DIY Integrated amp build : questions on attenuation

musicgeek

Member
2016-04-03 5:59 pm
Hi!

!Long post ahead!

So after I started looking for a project for DIY speakers, I decided to go for a DIY amplifier build as well to obtain the best VFM in my minimal budget(~$200-250).

While I was initially intrigued by Class A amps, I realized I won't get enough power at my budget to drive 84dB efficient speakers(Jeff Bagby's Continuum). Class D seemed to be an alternative to Class AB and also seemed easier to build(With all the advantages of not needing as many heat sinks).

Source : Raspberry Pi + (some i2s dac)

Power Stage:
Looking and reading about power amplifier stage : I like the idea of going with an IRS2092 based kit( I don't want to do much soldering), or a TK2050 if someone can assure me it sounds about the same. I was looking at the CDA-254 kit or CDA-254 chip powered by Connex(with secondary power out to the preamp stage). I was also looking at an L15D or Sure board but I was unsure where to buy from(There are too many on ebay). I don't want to experiment with quality as I am a student and even these 200 is a huge investment for me. However, if I can get the quality of the CDA-254 in a lesser cost, I'd be much happier and be able to stay in my budget. I'm also open to looking at Hifimediy's T1-4 range, if they can compete, and reasonably well drive 8ohm speakers(all their ratings are mentioned at 4?)

Pre Stage
I have an Objective-2 amplifier(assembled PCB) which I thought of using as an active preamp. From what I've read, this will help matching impedance on the power amp and the source.

My problem here is volume control. The O2 i have has a very sensitive volume pot, and being the only control in the chain makes it scary. I don't want to power my amp a lot or damage my speakers. I don't want to rely on digital volume to keep the system's safety.
So as of now I could think of 2 options :

- Use a Passive pre (Schiit sys) : allowing for 2-way source switching and also acting as a volume control.
Does this affect the impedance matching in any way? Should it go before or after the O2 in the chain? Is using both an active and passive pre-amp derogatory to the signal?

- Somehow modify the O2 to give more control over volume. (Bonus : source selection if possible in an easy way). Is there a simple way to replace the pot to allow for this? Could you recommend me to some pots within $20-25 that could do this? Has any one tried source switching on this?


Additional question : Can a headphone jack out from the O2 be split(duplicated) into multiple rca/headphone jacks without compromising SQ? For future purposes it will help me add a headphone out to the int amp.


Chassis : I will be building my own(wood/metal) as it will be the most affordable option


Subwoofer out : If at a later stage I do want to add this, where would it lie and are there existing chips to allow me to do this?


Final system in mind :

RPi- dac - (Schiit sys) - (unmodded O2) OR modded O2 - CDA-254 or other IRS module - Continuum.

Thoughts, recommendations, and inputs needed! Thanks!
 
Last edited:

bullittstang

Member
Paid Member
2013-05-09 2:14 pm
Ft. Worth, TX
I have bought 4 of these IRS2092 boards off this seller on eBay and had no issue. Actually bought things from them 6 times, without an issue.
Assembled LJM L20D IRS2092 Top Class D Amplifier Board 200 250W 2 CL 183 HL | eBay
He has L15D, L20D and I actually bought L25D boards and been using them for over a year and they work great and I have used with 8 different pairs of speakers and will power them all without issue.
I currently use the Abletec SMPS, which outputs +/-53V, which gives me about 120 watts at 8-ohms, so plenty. Link to a seller on eBay.
http://www.ebay.com/itm/Abletec-900-Watt-peak-class-D-audio-amplifier-power-supply-53V-DC-UL-cUL-/251804683031?hash=item3aa0ba8b17:g:7pYAAOxySfBR7ZTP
Just remember it has a 5.3V and 7.5V secondary supplies, which have to have a load on them, or you will get some noise. Easy as putting a 1-watt 150-ohm resistor on those pins. $50 for amp + $30 for PSU +$50 misc and you have a nice amp for $130 IMHO. YMMV.
 

musicgeek

Member
2016-04-03 5:59 pm
I'd consider the TDA7498 like this:
TDA7498 100W+100W HIFI Class D digital amplifier Board 12v 24v car AMP Audio | eBay

or a dual PBTL TPA3116 like this:
TPA3116 2*100W D2 Dual Channel Digital Audio Amplifier Board 12V-24V for Arduino | eBay

Good unmodded too.
Yesterday 12:11 PM

Thanks for the heads up on the 2050! I've had the SMSL 36A, and I don't think the TPA3116 will have headroom for 8ohm speakers(I want at least 50 clean watts into 8 ohms). I've heard as good things about the IRS as the TPA.

bullittstang I have bought 4 of these IRS2092 boards off this seller on eBay and had no issue. Actually bought things from them 6 times, without an issue.
Assembled LJM L20D IRS2092 Top Class D Amplifier Board 200 250W 2 CL 183 HL | eBay
He has L15D, L20D and I actually bought L25D boards and been using them for over a year and they work great and I have used with 8 different pairs of speakers and will power them all without issue.

This board looks really good! I hope it will be comparable to the CDA at 1/3rd the price though. I'm happy to give these a shot.

Does this power supply do better than or as well as the Connex one(65$)? Also, can I power both the mono amps with just one of these boards? How would that work?

Thanks!
 

bullittstang

Member
Paid Member
2013-05-09 2:14 pm
Ft. Worth, TX
This board looks really good! I hope it will be comparable to the CDA at 1/3rd the price though. I'm happy to give these a shot.

Does this power supply do better than or as well as the Connex one(65$)? Also, can I power both the mono amps with just one of these boards? How would that work?

It actually works quite well, I can't speak to it being "better", but it drives any of my speakers 4/8 ohm without a problem very cleanly with no hiss/noise. I attached a pic of my setup. Basically you run +53, -53 and Grd to each board and then +/- to your speaker posts.

This was my 2nd try at DIY amp building, so it was pretty easy to figure out. Main thing is triple check all wiring, post a pic on the forum for verification if you are unsure about anything BEFORE plugging it in and flipping the switch.
 

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