[rhing]

For grins, I took a Panasonic 2200uF 35V electrolytic cap and soldered it across J6 on my Sure TPA3110 board. This extra reservoir capacitance seems to have done a lot for bass dynamics. It no longer sounds like a "low-power" amp even when playing bombastic film scores through my moderately low-eff desktop speakers (W4-1052 full range with contour filters). I'm using the wall-wart SMPS from my DTA-1 to power the TPA3110 board, and I think the sound surpasses that of the DTA-1. Even though it's still a very 'literal' sounding amp as most TI amp chips are (which I like), without too much in the way of added sweeteners, it's still very low-distortion, and has a ton of grunt with this added capacitance. This goes to show how dependent these amps are on a good stiffened power supply. I found a FSP Group 40W 12V supply in a junk bin at work that I'm going to bring home to use with this board to make sure it's never wanting for current.

My ferrite beads are on the way. I will report back. Hopefully these work - it will be nice to have a working Class-D amplifier with no inductors in the output filter to saturate. I read about these inductors in output filters commonly being undersized for the task.

Thanks for sharing your experience with the additional off-board cap. Salis Audio keeps preaching the virtues of adding additional capacitance off-board. I should have added some 2,200uF / 25V Panasonic FM caps to my last Digikey order. 

As for the Ferrite beads, please keep us posted on your results. I wonder if your speaker wires are too long and positioned in a place where they can easily pick-up interference. Also, have you tried twisting the + and - pair from the amp to the speakers?

I forgot to mention that using a different outlet for my 110W SMPS powering the TPA3110 amp versus the multi-outlet strip where my line stage preamp and rest of my system is plugged helped reduce noise.

However, it's cheap enough to get a couple, and try it! What size wire is needed? Could I strip out the wires from Cat 5 cable? Are the 2 outside pins not used?

The Cat 5 cable wire should be okay. Hopefully, you have plenum grade wire with Teflon insulation. Anything like 22AWG solid core and smaller should be fine. Again, you really need a third-hand tool to properly solder wires to the Panasonic volume pot. On mine, I wrapped masking tape around one of the jaw pairs to keep the teeth from cutting or damaging objects like small wires. Since I have to closely look at my work when working with small parts, I always wear safety glasses like the 3M glasses sold at Home Depot.

Another trick is to use needle nose pliers and bend the volume pot leads that get connected to the amp inputs so that they are straight and leave the others in their bent configuration. This way, you add a little more working space between leads. You can do something similar with alternating "straightened" leads.

The two outside pins you are referring to are metal snap-in mounts, not signal connection pins. You would have to rely on tightening the nut on the threaded bushing to solidly mount the volume pot to a faceplate.

[Folsom]

Rich wait till you get some power conditioning...

SMPS's add noise not only to what it powers, but to the rest of your equipment. SMPS's and small transformer equiped things do this. But Using CMC/DMC's reduces it several fold, ingoing and out. The affect on the sound is pretty amazing.

In fact it's so effective that a lot of people were using the stock power supplies for their SqueezeBoxes along with a Felix, enjoying it as much or more than many linear options!

[rhing]

Rich wait till you get some power conditioning...

SMPS's add noise not only to what it powers, but to the rest of your equipment. SMPS's and small transformer equiped things do this. But Using CMC/DMC's reduces it several fold, ingoing and out. The affect on the sound is pretty amazing.

In fact it's so effective that a lot of people were using the stock power supplies for their SqueezeBoxes along with a Felix, enjoying it as much or more than many linear options!

Thanks Salis. I suspect that the SMPS is injecting noise into the ARC LS7. I will explore power conditioning in the near future. I know the power grid here in Northern California is always stressed.

In the meantime, I installed a Panasonic EVJ 50kohm volume pot into my TPA3110D2 amp. As I mentioned before, I carefully soldered the wires using a third hand tool. in the photo, you can see that I wrapped the jaws of one of the alligator clips to keep the alligator teeth from biting into the wire insulation. After soldering each wire in place, I slid a short segment of 14AWG Teflon tubing over each soldered joint to avoid possible shorts. It also serves as a strain relief.



