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Class D Switching Power Amplifiers and Power D/A conversion

need advice for newer small T or D amp
need advice for newer small T or D amp
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Old 9th January 2019, 03:30 PM   #1
kevinr is offline kevinr  United States
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Join Date: Jun 2009
Default need advice for newer small T or D amp

Quite a few years ago I purchased the Dayton DTA 120 , Topping TP20 and SMSL 36 T amps to use for the workshop , exercise area and computer desk.
These little T amps all seem to have some form channel imbalance issues , esp. at lower volumes that would probably be remedied by a better potentiometer or DACT.

Are there any newer 2 channel small form factor Class T/D amps from manufacturers that are better options than these ?

I want to move my very heavy and hot Class A tube amp out of the living room .
The Speakers are Seas 8 inch full range and DAC is a Schitt Multibit Bifrost.
Don't need USB , Bluetooth or Sub woofer outs.

Thanks for any replies you may be able to share .

At some point I will probably build my own from a chassis , boards and hardware but that is going to be later .
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Old 10th January 2019, 06:34 AM   #2
chermann is offline chermann  Austria
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Join Date: Jan 2017
Location: Vienna
Hi

are you interested do modifiy your old amps? here you will find a lot of informations...
TPA3116D2 Amp


what is your budget?

chris
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Old 10th January 2019, 10:05 AM   #3
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
Quote:
Originally Posted by kevinr View Post
Quite a few years ago I purchased the Dayton DTA 120 , Topping TP20 and SMSL 36 T amps to use for the workshop , exercise area and computer desk.
These little T amps all seem to have some form channel imbalance issues , esp. at lower volumes that would probably be remedied by a better potentiometer or DACT.

Are there any newer 2 channel small form factor Class T/D amps from manufacturers that are better options than these ?

I want to move my very heavy and hot Class A tube amp out of the living room .
The Speakers are Seas 8 inch full range and DAC is a Schitt Multibit Bifrost.
Don't need USB , Bluetooth or Sub woofer outs.

Thanks for any replies you may be able to share .

At some point I will probably build my own from a chassis , boards and hardware but that is going to be later .

If you have tried with three amplifiers:
Dayton DTA 120 (TK2050 based)
Topping TP20 (TA2020 based)
SMSL 36 (A) (TDA7492/TPA3118 based)
and find that all three suffers from channel imbalance it is hardly a fourth amplifier you need to solve that issue.
It sounds like the imbalance origins from imbalance in the source. A more expensive potentiometer may help but I am surprised you notice the imbalance as important. Even rather cheap potentiometers tend to have sufficiently good tracking for your ears not to notice. Else, you need to use an attenuator with fixed resistors. Then, how equal is your hearing on your two ears with varying sound level?

Chris can tell you more about the rather new TPA3250 which is the new class D low power standard. But, the channel imbalance may remain.

Last edited by FauxFrench; 10th January 2019 at 10:09 AM.
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Old 10th January 2019, 12:00 PM   #4
Khron is online now Khron  Finland
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Quote:
Originally Posted by FauxFrench View Post
If you have tried with three amplifiers:

It sounds like the imbalance origins from imbalance in the source. A more expensive potentiometer may help but I am surprised you notice the imbalance as important. Even rather cheap potentiometers tend to have sufficiently good tracking for your ears not to notice. Else, you need to use an attenuator with fixed resistors. Then, how equal is your hearing on your two ears with varying sound level?

That is, assuming the loudspeakers themselves don't have a (possibly noticeable) difference in sensitivity But the source is equally as likely.
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Old 10th January 2019, 12:34 PM   #5
chermann is offline chermann  Austria
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Join Date: Jan 2017
Location: Vienna
Quote:
Originally Posted by FauxFrench View Post
If you have tried with three amplifiers:
Dayton DTA 120 (TK2050 based)
Topping TP20 (TA2020 based)
SMSL 36 (A) (TDA7492/TPA3118 based)
and find that all three suffers from channel imbalance it is hardly a fourth amplifier you need to solve that issue.
It sounds like the imbalance origins from imbalance in the source. A more expensive potentiometer may help but I am surprised you notice the imbalance as important. Even rather cheap potentiometers tend to have sufficiently good tracking for your ears not to notice. Else, you need to use an attenuator with fixed resistors. Then, how equal is your hearing on your two ears with varying sound level?

Chris can tell you more about the rather new TPA3250 which is the new class D low power standard. But, the channel imbalance may remain.
Hi

yes.....my idea is to buy this little amp :

Fx502spro (TPA3250) if you just want to change just the opamps with DIL8 housing.
good sound for the buck and it comes with psu

TPA3250 somebody is listening?

if you are interested in learning and DIY modify...then try to get your old amps to the possible max...read a lot of pages and learn/ and ask nooby questions....

chris
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Old 11th January 2019, 02:39 AM   #6
kevinr is offline kevinr  United States
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Join Date: Jun 2009
Thanks for your posts .

