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Mods on a Reciver

Discussion in 'Home Theater Projects' started by Allen Ross, Apr 8, 2003.

  1. Allen Ross

    Allen Ross Supporting Actor

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    Okay my buddy in the dorm room accross from me, the guy who got me into DIY audio, is adding on to his list of ongoing projects, with modifications to his fideck (SP) amps along with his roomates cheap sony amps.

    What he is doing is bascily trippling the capacitors on the rail, going from somthing like 10 joules to about 30 jouls. he is also taking out the realitivly cheap binding posts and replaceing it with evenly spaced, nicer (for bannana plugs) binding post.

    I am just wondering if this will be worth the time and effort, he says he can snagg all of the caps off ebay for somthing like 20 bucks between the two fidecks he is putting somthing like 16 caps where it did have 4.

    Also has anyone else done any sort of mods on their recivers? and how has their experience been?
     
  2. Dave Milne

    Dave Milne Supporting Actor

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    Adding power supply filter capacitance can improve dynamic headroom. It keeps the supply rails from sagging during peaks.

    Before doing this, however, you MUST determine if the power supply rectifier diodes can handle the turn-on surge. This analysis is not always easy since surge current depends on the impedance of the power transformer, the ESR of the caps, and even the stiffness of the wall socket power!

    To be safe, you can install a soft-start circuit... whereby you charge the caps through a controlled impedance (resistor) briefly at startup (a second or two) and then close a relay across the resistor.

    The above assumes you have a conventional power supply. If it's a switch-mode, things can be better or worse, depending on whether the PWM controller has current limiting.

    Also... if you decide to go ahead with this... be sure to use standard safety precautions. The rails in a typical 100wpc receiver are on the order of +/-50 Vdc. The caps may hold charge long after the receiver is turned off.
     
  3. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    "The caps may hold charge long after the receiver is turned off."

    I learned that one the hard way on a sub plate amp. 12 hours after being unplugged it still had +/- 60V or so!
     
  4. Michael R Price

    Michael R Price Screenwriter

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    Allan,

    Yeah, be careful with the caps. The +/- 75V at 23,400uf I have isn't very safe, but I put 4.7kohm power resistors across the rails to slowly drain power when it's off. (Also, after I unplug it I play music until it distorts, to drain the power supply.) I use a thermistor wired to the power input so they don't draw absurd current at turn on.

    What kind of receiver is it? Frankly this kind of modification might not be worth the time and money if the amplifiers aren't very good sounding in the first place. You might get better bass and more power, that's for sure... but you'd probably be better off saving up and building a new amplifier (they can be cheap)!

    What results did your friend get from his other modifications?
     
  5. Craig Treusdell

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    Michael, how did you wire the thermistor? My house dims more than from the A/C when I cut this on. It plays for around 10 seconds after shutting off with average volume music.

    Allen, I think the more the better. [​IMG] But I do not think that will always produce better results.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  6. Allen Ross

    Allen Ross Supporting Actor

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    the apms that he is modding are two fideck rack mount amps from MCM, the brushed aluminum i think the specs have them at around 200watt/chanel. and he is also doing his roomates dolby digital ready sony reciver. Last night he checked the voltage on the rails of the sony and it was around 70vdc and it had no bleader, even when i was unpluged and i tried to turn it on it kept the same voltage wich is a little scary if you think about it.

    i don't kown what he is going to do with the rectifyer but i am sure he has it all worked out.

    He says that he thinks the Fideck (the ones hes going all out on) have a soft start where it charges the caps slowly for a few sec and then goes full so he thinks he will be alright. i am just ammazed that he hasen't poped a breaker yet in his room. my lights dim just with my 1100watt microwave, where he has 3 fideck amps totaling over 1200 watts and then a decent size reciver, active XOs, 2 EQs, DVD player, two computers fridge, and i beleive we are only on 15 amp breakers, oh well it will be an exciting adventure.


