Suggested affordable quiet amp for high efficiency speakers

[themrcul]

Hi everyone,
If you have seen my post history you might know that I have had a pair of Audio Nirvana 15"s in boxes for years.

Recently however I had the idea of possibly using them at my work on my desk in an open baffle config.

I hooked up my basic Accento 2x20W (https://www.theloudspeakerkit.com/ada40-accento-dynamica-40w-amplifier) to them yesterday to see if they still worked, and thankfully they do, however there was a bit of noise coming out of the speakers when the amp was turned on.

My understanding is this was happening because the speakers are 96db efficient and will therefore pick up any noise from the amplifier and make it audible.

So I had a look on AliExpress for possible low power amps to replace the amp with and was dazzled at the seemingly limitless number of amps for sale there.

I thought it would be a good idea to ask here instead as many here have so much more experience than me in this area - does anyone have any amp they can recommend to me, even if it maxes out at 10w, that is quiet enough to not have audible noisy output from my speakers when idling?
I'm hoping not to spend more than ~$70US or so including power supply.

Thanks for anyone's input in advance.

 

[lineup]

Build a simple LM1875T amplifier.
It will provide enough power.
The sound will be good.

 

[HAYK]

I have 105db/w/m speaker and I have numerous SET, many class A but what I get best is with $1 cost TPA3110 pbtl 30w from Ali converted into class ABD
https://www.aliexpress.com/item/329....order_list.order_list_main.22.5e7e1802HeCrDZ
100w 24v SMPS cost $6
https://www.aliexpress.com/item/100...!sea!TH!4284450371&curPageLogUid=hzKp1xed3egV

 

[bebo65]

In its power-range this one is hard to beat:

https://neurochrome.com/products/modulus-86

 

[HAYK]

His budget is 70$ psu included, Modulus 86 only one channel PCB costs 85$.

 

[Stuey]

Hi Hayk,

Have you used that exact PSU, and if so, is it quiet with your speakers?

Cheers

Stuey

 

[abraxalito]

With efficient speakers what you really need is an amp with lower gain than the usual amount (26dB) to get lower noise. There are a few chipamps with low gain options (16dB typically) and this gives significant noise reduction. TDA1566 is one of the amps that's able to give 16dB gain, however the leaded version is hard to find nowadays. The SMD version can be bought though.

 

[HAYK]

I used the 36v 7A from the same manufacture,$8 no any audible noise. These new generation of smps run at 500khz and the output has LCL filter. Just 15cm wire and 2200uF at arrival destroys all HF components.
What you don't see is the 100hz component which exhibits at power. This is best eliminated by driving the smps with DC and ripple eliminated by a mosfet. I have a working circuit if you want. On Ali you find various AC treatment modules. This how you put your money where is needed.

 

[themrcul]

Thanks to everyone who has replied.

abraxalito, I searched Aliexpress and couldn't find any amp using the TDA1566 chip, only discrete chips were available. Do you know of any other amps that offer a lower gain that might still be available?
Edit: linup, Do you mean something like this?: https://www.aliexpress.com/item/100...4!sea!AU!762615254&curPageLogUid=bTPl0zYGOlZb

HAYK, I have a few questions about the amp you recommended.
Firstly, the TPA3110 pbtl 30w is just a power amp, with no volume control. I assume it would need to be paired with a preamp, yes? If so, would you be able to recommend a pre-amp that would match well with it so that I could have a volume control? (would something like this suffice? https://www.aliexpress.com/item/1005001828613892.html?spm=a2g0o.productlist.main.61.5ae664d1ETutPQ&algo_pvid=53d82f4a-e495-4f9c-8907-aade80e041b6&algo_exp_id=53d82f4a-e495-4f9c-8907-aade80e041b6-30&pdp_npi=3@dis!AUD!34.32!24.37!!!!!@211bd93f16838137129485679d0814!12000025767149777!sea!AU!762615254&curPageLogUid=ii9jhtTQ9B1S)

Your comment on the power supply was also interesting - I would be interested in seeing your working circuit for DC ripple elimination - like for the TDA1566 I couldn't find what you were describing on Aliexpress either.

I'll ask for more details about the mods you did to convert the TPA3110 chip you referenced from class D to ABD in the thread you made about it originally - that sounds like fun.

 

[HAYK]

You only need 10k log volume control. The gain of the amp is 20db. To convert into ABD mod you need to cut the track that grounds the output capacitors and add a 3w resistor 120 ohm to ground it (or 2*220 2w). I have a giant horn 70cm *70cm diameter with 110db driver, my head in the horn I hear total silence. The chip has 80db PSRR and 102db S/N, output noise 65uv. What goes for sound quality, my 2A3C SET has become a decorative object.
I am using an old SMPS 24v 2A for 2 channels without any ripple eliminator, just 2700uF at the DC inputs of each board.

 

[lineup]

Yes. But I would run LM1875 lower than 2x30W.
It is a matter how much voltage supply.