It turns out the channel imbalance issue I mentioned may be either from my Logitech Squeezebox source or a cable . I have to do some troubleshooting to isolate the problem area.Several years ago I did try modding a TPA 3116 amp board or 2 when that topic began showing up on the forums, but there were popping and dropout issues so I lost interest . The boards seemed sensitive to power supply and source.
I did build a Folsom Chip Amp and it sounds very good, but the slight hum from it's transformer keeps it in the exercise room instead of the listening room .
I added rubber washers to the mounting bolts and a sound deadening vinyl sheet on the case.... but the hum is still just audible enough to be a distraction . Some say a toroidal transformer has no hum issues on the Folsom amp.
I returned to using a Class AB amp in the living room for the interim but posted my query and wondered if there were any newer Class D amps under $200 that have bettered the amps I mentioned purchasing quite some time ago .

The newer 3250 Class D link posted sounds interesting and I will definitely do some reading on those .
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Old 11th January 2019, 05:57 AM   #7
chermann is offline chermann  Austria
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Join Date: Jan 2017
Location: Vienna
Quote:
Originally Posted by kevinr View Post
Thanks for your posts .

I...
I did build a Folsom Chip Amp and it sounds very good, but the slight hum from it's transformer keeps it in the exercise room instead of the listening room .
I added rubber washers to the mounting bolts and a sound deadening vinyl sheet on the case.... but the hum is still just audible enough to be a distraction . Some say a toroidal transformer has no hum issues on the Folsom amp.
.... .
Hi kevin

to avoid hum with transformer i might help to turn the transfomer away of the pcbs. because the leakage is there where the cables came out.......pic 1
additionlly i can happend that a tranformer is not well made so this could also be helpful..antek tranformer cover - pic 2
additionally the earth + grounding could be an issue...FF is an electronic expert...maybe he has some ideas more

read some threads of nelson pass forum there....read, post and ask you will get help...i follow up a little bit from my brothers F5 handmade amp and it is fantastic !...my M2 pcbs lie around sind 10 month

chris
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Old 11th January 2019, 09:48 PM   #8
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
Quote:
Originally Posted by chermann View Post
Hi kevin

to avoid hum with transformer i might help to turn the transfomer away of the pcbs. because the leakage is there where the cables came out.......pic 1
additionlly i can happend that a tranformer is not well made so this could also be helpful..antek tranformer cover - pic 2
additionally the earth + grounding could be an issue...FF is an electronic expert...maybe he has some ideas more

read some threads of nelson pass forum there....read, post and ask you will get help...i follow up a little bit from my brothers F5 handmade amp and it is fantastic !...my M2 pcbs lie around sind 10 month

chris
Sorry, my first reply was rejected due to a problem with a “security token”.

I will try again. It is very kind of Chris to call me “expert”. Reality is that very few are “experts” in hum and removing hum in amplifiers. At least not I. Hum problems are unique in the sense that they depend on exactly which components are involved, how they are physically located relative to other components and how the components are connected. No two cases are fully alike.

I will try to categorize into three types of hum-conduction/coupling: electromagnetically coupled hum, electrostatically coupled hum and wire conducted hum.

Electromagnetically coupled hum: Depends on distance and orientation. Try to remove the transformer from the amplifier chassis and connect it with longer wires to the amplifier. Is the hum gone? Does it make a difference how the transformer is turned? Chris shows a MU-metal shielded toroidal transformer – really good stuff but expensive.

Electrostatically coupled hum: As test probe you use your finger (only touch with one hand for safety reasons! and NOT for vacuum-tubes with high voltage!). When you touch the amplifier chassis, the transformer core, amplifier ground does it reduce the level of hum? If so, you are probably missing a beneficial ground connection. In the old days with high impedance amplifier circuits, a missing ground connection to the chassis could cause loud hum. The beneficial ground connection may be direct, through a resistor or through a (safety) capacitor. A safety earth connection may be useful in removing hum but it depends on the quality of the earth connection.

Wire conducted hum: The worst because the reasons can be so many. For a a start just check for insufficient power line decoupling (capacitor buffer) causing a high power line ripple from rectification of the AC input which propagates to the amplifier. Else, the method is “working your way backwards”. First, the power amplifier alone with no input signal and 1KOhm shorted inputs. Hum to be heard in the speakers? If not, go on with the SmartPhone Test. Use the headphone output on your smartphone and let the smartphone run on battery (no charger). Does the power amplifier play without hum with the smartphone as source? The advantage of the smartphone as source is that it is “floating” when running on the internal battery. If the smartphone test is successfully passed (without hum), connect the pre-amplifier to the power amplifier and use 1K shorted pre-amplifier inputs (no pre-amp inputs). Is the hum back with the pre-amplifier connected? You may repeat the smartphone test at the pre-amplifier input. Then, you connect the music-source to the input of the pre-amplifier, any hum?

I recall a forum member having such hum problems and working through his chain backwards when he realized it was the power supply for his Raspberry PI (used as music source) that caused the hum in the power amplifier. Tracking hum can be very tedious.

High impedance amplifier circuits are much more likely to pick up hum than low-impedance circuits. In modern amplifier constructions using OP-AMPS in the pre-amplifier, I often connect 4K7 resistors across the power amplifier inputs to lower the impedance level. OP-AMPs can easily drive 4K7 and I do not want the power amplifier to pick up noise due to a high input impedance.

Last edited by FauxFrench; 11th January 2019 at 09:50 PM.
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