# Modifcations for a cheap Logitech amp/sub?



## TheLaw

So,
   
  I have a cheap piece of crap Logitech 2.1 setup for my computer. Don't hate on it please. It cost me $30 and for the most part, it does well. However, I was wondering if there are any general amp mods that I can do...?
   
  I have heard that increasing the capacitance on some of the capacitors should give it better response during peak output...Along those lines....
   
  Are there any things that can be done to increase the amp that would have some benefit?
   
  I'm also considering replacing the sub itself with a cheap HiVi/Swan woofer.
   
   
  Thanks.


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## TheLaw

Anyone?


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## TheLaw

Bump


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## Avro_Arrow

Model #s, Pictures...
   
  You didn't give us much to work with...


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## googleborg

i've thought about using a cheapo 2.1 sub on my tape outs to give my hifi a bit more bass...perhaps even hack it up and create my own subwoofer!
   
  i've got both the s220 and x-210, and they are both very cheap and cheerful, good units, not sure there's anything you can do to make them better that's worth the cost though, perhaps replacing the filter caps but these units are built to cost, upping the capacitance = too much inrush current and these things will likely melt, the volume pot in the control pods are the cheapest you can possibly get, but adequate considering the quality of the satellites.
   
  i can't think of upgrading any one thing that won't be rendered useless by all the other bottom-barrel components.


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## TheLaw

Sorry for being so ignorant about this. I decided I would take apart the powered sub...Easier said than done. I wound up destroying the box....Of course, I didn't harm anything else, but I guess I'll have to be building me a new sub box sometime...
   
  Anyway, the model number is Z313. It cost me $30 on sale....Does the job mostly.
   
  Not sure how huge these pics are going to be, but here it goes....As you can see, really cheap stuff on board. It's not like they really have a choice....for the price they want to sell at. I think I'm going to replace value for value on the electrolytic caps with a higher quality alternative. I might see if I can get a better sub. Again, it was cheap, so I don't really mind messing with it too much. 
   
  Oh and yes, the inline volume adjuster absolutley sucks. How should I fix that? It cracks and I have to fine tune it to get both satellites working at the same time...Pretty annoying
   
  Caps by Chang, CapXon and Samxon. All general purpose as far as I can discern.  Pretty crappy....Note the LOVELY rectifier circuit.
   
  The heat sink for this thing has about as much potential as a piece of aluminum foil.
   
  Too much inrush current....Hmmm....Bigger heatsink to cover that?
   
  It has a massive transformer by the way. Don't know the actually output spec, but I think it would have to be fairly decent. Probably either @ 16V or 25V.


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## TheLaw

So this might sound absolutley stupid, but what if I just literally use the PCB and nothing else, replace EVERYTHING on board. Resistors, jacks, wires.....There's no guessing work involved. Just drop in a higher quality part in place for the crap parts.
   
  I think for now, higher quality capacitors would be most useful.


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## TheLaw

So I grew impatient with myself....I ordered about 25 replacement caps off Mouser. Main input power cap is a Nichicon Muse KW. The rest are a combination of Panasonic FMs, Nichicon Muse FGs, and Nichicon Muse KWs. All are exact replacements. One or two may have different voltage rating, but otherwise same capacitances. 
   
  I also purchased a Switchcraft 1/8in audio jack to replace the POS that is currently in the amp.
   
  Additionally, I bought 4 new rectifier diodes. They were cheap, so it doesn't matter if I don't use them...but I want to replace the 3A diodes with 5A diodes for several reasons.
   
  Lastly, I bought 2 big heatsinks for the amplifiers themselves. Might be able to push a little more out of them without melting them. But I could be making up things.
   
  Total cost was $18. I think it may be worth it in the end. I'm mostly doing it for the fun though, so don't get too critical about it.
   
  Hopefully it works. I still need to scrounge around for some decent pieces of MDF to make the new box...and then get the router out...Oh my....


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## TheLaw

Would it make any difference if I used a thicker guage wire from the amp board to the subwoofer itself? As in, the actual signal wire to the subwoofer....I think it's about 20AWG right now. If I used something bigger, would that be good? What guage? I'd expect solid wire for less resistance....?


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## TheLaw

Bump


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## civilmonkey

I think a lot of people around here have a primary focus on headphone amplifiers, usb dacs, etc, and the design of lower current applications may not transfer over 100% to sub amplifiers.  You could try googling 'gainclone'.  It's a solid state speaker amp using a LM3875 or similar chip that is often built point 2 point, and some who build it swear by it.  If you can find the forums dedicated to gainclones, you may be able to get some more answers re sub amps over there.  good luck!


