need advice for VOLUME CONTROL for my tripath ta3020 amp

[Lee Spencer]

Hi, newbie to the forum here. I have a connex ta3020 v3c module (with the optional upgraded mosfets and 71v elna caps), with one of his SMPS. I've had this setup for about 5 years or so and I'm very happy with it. It's been extremely reliable and I leave it plugged in 24/7, and it sounds really great.

However, I'm trying to optimize my setup to squeeze out that last little bit of awesomeness.

My source is my computer, through an HRT MusicStreamer II, which also sounds great. The only thing is, I'm not using a pre-amp, so I'm going directly from the MSII to my ta3020. Firstly I don't even know if this is a "good" match, impedance wise, although I don't notice any issues with it performance wise... it seems like it's a decent match. If anyone could enlighten me about this issue I'd appreciate it.

The only issue is that, at 2.4v max output from the HRT, this is a HOT signal, which I have to significantly attenuate on my computer. DAC is set at 24-bit which significantly lowers the noise floor, set to 16 bit the hiss is rather loud. at 24 bit the hiss is noticeable but only very slightly, as I have rather sensitive speakers (midrange horns). But for music I'm typically running at between -36 to -24db... -42 for very quiet listening, -18db for very loud listening. I'm wondering if some kind of volume control between my DAC and the amp would be a superior solution, sound quality wise. My DAC at 24 bits produces ZERO audible hiss, the audible hiss I have is from the ta3020 amp itself, and sounds the same with or without any input hooked up. Given the max output of this amp, and the sensitivity of my speakers, I'm pleased with the low level of this noise, which is unnoticeable even with quiet music levels.

So, should I attenuate my input signal with some high quality ALPS potentiometer vs. lowering my volume with my computer?

To know what resistance value pot to use, do I need to measure anything? I could probably talk to Cristi at Connex for advice... I'm still waiting on a reply from him though about a few things, he's been slow getting back to me.

If anyone has any other advice to optimize my setup I'd appreciate it... such as changing input caps on the ta3020, I feel like that's an area that could be improved upon.

Thanks! 🙂

 

[rayma]

My source is my computer, through an HRT MusicStreamer II, which also sounds great. The only thing is, I'm not using a pre-amp,
so I'm going directly from the MSII to my ta3020. I'm wondering if some kind of volume control between my DAC and the amp would be a superior solution, sound quality wise.

The streamer has an output impedance of 100 Ohms, so a 1k volume control should be ok, unless there's an output capacitor in it.
Can you ask if there is one? A 1k control will be relatively noncritical of cables. A 10k control will work with low capacitance cables.

The only amplifier schematic similar to this that I could find has a 3.3uF capacitor and 50k input resistor. This means any pot from 1k to 10k is fine.
With the coupling capacitor, there won't be any wiper noise problems from leakage currents.

 

[Lee Spencer]

The streamer has an output impedance of 100 Ohms, so a 1k volume control should be ok, unless there's an output capacitor in it.
Can you ask if there is one? A 1k control will be relatively noncritical of cables. A 10k control will work with low capacitance cables

I've never taken the streamer apart to know if there's an output capacitor on it. I suppose I could take it apart and try and check. also, I attempted to find data on the MSII and found some varying specs, possibly because it's hard to pinpoint exactly which model I have or which model is being spoken of in the write ups... there are at least 2 different version of the "music streamer 2". mine is the rounded case one, not the hexagonal (cross-section) case one. it could have an output impedance of ~200 ohms, I'm not sure, but this I assume would change the value of the pot.

The only amplifier schematic similar to this that I could find has a 3.3uF capacitor and 50k input resistor. This means any pot from 1k to 10k is fine.
With the coupling capacitor, there won't be any wiper noise problems from leakage currents.

I suppose then that I could try one or more pots within this range and see how it goes. I don't understand all of what you're saying though (sorry I'm a noob). You're speaking here about the ta3020 amp board now, regarding the 3.3uF cap and 50k input resistor, correct? Here is detailed information about my amplifier: http://www.connexelectronic.com/documents/TA3020_Audio_Amplifier_Module_v3c.pdf
I can't copy/paste from the pdf, but regarding the input stage, he states there are DC coupling capacitors, but doesn't state the exact value, just a range of 1.0uF to 4.7uF, perhaps this value is chosen based on customer needs/request. For instance he will also alter the gain setting and mosfet dead time based on customer request. Since I have the upgraded IRFP4228 mosfets mine is set to the 80ns BBM (break before make) value, which improves sonic performance. I believe I opted for the higher of the 2 default gain settings he offers, 23.5db, but without checking the values I can't be 100% positive on that... but knowing me surely that would have been my request. I don't know the exact voltage my smps is sending the board either, but again, I surely would have requested the highest reasonable and safe voltage as well, for maximum power, probably in the 61v range. I don't know the value of the input resistors, but I believe this is related to the gain setting, correct me if I'm wrong.

I do not know what wiper noise problems from leakage currents are or how that affects me. Please educate me a bit if you have the time. Thank you for your reply, it's a good place to start, at least for the pot value.

Ultimately though, I want to know if using a volume pot to raise the output level of the HRT (no more attenuation in foobar) and then attenuate it with the pot will increase my sound quality. If not, then I'm not interested. Also, should I be looking into a pre-amp stage between the DAC and amp instead of just a volume pot? Basically I want to know the ideal way to be feeding my amp, in terms of sound quality and SNR. So far I haven't had much luck finding out what the best pre-amp options in the sub ~100 dollar range are. It's not as easy as finding out what the best tripath based amps are for instance, there's many good options there. I'm considering getting a 2nd, perhaps an Amphony 200, or a Topping TP60, or a HiFimeDIY T1.

My setup sounds very good, maybe I shouldn't be worrying about it. But, maybe I don't know what I'm missing either.

I'm driving some custom vented 3-ways, big cabinets with horn mids (I'd have to take them apart to see what they are, I've forgotten... I think altec something but I could be wrong... they're phenolic), ribbon tweeters from the JVC zero 3 or zero 5, and 15" JBL woofers (2225H's). I've considered modding the 2225H's by removing the mass ring, turning them into regular 2225's, which increases their sensitivity even further and arguably would probably improve midbase/mirange definition, the tradeoff being less low end range, which I could somewhat compensate for with EQ'ing (I use george yohngs vst wrapper with the KarmaFX 31 band EQ, it's very good much less SQ loss than a traditional outbound analog EQ). Overall great speakers but some sensitivity mismatches between the drivers that I have to compensate for with the EQ, no biggie. The speakers (including crossovers) were designed and built by someone with an engineering background. I don't even know the crossover specs, but I do know for instance the woofer section of the x-over is pretty serious, lotsa copper in there, so that seems like a good thing at least! Wish I knew more about them. Also I did the whole mod-podge coating thing to the woofers. Probably wasn't necessary given their quality design, but hopefully it couldn't hurt. It made them look cooler!