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chip amps: Almost everything you ever wanted to know


DizRotus

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  • 11 months later...

A little knowledge can be dangerous. I acquired the Yuan-Jing TDA7293 x2 Stereo Power Amplifer Board [85W + 85W] shown below, not realizing it requires a 25v 0v 25v power supply. I also happen to have the pictured transformer that seems to convert 110v 0v 110v to 25v 0v 25v.

It may all be for naught, but my curiosity compels me to attmpt to try powering the amp by the transformer. Nonetheless, I'd rather not immediately produce smoke. I suspect the output wiires are 0v black, 25v blue, 0v black, 25v blue. Similary, I suspect the input wires are 110v red, 0v black, 110v red, 0v black, but what about the yellow/green wire?

Any advice, criticism, warnings, etc. regarding the amp, the transformer or my, perhaps, misplaced curiosity, are welcomed.

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Edited by DizRotus
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The windings are one color. So, on the primary side, it is probably Blk-Blk for 110V input, and Blu-Blu for maybe 220V. You can confirm that Blk-Blk is one winding by measure resistance. Should be very low on Blk-Blk, but much higher on Blk-Blu. That will mean Blu is another winding.

 

Same on secondary side. The pairs of one color are one winding. A CT is usually coded with a stripe. Such as Red-Red/Y- Red. The GR-Y might be a CT or as previously mention a shield. Once you know the primary, you can connect the bugger to a 120V outlet, and then just measure the various secondaries.

 

I see it is only 10VA. That's not much for a 85W power amp!

 

Thanks for the advice Mark,  I'll try it and report back.

 

I've attached additional photos to confirm that nothing else is printed on the transformer.

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I hope I was doing this correctly. Setting the meter on 200, I checked a 5W 100 ohm ceramic resistor. The reading was 99.3. On that same setting, I then measured the transformer. I'm assuming the red wires are the primary, that is 110v input side, and the blue wires are the secondary, that is 25v output side. The combinations that produced readings were between red/black or blue/black pairs. As expected, measuring black/black, red/red, blue/blue or red/black or blue/black across pairs produced no readings.

Measuring a red or blue wire and the adjacent black wire produced the following:

Red - Black = 101.6 ohm

Red - Black = 102.2 ohm

Blue - Black = 6.9 ohm

Blue - Black = 7.1 ohm

The amp has inputs labeled, " 25v 0v 25v." Do I connect one blue lead to one 25v input, the other blue lead to the other and both black (secondary?) to the 0v input? If so, how do I connect line voltage to the red/black (primary?) wires?

Please elaborate on your comment regarding 10va. My experience powering 12v chip amps is that brick power supplies with 1.5 amp ratings work, but supplies with ratings of 3 or more amps are better. Am I comparing apples to oranges?

If I want to experiment with this amp, am I better off getting a 25v brick from Parts Express?

Your expertise and assistance are greatly appreciated. I do not want to get better acquainted with local firefighters, except, perhaps, over a beer.

Edited by DizRotus
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The VA rating indicates the maximum amp draw for the transformer.

 

10 VA / 25 Volts = .4 amps.  Not much  :(

 

If I read the TDA7293 datasheet correctly, it draws a max of 6.5 amps.  6.5 * 25 =  162.5, so a 200 VA transformer would probably work

 

The amp requires 25-0-25 AC, so a DC brick won't work  :(

 

I'd be happy to help you with the wiring!  Do you have a spare terminal block to work with?  I always test transformers outside the amp.

I wouldn't use this transformer for your amp, but all dual primary/dual secondary transformers are wired the same.

 

Mike

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This may help.

 

http://classdaudio.com/documents/transformer_115VAC_instructions.pdf

 

Primary side will be wired in parallel, as shown.

 

On the secondary side, your black wires equal the blue secondaries in the illustration

                                      your blue wires equal the green in the illustration.

 

Again, I'd test this outside of the amp.  I like this illustration because it includes the fuse.

 

Mike

 

 

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The VA rating indicates the maximum amp draw for the transformer.

