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Old 16th June 2005, 06:02 AM   #1
Sushii is offline Sushii  Hong Kong
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Default T amp + 16 ohms speaker?

Hello,

I am wondering is there any way to mod the T amp to play on 16 ohms speaker? right now when I hook up the T amp to my 16 ohms speaker, it distort greatly even in low volumne

Thanks!
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Old 16th June 2005, 11:50 AM   #2
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Default Re: T amp + 16 ohms speaker?

Quote:
Originally posted by Sushii
Hello,

I am wondering is there any way to mod the T amp to play on 16 ohms speaker? right now when I hook up the T amp to my 16 ohms speaker, it distort greatly even in low volumne

Thanks!

If you have a SI 5066, try removing the 0.15 cap on the speaker connectors. The on board caps are already the 0.47 which is what Tripath recommends for 4 ohms.
These output filters are there to remove the ultrasonic switching noise. They are very forgiving of load mismatch.
There might be another problem is you are getting a lot of distortion.

George
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Old 19th June 2005, 06:26 AM   #3
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Default Re: T amp + 16 ohms speaker?

Quote:
Originally posted by Sushii
Hello,

I am wondering is there any way to mod the T amp to play on 16 ohms speaker? right now when I hook up the T amp to my 16 ohms speaker, it distort greatly even in low volumne

Thanks!

Sushii,
You have only around 3 watts to work with into 16 ohms. Unless your speakers are extremely efficient this won’t work. Get a pair of 25 watt decent quality line matching transformers and connect the 4 ohm tap to the amp and the 16 ohm tap to the speaker. This will give you around 10 or 11 clean watts and will work a lot better.
Roger
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Old 20th June 2005, 05:56 AM   #4
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Default Re: Re: T amp + 16 ohms speaker?

Quote:
Originally posted by Panelhead



If you have a SI 5066, try removing the 0.15 cap on the speaker connectors. The on board caps are already the 0.47 which is what Tripath recommends for 4 ohms.
These output filters are there to remove the ultrasonic switching noise. They are very forgiving of load mismatch.
There might be another problem is you are getting a lot of distortion.

George
George,
The output filter caps don't have much to do with what load he is trying to drive but do have a large sonic impact. I had 2 nearly identical modified SI units that I was experimenting on. I was listening to them with a 2" full range type 8 ohm speaker. This speaker was driven directly with no cross over.
In comparing the 2 units I thought something must be wrong with one as the other sounded much better. After checking it out I found the one that sounded better did not have the .15uf output caps installed. Removing them from the other one changed its sound to be the same as the good sounding one.
I am sure these caps were included to reduce radiated EMI so removing them should do no harm except possibly to AM radio.
Roger
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Old 3rd July 2005, 04:08 AM   #5
! is offline !  United States
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Default Re: Re: Re: T amp + 16 ohms speaker?

Quote:
Originally posted by sx881663

I am sure these caps were included to reduce radiated EMI so removing them should do no harm except possibly to AM radio.
Roger
When I removed mine I noted the result was DC offset on the outputs. Not 100% sure but believe the attached speakers were 6-8 ohm load at the time.
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Old 3rd July 2005, 05:06 AM   #6
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Default Re: Re: Re: Re: T amp + 16 ohms speaker?

Quote:
Originally posted by !
When I removed mine I noted the result was DC offset on the outputs. Not 100% sure but believe the attached speakers were 6-8 ohm load at the time.

All the units have some dc offset. The early ones seemed worse, one channel -100 mv, the other +80 mv. The latest with no solder slug seem to be +/- 30 mv or so.
I did not see any change in offset when changing the 0.15 ufd caps for smaller values.
I think that slightly larger chokes may help the sonics with higher loads. The onboard 0.47 caps can be swapped too, maybe 0.15 if available.

George
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Old 7th July 2005, 04:46 AM   #7
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"Get a pair of 25 watt decent quality line matching transformers and connect the 4 ohm tap to the amp and the 16 ohm tap to the speaker. This will give you around 10 or 11 clean watts and will work a lot better.
Roger"

Roger,

Do you have any links to the sort of matching transformers you're suggesting? I've been thinking along similar lines as a way to extract more power from my T-amps. I have a slightly different application than HI-FI; I'm trying to use these for battery-powered sound re-inforcement at a remote (that is to say rustic, as in no convenient power lines) location. I'm trying to maximize the speaker efficiency, but am stuck with 16 ohm woofers. They are very good quality, efficient drivers, but they're 16 ohms! I have good quality 60W tube output transformers with 4-8-16 ohm tapped secondaries, and considered using those as auto-transformers. But that's a lot of iron to haul over the hills and through the woods, etc. Not to mention the relatively high voltage that will be induced back into the primary windings!