Here is the volume pot installed next to the RCA inputs to keep the signal path as short as possible to minimize any RFI effects. Using my DMM and my ears, this volume pot is very well balanced, even at very low volumes. Interestingly, I have absolutely no noise coming through my speakers with my Sony ES SACD/DVD/CD player connected directly to the inputs of the amp integrated amp mode. The starting volume position is about 7 o'clock, and pushing it to 10 o'clock is plenty loud for my man cave. This little amp never ceases to amaze me.




Next, I am going to build a second unit. Both the new amp and this prototype will be encased in a couple Context Engineering extruded Aluminum enclosures.

[Folsom]

I got one in the mail. We'll see how it does... The TDA7297 is still one of the most transparent things I've heard.

[rhing]

Salis, keep an open mind and make sure you minimize the signal path. If you have shielded hook-up wire, that would be better. You'll need to add a volume pot or stepped attenuator to make an apples-to-apples comparison with the TDA7297 chip amp. You can then be the judge on which amp is better.

I just connected the amp to my LS7 line stage, and it sounds fine. The Panasonic EVJ volume pots are a bargain as long as you can work with the small spacing and somewhat fragile leads. I wish someone would make a small PCB to mount these and make them easier to work with. But for $1.70 each, I shouldn't complain.

[Folsom]

I use a stepped attenuator populated with dales. It's not bad. But I can hear the need for a buffer unless it is turned up a fair bit. That's how transparent the TDA7297 actually is in my system.

[wangch32]

I have one of the 3116 based amps what or which speakers do you recommend, to go well with the amp thank you

[Taterworks]

With the TPA3110, I'd look for a speaker with sensitivity in the low to mid 90s, with an impedance that doesn't dip too far below 4 ohms. (Edit: If sitting at your desktop, a speaker with 80 dB sensitivity is adequate for achieving hi-fi listening levels at your desk.) With the TPA3116, choose a speaker in the mid-80dB sensitivity range, and then also make sure the impedance doesn't dip too far below 4 ohms. I would recommend against big three-ways unless you have a measured impedance curve that shows the speaker impedance doesn't dip too low. Two-way monitor speakers, larger speakers with horn loading and high-efficiency drivers, or single-driver speakers would be ideal. These chip amps are very sensitive to low impedances, which usually won't burn anything up but you will experience an increase in distortion at the nominal power rating. Low impedances require de-rating the chip's power output. I wouldn't recommend using any class-D chip amp with speakers over 100dB sensitivity unless you need high output, because at normal listening volumes the noise floor would become audible as hiss during quiet passages. There are beefier IC-based Class D amps out there if you need to drive demanding speaker loads at high volumes, such as the new Dayton Audio DTA-120 which uses a TC2000 and dual Class-T output chips running in PBTL mode to handle low impedances.

Also, I found a schematic for the Sure TPA3110 board: http://www.parts-express.com/pedocs/tech-diagrams/320-329-parts-express-technical-diagram.pdf

Note that the schematic shows output filter ferrite beads L1 thru L4, but I can't find these anywhere on my board, so there may be other deviations from this schematic.

[lacro]

In the meantime, I installed a Panasonic EVJ 50kohm volume pot into my TPA3110D2 amp. As I mentioned before, I carefully soldered the wires using a third hand tool. in the photo, you can see that I wrapped the jaws of one of the alligator clips to keep the alligator teeth from biting into the wire insulation. After soldering each wire in place, I slid a short segment of 14AWG Teflon tubing over each soldered joint to avoid possible shorts. It also serves as a strain relief.

Rhing,
 Thanks for the wiring drawing and the third hand pic. I do have a third hand, actually mine is so old it was made in USA I assume you use one clip to hold the shaft and another to hold the wire close to the pin? I will definitely give it a try. 

