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Old 8th January 2011, 11:09 PM   #1
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Default Patchwork 6: Power Supply Upgrade

Here it is:

Picture 1184.jpg Picture 1052.jpg

6 channels of my Patchwork amps. This is used exclusively to actively drive my main speakers - 3-ways. It has been in daily use since I finished it.
Though I am perfectly happy with its performance, I want to improve the power supply. Mainly, this is just whimsy - the existing power supply is more than adequate but I can't leave well enough alone.
The Plan:
I will change the main power transformer from the current 700VA, 40-0-40 toroid to a ~600VA EI 46-0-46. I may (depending on space within the existing chassis) regulate this supply. This will supply the output stages of the amp modules.
I will add two 12VA 48-0 transformers to create a highly filtered and regulated supply for the front end of each amp module.
At this time, I'm not sure how I want to filter the front end supply. Cap multiplier or passively, CLC perhaps.
Create a new softstart circuit. I already have a softstart in the amp, but I can improve upon the original design.

Thoughts, comments, concerns welcome.
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Old 8th January 2011, 11:29 PM   #2
Bigun is offline Bigun  Canada
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If it means messing up that gorgeous chasis - don't do it !

On the other hand, if it means you'll have a redundant 700VA 40-0-40 you can send to me, go for it

I like the split supply for front-end and back-end. I've no experience with cap mux but a CLC has little to go wrong, using a common mode choke for the L to keep size and cost down.
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Old 8th January 2011, 11:37 PM   #3
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Quote:
Originally Posted by Bigun View Post
On the other hand, if it means you'll have a redundant 700VA 40-0-40 you can send to me, go for it
.
I won't be doing anything with the outside of the chassis and I'm afraid I'll need to re-purpose that transformer Gareth...next amp project needs it.

This is the preliminary stage - the planning stage. I'm not actually going to do much yet but I would like some input.

The amp as it is today:

NPX_01193.JPG

needs a dusting! (one of the reasons for upgrading it - to clean it! ).
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Old 8th January 2011, 11:40 PM   #4
Bigun is offline Bigun  Canada
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I think it looks superb, I wouldn't mess with it if I were you -just build a new project.
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Old 8th January 2011, 11:54 PM   #5
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Playing it safe is no fun Gareth.
I have had THIS project on my schedule for quite a while now and it's nearly time to start. I just have to finish up another mega-project first - This One.
I have simulations to run, transformers to test.
One question for anyone out there that might know: is there any problem completely enclosing an EI transformer? I would like to make a steel box that covers it. I thought I read somewhere that this can be a problem.
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Old 9th January 2011, 01:39 AM   #6
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I ran a series of load tests on the proposed new power transformer for the output stages. I initially estimated the transformer to be in the 600VA range and it looks like I'm off by a bit.
The series output voltage with no load is 93VAC. I worked my way down to 13.7ohms of nichrome wire and I have 86VAC at that load. That is 6.28A at less than 10% regulation - not bad and should be suitable for this part of the project.
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Old 9th January 2011, 02:57 AM   #7
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by MJL21193 View Post
I just have to finish up another mega-project first - This One.
Wow, that's what I call a project.
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Old 9th January 2011, 10:12 AM   #8
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I liked your original amp a lot.
Shame to muck about with it.

I loved the aesthetics.

What about two 3channel versions? The extra space would allow the room for the HV transformer and the HV PSU.

I am not keen on replacing a 8.75Aac low regulation transformer with a 6.28Aac higher regulation transformer.

BTW,
How do you check that your 13r7 nichrome wire is still 13r7 when passing 6.28Aac?
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Old 9th January 2011, 11:20 AM   #9
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Quote:
Originally Posted by AndrewT View Post
I loved the aesthetics.
Thanks Andrew,
The outer appearance will remain unchanged, just guts will get 'improved'.

Quote:
Originally Posted by AndrewT View Post
What about two 3channel versions? The extra space would allow the room for the HV transformer and the HV PSU.
I need 6 additional channels in my next project (centre channel - 2, rear surrounds - 2 each) and if it were possible, I'd put those in that case too! I'd really like to reduce the quantity of individual components.


Quote:
Originally Posted by AndrewT View Post
I am not keen on replacing a 8.75Aac low regulation transformer with a 6.28Aac higher regulation transformer.

BTW,
How do you check that your 13r7 nichrome wire is still 13r7 when passing 6.28Aac?
Regarding the transformer, I ran one more load test last night - 10 ohm load and the voltage dropped to 83.4. Allowing for a rise in resistance with temp, say a worst case 1000*C rise will increase resistance to ~11.4 ohms. That gives me 7.3A at ~10% regulation and I believe this is more than adequate for this application.
TBH, I don't think the transformer that is in place now has seen anywheres near it's potential, as for actual loading. Over-speced, current wise but not having a high enough voltage (and its size) is the reason I want to pull it.
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Old 9th January 2011, 11:27 AM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by MJL21193 View Post
the voltage dropped to 83.4. Allowing for a rise in resistance with temp, say a worst case 1000*C rise will increase resistance to ~11.4 ohms. That gives me 7.3A at ~10% regulation
Your measurements are showing 11.5% regulation at 600VA (7.3Aac).
I would expect the toroid to be <4% at 700VA (8.75Aac).
I still don't like it. I think you are going to see 4times as much voltage variation coming from the EI transformer vs the toroid transformer.
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