 

[HAYK]

Here are some smps filters from Ali.
https://www.aliexpress.com/item/1005004859087986.html?spm=a2g0o.productlist.main.99.77571f7fZYIPZY&algo_pvid=5131837d-55cb-469f-a69c-8dabf5feaee8&algo_exp_id=5131837d-55cb-469f-a69c-8dabf5feaee8-50&pdp_npi=3@dis!USD!13.26!11.01!!!!!@212279a216838497509061637d07dc!12000030778701887!sea!TH!4284450371&curPageLogUid=adgsxho1PMgO

https://www.aliexpress.com/item/1005004174449699.html?spm=a2g0o.productlist.main.43.77571f7fZYIPZY&algo_pvid=b4d44ca4-c5b0-4bfd-83c0-e3ba5ffbab13&algo_exp_id=b4d44ca4-c5b0-4bfd-83c0-e3ba5ffbab13-21&pdp_npi=3@dis!USD!13.35!10.41!!!!!@211be10916838500353897275d07e2!12000028284206918!sea!TH!4284450371&curPageLogUid=fcPs12aoUECG

https://www.aliexpress.com/item/1005001564830253.html?spm=a2g0o.productlist.main.53.77571f7fZYIPZY&algo_pvid=b4d44ca4-c5b0-4bfd-83c0-e3ba5ffbab13&algo_exp_id=b4d44ca4-c5b0-4bfd-83c0-e3ba5ffbab13-26&pdp_npi=3@dis!USD!1.0!0.95!!!!!@211be10916838500353897275d07e2!12000016608789788!sea!TH!4284450371&curPageLogUid=9iFLatXxCzWY

https://www.aliexpress.com/item/1005005528172693.html?spm=a2g0o.productlist.main.97.77571f7fZYIPZY&algo_pvid=b4d44ca4-c5b0-4bfd-83c0-e3ba5ffbab13&algo_exp_id=b4d44ca4-c5b0-4bfd-83c0-e3ba5ffbab13-48&pdp_npi=3@dis!USD!1.9!1.04!!!!!@211be10916838500353897275d07e2!12000033424719747!sea!TH!4284450371&curPageLogUid=iivPUyxxMz0q
I advise you to use the last $1 emi filter with the low cost smps as it doesn't have Earth input to filter common mode noise. Use the In as out and Out as in.

 

[HAYK]

This is my 150w ripple rejector. I use it for an amp under development which has only 40db PSRR.
The mosfet can be any >600v >2A isolated.

 

[themrcul]

Thanks to both lineup and HAYK for your replies.

HAYK, If I am to construct the amp by doing the following, can you comment on whether you think I have got it right or not please?

Firstly, I plug a 3 pin kettle cable from the wall into an kettle plug, that wires up to an EMI filter like this one:
https://www.aliexpress.com/item/4001012248154.html?spm=a2g0o.productlist.main.51.7e706040UQcB72&algo_pvid=141436b9-9a99-4234-9a76-d89fef79ad12&algo_exp_id=141436b9-9a99-4234-9a76-d89fef79ad12-25&pdp_npi=3@dis!AUD!3.92!3.41!!!!!@211bc2a016839021570743019d0744!12000029106670723!sea!AU!762615254&curPageLogUid=0zX89wbqCqfi

2 pins connect the output of that EMI filter to the 2 input pins of the power supply you recommended to me earlier. 6 amps should be more than enough, I calculated the two amps recommended need 1.25amps each (2.5w-3w total to to get to 30w output, unlikely I will be able to listen to it that loudly!)
https://www.aliexpress.com/item/1005001393830470.html?spm=a2g0o.productlist.main.31.55641f7aR79V7T&algo_pvid=ea9911b9-008b-401d-adaf-50b9dade8754&algo_exp_id=ea9911b9-008b-401d-adaf-50b9dade8754-15&pdp_ext_f=%7B"sku_id"%3A"12000015923585537"%7D&pdp_npi=3%40dis%21USD%213.54%213.36%21%21%21%21%21%40211bf55216775671961943622d06c7%2112000015923585537%21sea%21TH%214284450371&curPageLogUid=hzKp1xed3egV

Between power output of power supply and amp I connect this bypass cap (positive line to positive, negative line to negative):
https://www.aliexpress.com/item/1005004629436895.html?spm=a2g0o.productlist.main.99.28534e9dncChIl&algo_pvid=24429976-e5f8-4149-9cd9-27b256af8073&algo_exp_id=24429976-e5f8-4149-9cd9-27b256af8073-49&pdp_npi=3@dis!AUD!1.11!0.67!!!!!@211bf12316839008765434251d07ae!12000030072379135!sea!AU!762615254&curPageLogUid=5XXkEUQeyWuv

Then power outputs from the power supply continues to two of the amps you recommended before, 1 for each left/right channel:
https://www.aliexpress.com/item/329....order_list.order_list_main.22.5e7e1802HeCrDZ

Between the audio input to the amp (which is the audio output of my dac) and the amp board audio inputs I will need a volume pot, like this one:
https://www.aliexpress.com/item/4000086278540.html?spm=a2g0o.productlist.main.23.13efca72VCuNof&algo_pvid=18ad2089-f6cb-4c84-a0c2-cec81c90d7f4&algo_exp_id=18ad2089-f6cb-4c84-a0c2-cec81c90d7f4-11&pdp_npi=3@dis!AUD!17.99!17.8!!!!!@211be3d216838973304257549d07bd!10000000231621669!sea!AU!762615254&curPageLogUid=xbKOBfhWNWqR

And then I perform the mod to the amps as you specified, by cutting the trace from the output cap to ground and inserting a 130ohm 3w resistor between the output cap and ground.