    BTW i have no intentions of having him mod my onkyo, its still under warrenty and sounds fine, but maybe next year.
     
  7. Dave Milne

    Dave Milne Supporting Actor

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    Craig,
    That's a great looking amp. Is it your own design? Simply beautiful layout and construction!

    I see you decided that six separate power supplies was a bit over-the-top [​IMG] What is the power output?

    'Love the bank of rail fuses...
     
  8. Michael R Price

    Michael R Price Screenwriter

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    Craig,

    Very impressive looking! What kind of amp is it?

    The thermistor is a Keystone CL-60 from Digikey (what Pass uses) and it's just wired in series with the transformer primary. I occasionally hear some hum from the transformer when it turns on, but there's no dimming of the lights or anything. (And surprisingly, no turn on thump.)

    Here's my much less professional-looking one (this is a monoblock sitting behind my speaker). Who needs a chassis? [​IMG]
    [​IMG]
     
  9. Allen Ross

    Allen Ross Supporting Actor

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    [sleazy common]hey you got a nice set of heat sinks[/sleazy common]
     
  10. Craig Treusdell

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    Dave - thanks. This is a modified Leach Amp. I built it for a 1 hour credit (and because I like challenges). 6x120W @ 8 ohm and 2x240W @ 4 ohm, but it sags due to the small transformers when pushing 6 channels at 4 ohms with sine waves. I actually bought 4 transformers and was going to parallel 2 for each of three channels, but between Dr. Marshall Leach (my professor at the time) and another EE prof, I could not decide if I should parallel before or after the bridge rectifier -- each had problems. I also could not figure out how to mount one on top the other and make it look nice, so I stuck with 1 per 3 channels.

    The front and back are made from 3/8" Lexan. The heat sinks had to be interwoven for space, but there are 2-4" fans below them pushing cool air up. The layout and wiring took a long time to get everything symmetrical, and the circuit boards took many nights of soldering. I think it was around 200 hours and $1000 in parts.

    Michael - thanks. Great heat sink. And anything you build yourself always seems to sound better. [​IMG] I'll look into adding the thermistor. I still have to add bleeder resistors to the power caps. This amp comes on the instant the power rocker is pushed. No turn-on delay and no turn-on thump! Also no volume knob.

    I was going to build a preamp, bought the parts, built the circuit on a breadboard, and stopped. That was 8 years ago.

    I have been debating on building a full active-crossover HT setup using all Leach amps and Leach Super amps, but it sure does seem like a lot of work after using a QSC RMX 2450 amp for my sub. Pro amps are cheap, high-powered, and durable. The Leach Super amp is 300W @ 8 Ohm, 600W @ 4 Ohm, and he told me it can be set up to drive a 2 Ohm load. So bridge two together and get 2400W @ 4 Ohm. Or buy a QSC amp for $570.
     
  11. Dave Milne

    Dave Milne Supporting Actor

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    Craig,
    I think it's time to drop in a couple of 1KVA AVEL torroids. 'Should solve the sagging problem!

    I know what you mean about DIY... sometimes hard to justify when there's lots of good, cheap stuff out there.

     
  12. Michael R Price

    Michael R Price Screenwriter

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    I hate to sidetrack this thread, but it's already been derailed.

    Craig,

    So you had Marshall Leach as a professor? Nice. How does his amp sound to some others?

    My amp's the symmetrical Mosfet-output one by Anthony Holton (he's from the University of Tasmania, I think). Power and heat are not a problem... 750VA Plitron toroid, 47,000uf capacitance and a 0.2-0.28C/W heatsink for each channel. I'm not really sure about how I like the sound yet, since only one channel worked reliably so far.

    Dave,

    What you said about spectacular. On my right channel, I've had nothing but problems. A few of the failures have been loud pops/sparks, but the most recent time it turned on and looked OK... when I touched the multimeter leads to the board to check the voltages, one of the input stage transistors *exploded*. Ouch.

