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Old 29th March 2004, 12:29 AM   #11
matjans is offline matjans  Netherlands
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yes there is. a diode should have a low resistance one way (red probe on anode or + and black probe on cathode or -) and a very high resistance the other way around.

these are REALLY basic electronics questions. Before building an amplifier, or in general trying anything having to do with high voltage may i humbly suggest either reading up on your electronics knowledge or better, try something *NOT* having to do with high voltage?

It might save your life... or your house, if the whole thing decides to go up in flames. One very nice project to get you started with is this headphone amplifier . It's basically a gainclone. A very simple headphone amplifier run off a battery. Better still, this headamp makes a perfect preamp (i'm using one as we speak/type).

This will get you started on the basics of electronics / opamps. Not that i'm such an EE god but i do know my basics and i must say this makes it a lot safer. Good luck.
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Old 29th March 2004, 08:31 AM   #12
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Well,

Notwithstanding the fantastic help i have been getting from everyone in this thread so far(for which i must say at the onset, i am eternally grateful for), i feel i need to rant a little.

Its not the first time someone has told me to 'try something easier'. Forgive me for saying this but i thought that this forum was about helping people with an interest to learn things they want to? I admit, i have no formal education in EE besides high school physics which i took a decade ago but that doesnt mean that just because i'm not an EE means i have to keep trying something easier do i?

I spent months researching on what DIY project to go for and when i finally came across the decibel dungeoun website i read what the guy said, looked at the schematic, played it out in my mind and thought to myself, hey, i think i can do this. The fact that the site said no EE background required was a big thing for me and i trusted it. So i gave it a shot and read as much as i could and tried to teach myself as much as i can, using this forum as a last resort only so i dont bother the experts here.

I'm not very rich, and after taking the big leap and ploking down about 150USD worth on electronics for a 4 channel gainclone(with the transformer eating a large portion of the cost) it just makes me feel awful when i get told to 'forget it and try something else'. It seems like such a waste to throw this stuff i spent so long saving up for away and not using it.

I mean, i've already committed myself and i really want to finish it. I know i've got this licked, and i sincerely believe i can actually build this thing once i find out what in the world is wrong with my PS wiring.

I've followed every piece of advice in this thread but the problem persists. its not that i havent tried the tips, but nothing seems to be working. I guess what i'm really trying to say is that i know i dont know very much, but is it too much to ask for a little help?

/end rant

I'm sorry if i offended anyone, i really do. Its just that sometimes i think this forum has an "Experts only, beginners not welcome" sign hanging on the door and somewhere along the line i forgot to read it before i came in
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Old 29th March 2004, 09:01 AM   #13
matjans is offline matjans  Netherlands
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rereading my post i may have sounded a little harsh. But then again, playnig around with 230V can be pretty dangerous. Just make sure you don't get killed and we'll all be happy.

to prevent you from getting killed i *REALLY* think you should use a fuse. get one (with a holder), place it in line with one of the primary windings. use a 2-3 amp slow blow fuse. And get a handful of fuses. DONT DO ANYTHING WITHOUT A FUSE !!

OK, back to the rectifiers. Have you tested them yet ?

if not:

put the multimeter in resistance-measruring mode.

to test the diodes in a rectifier bridge put the red probe on the lug with the AC marking, the black one on the + marking. the mm should give you a resistance of a few ohms (depending on type of rectifier). switch probes (ac black, + red) and it should gice you an infinite resistance (or unmeasurable anyways).

now, turn the rectifier a quarter to the right. repeat the process. and again, and again. each side of the rectifier should only have a "one-way" resistance, the other way around, it should be infinite.

If this is true, your bridge is OK, if it isn't get a new bridge.
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Old 29th March 2004, 09:08 AM   #14
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Default to L S ( S S)

I think some people are forgetting the values when dealing with the 3875.........


Quote:
Originally posted by lovely slut
i connected black to yellow(0V) with red and orange going to the AC terminals of the recitifer. Done this way, i get 25V from either of the secondaries to the 0V secondary and 50V from one AC secondary to the other AC secondary. When i connect this to the rectifier, i get that terrible sound and heat
Interesting. the basic power supply for any gc needs a ct that serves as the 0 volts. however you configured the transformer so that 50 volts goes to the rectifier, meaning that after the rectifier you will get approx 50 volts multiplied by 1.4 (grosso modo) and then the result will be more than 70 volts DC (EE's please correct me if I am wrong) a little bit too high if you ask me.
most guys here use a 18, 22,24 or 25 volts CT (centertapped) tranformer and so after rectification this # goes up to 38 volts or so, pretty high for it's purpose in this case.

I do not posess the knowledge to help you (although I would like to) , mainly because I am completely incapable on the electronics field, however I would tackle your problem by using another transformer, one that has 3 or 6 wires.
3 wires representing x volts, 0 volts or CT, x volts , with x = # of volts.
6 wires would be good for 2 gc's
the measurement of the 3 wire trannie should preferable not exceed 25 volts or 13 volts between one lead and the CT.

