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Old 9th December 2005, 06:55 AM   #851
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Default Re: Killer amp

Quote:
Originally posted by Chul


WANRING! do not use this right from the sound card of your PC. There may be some ground problem. A input transformer will solve this but..too bulky :-)
Did you build this to be a Christmas present for someone you wish to murder?

Yikes! You have the shield/ground sleeve of the RCA input jack wired directly to the 220 volt mains as well as the speaker output leads. I would suggest that the Amplifier Police raid your establishment pronto and supervise the destruction of that device. If that ever got into someone else's hands who didn't knoiw imagine what could happen., not to mention that you yourself could quite easily become it's victim also.

Please, please Chul, put a mains isolation xfmer (or a power transformer of some sort) on this amp or destroy it.
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Old 9th December 2005, 08:55 AM   #852
Giaime is offline Giaime  Italy
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I agree. Let's avoid posting unisolated amps schematics.

Just for adding something mine, I just found a quartet of 220V/110V autotrasformers. Now I can hear what are you going to say, that those also are uninsulated...

...well I took my trusty multimeter and measured: no continuity between the 220V winding and the 110V one. So I build a voltage doubler ps, 2x1N4007, 2x470uF, 150ohm, 100uF and I'm extremely happy of the 320V that it makes

This is now powering a one-tube line stage, consisting in a ECC81 in cathode follower (one section for channel), into my Marantz 1060 power amp sockets. Well... beautiful sound!

What a pity I don't have a camera because you MUST see it... it's laid on a wooden board, very messy but very un-definitive
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Old 9th December 2005, 01:00 PM   #853
Chul is offline Chul  South Korea
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Default Re: Re: Killer amp

Quote:
Originally posted by rcavictim


Did you build this to be a Christmas present for someone you wish to murder?

Yikes! You have the shield/ground sleeve of the RCA input jack wired directly to the 220 volt mains as well as the speaker output leads. I would suggest that the Amplifier Police raid your establishment pronto and supervise the destruction of that device. If that ever got into someone else's hands who didn't knoiw imagine what could happen., not to mention that you yourself could quite easily become it's victim also.

Please, please Chul, put a mains isolation xfmer (or a power transformer of some sort) on this amp or destroy it.
Hi rcavictim,

Actually I tried more than 4 version of these direct rectifiction amps and I got to know how safe or dangerous this can be. Many old radios rectified the AC inlet direct because it is not connected to other component and have no groud problem. I just wanted to have some fun. And DIY is just about to have fun, right?
Just in case, I use this amp only in my office where designated circuit breaker is used. But I do not think this is as dangerous as 845 or 211. Signal or speaker ground is actually isolated not by the transformer but by the rectifiers. I heard the same from local DIYers here too.

Anyway thanks for the comments..

* I showed the circuit after a request, but to some novice this can be dangerous. But how do I delete the circuit? I have not done this before.

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Old 9th December 2005, 05:48 PM   #854
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Quote:
Originally posted by Giaime
I agree. Let's avoid posting unisolated amps schematics.

I say let's not. They are hundreds opf postings on this board where schematics have been presented for member's evaluation. Many have potentially dangerous flaws which are spotted and ironed out by peer evaluation. That's the beauty of diyaudio.com and as a newbie that's where I have learned the most.

Goodness knows how many circuits here involve voltages that can & will kill you if handled incorrectly. I do not think we should start policing ourselves based merely on the premise that someone might do the wrong thing.

It seems that many of the Asian diyers are quite happy building equipment without isolation transformers. If so, more power (he he) to them, I am sure they are well aware of the risks & benefits involved.

Let's face it, with a few notable exceptions, most of what we discuss here would horrify the UL or whomever polices electronic equipment in your country.

PB
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Old 9th December 2005, 06:19 PM   #855
Giaime is offline Giaime  Italy
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Quote:
Originally posted by philipbarrett
Let's face it, with a few notable exceptions, most of what we discuss here would horrify the UL or whomever polices electronic equipment in your country.

PB
Ehehehe, that's for sure!
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Old 11th December 2005, 02:54 PM   #856
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Default My amps

http://dragon-hifi.pochta.ru/photo/
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Old 11th December 2005, 09:15 PM   #857
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heres my 50c5 guitar amp so far (yes I know its kinda messy.. ) :

Click the image to open in full size.

The transformer board is how I step the wall voltage down and then back up. A bridge rectifier setup gives me between 130-140 volts. By changing the transformer leads I can get 240v.
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Old 14th December 2005, 07:50 PM   #858
ddd is offline ddd  Bulgaria
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Default Re: Nothing special..but

Quote:
Originally posted by Chul
here it goes..It has two SE OPTs inside.I used partial feedback but just for fun. This makes sound and I am happy to show around to friends.

WANRING! do not use this right from the sound card of your PC. There may be some ground problem. A input transformer will solve this but..too bulky :-)
Just put an input trafo and it'll get safe.
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Old 15th December 2005, 11:48 AM   #859
jane is offline jane  Norway
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Default 6LU8, Sweep AMP

6LU8, Sweep AMP:

Some data and measurements:
2x12W rms, 2x25W peak
NFB: 14dB
16Hz-30kHz (-1dB)
THD: less than 1%, 12 watt output.

On the work bench:
Click the image to open in full size.

Front side:
Click the image to open in full size.

Final schematic:
Click the image to open in full size.

Thanks to Birger, the flight mechanic that did the metal work.
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Old 16th December 2005, 02:17 AM   #860
Cassiel is offline Cassiel  Libya
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Nice tubes, nice chassis, nice amp.
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