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I just picked up one of these little amps the other day from Parts Express and I'm planning on doing some pretty extensive mods to it in pursuit of better sound. I realize there's already plenty of mod sites about this little amp on the web, but the circuit board in mine is a different version so it has a different parts layout. Plus a few people here are using this amp for their K1000 earspeakers so I figured there'd be some interest.
Stock Insides
The audio connectors are very low quality, but what does one expect for $30. Also I found the volume "knob" to be next to useless since it's almost flush with the front panel. So first on the agenda was a recase with much better connectors and a proper vol knob. I'll eventually use a nice wood or metal case, but for now I'm just using an open layout on a scrap piece of wood. It's ugly, but it'll make testing and modding much easier.
New Connector Panel
Test Rig
Next I replaced the vol pot with the stock one from my Xiang Sheng 708B. The power switch in the T-Amp is part of the stock vol pot so if you remove it you'll have to hook up a switch of somekind. Since the Pyramid 5A regulated linear power supply that I'm using already has a power switch on it I just looped the switch wires in the plastic connector together. The new pot sounds better, but the channel balance is bad at low volumes so it was a trade off. An ALPS Blue Velvet will be on the way soon.
Using old 708B vol pot
I took some close up pics of the PCB and I'm going through them to add the arrows and circles to show how to connect things for this version. I'll post those soon. Next I'm doing the input capacitor mod that is detailed here using some Solen 3.0uF caps.
Home rig:
EMU 0303 -> Entech Number Cruncher 205.2 -> MAD Ear+ Purist HD -> Denon D5000, AKG K-1000
Work rig:
Asus eeePC -> Denon D2000
Lawn Mowin' rig:
iPod 2nd Gen Shuffle -> JVC Marshmallows.
My disclaimer:
My posts are my opinions, please take and respect them as such, and I will do the same for yours. Everyones ears are different sizes and shapes, and we all perceieve sound and music in different ways. Other variables to consider inculde the type of music one prefers, the type of gear one owns, and the type of presentation one prefers in a set of headphones. As such it is up to *you* to use your own ears, gear and music to decide what ultimately sounds the best, since your opinion is really the only one that matters at the end of the day.
For the input capacitors, it's better to use RXF capacitors which are low ESL and low ESR than to use botique capacitors. I had best results with Mundorf RXF. There's also a way to get rid of the capacitor completely but it's a complicated procedure.
Most important are the output inductors. You want to use air foil inductors. This is the mod that has the largest impact on sound.
I find that the T-amp is quite limited in terms of mods because the power supply stinks. I had much better results building the 41Hz AMP5. Mods were easier since you're basically building from stratch, and the AMP5 can drive headphones while the T-Amp requires that the headphones be dual mono. It also has much, much better sound quality than the T-Amp.
Just curious, what value are the resistors that you used across the speaker jacks?
They're the stock 0.15uF mylar caps, but I have some cheap Dayton 0.10uF film and foil caps that I'm going to try later.
Originally Posted by cotdt
For the input capacitors, it's better to use RXF capacitors which are low ESL and low ESR than to use botique capacitors. I had best results with Mundorf RXF. There's also a way to get rid of the capacitor completely but it's a complicated procedure.
Most important are the output inductors. You want to use air foil inductors. This is the mod that has the largest impact on sound.
I find that the T-amp is quite limited in terms of mods because the power supply stinks. I had much better results building the 41Hz AMP5. Mods were easier since you're basically building from stratch, and the AMP5 can drive headphones while the T-Amp requires that the headphones be dual mono. It also has much, much better sound quality than the T-Amp.
I've been wanting to try out those Mundorf RXF caps in a project for a while now, but I not going any fancier than Solens for the T-Amp. I just wanted to see what a cheap Tripath based amp would be like after doing a few mods for as little money as possible. I like the overall sound so I'm going to build something much nicer later like a 41Hz kit, a Charlize, or even a Winsome Labs Mouse amp kit. That's when I'll get all the good stuff.
Could someone please help me with the DC offset problem I've asked about here?
Also, on the Michael Mardis website linked above there is a mention under the "headphones" heading about the ultrasonic noise which is present even with the normal 4 to 8 ohms load. Can this be a problem with the K1000? I know that:
1. many people have used the t-amp with the K1000, but these parameters like DC offset and, I suppose, ultrasonic noise, vary from unit to unit, so some might have had better luck than me with my particular unit; also, there was a time when there was this rumour that the t-amp can fry one's K1000 and it is not clear to me if there was a good reason behind this and if the problem was the DC leakage or something else (ultrasonic noise?)
2. somebody asked AKG if it's OK to use D class amplifiers with the K1000 and the answer was positive, but the t-amp is not, to my understanding, a typical D class amp (they say it's a T class, right?!)
Thanks!
__________________
My review of Stax 3030:
My (older) review of AKG K501 vs. Sennheiser HD600
(so that you can learn my bias and take it into account when reading my posts)
Finally got around to installing the Solen 3.0uF input caps. I used 30ga wire wrapping wire to make it easier to solder to the pads left over after removing the stock 0.33uF surface-mount caps. The Solens definitely improved the resolution of the T-amp, but I really can't comment on any changes in the bass response due to the small speakers I'm currently using (see sig). I upgraded the stock 0.01uF Mylar output filter caps to some Dayton 0.1uF film/foils, which you can see in the pic too. I also wrapped some copper foil around the four output inductors to help reduce high-frequency emissions a bit.
Since I use my XS 708B as a preamp to control the T-amp I wanted to get rid of the extra vol pot in the signal path, especially since it's low quality. I also wanted to reduce the gain since it's very high so I built a voltage divider network using four NTE 51k resistors. The resolution jumped up a bit as did impact compared to the pot I was previously using.
Here's the area of interest for this version of the T-amp. C4 is the left channel input cap and C3 is the right channel cap.
Now I need to figure out something for a case. I want to do something a bit different by using a round case, like 4" PVC cap only much nicer. Need to start scrounging around local stores.
a shovel, what are you planning on doing to your T-amp? Are you going to redesign the output filter too?
Modifying the Sonic Impact T-Amp & 41Hz AMP6
Linear Mode
