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Old 2nd December 2004, 08:42 AM   #1
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Default Burning in GC, results and problems

Hi all,

I'm burning in a GC built using Brian's 3875 basic kit as follow:
- all components from Brian (without zobel parts) are used
- all components are new
- 100K log pot (Tyco)
- dual mono with 2 x Talema (RS component) toroidal transformer, each is 2 x 18V/160VA
- non-boxed yet, still on the open trial board.
- not-grounded to the earth (the CHG do not connected to the AC ground) since in my home I do not have a "real" earth ground. In Indonesia, although we use European Schuko power connector (2 pin + 1 ground), it is very rare in houses to have a Live-Neutral-Gnd electricity installation; as in my house I only have Live-Neutral, while the Gnd is actually wired to the Neutral at the distribution panel.

Accompanying equipment is:
- CD player: Meracus Tanto
- Speaker: Dynaudio Audience 40 (86.5db sens./3.9Ohm min.)
- cable, I/C: various DIY: tighly twisted thin magnet wire and parallel/taped magnet wire
(my serious I/C, Eichmann express 6 is being broken on it's connector and cannot be used temporarily)
- cable, spk: Supra 4.0 and DIY cat-5

The very first experience I had, was a bad experience. I blew up my old car speakers that were connected to the amp. I was stupidly connected the speaker to the amp without any protection and forget that the powering-up amp is a very dangerous process. With the speakers connected, I powered-up the amp: one speaker dead suddenly and the other one after playing a song for about 5 seconds.

(yes... I should test the DC voltage accross the output with dummy load first... but I was so tempted to hear the sound... and the GC seems too simple to make a mistake with...)

It reminded me that I need to install a delay/speaker-protector circuit and relayed to protect precious speakers. I'm also thinkin to add a soft start circuit before the ac mains touch the transformer (although very rare I hear a low "bump/bang/dang" sound on the transformer when it was start. In-rush current while power-up must be "bad" in a long term).

So far, the amp has been burned for about 30 hours, though I cannot burn it continuously. Mostly only about 8 hours a day. And, I can only play it low (almost very low) since I can only play it continuosly after my family went to bed at night.

My feeling with the GC is mixed. The amp actually works...

The GC sounds detailed, forward but very smooth, even from the very start. Voices (especially females) sounds beautiful. My current amp, Nakamichi IA-2 Integrated Amp, sounds cold, laid back and veiled compared to the smoothnees, forwardness and details of GC sound. Too smooth for my taste actually, since my CD player is already a refined and smooth machine. I also found that GC sounds a lot better when warm than when it is cold (something normal).

I have some annoying problems with the amp, however... (that's why my feeling is mixed...)

1. The amp sometimes sound thin, especially with rhythmical music, but do not really annoying with slow music

2. less of attack, very hearable with rhythmical music like jazz fusion, tango and rocks, for whatever the volume I set (low/soft or loud)

3. after got warmed, maybe after 5 hours, there is a soft rattling (something like mechanical hum) seems comming from the amp board (I try to distinguish, whether the sound come from the transformer or the board, but it seems they come from the board)

Guys, as more experience builders, what do you think for the cause of the problems?

For the thin and less of attack problem: Is it true that my speaker is a very bad match for my GC version?

If it is not my speaker, will one (or all) of the following updates help?
- still in passive-pre style, change pot to lower value (10K or 25K)
- use regulated PS (using LM338, CarlosFM based one)
- use snubbered unregulated PS (as CarlosFM idea)
- grounding to the earth
- burning further, maybe to more than 100 hours

For the rattling sound, what can be the source of it?

Sorry for the long post. Also, I'm living in Indonesia, which has about 12 hours difference with most US states. I will be off from the forum for the next 14 hours after this post.

Thanks,
---
David
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Old 2nd December 2004, 09:03 AM   #2
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Your problems are probably caused by too small heatsink - inside chip is thermal protector, which fall output power after overheating ( this is that " rattlesnaking " ). Try to use bigger one.
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Old 2nd December 2004, 10:34 AM   #3
kmj is offline kmj  Sweden
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Quote:
The very first experience I had, was a bad experience. I blew up my old car speakers that were connected to the amp. I was stupidly connected the speaker to the amp without any protection and forget that the powering-up amp is a very dangerous process. With the speakers connected, I powered-up the amp: one speaker dead suddenly and the other one after playing a song for about 5 seconds.
Blew up, why?
Had you made a faulty connection or something?

