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PostPosted: 07 Jun 2013, 15:44 
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Joined: 04 Jan 2013, 16:59
Posts: 6
Location: Alabama, USA
Hello, all!

I've been having a blast reading through this thread. Just thought I'd share my own build based on the TDA2050 and Tom's excellent write-up.

Attached are the images of the nearly-complete amp.

The tube pre-amp is a treble/mid/bass tone control based on the '3 Band Tone Control You Can Love' from http://www.angelfire.com/electronic/funwithtubes/Amp-Tone-A.html. I had to tweak the design somewhat to work with 12AU7s (as I have a bunch of those) and 250k Linear pots. The tube heaters are driven by an additional secondary that I hand-wound on the toroid.

The box for the amp came from TJ Maxx (a discount home decor store) and cost $15. It was originally intended to be a wall-mounted necklace storage/display case. I popped the glass out of the door and replaced it with a piece of scrap aluminum cut to size, then pulled all the pegs off the back to make room for the good stuff. I left the 'wallpaper' in the back because it looked like it would be a pain to remove. ;)

The +/- 25VDC power supply was made on vector board following Tom's instructions. The 170VDC power supply for the tubes is next to it and very simple in design.

All the pcbs were drafted in Eagle 6.4.0 and exposed/developed/etched at home.

All the signal wire used in the build came from about 10 feet of CAT-5e cable. Amazing how much wire is in that stuff. This particular cable uses solid wire, so once you form them, they stay that way.

I need to make some labels for the tone control knobs. If anyone knows of a good place to buy dial faces, please let me know! I also need to install some feet on the bottom of the box, and neaten up/permanently anchor some of the wires on the underside of the lid.

Last, but not least, it sounds *great*. My kids love to come dance in my workroom when I have it cranked up.

Let me know if you have any questions or suggestions!

Regards,

~ T


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PostPosted: 07 Jun 2013, 21:46 
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Joined: 04 Jan 2013, 16:59
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Location: Alabama, USA
Apparently, I can't figure out how to attach images.. :confused:
Attachment:
outside.jpg

2nd try.

~ T


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PostPosted: 07 Jun 2013, 22:10 
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Joined: 04 Jan 2013, 16:59
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Location: Alabama, USA
Aaaand attempt 3...
Attachment:
inside.jpg

(I'll catch on sooner or later.)

~ T


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PostPosted: 15 Jun 2013, 11:11 
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Joined: 28 May 2008, 21:53
Posts: 4579
Location: Winnipeg, CANADA
Hi Terrin2k, welcome to the forum.

Great job. The amp really looks great.

Enjoy your build!

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PostPosted: 19 Jun 2013, 06:06 
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Joined: 18 Jun 2013, 11:39
Posts: 6
Hey guys
i am new to this forum, but i joined it specifically for tda 2050 thread.

I am going through a problem, i ordered a transformer from my local manufacturer which was supposed 18-0-18 VCT 8AMP transformer.

The transformer came in looks alright but when i brought it home, and tested Vac between center tap and one of the two rail (before rectification) it shows me whopping 24.5 volts!! i wonder after rectification and smoothing the value would become around 28 volts! will it be safe to run TDA 2050 on such high voltages on 6 ohm loads?

or please suggest some cure to this problem :( i am goin insane...


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PostPosted: 19 Jun 2013, 09:52 
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Joined: 06 Apr 2009, 10:08
Posts: 1592
Location: US Pacific Northwest
godslayer wrote:
The transformer came in looks alright but when i brought it home, and tested Vac between center tap and one of the two rail (before rectification) it shows me whopping 24.5 volts!!
This is because you tested it with no load. Since you specified an 8A secondary, the transformer must be wound such that the output voltage AT LOAD is as specified. This is a beefy secondary. Put a load on the secondary and as you get closer to 8A the output voltage should settle to the specified 18VCT.

Test and report back.

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It's all about the Glass!
http://www.CascadeTubes.com
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PostPosted: 19 Jun 2013, 10:40 
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Joined: 18 Jun 2013, 11:39
Posts: 6
Suncalc wrote:
godslayer wrote:
The transformer came in looks alright but when i brought it home, and tested Vac between center tap and one of the two rail (before rectification) it shows me whopping 24.5 volts!!
This is because you tested it with no load. Since you specified an 8A secondary, the transformer must be wound such that the output voltage AT LOAD is as specified. This is a beefy secondary. Put a load on the secondary and as you get closer to 8A the output voltage should settle to the specified 18VCT.

Test and report back.


i know sire, the voltage is a bit off, at complete 8Ampere current usage, the voltage should sag to 18v and remain constant there. but i was wondering, can i connect only two tda 2050 to it? ( i had plan for 6 channel system drawing out 6 TDA2050 thats why i used such a huge transfomer) for the test purpose only, will it still blow up the chips? ( I REPEAT THAT VOLTAGE IS ONLY BEFORE RECTIFICATION) i had made a filter circuit and one tiny capacitor rated at 2200uf 25v exploded on my face with lots of smoke sound and wool in my hair :geek: i know it was my mistake, i shouldve taken bigger caps, but this was pretty much unexpected as i expected it to be 18v only. ill be scouting for better caps in a while (i have pair of 3300uf 63v kenwood audio caps.. but theyre just too delicious to be used in power supply.) ill work on my supply but the question is, will two channels be able to digest this high voltage?


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PostPosted: 19 Jun 2013, 13:14 
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Joined: 06 Apr 2009, 10:08
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Location: US Pacific Northwest
Have you thought about throwing in a couple of paralleled pass elements to drop some of the voltage? Just high current transistors appropriately biased should work.

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PostPosted: 19 Jun 2013, 22:51 
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Joined: 18 Jun 2013, 11:39
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Suncalc wrote:
Have you thought about throwing in a couple of paralleled pass elements to drop some of the voltage? Just high current transistors appropriately biased should work.


what about forward biased diodes?


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PostPosted: 29 Jun 2013, 22:24 
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Joined: 04 Jan 2013, 16:59
Posts: 6
Location: Alabama, USA
What kind of transformer is it? If it's a toroidal transformer, you could always counter-wind both sides of your secondary. Depending on the construction of the transformer it may only take 10-20 turns to drop the voltage to the desired level. If you test it and the voltage has gone up, then you've wound in the wrong direction. ;)

Good luck!

~ T


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