connex TA3020 psu/rectifier bridge question

Artcore87

Member
2009-10-24 11:07 pm
Hi folks, I've been using a Connex Electronics TA3020 v3c amp with the Connex a350w smps for some time now (this SMPS is more than sufficient for driving my 15" jbl 2225's to their limits and keeping an incredible grip on them the entire time regardless of the material).

I am extremely happy and in fact frightened by the quality of this amplifier now that it is broken in, however I have one question. I was re-reading the PDF, and it says this under the EMI reduction section:

"In [the] case of using an external power supply, either linear or smps, bypassing the rectifier bridge is strongly recommended to eliminate the voltage drop and [to add] more capacitance to the voltage rails."

Here's a link to the pdf for the connex TA3020:
http://www.connexelectronic.com/documents/TA3020_Audio_Amplifier_Module_v3c.pdf

I don't get it... I thought one HAD to use an "external" power supply, such as the one I got, or the a500 or a1000w connex versions, or if you preferred, a linear power supply. But how could someone NOT be using one of those? Can you hook the A/C current up directly to the TA3020 board? I think that's probably a stupid question but it's the only reason I could see the inclusion of this sentence. It appears that everyone should be bypassing the rectifier bridge who has any kind of PSU for this board... and I never did anything to bypass it. More capacitance would be nice although I don't feel like I suffer from a lack of it in any way.... but I'm more interested in the increase in voltage stability (increased efficiency/output capability?).

When I originally purchased and set up the amp no one brought this to my attention, is this something I should have done? I don't fully understand the concepts behind it, or whether it is even an issue. I want to make sure I'm getting the best performance out of my amp though, so I'd appreciate any input on the matter, and if I need to make a change I'd also appreciate any help or instructions on how to do it also. I'm confident enough with a soldering iron.... but not if it involves small SMD components.


One other question... for anyone else using this board or a similar setup. Has anyone started with a particular power supply and then upgraded the power supply (power output wise) and noticed a difference in sound? Assuming that the maximum power of even the 350w psu I'm using is not needed, am I still missing out on something the 500 or 1000w would offer?

In my experience this amplifier started out good but a tad strident, but over time this has disappeared completely. Its still got that crisper-than-reality class-T sound, but it's 100% more natural than when I first played it. Personally I like the class T sound (which to me sounds flat, in the literal sense of the amplification being frequency-independent, and thus extremely low in linear distortion) , and broken in it is VERY natural sounding (with the "thick" midrange everyone describes... each instrument range however small seems vast within itself... so much precision, definition, and character in every range simultaneously). It's hardly shrill or aliased sounding, or like artificial sharpening... nothing like that. It sounds like nothing but pure distortionless signal amplification... which of course it's not but it comes damn close to my ears. I have not found the limits of this amplifier I have only discovered the limits of my source equipment and musical source. The input is from my computer, using a Gadget Labs Wave 8/24 24-bit recording interface and sound card. All inputs and outputs are disabled except for 2 outputs, and it can run native in any sampling rate up to 96khz, which is nice since I don't have to re-sample in foobar with SSRC even though that was better quality re-sampling than the hardware re-sampler on my chaintech (VIA) AV-710, which I thought sounded great (with upgraded output capacitors) until I heard something through the gadget labs, which in comparison sounds perfect. The absolute worst part of my system is my EQ.... it's a decent EQ it's just old and has a high noise floor that I can tell wasn't there when it was new... not to that extent anyways. Phase smear doesn't seem to be an issue with or without the EQ, even with 3-way speakers with 15" woofers, rectangular midrange horns, and vintage JVC ribbon tweeters, and a mix of 1st and 2nd (or is it 2nd and 3rd?) order speaker x-overs, the phase should be all over the place, but it sure doesn't sound like it. Perhaps EQ correction is helping to properly re-align the phase. But overall it sounds better if I use a VST dsp-type EQ in foobar and bypass the physical EQ... I don't know what type of EQ the "karma-fx" 31 band vst eq is (what I use)... FFT, FIR, IIR, and what effect on the phase it may be having, but the noise floor virtually disappears without the outbound EQ... unfortunately my desktop is a loud noise-floor in itself. I prefer the outbound EQ when listening at volumes loud enough to not hear the noise floor, because the bass boosting capabilities of the graphic seem much better than the software EQ... more punch. The same "12db" boost applied at 31hz (just as an example, the same is true for the entire low bass range) is much louder with the graphic EQ than my software EQ. Phase related?

Anyways I'm rambling, I'm mostly just curious about bypassing the rectifier bridge and whether I can or should do this and why. Thanks!!!!!