I shouldn't need any extra components or protections to start to use the GC if I have a vloumecontrol installed, should I?
(gettin a little worried here).
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Old 2nd December 2004, 12:37 PM   #4
Nuuk is offline Nuuk  United Kingdom
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Selamat pagi David,

Presumably there was a fault that caused yor speakers to blow! Did you find it and if so what was it?

As suggested, make sure that you have adequate heatsinking on your GC (or move to England - I don't mind a swap for the winter ) .

A 25K pot should be better, I believe around 22K is meant to be the optimum, with the BrianGT kit.

A zobel may help.

Personally, I prefer some sort of buffer on a GC. A regulated supply improves things but also makes the chips run hotter - something to be aware of in your part of the world.

As regards a soft start, it shouldn't really be necessary. Why not just switch on each of your 160 VA transformers separately?

I was advised to make a separate earth connection by burying a coppler plate, pipe, suacepan etc in a patch of damp ground as near as possible to the hi-fi and then running an earth wire from that back to my hi-fi. Perhaps the more knowledgeable would like to comment on this!
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Old 2nd December 2004, 12:40 PM   #5
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Quote:
Originally posted by kmj


I shouldn't need any extra components or protections to start to use the GC if I have a vloumecontrol installed, should I?
(gettin a little worried here).

No, you shoulden't need other protective components.
I did not even use a pot, as ong as the source have a variable output. (discman)


dw1narso: as for the sound, i'v had simelar findings with the lm3886 amp i built. equlization is a must with my amp, oterwhise the "rawness" gets lost in the music, and "bassrumbling" turns into a seriouse problem. the sound being TO smooth!
I'm going to try the tip i got of soldering one of the resistors on the legs of the IC instead of on-board, cutting the feedback loop short, or so the guy said.

as for burning in, i played somwhat high for about 3-4 hours after asembly, and that alone improved the sound very much, so 100 hour seem a litle overkill...

and as for speakers i personally use very hard-to-drive DIY speakers, an i dont think the gc like them very much, but your speakers apear to be what gc's like, easy to drive..
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Old 2nd December 2004, 07:05 PM   #6
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Hi David,

D>The very first experience I had, was a bad experience. I blew up my old car speakers that were connected to the amp.

Did you measure your cdp out ? maybe the source sends dc and theres no coupling cap at GC input.

D>So far, the amp has been burned for about 30 hours, though I cannot burn it continuously. Mostly only about 8 hours a day. And, I can only play it low (almost very low) since I can only play it continuosly after my family went to bed at night.

I use fm signal and 8ohm 80W dummy load set at 2V AC across the load to burn GC3875

D>My feeling with the GC is mixed. The amp actually works...
The GC sounds detailed, forward but very smooth, even from the very start. Voices (especially females) sounds beautiful. My current amp, Nakamichi IA-2 Integrated Amp, sounds cold, laid back and veiled compared to the smoothnees, forwardness and details of GC sound. Too smooth for my taste actually, since my CD player is already a refined and smooth machine. I also found that GC sounds a lot better when warm than when it is cold (something normal).

pakai komponennya apa aja ? gw pake 3875T, R full riken (ga nemu caddock uk besar, yg ada nilai2 kecil watt gede buat pasif xo) dan C black gate, dual maryland toroid... stl break in 150jam cont imo susah cari lawan 3875 ini. I have been using various amp, tube and ss inc Densen, ML, Pass Labs, Audion, Connie J, ARC, Creek, Threshold and listened many amp at any price... the CG have something that many $$$ amp cannot match. Of course its not the best amp in the world but overall it have so much rightness, directness and musicality. Some of my friends mostly mature audiophile that have well trained ear said so, komponen jg sangat berefek, begitu juga diode bridgenya, I prefer fast than ultra fast like MURxxx

D>3. after got warmed, maybe after 5 hours, there is a soft rattling (something like mechanical hum) seems comming from the amp board (I try to distinguish, whether the sound come from the transformer or the board, but it seems they come from the board)
Guys, as more experience builders, what do you think for the cause of the problems?

Did the transformer get hot ? have u installed a slo blo fuse ? The hum maybe diode from the rectifier board or transformer. Check diode rectifier, if it gets hot then replace the diode.

D>For the thin and less of attack problem: Is it true that my speaker is a very bad match for my GC version?

dyn memang berat, mungkin juga kurang match.