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## TheLaw

Ah thanks. I was just mainly curious as to ideas on general component selection. But I'll give it a try somewhere else.


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## nullstring

Errrrr...
   
  I think you're going out this the wrong way..
   
  It would be much more worth while to build a seperate gainclone or T-amp
  http://www.diyaudio.com/forums/chip-amps/
  http://www.diyaudio.com/forums/class-d/
   
  and then get something like this
  http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-652
   
  Or build your own speakers and sub...
   
  Whats your end budget?


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## nikongod

bump.


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## nikongod

ToTheTop


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## nikongod

One more because nobody has replied within the last 30 seconds.


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## nikongod

I think the chips on there now are part of a gainclone(ish) circuit.


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## TheLaw

My end budget...That's kind of the reasoning behind what I'm trying to do. I have an amp board. I have the transformer and wiring harness and satellite speakers. I don't see a purpose of trashing these parts or reusing them on something else...as that would render everything else remaining in the 2.1 setup useless. 
   
  I'd really like to keep it sub $50 which is why I'm trying to base it off something I already have.
   
  I bought a new subwoofer as well. It's a HiVi (Swan) M4N. It's an 8Ohm speaker whilst the sub that it is replacing was a 4Ohm speaker. The datasheet for the TFA9842J says that it can do only 7.5W on a 4ohm speaker and 15W on an 8ohm speaker. Hopefully that will work out and there won't be any power issues.
   
  It cost me $20 shipped. So with the $20 I spent on replacement parts and $20 on the woofer, I have about $10 left in the budget to go towards building a new sub box. I think I have MDF in the garage, but I might need to get some sealant or something.
   
  Hopefully I'm not sounding too noobish. I guess trying to fix something that is already a piece of crap is sort of useless, but to my ears, the stock Logitech sub really didn't sound all that bad...
   
  Well, everything should be in within about a week. I hope it works out well. There's really not much that could go wrong.


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## nullstring

It bewilders me how people can have budgets like $50 that aren't adjustable..
   
  Must be all children?
   
  IDK


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## TheLaw

If you have an adjustable budget, then you have no budget at all.


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## TheLaw

What would you recommend I add? I seriously don't know what else I could dump into it, without being outrageously stupid.


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## TheLaw

This is the sub I bought by the way. I'd say it's quite a good speaker for the price. http://www.youtube.com/watch?v=ROsEcXnHv_I&feature=related


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## TheLaw

Wow now I feel stupid as hell....I just bought an 8ohm speaker for a 4ohm amplifier. According to the datasheet, I thought it was an 8ohm but I was wrong....Shoot...


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## nikongod

these things happen


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## nikongod

what does the datasheet for the amplifire chips say?


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## nikongod

what makes a 4-ohm amplifire one?


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## nikongod

is it the fact that its marginally stable into 4 ohms?


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## nikongod

generally yes.


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## nikongod

it cant hurt that the power output is moar


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## nikongod

this is important to an OEM with a shoestring budget.


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## nikongod

power supplies to drive 8 or 16 ohm speakers cost money.


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## nikongod

voltage swing costs money every which way


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## nikongod

more current from a class-AB amp? Thats easy!


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## nikongod

just put the lowest impedance speaker you can find on it.


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## nikongod

more current same (sucky) voltage.


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## nikongod

its simple!


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## nikongod

they would use a 1 or 2 ohm speaker if the amp chips were stable into that load


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## nikongod

does the speaker "fit" the box for TS parameters?


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## nikongod

Im kind of curious why I didnt just edit my first post to add more randomness.


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## nikongod

no actually, Im not.


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## nikongod

anyways, check the datasheet


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## nikongod

it will (hopefully) tell you what impedance the amp chips weree designed for.


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## nikongod

after that it should be easy.


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## samsquanch

Well played sir, well played.


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## TheLaw

Sorry, do I really spread out my posts that much....?
   
  The datasheet says 4ohms for single operation, and if you use two amplifier chips and bridge them, you get 8ohms...Stupid me, I just saw 8ohms and thought bingo, it'll work.
   
  I think I may just buy another sub and run them in parallel, which would technically give me one 4ohm speaker.
   
  7.5W output for 2 8ohm speakers. Is that too little? It's technically "1x 4ohm" speaker....Would this be a dumb idea at this point?


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## BobSaysHi

lmao. I wouldn't have spent so much on your speakers and bought new ones.


