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60 WPC Amplifier for DIY Turntable Motor Drive
60 WPC Amplifier for DIY Turntable Motor Drive
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Old 13th January 2018, 04:42 PM   #221
alexkosha is offline alexkosha  United States
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60 WPC Amplifier for DIY Turntable Motor Drive
I found the answer in Pyramid’s video on YouTube. Thank you.
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Old 13th January 2018, 05:01 PM   #222
coolmaster is offline coolmaster
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Quote:
Originally Posted by alexkosha View Post
I found the answer in Pyramid’s video on YouTube. Thank you.
For anyone constructiing the SG4, populate every part required and supply regulated 12vdc. Its this straight forward.
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Old 15th January 2018, 12:29 AM   #223
alexkosha is offline alexkosha  United States
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60 WPC Amplifier for DIY Turntable Motor Drive
Got a couple of TDA7293 apms from advised eBay guy and I can say it is not a good quality of assembly and also packing is not nice either. TDAs got bent on all units and I got one that was not soldered straight. I desoldered and soldered all back. Also changed PSU filter caps to better quality once and bit higher capacity (4700uF instead of 2200uF). R12 (Pyramid's advice) changed to 8.6k (instead of 22k)and its position marked in attached image. What I'm sayng, its very affordable, but requires some fixes.
Although, I was surprised by sound quality of these amps during my test. Very interesting.
Now is my question.
I found very nice 100-120VA toroid trany in my junk with two outs: 26.2v-0-26.2v and 0-14V. I can use 14VAC to make 12VDC for SG4. Question is if I can use 26.2V instaed of 24v for TDA amps? Any negative side?
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Last edited by alexkosha; 15th January 2018 at 12:33 AM.
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Old 15th January 2018, 01:24 AM   #224
Pyramid is offline Pyramid  United States
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Quote:
Originally Posted by alexkosha View Post
Question is if I can use 26.2V instaed of 24v for TDA amps? Any negative side?
The TDA7293 is rated for 120VDC/±60VDC. 26.2VAC dual secondary will give you ~ ±40VDC. The amp may run a little warm as the DC rails are higher than they need to be, but it should work. I would use a large heat sink for the amp.

The 14VAC winding will give you ~22VDC to supply the SG4. Use a 12V regulator between the SG4 and the supply or add a decent heat sink to the 5V regulator on the SG4.
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Old 15th January 2018, 01:24 AM   #225
alexkosha is offline alexkosha  United States
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60 WPC Amplifier for DIY Turntable Motor Drive
This is how one is arrived soldered.IMG_1553.JPG
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Old 15th January 2018, 01:29 AM   #226
alexkosha is offline alexkosha  United States
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Quote:
Originally Posted by Pyramid View Post
The TDA7293 is rated for 120VDC/±60VDC. 26.2VAC dual secondary will give you ~ ±40VDC. The amp may run a little warm as the DC rails are higher than they need to be, but it should work. I would use a large heat sink for the amp.


Thank you a lot. I used same heat-sing as your enclosure has for 2 hours. Temp is stabilized after about 40 min and raised by 5-6 deg C above ambient. I measured on the chip. It is “cool” small amp. Thanks for so quick answer.
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Old 17th January 2018, 10:05 AM   #227
coolmaster is offline coolmaster
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Just to highlight my recent trials and tribulations of this TDA8950 Class D amp module for SG-4 speed controller.
I'm not exactly happy with this module and how its performing.
With what I have on hand to rig up this module was initially a 22V AC input, then 24V input direct to the board. At these voltage input, the DC rail is anywhere from 33VDC to 36VDC. This is on the high side, necessary or not, or testing with a oversized VA transformer isn't issue. It should work as designed out of the box but apparently it didn't. If there's ONE advantage of this model of amp board is direct AC supply input from transformer that simplify everything. The dangerous part is there's no safety measures such as fuses or anything in case anything goes awry. I have to rely on the board's relay or whatever protection circuitry on board.
With high AV voltage (22-24VAC) in, the LPF coils become finger hot and the main heatsink is very warm to finger hot after sometime in my tropical weather. On the good side, it works but I seem to think its a little over than expected. DC offset is also more than 90mV per channel and not a good thing. I also had to replace the volume pot to 10K and mono the inputs since its a mono input from SG4. I now use a 12V twin primary stepped up to 230VAC.
This is when the perplexing start to appear. Its apparent to me this module of mine do not like DC rail voltage in excess of 33VDC. The output voltage on each channel register alright with no load. When connect to single 12V winding of a twin wound toroidal (it was 15V on another test tranny) the output will build up to 230VAC and stay. Next is to connect each winding to each L&R channel, switch on the SG-4, will oscillate and shut down or a clicking sound maybe faintly heard. Its like there exist some short circuit. Next is to connect output in BTL mode, it works and constant voltage is stepped up. After this was to input a smaller mains transformer 15-0-15 to the AC input resulting with 22VDC on the DC rails. The same consequence occurred, only working in BTL mode but not in stereo mode. Its noticed that it doesn't matter if the AC input is 15 or 24VAC, no further adjustment is needed and 230VAC is still maintained. Of course, with 15VAC supply input, it seemed performing stable and lukewarm temperature. Again, I think this module do not like high DC rail voltage for it to operate. I didn't exceed any specs.

For now, I can't establish whether this TDA8950 module have some quality issues, shortcomings in the design, incompatibility for transformer output drive or flawed quality altogether. Its just my observation so far.
Considering all the above, I think I'm going to ditch this TDA8950 as a suitable amp for the SG4. This is one weird animal. Maybe its just mine.

Last edited by coolmaster; 17th January 2018 at 10:08 AM.
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Old 17th January 2018, 01:45 PM   #228
Pyramid is offline Pyramid  United States
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If you look at the datasheet for the TDA8950, it might explain what is happening (section 8-4, page 11). ±36VDC is near the limit for the device, and when operated in SE mode, power supply "pumping" occurs which will increase the supply rails and push the device into OVP. The inputs and outputs should be connected out of phase in SE applications and this has to be accounted for when connecting to the windings of the transformer connected to the outputs. If you don't account for this, the amp will see a nearly short circuit on the outputs because the phases are opposite. Even operated correctly, the amp is running too close to the max supply and will be subject to shut down due to supply rail pumping.

I think the answer is to run the amp in BTL mode using lower voltage supply and 12VAC input step ups on the output. In BTL mode, you would only need ±15VDC supplies which you could get using 12-0-12 AC input.
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Old 17th January 2018, 05:59 PM   #229
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Bill, I appreciate your insight to this chip amp. I hope to have this up and running very soon. My turntable need this controller quite badly. I've already heard the improvement during some tests connected to the turntable.
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