    Check those zener diodes and other voltage references. The exploding transistor was in a cascode stage supposed to drop all but 15V of the power supply to the main input pair... a zener diode was used as the 15V reference. When the zener got damaged somehow, its breakdown voltage went down to 0.3V so the cascode then had most of the DC supply across it (75V, and the transistors are rated 65V). Lesson learned, check every component, not just transistors.
     
  13. Craig Treusdell

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    I've never really listened to it with a good set of speakers. When Leap 5 arrives I plan to build such a set. I can hear the faintest hum but only with my ear almost touching the tweet/mid in a quiet room. Even after playing 2 channels into a 4 ohm load for several hours at full volume the heat sinks were only warm enough to tell which ones were being used (2 warm, 4 cool). It seems to have a better punch to music than any of my receivers (which are not of audiophile quality). It is capable of driving 2 ohm loads.

    Dr. Leach told me many stories about students having problems: backwards caps and transistors, bad solders, the trace coming off the board due to multiple solders/desolders. I was very careful about everything I did and got a good run on the first attempt for all six channels. It took several months just to order all the parts and find the best cost. I have not been running it continuously, but every time I pull it out it works fine.

    Dr. Leach has a 2 channel Leach amp he built in seventy-something. I believe it has played every day in his office since then without one problem. Find a receiver today that will do that! I still am leaning toward the QSC PLX series with a 107dB noise floor for my future system.

    Dr. Leach was an excellent prof -- one couldn't ask for more. I had him for many classes from op-amp design to transistors to audio engineering. I also took a great class from Dr. Eugene Patronis relating to the physics of acoustics. He spoke about a project for the military for shell shock simulation that could generate a flat response well into the infrasonic range at 170dB SPL.
     
  14. Nathan Smith

    Nathan Smith Agent

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    while the resisters and transisters and diy your own whole amp thingy is way over my head im interested in imput on the

    worthwhilenessness [please dont let my english teacher read this[​IMG][​IMG]] of installing nice gold binding posts instead of these stupid tin spring clips on my kenwood reciever

    besides the fact that i can HARDLY fit my 12gauge wire into the clips wouldnt gold plated 5ways posts be much better conducters [noticable?]

    will cost me 20bux to put nice binding posts on what do ya think?



    eventualy im getting i believe a denon 2803 but not quiet yet so is this worth while?
     
  15. Dave Milne

    Dave Milne Supporting Actor

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    Although I also hate "stupid tin spring clips", I doubt there would be any sonic difference. You can always solder on some pin contacts to your wire to make them fit better. Save your money for the receiver upgrade... that will be noticeable.

    There are always risks associated with modifying a component: You would likely need to drill into the chassis to mount the new posts. It might be difficult to avoid drilling into something important inside without completely disassembling the entire chassis --which brings the risk of not getting it back together right. You would also need to make sure you absolutely clean out every last metal shaving. They do not mix well with electronic components!

    Even if you're successful with the mod, it will likely reduce the resale value of the receiver. People are spooked about buying something that has been tinkered with...
     
  16. Nathan Smith

    Nathan Smith Agent

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    thank u [​IMG]

    very goods reasons iv decieded not to go forward with it and continue saving...

    McDs dont pay of to much but i dont pay any rent so ill get there eventualy

    :b denon 2803 calls to me...:b aaaahh


    lol i juz snapped up 18 REALY CHEAP gold binding post terminal cups for use on this project and others

    they were only 72c each OMG i had to get a bunch
     
  17. Allen Ross

    Allen Ross Supporting Actor

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    hot deal!!

    he finished the speaker terminals and they look nice, he lined them just right so the bannana plugs and wires won't interfer with each other.

    I still can't wait to check out his huge external capcitor bank, i can't think of anything more sexier then that, well i can but thats for a different forum [​IMG]
     

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