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## TheLaw

Well here's the thing. If this doesn't work out, I'll have some brandy new speakers for another setup. But it'll work.


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## googleborg

i just decided to do my logitech sub, works a treat, though can't test at any kind of volume at this time in the morning....
   

   
  connects via 2 phono to the tape outs on my amp, the squiggly wires on the volume pot are for support ^_^ thought about using those caps but i couldn't get them to fit, oh well...hotwired the on switch cable to ground so it's always 'on' now, bass is adjusted on the back of the sub.
   
  shame i don't have a drill, could have mounted it all in the sub itself.  will report back tomorrow on this £10 subwoofer


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## googleborg

Quote: 





thelaw said:


> Sorry for being so ignorant about this. I decided I would take apart the powered sub...Easier said than done. I wound up destroying the box....Of course, I didn't harm anything else, but I guess I'll have to be building me a new sub box sometime...
> 
> Anyway, the model number is Z313. It cost me $30 on sale....Does the job mostly.
> 
> ...


 

  nice pics  you've actually got better quality parts in there than my ubercheap one, but the sub is the same as my other logitech i think, but i've no intention of hacking that one up haha...
   
  "Too much inrush current" inrush current is the juice the main filter caps initially draw from the mains as they fill up, too much and you'll nuke your fuses, even the rectifier diodes probably, but your diodes look quite beefy, might handle a little increase in capacitance?  there is bound to be a way of calculating inrush current with voltage and capacitor size and ESR and stuff, but i don't have a clue


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## TheLaw

Wow that looks interesting. I see a pot and some other stuff. What exactly did you do to it? I'm kind of confused. =D
  
  Quote: 





googleborg said:


> i just decided to do my logitech sub, works a treat, though can't test at any kind of volume at this time in the morning....
> 
> 
> 
> ...


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## TheLaw

Haha. Thanks. Yeah, I decided to get new caps all around. I decided to just get the same capacitance on the input because of space limitations...They should be here tomorrow or Friday, and I'll recap the board. I'll be sure to post some pictures. When's the last time you've seen a logitech sub with Nichicon Muse? Oh wait...never....


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## TheLaw

Quote: 





googleborg said:


> Quote:
> 
> 
> 
> ...


 



 Haha. Thanks. Yeah, I decided to get new caps all around. I decided to just get the same capacitance on the input because of space limitations...They should be here tomorrow or Friday, and I'll recap the board. I'll be sure to post some pictures. When's the last time you've seen a logitech sub with Nichicon Muse? Oh wait...never....


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## googleborg

interesting eh...yes this is the first time i've done something like this, wasn't sure where to start haha...
   
  i chopped the pod off and desoldered all the bits off it to use later  then i got a motorised alps pot i took out of a very dead yamaha AX-396 amp (yamaha seem to use all elna/nichicon caps fwiw), along with the phonos and a 3 wire ribbon cable scrap, and wired it all together, at first i had soldered the power on wire to the right channel, not ground, and was like 'why is this humming so badly?', then i rectified the mistake and put it all back together, am quite pleased that i never broke it honestly  if it passes mustard when i use it tomorrow i'm keeping my eye out for cheapy second hand PC subs on ebay to perhaps do an upgrade jobbie on...my NAD amp has two tape outs so i could use two identical subs O_o
   
   
  and for curiosities sake the inside of the satellite speakers....my thumb looks odd...

   
  i think that circular thing on the end is the magnetic shielding or something.


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## googleborg

the sonic results in short; for electronica type stuff - great! extends to bass down nicely, but with rock and such, just not high enough quality, bass sounds disembodied...i think the quality of the driver and the crossover point setting has a lot to do with this.


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## raindog1975

@TheLaw , I modified a pair of Logitech x140 ( even cheaper and crappier then your speakers ; I just wanted a small system for my work bench and I have experience in building and repairing speakers and amps ) with good results. I would suggest you use a metal enclosure for your amp ( to avoid EM interference  ) and put the power supply ( transformer and rectifier bridge+smoothing cap ) in a separate enclosure or at least use a separate board for the rectifier and place it as far as possible in the enclosure from the main board . Also is  a good idea to use the ground on the rectifier board as ground connection for the speakers ( to avoid creating a ground loop ). To improve the power supply you can also use 0.1uF polyester or even ceramic caps  in parallel with each rectifier diode and place one in parallel with the smoothing cap ( btw a bigger one - 6800 uF ar even 10000 uF wouldn't hurt providing you use the 5amp diodes ).


