T-Amp Gen 2 - With HP Amp

[classicalguy]

Here is my first impression of the Sonic Impact T-Amp Gen 2 that I received today.

I ordered the T-Amp Gen 2 from Parts Express on February 29. Cost was $50 plus $9.18 shipping. It arrived in 7 days.

What’s in the box: The T-Amp Gen II, a 12v 3A switching power supply (BI Model BI42-120300-E2), a female RCA (L&R) to mini-jack adapter, Male RCA (L&R) to minijack cable (looks like 3 foot), a very brief manual.

Physical Inspection: The new model is significantly smaller than the old in height, and is much easier to stack with other small products. The volume knob pushes in to turn off (the old one clicked off when turned to the left). The new model looks nicer in my opinion. It has the same cheap push-pin speaker connectors, the same mini-jack input, the same 12v adapter input, and the same capability to run on 8 AA batteries. The manual says it outputs 10 watts with the AA batteries, and 15 watts with the AC adapter. The only new connection is a mini-headphone jack on the right side.

Cost Comparison with Old T-Amp. The Old T-Amp sold for $35 without a power supply. The power supply retailed for $15. So the price with a power supply would have been about $50. The price really hasn’t changed between the old and new models if you account for the 12 v 3A power supply. In addition, I believe the former SI power supplies were 2A and not 3A supplies. So the power supplies appear to have been improved. I’ve read a lot of carping on the internet about the “higher price” of the Gen 2 – the commentators don’t seem to notice that the Gen II includes the power supply and the Gen I did not.

Headphone Amp. This is an entirely new addition to the Sonic Impact line. The prior versions did not include a circuit for headphones. Moreover, adopting the speaker outputs for headphone use was problematic. According to web resources, the T-Amp chip was designed to work with 4 and 8 ohm speaker loads using special digital filters. It produces noise and artifacts when used outside of the filtered range. Moreover, the amp is bridged and cannot be used with headphones that share a common ground without causing damage to the headphones or the amplifier. Therefore, one would have to cable the headphones for dual mono use. Presumably, these issues have been addressed in the design of the headphone connector. But read on.

Headphone Output

The headphone output sounds pretty good with my Koss KSC-75s, which have a 60 ohm impedance. But high impedance headphones don’t work right at all. The sound completely fell apart on my big Senn HD-580s (300 ohm impedance). I got really bad and strange distortion artifacts even at modest listening levels. The same music on the KSC-75s sounded fine. I suspect the problem with the 580s was the lack of proper digital filtering designed for high impedance phones. I don’t know what impedance range the digital filtering of the headphone output is designed for. It seemed to work fine with my low 16 ohm impedance Shure E2cs. No hiss, clear sound.
So, what do I think of the sound quality with low impedance headphones? Well, I think it’s fine. Nothing great or earth shattering, but it’s an adequate sounding convenience. It’s not a world beater by any means. I’d say the sound is similar to your average dap. I would not recommend this to someone looking specifically for a headphone amp. Still, having essentially free headphone output thrown in with such a great sounding little speaker amplifier is a big plus. One warning. Make sure you turn off the power before plugging or unplugging your headphones. The shorting noise is a real killer on this amp.

Speakers

I played the same music through both the old T-Amp and the new T-Amp Gen 2 using Kef Chorale speakers. Based on my initial comparison, I couldn’t tell any difference. The Gen 2 sounded virtually identical to the old. That’s not a bad thing, because the T-Amp in my opinion sounds terrific – very musical. My guess is that the so-called “bass rolloff” problem has not been fixed – although I’m basing this on listening to organ music through relatively small Kef Chorale speakers, so it’s possible that the Kefs just don’t go low enough for me to notice any difference. I have neither the test equipment nor the skill to do a scientific test. I’m sure there will be detailed reports on this from others more capable than I. However, I can say that the amp sounds just beautiful with speakers. Delicate, quiet, detailed, and musical. It’s still shocking to hear such great sound from such a light and cheap amplifier. So I continue to recommend the amp most highly for people on a budget. There is nothing I know if in this price range that can compete with it for sound quality with a set of bookshelf speakers.

[Penchum]

Thanks for the review!! I had suspected the headphone out would be for "portable" headphones only. I was hoping the bass situation had been addressed in the V2. Hopefully, someone will be able to check that part out soon.

[xnothingpoetic]

Appreciate the review/headphone warning!

[Jon L]

Originally Posted by classicalguy

Presumably, these issues have been addressed in the design of the headphone connector. But read on.

Headphone Output

The sound completely fell apart on my big Senn HD-580s (300 ohm impedance).

Can you open the amp and take a photo or describe how the headphone jack is wired? From what you describe, I'm thinking they stuck in some large resistors in the headphone output, which will reduce background noise for low impedance 'phones but may represent too much resistance/power loss when powering already-high impedance 'phones.