[rhing]

Rhing,
 Thanks for the wiring drawing and the third hand pic. I do have a third hand, actually mine is so old it was made in USA I assume you use one clip to hold the shaft and another to hold the wire close to the pin? I will definitely give it a try.

In the photo, the third hand alligator jaws without the masking tape wrap is holding the nut that is on the shaft of the volume pot. The other alligator jaws wrapped in beige-colored masking tape are holding the red insulated wire.

• I strip off a length of insulation off each wire that is the same length as each lead on the volume pot.
• It really helps if every wire you solder on the volume pot is straight, especially the stripped end that gets soldered to the lead.
  
• Then I position and line-up the wire to the lead to maximize the contact area.
• I touch the lead with my soldering iron tip and allow enough solder to flow and encapsulate the wire and lead.
• After it cools, I clean any rosin flux off with an alcohol-soaked cotton swab and slide the small segment of Teflon tubing over it.

It looks daunting, but you just solder all your wires to the pot leads first before installing it. The tinned leads on the Panasonic pots are soft and bendable, so be careful not to bend the leads back and forth repeatedly, or they'll snap off. This is probably something you wouldn't want to do after a few coffees or Mountain Dews.

[Taterworks]

Update on the ferrite beads: I received them today, and slid them onto my speaker wires just after the screw terminal outputs. The RF interference with my keyboard and mouse is gone, with no loss of sound quality. The beads I used are Amidon Associates FB-43-801. For anyone building a DIY amp with the Sure TPA3110 board at its heart, these beads are essential. According to TI, this will allow the system to pass FCC Class B with speaker wires up to 1.25m in length.

A workable class-D amplifier without an LC output filter is a big deal, because the output filter is a big source of distortion and instability in conventional Class-D amps. With no load connected, the reactance of the filter can lead to oscillations that can burn up the output capacitors or the chip's output transistors. Also, this filter can create voltage pulses on the outputs of the chip that cannot be compensated properly by the feedback loop, causing the loop to induce harmonic distortion. The ferrite bead filter has much smaller reactance, so it won't have these issues, and it also won't experience the HF peaking that occurs in typical output filters with high impedance loads or reactive loads with high inductance. The TPA3110 is a very nifty little IC for this reason.

[rhing]

Thanks for the information on the Ferrite beads. I'll have to check those out, although my noise problems have been virtually eliminated with the addition of the volume pot.

[Taterworks]

Thanks for the information on the Ferrite beads. I'll have to check those out, although my noise problems have been virtually eliminated with the addition of the volume pot.

The effect of the ferrite beads shouldn't be audible. The PWM switching activity of Class-D amplifiers creates large amounts of RF energy from their outputs, which can cause interference with TV, radio, and wireless communications, and can cause excess heating in some drivers that do not have an inductive component to their impedance such as piezos, planars, and AMTs. Normally this is resolved by using an LC output filter to clean up the amplifier output, but these new TI chips use a different switching scheme ("BD" switching instead of "AD" switching, per the tech documentation) that produces less RF noise, and they only require ferrite beads in their output filters, instead of the common LC output filters, because the inductance of the speaker driver is enough to block the RF noise from causing heating in the driver. The ferrite beads are just needed to block the radio-frequency noise content that can be radiated from the amplifier using the speaker cables as antennas.

If you notice anything anywhere from adding the ferrite beads, it would be that a nearby radio-frequency device that formerly suffered from interference caused by your amplifier now no longer does. That's how I understand it, and that's what I've noticed.

[rhing]

Thanks for the clarification. As far as I can tell, I have not had any issues with RFI from my TPA3110D2 amp.

Based on the schematic that Taterworks shared in a previous post, has anyone tried input caps with a capacitance >0.22uF to obtain a lower bass response (Fc)? My DMM capacitance meter doesn't have the connectors to test the capacitance, and I'm too cheap to invest in a true capacitance meter.

