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Transformer for F5 - 1 or 2 secondaries?
Transformer for F5 - 1 or 2 secondaries?
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Old 3rd August 2019, 06:18 PM   #1
Staka is offline Staka  Croatia
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Default Transformer for F5 - 1 or 2 secondaries?

I need to order transformers for my F5. I planned to install two torodial transformers 320VA with one secondar 18V per trafo. Now I see that others are buying two transformers with two secondaries per trafo for dual mono and I don't understand why? What is the benefit of four secondaries instead of two?

Will 300VA 10A per channel be enough? I'm doing a custom order so suggestions are welcome
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Old 3rd August 2019, 06:55 PM   #2
ColinA123 is offline ColinA123  United Kingdom
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You need a centre tapped transformer -18 0 +18v for the power supply on one amp.
So for two amps (dual mono) two transformers are the best option.
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File Type: jpg F5PSUschematic.jpg (87.1 KB, 334 views)

Last edited by ColinA123; 3rd August 2019 at 06:58 PM.
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Old 4th August 2019, 05:16 AM   #3
Hikari1 is offline Hikari1  United States
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If dual mono you need a +, ground and - for each channel. This is a bipolar power supply, not a single rail. So you need 2 secondaries per channel or a center tap.

300va is enough if you don’t plan on biasing much higher than stock. But with monoblocks you will be able to bias higher. 300va per channel is fine up to about 3A bias. But personally I would choose a bigger transformer.
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Old 4th August 2019, 07:35 AM   #4
Staka is offline Staka  Croatia
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These are stupid questions but I'm totally new to this (and in electronics generally) and this is my first project ...
I know all the questions have already been asked, but I get lost reading through the forum

If I understand correctly: for dual mono I need two transformers each with two outputs (-18 0 +18 x 2) and two boards like this: diyAudio Power Supply Circuit Board v3 illustrated build guide

Simplified:
2 x transformer, each with 2 x -18 0 + 18
4 x diode bridge
16 x capacitor
did i understand correctly?

if so, how do i connect the channels to the power supply, the boards are double and each has 2 x + and 2 x - at the end?
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Old 4th August 2019, 02:32 PM   #5
Attila I is offline Attila I  Germany
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@Staka
you connect plus and minus at one end of the psu-board and get your psu-groundpoint

and read here-> diyAudio Power Supply Circuit Board v3 illustrated build guide

A.
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Old 5th August 2019, 01:38 PM   #6
dantwomey is offline dantwomey  Canada
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Transformer for F5 - 1 or 2 secondaries?
Quote:
Originally Posted by Staka View Post
These are stupid questions but I'm totally new to this (and in electronics generally) and this is my first project ...
I know all the questions have already been asked, but I get lost reading through the forum
Everyone was a beginner at one point in time and everyone had their first project. These are not stupid questions and yes this a challenging and rewarding hobby. Hang in there. These are great forums and you will get lots of help.

Regards,
Dan
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Old 6th August 2019, 01:53 AM   #7
aspringv is offline aspringv  Australia
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Transformer for F5 - 1 or 2 secondaries?
Quote:
Originally Posted by Staka View Post
These are stupid questions but I'm totally new to this (and in electronics generally) and this is my first project ...
I know all the questions have already been asked, but I get lost reading through the forum

If I understand correctly: for dual mono I need two transformers each with two outputs (-18 0 +18 x 2) and two <snip!>
There's a caveat to reading the posts for info. A lot of folks here are going to the next level of build in the name of fun. Can you hear a difference? I couldn't say, but if folks are enjoying themselves building stuff, thats the whole point.

Why am I saying this? Nelson used a single transformer with dual secondaries in his commercial builds, so I'd say that's a fine standard to build to.

After that you could run dual capacitor banks, ie 2 positive rails, and 2 negative rails, off one transformer, (separating them after the R in the CRC)

After that you could get a transformer with quad secondaries, and dual capacitor banks...

After that you get to dual mono setups, and then at the truly ridiculous end, 4 transformers, 4 cap banks.

Does any of this make a difference? If you enjoy doing it, then yes!
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Old 6th August 2019, 02:34 AM   #8
Hikari1 is offline Hikari1  United States
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Staka,

Also, most people here building dual mono F5s are making them dual mono for one reason only. That reason is because they are using two chassis.

The reason to use two chassis is because of heat. Most people using two chassis are building the turbo version with higher rail voltages or more bias. So they have more heat to dissipate.

If you are using 18V transformer and stock bias there is no need for two chassis. Therefore, you don’t really need dual mono.

Dual mono gets more complicated with the grounding...so, if you build dual mono and the grounding is not right it could sound worse.

Some things to think about.
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Old 6th August 2019, 04:08 AM   #9
aspringv is offline aspringv  Australia
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Transformer for F5 - 1 or 2 secondaries?
I should also say...
My first F5 build was done with a 300VA transformer, feeding both channels. Dual 18V secondaries, and a power supply exactly as described on the above schematic. It's still in use today, and as a learner about class A amps it was great!

I'd say, if you're getting a custom transfo made, a single 320VA unit, with dual 18VAC secondaries is completely fine for an F5. If you want to be extra certain, then get a 400VA unit. Save your second transformer money for the next build, or spend it on a lovely case that you can use for the next build once you get curious about another amp... I guarantee that you will build one.
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Old 6th August 2019, 05:46 AM   #10
Staka is offline Staka  Croatia
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Thank you all for the answers, you helped me a lot! Now I can make a decision more easily before I continue :-) My plan is to build a serious system which means I need everything... A new dac (which is the next project) and refreshing the speakers with a new crossower, all that costs, takes time and learning... So I'm trying to find the balance and do the best that my budget allows and not change it later...
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