-Lee
 
When i first designed this amplifier, the intended supply was mainly the mains transformer, that's why i added the rectifier bridge and the capacitors on the board directly. having the speaker protection circuit on the board, simplify the installation as well.
as i wrote in the manual, (probably not very clear) the amplifier can be supplied both with AC voltage, using the on-board rectifier bridge or with DC voltage,
if the amp is used with SMPS, DC voltage, i recommend to bypass the bridge. there are few reasons to do that. first, the voltage drop. at any time, two diodes are conducting, loosing about 2x0.8V up to 2x1V depending on the current which the amp consume. then, without the bridge, the total capacity of the caps from the amp and smps can be summed, but with the bridge, is not that simple. this is important when the amp plays loud volume low freq. and tends to pump the voltage. is well known that one of the solutions to decrease the pumping is to add large caps. but the caps from smps are connected through series diodes and they won't absorb this energy, since the diodes will be blocked when they are inverse biased. another problem which might arise from here is that the smps can prematurely trigger overcurrent or overvoltage protection when the caps are charged above the smps voltage and discharged below the smps voltage.
 

Artcore87

Member
2009-10-24 11:07 pm
Ok then what kind of mains transformer should I be looking at? Does your amp need 220v or something, I'm not even sure why I'd be needing a transformer? Isn't that just for stepping up or down the voltage 110 - 220 or vice versa? Do I literally just hook the AC directly into the amp with no equipment in between?

Would sticking with the SMPS and bypassing the rectifier sound better? I'd prefer to go with whichever offers the best performance. I'm surprised I've been using my amp in a non-ideal fashion this whole time and yet it STILL sounds this amazing! The pumping effect and power loss issues simply haven't come up due to the average output power I'm using.

Can you tell me how to bypass the bridge? Is it easy enough for a relative novice, like just a simple bridging of some connections on the bottom of the PCB? Like I said, I'm pretty good with a soldering iron with averaged sized stuff, but I have no equipment or experience to do SMD soldering.

I'm not upset or anything, but why did you recommend an SMPS to me when I purchased it? Just curious. I like the sound of adding the capacitance of the smps and the amplifiers capacitors, I think that may appeal to me more, and I won't have to buy any other parts.
 
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I do not recommend to replace the smps with a mains transformer, especially that you already have installed the smps with the amp, and can perform better than a mains transformer. there has been a long debate on weather should use a transformer or smps for the amp. my personal choice is smps. there are many advantages, and the stone edge of semiconductors has passed and there are available power transistors both MOS and IGBT with superior performances which allow more performant, small and quiet smps design than a similar transformer plus rectifier brigde and capacitors, at a fraction of the cost and weight.
Offtopic: at my main job, right now i'm involved in smps design for flat screen, LCD and PDP displays, where the battle is on the thickness and efficiency. except the resonant smps's, there are not too many (none) solutions available to make a 8-10mm thin smps capable to deliver 300W continuous with efficiency higher than 92% at max. load with universal mains input voltage.

so, keep the smps with the amp together. to bypass the rectifier, just connect the positive terminal to the closest AC pin then the negative terminal to the closes AC pin and then to the smps. be very careful to not swap the positive and negative polarity, which can damage the amplifier.
 

Artcore87

Member
2009-10-24 11:07 pm
I'm glad to hear this, and I thought this was the case and is why I originally went with an smps.

So Cristi do you think I would notice a benefit by upgrading to a newer and more powerful version of one of your SMPS's, or is my a350 giving me the same audio quality assuming I'm not placing any demands on it outside of it's capabilities.


so, keep the smps with the amp together. to bypass the rectifier, just connect the positive terminal to the closest AC pin then the negative terminal to the closes AC pin and then to the smps. be very careful to not swap the positive and negative polarity, which can damage the amplifier.


This is not clear to me... Are you saying that on the v3c amp module, where the AC input AND speaker outputs are located, that I am to connect the closest AC (AC1 and AC2) to the positive ("out", not "gnd") of each speaker output, while leaving the SMPS hooked up just as it is now, which is to the AC1/AC2/GND input in between the speaker outputs on the v3c board.


P.S. Your amp and smps design must both be very good and durable because when I first hooked them up I accidentally shorted out the AC +/- output from the SMPS while it was plugged in and also hooked up to the amplifier module. I shorted the negative to the ground, and there was a large spark. After unplugging it and plugging it back in everything worked fine and a multimeter read the exact same numbers for everything as before. There is a black spot on the bottom of the SMPS next to the AC +/-, but it still works! Lol.
 

Artcore87

Member
2009-10-24 11:07 pm
If you use DC input, you can remove the rectifier and bypass it.
That way you will gain about 0.7-1.4v and you will be using the caps in the psu more efficient.
Also, youll remove the noise induced by the rectifier.

How do I bypass the rectifier? For the life of me I can't find out how with google or the forums search filter, and certainly not by the product PDF. Is soldering involved? I'm sorry but based on my knowledge of the technical things behind my question, Cristi's answer was far too vague to help =/.