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Which transformer for 3886 chipamp.com kit?
Which transformer for 3886 chipamp.com kit?
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Old 7th October 2016, 01:32 PM   #1
Schlumpfpeter is offline Schlumpfpeter  Germany
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Default Which transformer for 3886 chipamp.com kit?

Hi!

I feel kind of stupid for asking this question, because I got all the information I theoreticaly need to make I choice by myself, but all those additional numbers and values I see at mouser are completely confusing me.

The quest:
I need to find a fitting transformer for my stereo chipamp.com 3886 kit at mouser.com (I am ordering additional parts there, so it would come handy to buy those transformers there as well).

The information I got:
"For the transformer, a transformer with dual secondaries producing between 18vac and 25vac is recommended. One DIYer has used a 2x30vac transformer without issues, but 2x25vac should work best for a wide variety of loads. One can choose a variety of VA ratings and rail voltages. Keep in mind that after rectification, the rail voltages are somewhat higher than the non-rectified AC secondary rating of the transformer. The secondary voltage averages to 1.4 * the AC voltage, minus diode losses. The transformer regulation is also a factor, dependent on the size and regulation characteristic of the transformer in question. Suffice it to say that a commonly used 18V transformer results in approximately 25V rectified, while a common 22V supply produces around 34V rectified."

So in my naiv state of mind, I went to the mouser website and looked for a transformer with those specifications.... and know I do not even know where to start describing the confusion in my head

Can you guys please point me out to a transformer at mouser that would work for this particular case?

Thank you very very much,

SP
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Old 7th October 2016, 03:34 PM   #2
AndrewT is offline AndrewT  Scotland
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For 8ohms load use a maximum of dual secondary 25ishVac.
For 4ohms use maximum of 22Vac

For EU mains voltage you need a 230:0-25,0-25 Vac and >50VA per channel. I prefer a minimum of 160VA, some go as high as recommending 300VA.
Look up Rapid, RS, Farnell, CPC and dozens of other EU retailers. They all have suitable transformers.
Why use a USA retailer for EU? For a start they operate on 110/120Vac instead of 220/240Vac.
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Old 7th October 2016, 06:45 PM   #3
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by AndrewT View Post
For 8ohms load use a maximum of dual secondary 25ishVac.
For 4ohms use maximum of 22Vac
I concur. That'll give you roughly 28 V for 4 Ω and 35 V for 8 Ω. That'll ensure that the LM3886 operates within its limits.

Quote:
Originally Posted by AndrewT View Post
>50VA per channel. I prefer a minimum of 160VA, some go as high as recommending 300VA.
Depends on the application. For sine wave reproduction you need:
2 x 22 VAC @ 121 VA per channel for 4 Ω operation.
2 x 25 VAC @ 101 VA per channel for 8 Ω operation.

For music signal (14 dB crest factor), you need:
2 x 22 VAC @ 51 VA per channel for 4 Ω operation.
2 x 25 VAC @ 44 VA per channel for 8 Ω operation.

I recommend aiming for somewhere in between these two extremes. So 2 x 22 VAC @ 160 - 200 VA for a stereo amp intended for operation down to a 4 Ω load.

For US buyers, I'd go with an Antek AS-2222 (2 x 22 VAC, 200 VA) transformer. For buyers elsewhere, I suggest the Hammond 1182N22 (2 x 22 VAC, 160 VA). You can get the Hammond transformer at Mouser.

Tom
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Last edited by tomchr; 7th October 2016 at 06:48 PM.
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Old 7th October 2016, 08:24 PM   #4
jvhb is offline jvhb  Europe
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Which transformer for 3886 chipamp.com kit?
TTSA0200 - Transformer AUDIO TSA200VA - voltage to 50V - Shop Toroidy.pl

Very good transformers from Poland.

- and a nice german one:
http://hifituning24.de/transformator...60va-2x22v.php
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Last edited by jvhb; 7th October 2016 at 08:31 PM. Reason: link added
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Old 9th October 2016, 01:13 PM   #5
torgeirs is offline torgeirs  Norway
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Is the crest factor VA numbers the effects of Intermittent operation described in page 4 in:
http://www.noratel.com/fileadmin/con...ransformer.pdf ?
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Old 9th October 2016, 01:58 PM   #6
6L6 is offline 6L6  United States
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Which transformer for 3886 chipamp.com kit?
To directly answer your question:

Quote:
I need to find a fitting transformer for my stereo chipamp.com 3886 kit at mouser.com
160VA -

http://www.mouser.com/ProductDetail/...e2gpyF4Q%3d%3d

225VA -

http://www.mouser.com/ProductDetail/...Xk9OHOKA%3d%3d

That said, especially being in Europe, I'd get the Toroidy or the one from hifituning24 that jvhb linked to.
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Old 9th October 2016, 04:29 PM   #7
davym is offline davym  Scotland
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I buy direct from Airlink, good prices, options for screening & with a low pound rate - might be worth considering. Standard Range Toroidal Transformers: CM0225222: 225VA 230v to 2x22v
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Old 9th October 2016, 09:47 PM   #8
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by torgeirs View Post
Is the crest factor VA numbers the effects of Intermittent operation described in page 4 in:
http://www.noratel.com/fileadmin/con...ransformer.pdf ?
You can find my write-up on the crest factor in the Thermal Design section of my Taming the LM3886 pages. I expand on the implications for the power supply in the Power Supply Design section.

Tom
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Old 10th October 2016, 12:01 AM   #9
asuslover is offline asuslover  Romania
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Which transformer for 3886 chipamp.com kit?
Multicomp Torroid Power Transformer 25V x 2 - 5A | MCTA250/25 (MCTA25025) | Multicomp
they have 15% off coupon online and they have free shipping deals (sometimes).
These toroids are actually noratel brand.
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Old 10th October 2016, 12:45 PM   #10
Schlumpfpeter is offline Schlumpfpeter  Germany
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Guys, you are awesome. Thank you very much for all the advices.

My profile flag is a bit misleading, as I am actually German, but I live in the UK, but obviously still in Europe.

I think I will go with the Polish manufacturer JHVB did mention, the product seems rock solid and quite cheap for what is mentioned. They want 20 Euros for the delivery to UK, but I also need two additional transformers for the Myref Freman edition I am going to build, so at the end the additional delivery costs will pay out.

Mouser will provide the myref parts and the Toroidy guys the transfomers.

Thanks guys!
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