 

10 VA / 25 Volts = .4 amps.  Not much  :(

 

If I read the TDA7293 datasheet correctly, it draws a max of 6.5 amps.  6.5 * 25 =  162.5, so a 200 VA transformer would probably work

 

The amp requires 25-0-25 AC, so a DC brick won't work  :(

 

I'd be happy to help you with the wiring!  Do you have a spare terminal block to work with?  I always test transformers outside the amp.

I wouldn't use this transformer for your amp, but all dual primary/dual secondary transformers are wired the same.

 

Mike

 

Thanks for the information.  I can see that this is way beyond me.  It was acquired while sampling various 12v chip amps.  I have neither the need, time, ability, interest or resources to put this into service.  To keep them out of the recycling center or, worse, landfill, the amp and/or transformer will be sent to any forum member in 48 contiguous states at no charge.  If interested, send contact info by PM or email through forum.

Edited by DizRotus
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What I was asking was different. You should measure Blk-Blk and then Blu-Blu, etc. Each winding should be one color. That's what we are trying to confirm. So, measure each PAIR. The values will be low, that's OK.

10VA is 10 watts of power. You mentioned connecting it to some 85W amps. You won't get much out of those amps using a 10 watt power supply.

 

Again, thank you for sharing your expertise.

 

I must be misunderstanding you.  I measured black-black, blue-blue, red-red, etc., every combination I could imagine.  With the DVM set on 200 ohms, the only readings were obtained when measuring blue-black or red-black, and then only between adjacent wires.

 

As mentioned above, to keep them out of the recycling center or, worse, landfill, the amp and/or transformer will be sent to any forum member in 48 contiguous states at no charge.  If interested, send contact info by PM or email through forum.

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I understand  :)

 

I'm pretty sure those chips will need to be attached to heat sinks as well.  Can O' Worms.

 

My favorite 12 volt DC chip amp is still the TDA7297.  Have you tried it?  I'm bi-amping my K'horns with two of them. 

 

Good luck on your quest.

 

Mike

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I understand  :)

 

I'm pretty sure those chips will need to be attached to heat sinks as well.  Can O' Worms.

 

My favorite 12 volt DC chip amp is still the TDA7297.  Have you tried it?  I'm bi-amping my K'horns with two of them. 

 

Good luck on your quest.

 

Mike

 

Yes, I own a couple TDA7297 chip amps.  They are amazing.  People are always flabbergasted at the sound produced by such a small and inexpensive amp.

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  • 3 months later...

It's been a while since I've posted here. I've been experimenting with the Texas Instruments TPA3116 and TPA3118 Class D amplifiers and ST Micro TDA7297 Class AB amplifiers, and a few hundred dollars of parts and amplifier modules, I've come to the conclusion that the TDA7297 is a worthy chip amp champ in terms of sound quality, energy efficiency and value.

 

This little amp driven with my modified Astron RS-12A regulated linear power supply (14VDC) can generate as much as 8 watts within reasonable distortion levels. This is plenty of power to drive most efficient Klipsch speakers. I can drive my Forte II's to ear-splitting levels with plenty of headroom with this amp. As discussed earlier in this thread, there are many possibilities for powering these miniature amps. I've found that my Astron regulated linear power supply provides clean power (i.e., voltage and current) that allows this amp to create a huge soundstage (deep, wide and tall), articulate bass, warm mids and extended highs an a focused image with excellent separation between performers. As a reference, my system consists of the following:
 