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## raindog1975

P.S. a good source of information about amplifiers , power supplies , grounding etc are Rod Elliot's articles : http://sound.westhost.com/articles.htm


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## raindog1975

@googleborg , the "circular thing on the end" is indeed magnetic shielding -the cheap version , it's just a another magnet glued to the pole piece in opposite polarity with the main magnet - good quality shielded speakers use a metal can over the magnet .


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## googleborg

oh right, i hope it's glued on well else it might fly off or something ^_^
   
  thanks for the link, have added it into my electronics folder in chrome


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## raindog1975

don't worry , it won't fall of , just don't keep the speakers too close to the monitor ( the "shielding" isn't very effective ).


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## raindog1975

P.S. another good source of information ( on everything related to audio ) is www.diyaudio.com


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## TheLaw

Well...I got all the stuff in yesterday. First thing I have to say: Logitech circuit boards are the biggest pieces of sh!t in the world. I tore about 50% of the pads off the bottom. Wound up having to put about 8 jumpers on the bottom of the board to compensate for me tearing off pads. I've never had a board where simply heating up a joint on medium heat would lift the pad. It was nuts....Even so, I got it working. Hopefully nothing comes loose. It's going to be stationary so I don't really see how that could happen. It's a MESS. But....it works. I didn't even bother to replace the really small electrolytics. The medium sized ones were already a pain in the arse. But it is pretty enterataining to see Nichicon FGs, KWs and Panasonic FMs on this piece of crap board. ....This board has really turned me off to doing anything special with it at all. I'm just going to try to get it working and get the new speakers hooked up and get it over with...=P


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## raindog1975

The PCB was probably designed for wave soldering and was never intended to have parts replaced ( if it brakes while still in warranty it's cheaper to replace the unit than to repair it ). I didn't bother to replace parts and modify the PCB on the x-140 , I just removed the IC and reused it on veroboard .


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## TheLaw

Yeah, I know it was never meant for components to be replaced....It's a super cheap unit. But I wanted to shoot myself in the foot desoldering/resoldering stuff. It does work, so I guess that's all I care about. I just got one of the subs in the mail about 30 minutes ago. Running off a 7.5W amp @ half power (because its an 8ohms and amp is stable at 4ohms), not in an enclosure, and using 22AWG wire....and it still sounds awesome!
   
  I'll get some pictures up for anyone interested.


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## TheLaw

(Above): Attached the big black heatsink to the stock one. It goes through holes I drilled out but I don't really thing its doing much. =P
   
  (Below Nichicon Muse FGs and some Panasonic FMs.

  (Below Nichicon FW audio cap on the power supply another Panasonic FM. Unfortuneatly, I left some CapXons on the board. The pads are so small for those, I didn't want to risk destroying the entire project.

   
  (Below More Panasonic FMs. In the foreground is a Nichicon FW. Still have some Samxons on the board. They're small so I'm hoping they won't have much effect on the sound.

   
  (Below Next one is pretty scary huh? Yikes. Somehow that works...Only God knows how.

  (Below Still waiting on my second HiVi M4N driver to come in...But here's one of em.


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## BobSaysHi

Quote: 





thelaw said:


>


 

 I lol'd


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## TheLaw

Haha. Is it that funny?


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## TheLaw

Bah humbug. It's not working now. I've checked everything and I'm lost as to what has happened....It just makes a popping sound when I turn it on and I can't get crap from it.


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## TheLaw

Well....I guess after wasting about $20 on random stuff...I'll just build my own amp


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## TheLaw

I knew this would happen...and I did it for some reason anyway. I'm so dumb. What made me think that I could just overhaul a Logitech amp board.  Damnit, I'm a retard.


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## BobSaysHi

Quote: 





thelaw said:


> I knew this would happen...and I did it for some reason anyway. I'm so dumb. What made me think that I could just overhaul a Logitech amp board.  Damnit, I'm a retard.


 

 Don't beat yourself up. Take it as a learning experience.


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## TheLaw

Well, there's not much else I can take from it...=P Ah well...into the world of crossovers and other confusing things we go.


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## bogdanxd

Hi u can make for me 2 photos from S220 remote control?  at front of circuit and back.. because


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## Pierrus60

i am not an électronicien , but i think that driving a 8 ohm speaker should be more eazy than 4 ohm  for your amp , you will get less heat


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## SoundDouble (Jan 30, 2022)

Deleted... didn't realize how old the thread is


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