(10 votes, average: 3.40 out of 5)
Loading...And here comes another tube amplifier. I was very skeptical when I saw this thing on ebay at first. $86 shipped for a tube am, I thought. It must be a piece of sh**. But I wanted a tube amp for my office at work. It had to be something small. So I started to research about this tube amp and a couple of other amps on ebay. After a bunch of research and being guided by the following thread, I was very close to making my decision.
http://rockgrotto.proboards.
Based on the thread it was obvious that the amp is OK sounding device as is, but could be turned into a fantastic headphone amp if a couple of mods are made. I decided to take a plunge and buy the little thing. I got lucky and found it on ebay – used. All together with shipment was $50!!!
I got the amp, plugged the tube it came with and as expected, the sound quality was very average. The tube it came with, ShuGuang, was a piece of crap, so the results were not stellar. I plugged my good NOS 12au7 tube into it, pared it with my Sennheiser HD650 headphones and the sound transformed immediately, but you could hear that there was a lot missing – extension and details wise.
The next step was to mod. All the mods with 2x extras cost me about $33 (see here for the complete list of items from Mouser with parts number). Did the majority of the mods that are described on the board and lo and behold, the amp transformed into a beauty from a beast (although it looks like a beast after the mods 🙂 ). The background noise went all the way down to none existent (depending on a tube). Details opened up beautifully. High frequencies went through the roof figuratively speaking 🙂
One mode I was not really sure about is replacing bias resistor with a trim-pot – all my other tube amps didn’t have any problems excepting tubes from 12a*7 family, but I was happy that I did at the end. Without the change, the amp would only accept tubes from the 12au7 family. With the change, I was able to feed it with any tube from 12ax7 & 5751 family!!! Plug a tube, adjust bias on both channels and you have a great working amp. It was funny to see $200 tube in a $50 amp, but the sound it was able to produce was superb.
So in conclusion, don’t buy the amp if you are not planning to make the mods. But go for it if you can solder (it would take about 2 hours for all the mods with a lot of verifications in between (DO THE MODS ONE AT A TIME!!!). Get a good NOS 5814 tube and you are set. You will be amazed by the sound that’s coming out of that little monster!
A bit more testing and using the amp. The amp is truly defined by a tube you use, which is not surprising considering that there is very little circuitry in the signal path outside the tube. Using something like Westinghouse 12au7, Sylvania GB-5814 or CBS 5418, really makes the amp into a beautiful sounding machine.
One issue that I’ve noticed is that if the map is used with very high sensitivity headphones, which is the majority in ear headphones, the amount of hissing is excessive. I tried many different tubes with similar results. With Sennheiser HD650 it sounds very quite, but with iGo with sensitivity of 105db, it’s almost unusable. So be careful – depending on the headphones, it could be great or really bad – even with upgrades. Right now, I’m waiting on Monoprice 8320. They have higher impedance of 32ohm and lower sensitivity of 96db. I will post update when I get the headphones and see if it’s any better.
Another update, I got the Monoprice 8320, which are fantastic headphones considering $7 price. Even with low sensitivity and higher impedance, the amount of hiss is extremely high. This is definitely a major issue. the hiss doesn’t go away even after turning volume all the way down and it’s independent of a tube used.
The issue is resolved now. It lookes like after the mods – including Vishay trip pots, the amp’s noise level went quite high. Removing Vishay fixed the issue.