Hi Folks,
I am listening to the TPA3255 at present driven by my Aksa Lender (with the SMD daughterboard, although TH would work just as well) as a preamp. I have used a Sparkfun THAT1646 a SE to Bal converter before and that works fine, but I am testing a new converter designed by Jhofland that uses an LME47924 and a $5 Murata isolated DC-DC converter 12v to +/-12v PCB that is ultra clean and simple. The setup is absolutely low noise (cannot tell that the amp is turned on with ear pressed to the speaker cones). This converter is part of a two-way converter board that does SE-Bal and Bal-SE conversion. For the purposes of providing a useful and clean preamp for the TPA3255, just the SE to Bal converter is probably all that is needed. Adding a jumper selectable 0dB, 12dB and 20dB gain stage in front of the the LME47924 would probably be useful. I would probably change the 12v DC-DC converter to +/-15v (CMR1215S3C) for the maximum output headroom possible.
Anyhow, I am really enjoying the combo of the Aksa Lender preamp and this SE to Bal converter with the TPA3255. It makes it almost sound like an Alpha Class A amp but with a 100w of power.
Although the LME49724 is only available as SOIC8 package, they are easy to hand solder. Let me see if Jhofland can design a basic converter board like this with Molex KK inputs and outputs and we can install it inside our amp cases.
I am listening to the TPA3255 at present driven by my Aksa Lender (with the SMD daughterboard, although TH would work just as well) as a preamp. I have used a Sparkfun THAT1646 a SE to Bal converter before and that works fine, but I am testing a new converter designed by Jhofland that uses an LME47924 and a $5 Murata isolated DC-DC converter 12v to +/-12v PCB that is ultra clean and simple. The setup is absolutely low noise (cannot tell that the amp is turned on with ear pressed to the speaker cones). This converter is part of a two-way converter board that does SE-Bal and Bal-SE conversion. For the purposes of providing a useful and clean preamp for the TPA3255, just the SE to Bal converter is probably all that is needed. Adding a jumper selectable 0dB, 12dB and 20dB gain stage in front of the the LME47924 would probably be useful. I would probably change the 12v DC-DC converter to +/-15v (CMR1215S3C) for the maximum output headroom possible.
Anyhow, I am really enjoying the combo of the Aksa Lender preamp and this SE to Bal converter with the TPA3255. It makes it almost sound like an Alpha Class A amp but with a 100w of power.
Although the LME49724 is only available as SOIC8 package, they are easy to hand solder. Let me see if Jhofland can design a basic converter board like this with Molex KK inputs and outputs and we can install it inside our amp cases.
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All amps have been sent out. You should all have received an email with the tracking number. That was 5hrs of work to relabel via PayPal because the order took too long to fulfill, Etsy would not let me use their shipping service. That was a pain but I learn now that it was self-inflicted. I just need to put a very long lead time so it doesn’t expire. I thought 2.5 months was long enough but experience shows these things take 3-4 months.
Thank you all for your patience. Your amps should be arriving soon.
Cheers,
X
Thank you all for your patience. Your amps should be arriving soon.
Cheers,
X
I assembled the 6-pin Molex Minifit speaker out connectors with two pairs of ultra supple 16ga silicone RC car wire crimped onto the Minifit connectors on one end and doubled up to female bullet connectors on the other end. I connected the banana plug of my 12ga speaker wire to this and I think there is a noticeable improvement in bass authority vs the 16ga wire connected via the Faston spade. Maybe two 16ga wires on the spade would have done the same thing.
I think that silicone RC race car wire is really good stuff for high currents. We should make entire speaker cables with it.
I think that silicone RC race car wire is really good stuff for high currents. We should make entire speaker cables with it.
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I agree. Silicone is great. Started using it with my quad-core builds a few years back. Now it's my go-to wire in all my audio builds as well. Keep about 3 different gauges on hand.
Have the 3255 singing quite nicely on my bench this morning, letting it break-in a bit. For testing purposes, I decide to wire up some XLR connectors. This allowed me to use my Doug Self pre directly, without wiring up the 1646 THAT adapters. Listening to it now as I write this. Even using some cheap speakers on my bench, all I can say is that it is very articulate, lots of dynamics and quiet, quiet, quiet. No PSU, pre, or amp artifacts getting in the way of the sound. The way it should be.
Attaching the heatsink to the chip was a bit tricky (and delicate), but I managed for purposes of testing. Not sure if this will be the approach I will use when I fit it all in a enclosure.
The pictures below illustrate my approach using thermal tape and a small piece of copper to act as a riser and heat spreader for the heatsink. I then cover the bottom of the PCB with fish paper to avoid any shorts to the HS. This way I can reuse the same strategy if I use its final enclosure as a the heatsink.
Thanks X for producing a very nice smooth sounding amp, with equally outstanding build quality. Next phase will be putting it in a nice enclosure and adding it to my system (somewhere
) In retrospect, I'm glad I didn't try building this up from just the PCB. 
Rick
Attaching the heatsink to the chip was a bit tricky (and delicate), but I managed for purposes of testing. Not sure if this will be the approach I will use when I fit it all in a enclosure.
The pictures below illustrate my approach using thermal tape and a small piece of copper to act as a riser and heat spreader for the heatsink. I then cover the bottom of the PCB with fish paper to avoid any shorts to the HS. This way I can reuse the same strategy if I use its final enclosure as a the heatsink.
Thanks X for producing a very nice smooth sounding amp, with equally outstanding build quality. Next phase will be putting it in a nice enclosure and adding it to my system (somewhere
) In retrospect, I'm glad I didn't try building this up from just the PCB. Rick
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Very nice work, Redjr! Glad you had a balanced output Preamp. Doug Self one is outstanding. Kapton tape makes a nice insulator shield to prevent shorts. I found a 2mm spacer between the chip and heatsink clearly elevates it to prevent any shorts. Please try double 16ga silicone wire on the speaker outs of you get a chance. I was surprised by the difference in bass dynamics.