  1. Restored and modified Kenwood Trio PC-400U belt-idler wheel drive turntable (a la Thorens TD-124)
  2. Talisman Alchemist IIB high output MC cartridge re-tipped by Needle Clinic
  3. Sony ES DVP-NS999ES DVD/SACD/CD player
  4. Audio Research PH5 JFET/6922 tube phono stage preamplifier
  5. Audio Research LS7 tube line stage preamplifier
  6. Restored Dynakit Stereo 35 6BQ5/EL84 push-pull tube amplifier modified with Enhanced Fixed Bias (EFB)
  7. Klipsch Forte II speakers modified with Bob Crites Titanium tweeter diaphragms, capacitor replacement and internal wiring kit, and Pomona 3770 Copper binding posts
Recently, I modified a TDA7297 amplifier module purchased from eBay seller "homemart.usa." This amp cost under $7 with shipping from China. Delivery to the US takes about 7-10 days. The stock unit actually sounds pretty good, but significant improvements can be realized with a minimal investment of money and DIY time.
  1. Removed yellow 100nF ceramic cap
  2. Replaced the polarity protection diode with a sold core Copper wire
  3. Replaced the stock 2,200uF/25V electrolytic cap with a 470uF/35V Nichicon KZ Muse electrolytic cap for the power supply/DC decoupling cap
  4. Replaced the two (2) stock .22uF Mylar film caps with 1.0uF/250V Radio Shack Mylar film caps (http://www.radioshack.com/1-0uf-250v-10-metal-film-capacitor/2721055.html#.VTplAWd0zDc)
  5. Replaced the three (3) stock terminal blocks with Weidmuller terminal blocks
  6. Replaced stock 50k volume pot with 50k 21-step SMD resistor stepped attenuator, and used Mundorf Silver-Gold wire as hook-up wire
I installed this in a Context Engineering split-body Aluminum enclosure that had a previous TDA7297 build in it.
 
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To my ears, this amp sounds really good. It may not have the full tube bloom of my Dynakit tube amp, but it has a warmth and presence that could easily fool someone into thinking they are listening to a tube amplifier. Better yet, this amp is 80+ percent efficient, so it would make an excellent warm weather amplifier.
 
Probably the most significant modification is increasing the input capacitance from .22uF to 1.0uF per each channel. This lowers the high pass input filter corner frequency to below 20Hz, so that the bass response and definition are significantly improved. The Radio Shack film caps are some of the best kept secrets in DIY audio. Unfortunately, these caps are only available in 1.0uF/250V.

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Edited by rhing
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I still love my tube amps. I have a project to restore and modify a Magnavox 6BQ5/EL84 single ended pentode tube amp. These little gems sound great through Klipsch speakers. I just scored on a factory matched quartet of JJ EL84 tubes at Apex Jr. (http://www.apexjr.com) in Torrance, CA for $32 dollars. I was down in Southern California for my niece's wedding, and had to stop by Apex Jr. to pick up on some DIY goodies like wire, connectors, caps and tubes. If I had more time, I would have driven up to L.A. to visit Amoeba's and all the other great vinyl stores around Melrose.

The great thing about the TDA7297 amp is that I can use this as an integrated on warm weather days. It works well with my PH5 phono stage and my Sony ES player. With this amp being over 80 percent efficient, the power supply is everything in getting the most out of these chip amps. My Astron RS-12A is rated to put out 9A continuous current. Astron has been known to inflate their specifications; the regulated linear power supply is probably putting out around 6-7A continuously. Still, this is plenty of current to drive this chip amp with plenty of headroom. I purchased my Astron via Craigslist for $20 in San Jose, and replaced the electrolytic filter caps with a big 22,000uF Rifa PEH-200 cap, a Nichicon KZ Muse cap and a Panasonic FM cap. Even though the PSU was in physical mint condition, the caps looked like aging 1970's vintage Elna's. The cap replacement made a significant improvement in sound quality.

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I don't want to dumb down your thread, but I have had a lot of fun and success with the Lepai 168HA which is a 2.1 amp with 40w x 2 plus 68w x1 for a subwoofer (all exaggerated but that is what the spec says). I have built a 2.1 system for my computer at work with a couple klipsch 1.1 satellites and an 8" Dayton sub. But the most fun is building portable boomboxes. There are many good "full range drivers available (tang band, faital, prv) that pair up well with a small sub (best so far is a 6.5" tang band). The amp is about $27 and the speakers are all reasonable. Can do a cool little boombox for right around $100. I have a cnc router table at work that makes throwing these together and or tweaking the design very easy. I also ran my Belle's with a Dayton DTA 100 for several weeks before I got a chance to run wires to them from my main system and the sound was very good. I am amazed at these little amps.

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