I have a similar toroid like you and it is laying here waiting for another project, not for a gc system.


Jean-Pierre

as I said before, I have no knowledge in EE whatsoever so please consult a capable person before proceeding.
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Old 29th March 2004, 09:12 AM   #15
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Default I just proved my contribution

If you supply 70 volts dc to the 3875 nothing happens, except a loud noise and some sort of clipping. If my Microsoft netmeeting would work I could provide you with the proof!


J-P
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Old 29th March 2004, 09:59 AM   #16
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mat,

dont worry its ok, i really dont mind. i guess its all part of the learning process. for what its worth, your help was really..well...helpful, lol

OK based on your advice i have tested the leads of the rectifiers

The results dont seem to make sense!

I have tried the combinations you requested, and i dont get one way results. Basically it works like this, one way i will get very high(but measurable) resistance as i move across the terminals until i come to the second last set before i come full circle(where there will be an unmeasurable, i assume infinite, resistance). It works the other way round as well when i fip the probes

So basically 2 adjacent pairs will have high resistance and the other 2 pairs will have high resistance when i flip the probes. Other that those cases, i will get no reading.

All terminals on the rectifier have connectivity.

The result is also consistent with both recitifiers.

I'm not sure what to make of it. I hope this doesnt confuse you half as much as it confused me!

uvodee> After reading your post, it kind of makes sense. Unfortunately, i have no idea if you are right idea. I got the idea to wire up my transformer as given in my earlier diagram(which is causing the short) from another member here i emailed. How he told me to wire it was pretty consistent with the manual of the transformer which i read as well. I was actually planning on measuring the DC voltage off the recitifier to test before i actually finished the circuit just to make sure though. Unfortunately, i cant complete the PS so i am still unsure which method to use!
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Old 29th March 2004, 10:56 AM   #17
Ropie is offline Ropie  United Kingdom
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Lovely Slut,

There is a section on wiring up a transformer for a gainclone on this page: http://www.decdun.fsnet.co.uk/gaincloneFAQ.html

Re: your name; we are all a bit odd to be doing this hobby aren't we?
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Old 29th March 2004, 11:52 AM   #18
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Ah thats right, thats the motivation for me wiring it the way i did as in the first post when this problem started(in the learning process, i read the entire website back to front many many times so i wouldnt need to ask any questions here except the ones i really couldnt get answers to). Correct me if i am wrong, but doing it that way means i only need one bridge rectifier correct?

I believe mat's method is equally viable and makes use of 2 bridges instead of one. Looking at the diagram intuitively, both methods appear to be the same(with the exception that mat's uses 2 bridged)

I have tried to wire the rectifier up both ways and in both cases, i get that horrid buzz & heat( i presume shorting).

And yes, you're right, i am wierd lol
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Old 29th March 2004, 12:45 PM   #19
Ropie is offline Ropie  United Kingdom
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The difference between the two circuit diagrams is probably that one shows just one channel and the other shows both channels. Very often diagrams just show one channel and you have to repeat it to get stereo; the cause of much of my early confusion I presume you are building a two channel (stereo) gainclone. You have options as regards the transformers (tx) and bridges:

a) 1 transformer to 1 bridge, split to both chips: [tx]--------- [bridge]-----[terminalblock]========== to chips

b) 1 transformer split to 2 bridges, to both chips: [tx]--------[terminalblock]=======[2 bridges]====== to chips

c) 2 transformers to 2 bridges to both chips: [2 tx]=======[2 bridges]====== to chips

(by split, I mean feed the single wires into one side of a 5W rated (or higher) terminal block and then connect two to the other side)

Two bridges are nearly always recommended (as you know) and the difference between 1 and 2 transformers is a warmer but softer sound with 1 and a fuller but slightly harsher sound with 2. Basically it is down to what you prefer; I like option b best.

Please get yourself a new pair of bridges - I know it's a pain, but from what you say it does sound as if you have burnt yours out. Are you sure your bridges are rated high enough, ie: can they accept atleast 25VAC (50 to be safe) and around 15W?
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Old 30th March 2004, 02:15 AM   #20
lgreen is offline lgreen  United States
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Default Possibly a shorted turn

Toroid right? You might be experiencing "shorted turn" phenomina. In other words, your circuit might be perfectly fine but your transformer bolt could be conducting. This results in high temperature and a very very loud buzzing noise with mechanical vibration. Try it without any bolts on the xformer, if it is still screwy with nothing through the toroid it can't be this. It happened to me, but only when I deflected the lid on my chassis to complete a circuit to the xfrmer bolt. For more info see this thread.

Toroids, mounting bolts, and shorted turns
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