My TPA3255 came just in time for me to test my new Purifi PTT6.5 and RS28F passive Harsch XO speakers as they are 4ohm. All my other amps are 8ohm.
What brand of PSU are you using - sounds like it is quiet! This amp’s quietness is very impressive.
My TPA3255 came just in time for me to test my new Purifi PTT6.5 and RS28F passive Harsch XO speakers as they are 4ohm. All my other amps are 8ohm.
What brand of PSU are you using - sounds like it is quiet! This amp’s quietness is very impressive.
Hi Redjr,
I just noticed that your speaker out on the left side is reversed. Red should be on the back (C) and black on the front (D). On the right A (red) is on the front, and B (black is on the back) - you have that correct. The bass may be low and the sound will have a strange phasiness if output polarity is flipped on one speaker. This assumes Ain and Cin are +ve from the balanced preamp (which your photos shows correctly).
I just noticed that your speaker out on the left side is reversed. Red should be on the back (C) and black on the front (D). On the right A (red) is on the front, and B (black is on the back) - you have that correct. The bass may be low and the sound will have a strange phasiness if output polarity is flipped on one speaker. This assumes Ain and Cin are +ve from the balanced preamp (which your photos shows correctly).
At the moment, I'm using the positive side of a Connexelectronic SMPS300RE I had. I read in one of your threads awhile back that you mentioned that brand had a lot of noise. I've used many of his (Cristi) PSUs over the years, and been pleased with the results. Keep a couple on hand. Most of my little chip amps have them inside, as well as my ICEPower amp I built a few years back. I guess, if I can't hear any noise with my ear at the speaker it's good enough for me.
Maybe on a scope it's measureable. Either that, or my hearing is going after 68yrs - or both. I also used 2 of Cristi's SMPS800RE variants in my favor amp of all time (FirstOne), and thought it was an excellent sounding amp. One that I grew to love the sound of. At least to my ears, in my listening space. But I digress.
I think I will double up on the speaker cables and add the extra wires a see what that does to the bass. Anyway, I'm still testing it and letting it 'warm up' a bit more today.
Thanks for a nice sounding amp project, and the result ending up on a very positive note.
I'll follow-up later with more pics when I get this amp into it's deserving enclosure.
Hi Redjr,
I just noticed that your speaker out on the left side is reversed. Red should be on the back (C) and black on the front (D). On the right A (red) is on the front, and B (black is on the back) - you have that correct. The bass may be low and the sound will have a strange phasiness if output polarity is flipped on one speaker. This assumes Ain and Cin are +ve from the balanced preamp (which your photos shows correctly).
Thanks. I'll fix that now.
You are most welcome!
Your experience with the Connexelectronic PSU and this amp got me to give it another go. The last time I tried it was with the 3e TPA3255 amp and the Aliexpress/ebay EVM clone (blue board) and the SMSPS800RE. It had terrible hiss that could not be eliminated. I even tried adding a CLC filter in between. Finally, I gave up and relegated the Connex SMPS to the heap of unused "junk" boards.
So I dusted off my SMPS800RE and connected to MY TPA3255 Reference Class D amp, and it is quiet! There must be something in JPS64's layout and my extra RFI filters in the circuit! I know JPS64 pays extra attention to the filtering of his on-board DCDC step down circuit to make the 12v and 3.3v auxilary power for the opamps and digital logic. So great news is that my formerly $150 (with shipping) "door stop" of a PSU is now useful again. However, I see no benefit over the $44 Aliexpress LED 800w SMPS that I used previously.
So thank you for testing it with the Connexelectronic.
Let this be a retraction to my earlier comment that the Connexelectronic PSU cannot be used without noise on my particular design of TPA3255.
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No. It's more the thickness of light cardboard, fairly stiff, but has insulating properties. I buy it with a self-adhesive side for easy application. During my Heathkit building days, kits almost always included a small piece, if it was called for. I remember using it way back in the 60's.
Fish paper here.
Fish paper is 10 mils thick - that is very thick paper! With peel off adjesive backing that is good handy stuff - will keep it in mind for projects. Useful for where something might even poke through thin Kapton. Kapton has nicest feature of silicone adhesive that leaves no residue even once it is baked on.
You are most welcome!
Your experience with the Connexelectronic PSU and this amp got me to give it another go. The last time I tried it was with the 3e TPA3255 amp and the Aliexpress/ebay EVM clone (blue board) and the SMSPS800RE. It had terrible hiss that could not be eliminated. I even tried adding a CLC filter in between. Finally, I gave up and relegated the Connex SMPS to the heap of unused "junk" boards.
So I dusted off my SMPS800RE and connected to MY TPA3255 Reference Class D amp, and it is quiet! There must be something in JPS64's layout and my extra RFI filters in the circuit! I know JPS64 pays extra attention to the filtering of his on-board DCDC step down circuit to make the 12v and 3.3v auxilary power for the opamps and digital logic. So great news is that my formerly $150 (with shipping) "door stop" of a PSU is now useful again. However, I see no benefit over the $44 Aliexpress LED 800w SMPS that I used previously.
So thank you for testing it with the Connexelectronic.
Let this be a retraction to my earlier comment that the Connexelectronic PSU cannot be used without noise on my particular design of TPA3255.
Glad to hear your SMPS800RE is working with the new amp. You had me worried I'd been listening to more 'noise' than I should have for all these years!
I've always felt Cristi's designs and builds are top notch. He's my goto shop whenever I need a new SMPS for a project. Not inexpensive, but I've never had one fail. At the moment, he's building a couple lower voltage, single rail supplies for me.