Does that look correct? Have I missed anything or gotten anything wrong?

Also, a second question if I may, in the thread where you originally detailed the mod to the TPA3110 amp you recommended, it seems like in the schematic and photo you provided that there are capacitors (or are they inductors?) added between the output caps and the resistor to ground. They are the blue square things soldered to the resistors in the photo in this post:
https://www.diyaudio.com/community/...ass-d-into-abd-modulation.396664/post-7290300

Can I ask, are they needed for the mod, what are they, and what are their values?
EDIT: I see now you have removed C6 and C10, and inserted EPCOS 2x 680nF 63V caps instead (https://www.aliexpress.com/i/1005003974316127.html).
One leg for each of the caps on each output of the coils, then solder the other legs of the caps together and then connect that bridge to the resistor. The resistor goes to ground. Is that correct?

Thanks for all of your help!

 

[HAYK]

The mains with 220v, 2A is 440 watts. By faaar sufficient. With this EMI filter, respect the schematic on the module LINE, the Earth and Load that feeds the SMPS. You need Two capacitors one on each amp of low esr type. The one you selected is for rectifier. This one 2200uf 35v is good.
https://www.aliexpress.com/item/33030332216.html?spm=a2g0o.productlist.main.53.522840f36i9vBn&algo_pvid=681c466b-f991-42fb-b06f-85850139b86a&algo_exp_id=681c466b-f991-42fb-b06f-85850139b86a-26&pdp_npi=3@dis!THB!36.7!32.97!!!!!@212240a316841765881873393d0787!67240383190!sea!TH!4284450371&curPageLogUid=UDmeZMcg2P5W
The resistor to add is 120 ohm 3W, but you can apply 2× 220 ohm 2W in parallel.
https://www.aliexpress.com/item/328....order_list.order_list_main.25.59171802yZnM9C
The potentiometer you chose from Ali is not affordable and can be fake as I got one. It should be 10k.
The problem with the fake Alps, the stoppers are wider spaced and doesn't let you to adjust right, either too loud or too low.
The two blue capacitors are epcos 680nF. The ones on board give exactly the same sound. So no need to replace them.

 

[abraxalito]

abraxalito, I searched Aliexpress and couldn't find any amp using the TDA1566 chip, only discrete chips were available. Do you know of any other amps that offer a lower gain that might still be available?

No, I'm not aware of any finished boards using that chip. Which is what led me to make my own PCB using it. The first rev doesn't have quite enough heatsinking though so the board's going to be re-spun with a bigger HS. If you are interested, drop me a PM.

Incidentally there are other chips with 16dB gain but they're even more complex to get going than the 1566. All the others I've found need the low gain mode to be set in software over their I2C bus which calls for an MCU to initialise them.

 

[HAYK]

Just now, the version with smd output capacitors which was working 8hr/day since 2 weeks, stopped working on power up. Whereas the one with blue capacitors is running since 2 months without issue.
https://www.aliexpress.com/item/100...order_list.order_list_main.203.6c6e1802wolETG

 

[themrcul]

Interesting, thanks HAYK. I might grab the capacitors while I'm at it anyway. Also thanks for commenting on the parts I've chosen. You've given me more confidence in the build.

abraxalito: Thanks for your comment. If I come unstuck with this build I'll drop you a line for your design. Thanks again.

 

[themrcul]

Sorry HAYK I have two more questions, but I think they should be the last ones!

Firstly, do you think that the same amp, but 24V 3A, rather than 4A would be sufficient? I calculated that 30W x 2 should be 1.25A x 2 = 2.5A.
The reason is the 3A version will fit better in the chassis I am hoping to use.
The power supply I'm thinking of is this one: https://www.aliexpress.com/item/100...5!sea!AU!762615254&curPageLogUid=DHL7Xw0HNdEI

Also, I am finding it difficult to tell which ALPS volume pots are genuine and which ones aren't. Do you have any tips on how to find a genuine one or one that is better value than the one I found above?

Thanks again for all of your help. I feel I'm going to be able to build a killer amp with your advice!

 

[themrcul]

Sorry one more question! Is there a special reason why you recommend a 10K pot for volume rather than the more easily available 50K? If 50K ones are usable then that opens up a lot more options for volume control pots.

Thanks again!