it, but it turned out the only thing wrong was a loose spade connector to the sub driver.

Remember that there is no volume control on this, so when you are testing it, start low. Do no use "line-out" to drive this, use the head-phone out so that you have volume control on your iPod or whatever.

undertone 22nd October 2007 05:02 PM

Re: Does this help?

Originally posted by tashing

Intersting: if you look at this video (play it for a few seconds, then stop and bring the slider to the beginning), you'll see the version of the Z-5500 I have, which is clearly different than the one in your video!

So there are in fact 2 Z-5500's: one with RCA plugs for the speakers and one with spring-loaded speaker connectors. Odd thing is that clearly the electronics are clearly different.

undertone 22nd October 2007 05:02 PM

Re: Pin-out for the Logitech Z-5500 amp

Originally posted by lakata
Here is the pin out as I reverse engineered it...
Thanks Lakata for all this detailed information!

Based on my previous post, which Z-5500 did you do this mod on? Mine is the RCA speaker outs version, with the larger internal input board.

I'll try out these connections as soon as I have a chance (and after a little more tracing).

lakata 22nd October 2007 05:43 PM

Mine looks like the one in the video, with the spring terminals for the speaker outputs.

Interested, I didn't look at the video before. I connected the 3 "enable" pins to ground and it worked for, ie the amp went from standby/idle mode with zero output to a decent output level.

However, the maximum output level when I feed it -0 dB from my Turtle Beach Audium (yes, old school) is not as loud as I would expect.

Tashing - how did you determine 7.5V was the requires enable voltage? And where did you grab the 7.5V signal? Are we talking about the same enable pins, ie pins 6,7 & 8 on the DB15?

The worst part of my circuit is the sub, but I really don't have the time to build/find a mixer circuit ... this was more of a puzzle experiment, not an effort to save money. If I really wanted to save money (==time), I would have just bought a new system with a pod.


undertone 22nd October 2007 08:49 PM

Thanks, Mark. I got the feeling that Tashing was only pointing to the video. I don't think he did a mod yet.

Did you try grounding each control pin separately? The TDA7294 has a Mute pin and a Standby pin, so maybe the 2 of the 3 control signals are for these, while the third might be some kind of attenuation? (shot in the dark).

Regarding your "signal-sucking" sub arrangement, you might try DC blocking the line to the sub after the pot (with a large cap of course as it is a sub signal). The best of course would be to use an active buffer. My input board has 5 opamps, but tracing to the chip amps is difficult because of the liberal use of glue where the wires leave the input board and connect to the amp board. To really know I have to take the whole heatsink assembly apart, and separate the amps from the heatsinks.


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