I did a seach on this a few weeks ago, and turned up some guru's site where he was selling auto transformers wound on torroids as a way to improve damping factor at the speakers. Very interesting, until I saw the price tag! I'm on a strict budget, otherwise I'd buy new drivers and be done with it!

This isn't a hopeless situation (with a woofer in each of the two cabinets, I can place them in parallel and still present an 8 ohm load to a single T-amp channel), but it is an opportunity to learn something. Any and all suggestions are appreciated.

Mike
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Old 7th July 2005, 07:28 AM   #8
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Mike,
Learning is good!
The best part that will allow you to try this out, not cost too much and is light enough to pack in seems to be the Hammond part 117K16 or 117K32. I am too lazy to figure out the ratios at the various taps so will give you this simple way to determine what to do. A ratio of 4:16 ohms is an impedance ratio of 4:1, Sq. rt of 4=2 so the voltage ratio is 2:1. Apply a measured voltage (6-12vac from AC type wall wart) into the whole winding from pin 1 to com then go down taps till you are getting a ˝ voltage measurement to com. This pin and com will be your 4 ohm tap and pin 1 to com will be your 16 ohm output. A better way to connect it would be to connect the test voltage as above and then measure from 4–8 then 2-16, see if either of these are ˝ voltage. If one is close use that as your 4 ohm input. Since the SI has a balanced output it would be better if it saw a balanced load including parasitics. If none of the winding combinations are close, the normal output winding can be added in series to either end to give you more choices.
These transformers are $17.93 ea from Allied but are a special order item. All the major stocking distributors have zero balance with Allied having the best prices.
The difference between the 117K16 and 117K32 is power handling and a couple of bucks in price. The 32 watt one will carry better base so should be worth the extra weight and cost.
Actual performance will be considerably better than specs would lead you to believe. This is due to using it at a greatly reduced power and using it as an autoformer.
Hope this is useful for you,
Roger
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Old 7th July 2005, 11:00 AM   #9
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Quote:
Originally posted by sx881663


I like to dream. On a normal 0,4,8, 16 ohm output trannie the 4 ohm is the center tap. The ratio between the ground and 16 ohm tap is twice the the 4 ohm tap to ground. It seems it should work to connect the amp to the ground and the 4 ohm taps, The speaker can be connected to the gound and 16 ohm tap.
This will also double the voltage, gain, and get all the dc off the output. How it sounds is another big issue though.
I have tried many variations of the SI, stock to fairly heavily modified at home. My speakers are rated 15 ohms, but this is a low rating. They measure 12 ohms, dcr. Being a single driver the high inductance raises this to 40 ohms at high frequency. But this is taken care of by the zorbel on the SI board, It is 10 ohms in series with a 0.47 cap.
The only issue I think is the reduced power delivery into 16 ohms. With a battery you are looking at 4 watts or so. Sonically the Tripath seems seems to deal with this very well is implimented.
Several people use these with headphones. Most have reported good results. These are anywhere from 32 ohms up to several hundred. It is a low power application, at 300 ohms the SI can only output milliwatts. Something like 0.1 watts maybe.



George








Mike,
Learning is good!
The best part that will allow you to try this out, not cost too much and is light enough to pack in seems to be the Hammond part 117K16 or 117K32. I am too lazy to figure out the ratios at the various taps so will give you this simple way to determine what to do. A ratio of 4:16 ohms is an impedance ratio of 4:1, Sq. rt of 4=2 so the voltage ratio is 2:1. Apply a measured voltage (6-12vac from AC type wall wart) into the whole winding from pin 1 to com then go down taps till you are getting a ˝ voltage measurement to com. This pin and com will be your 4 ohm tap and pin 1 to com will be your 16 ohm output. A better way to connect it would be to connect the test voltage as above and then measure from 4–8 then 2-16, see if either of these are ˝ voltage. If one is close use that as your 4 ohm input. Since the SI has a balanced output it would be better if it saw a balanced load including parasitics. If none of the winding combinations are close, the normal output winding can be added in series to either end to give you more choices.
These transformers are $17.93 ea from Allied but are a special order item. All the major stocking distributors have zero balance with Allied having the best prices.
The difference between the 117K16 and 117K32 is power handling and a couple of bucks in price. The 32 watt one will carry better base so should be worth the extra weight and cost.
Actual performance will be considerably better than specs would lead you to believe. This is due to using it at a greatly reduced power and using it as an autoformer.
Hope this is useful for you,
Roger
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