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Class D Switching Power Amplifiers and Power D/A conversion

Substituting 3e 3255 in a ready made amp
Substituting 3e 3255 in a ready made amp
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Old 11th May 2020, 03:20 AM   #1
gilera is offline gilera
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Default Substituting 3e 3255 in a ready made amp

Hi,
I have been planning on putting together a 3255 amp in an enclosure. I will use the 3e board, LRS-350-48. I would like to also have on-off and volume.

This is where it seems to get a bit complicated. There seems to be mixed opinions of the impact a Pot has on sound quality and avoiding the on-off pop seems also problematic. My immediate thought is to avoid this and use a pre-amp. Then we are talking another piece of equipment and potentially unnecessary attenuation beyond 2VRMS.

I would like to keep it versatile so I can have input from CD player or laptop/phone. My older laptop does have straight digital out but I am not planning on a separate DAC or media player at this point - maybe down the track if the quality of my other gear justifies it. It all starts to become a bit beyond my understanding of audio electronics.

Basically, I am wondering if there is something ready made from china that has some of these features and is big enough that I could substitute the 3255 board and PSU? The fact that I have not come across anyone suggesting this make me think no, but doesn't hurt to ask.... Good enclosures along run at about $80AUD and some of the ready made amps coming out of china look quite nice and are not much more that.
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Old 11th May 2020, 12:09 PM   #2
ElliJ is offline ElliJ  United Kingdom
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The 3eAUDIO TPA3255 has anti pop built into it. I don’t think having a decent pot in your system will effect your sound quality as much as a preamp could.
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Old 11th May 2020, 10:59 PM   #3
gilera is offline gilera
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Thanks. I am looking at doing something very similar to your build.

Can I ask - why did you use the 10k DACT Type SMD Stepped Attenuator 21 step volume control as opposed to an ALPS pot (I don't really know the difference I have just read that ALPS pots seem to be the ones most commonly recommended).

Also what were your reasons for using the Douk PSU as opposed to the Meanwell LRS-350-48? Was it easier to get or better quality?

I might have to start a new thread for my build - yours was very helpful.
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Old 12th May 2020, 12:47 PM   #4
ElliJ is offline ElliJ  United Kingdom
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I read some reviews about the Tisbury passive preamp, this thing impressed a lot of people. It struck me that this was really well designed and it used a DACT type SMD Pot. The first one I got didn’t cut the sound at min volume so I found a better one on eBay. The signal only goes through one resistor and the two channels are extremely well balanced. Alp are ok but not great quality. Some attenuators cost more than my amp!

It was size and cost which made me get the Douk smps. I liked the heat sink, the way it wrapped round the unit and the fact it had no fan. I did not know if it would be any good when I got it, i still don’t as it could die tomorrow. I have both the 24 and 48vdc. I was having trouble finding a smps that met all my needs, I needed a high wattage, 48vdc, compact and that wasn’t dual output.
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Old 12th May 2020, 09:44 PM   #5
gilera is offline gilera
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Thanks for that. I had read there are 4 op amps at the input stage so did you need to use a 4 deck attenuator? How is it connected?

A link to the one you used would be great as at least it is proven. Yeah i notice that the genuine ones are several hundred dollars.

Sorry for the newbie questions....

Last edited by gilera; 12th May 2020 at 09:57 PM. Reason: Typo
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Old 12th May 2020, 09:54 PM   #6
gilera is offline gilera
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Looking at ElliJ's build photos it looks to be only a single deck. I had read on the TI forum when the question of adding a volume pot was posed that due to their being 4 op amps, 4 pots would be required if operating in btl mode (which I'm assuming most are). The support technician made it out to be quite an ask to put volume control on one of these yet all the ready made ones out of china have them (prob cheap ones). Has the sound quality likely been compromised in these?
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Old 12th May 2020, 11:43 PM   #7
ElliJ is offline ElliJ  United Kingdom
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The pot is stereo, it needs to attenuate the left and right channels. The amp has 2 inputs, the left and right channels. Your you source has 2 outputs, the left and right channels. The pot has an input, an output and a ground for each channel. When you wire your amp with a pot you will have a return from the amp and a return/ground from the pot which both go to the source return. There are various ways to wire your pot, google some diagrams and try to figure some out. It is important to understand that when the pot is at a low volume most of the input signal goes to the ground and at max volume none of the input goes to the ground and it all goes to the amp.

I am not sure about the op amps, there are probably 2 for each channel as the amp has 2 outputs for each speaker as it is BTL. The amps input is not BTL, it is Single Ended or in some cases Balanced.

I hope this is what you wanted to know. Don’t be afraid of wiring an amp with a pot, there are lots of people who can give you advice and like to be helpful. I am a bit of a noob here and have always had any questions I’ve asked answered quickly.
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Old 12th May 2020, 11:47 PM   #8
ElliJ is offline ElliJ  United Kingdom
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HI-END DACT Type SMD Stepped Attenuator 21 step volume control 10K 20K 50K-250K | eBay

I got the 10k version.
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