Toroid Transformer for Hafler DH-200

[rickrob2]

Hello,

Can anyone recommend a toroid transformer for a Hafler DH-200?

I'm looking for a source for two of them, and need a manufacturer and part number.

Thanks

[jackinnj]

see if an Antek 3245 will fit -- it's a bit over-rated for the application at 300VA -- the dimensions should be on their website www.toroid-transformer.com
while you're replacing the trafo consider boosting the filter caps and bypassing them with some WIMA's.

[jackinnj]

also Plitron

http://www.plitron.com/shopping/shop...tage+%2D+45VAC

[Dick West]

rickrob,

I have two toroids. They are too tall to stack two inside on Hafler chassis. Are you doing dual mono? Will you use two chasses?

If you want a toroid sized to power a DH-220 I have two. Here is a picture of how it was used. The transformer was made by Peachtree Magnetics, Atlanta GA, back in the early 90s.

My price for a toroid is $35 plus postage.

[rickrob2]

I have two DH-200's bridged to mono. The original transformers are now humming, so I'm looking to replace them.

I'm interested in the two you have-- Can you send me the specs on them?

Contact me at robertsrc AT comcast DOT net


Thanks

Rick

[Dick West]

rickrob,

When you convert an amp back to stereo and play it does its transformer still hum?

What is the impedance (load) of your speakers? A bridged amp should never be used with speakers whose impedance is below 8 ohms.

What is the capacitance of the large power supply caps in your amp?

What I am getting at is that the way you are using your amps may cause hum and your present transformers may be OK. Bridging an amp can put it under a different set of load conditions.

Tell us more.

I have no specs on my transformers other than to tell you they were used to power a DH-220 type amplifier used in stereo mode. These were amplifiers made by Smart Devices designed for motion picture theater sound systems that used DH-220 electronics under license. The amps were used in demanding situations and I am sure the toroidal transformers helped out. These transformer are 4.5 inches wide and 3 inches tall. I don't have a scale but I believe they are about the same weight as your Hafler transformers.

Here is a picture of the Smart Design amp from which it came. The heat sinks on either side are exact replacements for those in the DH-220. You can see that the wiring is closer to 18 ga. than 16 ga. The transformer is center tapped and does not have dual secondaries. It has 3 wires on the output side, just like your present Hafler transformer.

Obviously I am not pushing them as a solution. They are good tranformers for a DH-220 and because they are "pulls" they are cheaper than new ones. However, transformers don't really wear out. If you want both, the price is $70 plus $10 for USPS Priority Mail.

[rickrob2]

I built these in 1983 and then bridged them to mono with the DH-202 bridging board a couple of years later. They drive Dahlquist DQ-10's (8 ohms)

They have always been silent (as best I can remember) , but the other day I noticed the hum from both amps.

I replaced the power supply caps -- the two 10,000uF Sangamo's -- about a year ago. They are still at 10,000uF. I've read that beefing up those caps would help.

I haven't pulled one of the amps out yet and checked it out, but I figure after almost 25 years they may need some additional work. I know they need power switches.

So, I started searching for power switches and toroid transformers to see what I could find. Maybe it's time for a recap on the smaller EL's as well.

[jackinnj]

Originally posted by Dick West
...the toroidal transformers helped out. These transformer are 4.5 inches wide and 3 inches tall. I don't have a scale but I believe they are about the same weight as your Hafler transformers.

The DH-220 transformer is 4.6" high and about 5" wide.

There is at least one DH-220 mod-thread which goes live on an intermittent basis -- fwiw, I have replaced the 10,000uF Sangamos with 39,000 Panasonics, bypassed the electrolytics and have not touched the driver board. the DH-220 is in almost constant use here, what a work-horse -- I have it driving a pair of KEF 104ab's in the lab.

[Dick West]

I agree with you on how robust the DH-220 is. These amps continue to perform well over the years and still command a rather high price at venues such as an eBay auction.

I inserted "DH-220" in my earlier posts because I forgot the original poster states he has a pair of bridged DH-200. Earlier readings on my part found messages in which bridging of the DH-200 was not recommended.

So, question, if the OP's 2 bridged DH-200s have humming transformers, are they humming because the DQ-10 speakers present too low an impedance for his bridged amps?

Also, I have read about humming toroidal transformers. And, have read about the possibility of DC riding on the incoming AC supply as causing humming in transformers. And, we know the DH-200 is rather notorious for having DC offset as original signal transistors drift out of spec, and there is no way to null DC offset on the DH-200. Would DC offset from the amp cause its transformer to hum?

What should the OP do? I have a pair of toroidals sized appropriately for a DH-200/220 amp but will they cure his humming problem? How can he tell in advance of changing transformers to a different pair?

[jackinnj]

This PDF on the Plitron site might be helpful -- "Measuring Acoustic Noise Emitted by Power Transformers".

http://www.plitron.com/pdf/AES.pdf