The Fatman iTube (OEM Dared, which also sold its own-branded version, the Dared MP-5) is a tube-buffered gainclone first introduced c.2005, to target the iPod market with a bookshelf tube setup. It became a huge success over the next ~15 years, selling over ~100k units worldwide to a market where it was often their first introduction to vacuum-tube audio on a budget.
http://www.enjoythemusic.com/magazin.../dared_mp5.htm
One of the Fatman versions landed up for auditioning a few days ago, and I must say that I was impressed with its form-factor, pricing, build quality, finish and durability. However, there were some minor drawbacks in its audio quality - very bass-shy (like a lot of tube gear) and with a fair amount of glare/brightness in the upper-mids (not uncommon in chipamps/gainclones). In other words, it had some of the faults of both vacuum-tubes and chipamps.
I tried to address the glare issue first, since I don't really need a thumping bass response (I don't listen much to heavy-metal, disco, hip-hop and similar genres anyway). I generally prefer neutrality, with full-bodied mids for vocals and so on, and the MP-5 seemed to be a great candidate for upgrades.
Opened it up, and noticed that almost all resistors were generic 0.5W CFR, and all electrolytics were generic Chinese 105c TL brand. I swapped out the electrolytics first:
3x 2200uF/35V TL -> 3x 2200uF/35V Elna RKD (chipamp rail bypass, heater/aux DC bypass)
1x 100uF/250V TL -> 1x 100uF/400V Rubycon AXW (cathode-follower B+)
1x 47uF/400V TL -> 1x 33uF/350V Rubycon YK (B+ for magic-eye VU meter, value not critical)
2x interstage coupling capacitors were 1uF/200V, possibly MKT polyesters, and I had excellent MKP substitutes from Asahi Kasei, so that was the next upgrade:
2x 1uF/200V/10% generic MKT ->2x 1uF/250V/5% Asahi Kasei MKP
Finally, a couple of resistor upgrades. The input series resistor was a generic 10k/0.5W CFR, which I replaced with a non-magnetic PRP 10k/0.25W/25 ppm thermal-coefficient. This is in the signal path, so it's critical that it's non-magnetic to reduce EMI/RFI pickup.
The second was in the chipamp voltage-series feedback network - a 560E/0.5W generic CFR in the lower leg of an 18K/560E voltage divider. It's critical for sonics to have an extremely linear resistor here, with very low 2nd- and higher-order voltage coefficient of resistance. Only wire-wounds make the cut, so I swapped in a Vishay 510E/1W wire-wound here - the slightly lower value alters the default chipamp gain by about 10%, which doesn't matter.
2x 10k/0.5W generic CFR -> 2x 10k/0.25W/25ppm non-magnetic PRP
2x 560E/0.5W generic CFR -> 2x 510E/1W Vishay wirewound.
Checked everything, and there was a generic A100k carbon-track pot as the volume control. I left that alone, since I didn't have a quality pot like an Alps for a direct upgrade, and 100k wirewound pots are a rare item - it's a future to-do upgrade.
For now, these upgrades were sufficient to completely eliminate the glare and make it more neutral, but still warm, transparent, detailed and full-bodied,
Here's a pic of the circuit board after the upgrades:
http://www.enjoythemusic.com/magazin.../dared_mp5.htm
One of the Fatman versions landed up for auditioning a few days ago, and I must say that I was impressed with its form-factor, pricing, build quality, finish and durability. However, there were some minor drawbacks in its audio quality - very bass-shy (like a lot of tube gear) and with a fair amount of glare/brightness in the upper-mids (not uncommon in chipamps/gainclones). In other words, it had some of the faults of both vacuum-tubes and chipamps.
I tried to address the glare issue first, since I don't really need a thumping bass response (I don't listen much to heavy-metal, disco, hip-hop and similar genres anyway). I generally prefer neutrality, with full-bodied mids for vocals and so on, and the MP-5 seemed to be a great candidate for upgrades.
Opened it up, and noticed that almost all resistors were generic 0.5W CFR, and all electrolytics were generic Chinese 105c TL brand. I swapped out the electrolytics first:
3x 2200uF/35V TL -> 3x 2200uF/35V Elna RKD (chipamp rail bypass, heater/aux DC bypass)
1x 100uF/250V TL -> 1x 100uF/400V Rubycon AXW (cathode-follower B+)
1x 47uF/400V TL -> 1x 33uF/350V Rubycon YK (B+ for magic-eye VU meter, value not critical)
2x interstage coupling capacitors were 1uF/200V, possibly MKT polyesters, and I had excellent MKP substitutes from Asahi Kasei, so that was the next upgrade:
2x 1uF/200V/10% generic MKT ->2x 1uF/250V/5% Asahi Kasei MKP
Finally, a couple of resistor upgrades. The input series resistor was a generic 10k/0.5W CFR, which I replaced with a non-magnetic PRP 10k/0.25W/25 ppm thermal-coefficient. This is in the signal path, so it's critical that it's non-magnetic to reduce EMI/RFI pickup.
The second was in the chipamp voltage-series feedback network - a 560E/0.5W generic CFR in the lower leg of an 18K/560E voltage divider. It's critical for sonics to have an extremely linear resistor here, with very low 2nd- and higher-order voltage coefficient of resistance. Only wire-wounds make the cut, so I swapped in a Vishay 510E/1W wire-wound here - the slightly lower value alters the default chipamp gain by about 10%, which doesn't matter.
2x 10k/0.5W generic CFR -> 2x 10k/0.25W/25ppm non-magnetic PRP
2x 560E/0.5W generic CFR -> 2x 510E/1W Vishay wirewound.
Checked everything, and there was a generic A100k carbon-track pot as the volume control. I left that alone, since I didn't have a quality pot like an Alps for a direct upgrade, and 100k wirewound pots are a rare item - it's a future to-do upgrade.
For now, these upgrades were sufficient to completely eliminate the glare and make it more neutral, but still warm, transparent, detailed and full-bodied,
Here's a pic of the circuit board after the upgrades:
Attached Files