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Old 4th July 2013, 06:02 PM   #951
redjr is offline redjr  United States
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Originally Posted by Wembley View Post
It should be up now.

diyAB Amp The "Honey Badger" build thread

Any issues, and I'll try again.
Wembley - Please see my latest post to you in the HB build thread. Thx.

Rick
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Old 4th July 2013, 07:55 PM   #952
redjr is offline redjr  United States
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Right, this is a basic dual emitter follower design. Lower impedance speakers will put a higher load on the VAS than a triple EF output stage would. Simply adding more output transistors would help, but even at +/-70Vdc the VAS will be pushed harder than intended.

The amp was designed around +/-60Vdc rails. Unless you can do the calculations, and modify the design properly yourself, you should build it as the designer intended.
So, I'm reading these older posts in anticipation of building the HB - latest revision. Is there a consensus on the appropriate size traffo so as to meet the 150wpc into 8 ohms? It's been decades since I learned traffo theory, but I always thought you could go bigger VA wise without harming anything. The physical size of the traffo implies a higher current rating, not voltage. The current drawn by the amp is dependent on load which is determined by a lot of other factors - based on the design specs of the lowest (or highest depending upon how you look at it) common demoninator.

I'm thinking 1 x 600VA or 700VA traffo rated at between 42-45 CT would be suitable to my 8 ohm speakers, typical listening levels, and reserve factor - for both channels. (Antek AN-6445) I might also beef up the filter caps too, to 10k, or even 16k as an adequate reserve. Can too large ever be a problem?

Rick
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Old 4th July 2013, 07:59 PM   #953
6L6 is offline 6L6  United States
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More VA in a transformer is fine. It just costs more.
What's 20 bucks more when you are building one amp? Not all that significant. Build 1000 and that turns into real money.

More capacitance can cause some starting inrush issues at some point, but you need to get into big numbers before you have problems. And those problems can be fixed with a soft-start circuit.
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Old 4th July 2013, 08:22 PM   #954
redjr is offline redjr  United States
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More VA in a transformer is fine. It just costs more.
What's 20 bucks more when you are building one amp? Not all that significant. Build 1000 and that turns into real money.

More capacitance can cause some starting inrush issues at some point, but you need to get into big numbers before you have problems. And those problems can be fixed with a soft-start circuit.
Thanks 6L6. You confirmed what I always thought. I guess the theory hasn't changed after all - after all these decades! I agree, the bigger ones do cost more. But for my 1-off builds, I buy what I need. I've had good luck with Antek just down the road in Jersey, and their build quality seems high. I was just curious what size is sufficient to deliver the stated specs for this HB build. BTW, I was planning on using a soft-start circuit anyways.
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Old 5th July 2013, 08:31 AM   #955
AndrewT is offline AndrewT  Scotland
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the usual rule applies.
VA from one times to two times the total maximum power.
For a 150W amplifier pick a transformer from 150VA to 300VA.

For two channels then 300VA to 600VA.
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Old 5th July 2013, 04:23 PM   #956
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the usual rule applies.
VA from one times to two times the total maximum power.
For a 150W amplifier pick a transformer from 150VA to 300VA.

For two channels then 300VA to 600VA.
Can we assume this is for a class AB or will this rule work for class A as well?
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Old 5th July 2013, 07:23 PM   #957
6L6 is offline 6L6  United States
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Class A you need 6 times the output power or 2x the standing bias current.
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Old 5th July 2013, 09:04 PM   #958
redjr is offline redjr  United States
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Originally Posted by AndrewT View Post
the usual rule applies.
VA from one times to two times the total maximum power.
For a 150W amplifier pick a transformer from 150VA to 300VA.

For two channels then 300VA to 600VA.
I guess I figured it correctly then - albeit on the higher side. My strategy is... if you're going to build an amp like this, spend a little extra for a beefier traffo and PSU so you have the reserve when the music demands it.

Rick
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Old 7th July 2013, 09:16 AM   #959
Holgi is offline Holgi  Germany
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Originally Posted by ostripper View Post
#2 - Since I have 4 boards (really!! ... guys) I will make 2 "flavors" of the badger...
one bjt input and one FET!!! input.
Hey Pete,

did you already try it with FETs? I also was wondering that it could be an improvement to used matched 2SK170 (or one LSK389 in my case) for Q1/Q2 and since I'm re-doing the layout anyway to make the boards fit into my case I would give it a try. Or did you experience anything in the meantime that should prevent me from doing this?

Thanks and BR,
Holgi
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Old 7th July 2013, 11:34 AM   #960
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The correct size transformer for a two channel 150W amplifier would be 300VA-600VA. If to be used for 4ohm speakers, 600VA would be the minimum. Since the difference in cost is negligible, at least here in the states, it would be worth bumping this up to 800VA. 1000VA is overkill. If a toroidal transformer is used, a softstart circuit will be mandatory.

42VAC-45VAC is correct.
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