Sonic Impact should have plenty, plenty of power for any headphones b/c without any additional resistors, SI gen I drove AKG K701, K340, K1000 with power to spare..

[scompton]

I just got one delivered to work on Monday. I've tried MB Quart QP85, DT880, and Sextett. It was able to drive them easily. For the 600 ohm Sextetts, the volume knob was between 9 and 10 o'clock. Out of the box, it didn't sound as good as my XM4 which I have been using at work. Since this is at work, I didn't have a lot of time to compare, and I didn't have an SPL meter to level match. I might be able to do a better comparative listen later in the week. BTW, the XM4 is not running off a battery. I have it plugged in with a 12V wall wart.

[classicalguy]

I was getting terrible sounds through the high imp. phones even at low volume. It was not a clipping problem. I think it was the lack of proper filtering of the digital chip.

[JGP08]

Good review! I just tried my Gen 2 hp out and experienced exactly the same: distortion with HD650, ok with KSC75, brutal shorting noise when plugging phones in and out. I should emphasize the OP's point of buying this for speakers only, as they definitely have great value for speakers, but not so much for phones.

[scompton]

Originally Posted by JGP08

brutal shorting noise when plugging phones in and out.

I quickly learned to turn off the amp before plugging and unplugging. I already have the Super T for speakers. I might post pictures and ask for modding suggestions in the DIY forum.

[classicalguy]

There is some info in this thread and a picture of the board.

diyAudio Forums - Sonic Impact Gen 2 T-Amp ?

Might be helpful to some of you DIYers. There is also an interesting discussion about using the gen 1 with headphones here, suggesting that digital filtering is the problem. See the post in the link below from Michael Mardis's site.

Sonic Impact T-Amp 2 is good for cans too.

[jung]

Originally Posted by classicalguy

Cost Comparison with Old T-Amp. The Old T-Amp sold for $35 without a power supply. The power supply retailed for $15. So the price with a power supply would have been about $50. The price really hasn’t changed between the old and new models if you account for the 12 v 3A power supply.

I think the original was listed at $40, and the power adaptor at $20, while the new one is listed at $80, $20 higher. And it forces people to pay for its power adaptor, even if they want to use AA, or 12v battery, or other power supply.

Another problem is that the new Gen2 is available only at very few places, while the original was sold almost everywhere.

Originally Posted by classicalguy

Headphone Amp. This is an entirely new addition to the Sonic Impact line. The prior versions did not include a circuit for headphones. Moreover, adopting the speaker outputs for headphone use was problematic. According to web resources, the T-Amp chip was designed to work with 4 and 8 ohm speaker loads using special digital filters. It produces noise and artifacts when used outside of the filtered range. Moreover, the amp is bridged and cannot be used with headphones that share a common ground without causing damage to the headphones or the amplifier. Therefore, one would have to cable the headphones for dual mono use. Presumably, these issues have been addressed in the design of the headphone connector. But read on.

Headphone Output

The headphone output sounds pretty good with my Koss KSC-75s, which have a 60 ohm impedance. But high impedance headphones don’t work right at all. The sound completely fell apart on my big Senn HD-580s (300 ohm impedance). I got really bad and strange distortion artifacts even at modest listening levels. The same music on the KSC-75s sounded fine. I suspect the problem with the 580s was the lack of proper digital filtering designed for high impedance phones. I don’t know what impedance range the digital filtering of the headphone output is designed for. It seemed to work fine with my low 16 ohm impedance Shure E2cs. No hiss, clear sound.
So, what do I think of the sound quality with low impedance headphones? Well, I think it’s fine. Nothing great or earth shattering, but it’s an adequate sounding convenience. It’s not a world beater by any means. I’d say the sound is similar to your average dap. I would not recommend this to someone looking specifically for a headphone amp.

Maybe they tied two resistors to the common ground of the headphone socket.

[Xcalibur255]

Good writeup and I completely agree with the assessment. The headphone out jack on my computer soundcard produced superior results over the headphone out on the t-amp. It is purely there as a convenience item. Trying it with my K701's was quite the disaster. Personally I don't even think it does the KSC75 justice. It sucks all the weight and detail out of their reproduction and further scoops out it's already recessed midrange.

Also, the crazy loud popping sound you'll get from your connected speakers if you pull your headphone plug out when the t-amp is still turned on was not a pleasant surprise like others have mentioned.

[classicalguy]

Yea, on further listening I think it sounds bad. Period. I don't use it for HPs anymore.

[batmanwcm]

I ordered it last Friday for $41.99 shipped after GCO from buy.com and I'm eagerly waiting for it. For the price, it should completely meet my expectations. I just count the heaphone jack as an extra freebie they threw in there.