D>If it is not my speaker, will one (or all) of the following updates help?
- still in passive- pre style, change pot to lower value (10K or 25K)
- use regulated PS (using LM338, CarlosFM based one)
- use snubbered unregulated PS (as CarlosFM idea)
- grounding to the earth
- burning further, maybe to more than 100 hours
For the rattling sound, what can be the source of it?

mungkin bisa coba dulu pinjam/pakai spaeker lain sebagai perbandingan, selain itu komponen jg berpengaruh besar imo, coba2 saja ganti R dan C serta dioda bridge disamping karakter 3875 itu sendiri yg gak teralu tebal kaya tabung

Senang berkenalan dgn anda... ternyata ada juga yg bikin GC di indo he3
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Old 2nd December 2004, 07:22 PM   #7
kmj is offline kmj  Sweden
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is it just me or was that last post waaaay incomprehencible=

(mungkin bisa coba dulu pinjam/pakai )

Anyway Can anyone give me the dimensions of the PCB's incl components? depth, hight, breadth (condensors mounted) and it's Brians Basic-kit.

I'm goint to build the box prior to recieving the parts.

Best regards
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Old 2nd December 2004, 10:35 PM   #8
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Quote:
Originally posted by kmj
is it just me or was that last post waaaay incomprehencible=

Best regards

Nah, i'm fluid in Indonesian, aren't you? i thought everyone was these days..
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Old 3rd December 2004, 01:37 AM   #9
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Earth Grounding in the US

Also termed as Bonding, building code requires a 6 foot rod be pounded into the earth 5 feet. A bonding clamp tightened around rod and ground wire. I'm not sure of the ground wire gauge required. I would use a grounding wire same gauge as breaker/fuse circuit for serviced area (the area in house being supply electric). As for the ground run, as short and convenient as possible.

Never use grounding wire as curent carrier.

Phil
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Old 3rd December 2004, 01:50 AM   #10
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Ha, ha....

we are not supposed to talk in English only on this forum, right?

Surprised that some of you knows Indonesian language....

Don't worry KMJ and other else, it is just felt nice to have other people talk in your own language... I even speak Javanese language...: Ono sing biso?

to Pavel: when rattling, the sound from speaker is not affected, just when I come close to the amp that I hear that rattling sound. Could still be caused by the SPIKE?

to KMJ: it is not just blewing up my speaker actually. My house electricity breaker also shuted off when I power up the GC, while at the same time there are other big load electrical house hold running (like rice cooker and iron). I think in-rush current must be one of the reason for this. Also some gaincloner mention about "thump" sound during power up.

Anyway, speaker relay protectors and soft start circuits won't be a bad addition to the amp, right...?

to Nuuk: Selamat Pagi/Siang... (I live 7 hours ahead of you. :-) I must be older faster then... :-) ) AND yes, it is hot to live in Jakarta...

I forget to mention, I routed through all the wiring and connections and parts on the board, a few times before I turned it on. And then few times again after the speakers blown-up. My last suspect was that in-rush current..

Now, for the burning process, I turn on the amp first, wait few seconds to let it stable, then I connect the speakers. Safe so far.

If I read from previous Brian's threads, I saw that previously he put 20K. It was just after he run out of stock, he used 22K.

What will zobel help?

Separated switches... That's a good idea... why I never think about it!

About DIY-ing ground, it was already on my thought sometimes ago, but I will probably move to other house next mid-year so I cancel the idea.

to demorgon: I already solder the feedback resistor to the chip legs.

to Surya: of course no coupling cap. I build Brian's GC version which use very minimal components.

http://www.chipamp.com/lm3875.shtml

Transformer is never got hot. (Not even quite warm, I think...) Diode? I use MUR860... any replacement suggestion that obtainable in Indonesia? But I though MUR 860 found to be the right match by many gaincloners...

About thin tube sound, I think it is topology/design related. I have a friend that swear by 300B, then 10Y, then RS421... I follow some his evolution of 300Bs (at lease 7 times evolved), they sound very different one to another: some thin, some deep, some sweet, some even can rock...

Boleh off-air Pak Surya, kapan-2? Saya tinggal di BSD.

to Phil: I ever saw some grounding cables accompanyed by some networking equipment. It was 8AWG at least. Some even come with 4AWG grounding cable...

Regards,
---
David
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