[lacro]

Update on the ferrite beads: I received them today, and slid them onto my speaker wires just after the screw terminal outputs.

Do the beads go on both leads of the speaker wire? any pic of your set-up showing the size of the beads?

[Speedskater]

Almost everything that you need to know about ferrite's.  Don't let the title fool you, it started out as an audio paper then the Ham information was added.

A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing

by Jim Brown K9YC
Audio Systems Group, Inc.

The basis of this tutorial is a combination of my engineering education, 55 years in ham radio, my
work as vice-chair of the AES Standards Committee working group on EMC, and extensive research
on RFI in the pro audio world where I’ve made my living.

http://www.audiosystemsgroup.com/RFI-Ham.pdf

[rhing]

Update on the ferrite beads: I received them today, and slid them onto my speaker wires just after the screw terminal outputs. The RF interference with my keyboard and mouse is gone, with no loss of sound quality. The beads I used are Amidon Associates FB-43-801. For anyone building a DIY amp with the Sure TPA3110 board at its heart, these beads are essential. According to TI, this will allow the system to pass FCC Class B with speaker wires up to 1.25m in length.

FYI, Mouser and Digikey also carry comparable 43-type Ferrite beads:

Mouser PN 623-2643000801
Fair-Rite Ferrite Cable Cores 43 SHIELD BEAD Z=92 OHM @ 100MHz
$0.11 each

Digikey PN M8707-ND
Bourns FERRITE BEAD 200MHZ .297 LENGTH
$0.18 each

Do the beads go on both leads of the speaker wire? any pic of your set-up showing the size of the beads?

One bead should be placed on each wire between speaker output 2-pole terminal blocks and the speaker binding posts for each channel ("+" and "-"), so you'll need four (4) beads total.

I also added a Panasonic FC 1,800uF / 25V across J8 as Taterworks did, and just as he described, the soundstage became significantly more three-dimensional, and the bass gained some muscle. This was a nice change once I ran this amp standalone. Without the ARC LS7 line stage preamp in front of this amp, the sound thinned out and the bass weight disappeared. With the off board cap in place, the bass, the warm tonality and rich detail came back to life.



I have two more Sure TPA3110D2 boards coming soon. One of them will end up in this Context Engineering chassis, which I drilled out and assembled last weekend. For scale, this enclosure has a slightly larger footprint than my iPhone 5. It has the Pomona 3770-x Gold-plated Copper binding posts, Vampire CM1F RCA connectors, Switchcraft 722A 2.1mm x 5.5mm DC power connector and Panasonic EVJ 50k log volume pot. To mount the additional cap, I'll remove the 2-pole terminal block from J8 and solder in a Panasonic FC cap along with the power supply wires.

[rhing]

I received my second Sure Electronics TPA3110D2 amp today and installed it in the chassis.





Since this chassis has slots for mounting a 3 inch wide PCB, I didn't have to use stand-offs for mounting the board in place. However, I did have to remove the built-in DC power connector to be able to slide the amp into the chassis. Sounds great!

[MLS]

rhing

What is that third larger cap?

Scott

[rhing]

It is a Panasonic FC 1800uF / 25V electrolytic cap soldered into the J8 thru-holes where the power supply is connected to Vcc. The twisted wires from the power connector are routed beneath the board and soldered to the cap and thru-holes for Vcc (+) and Ground (0V). Taterworks had tried this and so I gave it a try too and obtained the same improvements in bass response, a larger soundstage and improved tonality. This was really apparent when using this amp as a standalone integrated amp in my system. I would have preferred a 2200uF / 25V Panasonic FC/FM cap, but the height would not fit in the compact chassis.

This is a fun amp to play around with if you have the right speakers to drive. I'm ready to try a TPA3116D2 amp now. I hope some good boards become available. The Yuan Jing boards don't look like they're as well constructed as the Sure TPA3110 board. I also need to explore power supplies that work well with these amps.