Russ Arcuri
20% more jawbone...15% less fat...
- Joined
- Oct 28, 2001
- Posts
- 1,126
- Likes
- 10
Note: I typed this up originally as a response to Joe Bloggs on this thread. However, I realized that the info might be useful to others, so I'm posting it here. This is also fair warning so you don't wonder why I'm referring (in a couple places) specifically to Joe.
---
I received my JMT Altoids amp (CHA 47) yesterday. I listened to it pretty much the entire evening last night. Here are my impressions:
1. Fit and finish are good. The only indication anyone would have that it's a DIY amp is the Altoids tin (there are no commercial amps available in Altoids tins, obviously).
2. When there's no source signal, this thing is SILENT. No hum, hiss, or noise, even with the volume turned up much louder than I would use to listen to actual music. I know that was a concern of yours after your bad experience with the Boosteroo.
3. It's pretty darn neutral -- i.e. it does not color the sound at all. Exactly what a solid state amp should do. One thing other people I've spoken with about amps said is that their first decent amp didn't "blow them away" -- as if the amp should somehow make the music sound different. You have to keep in mind that an IDEAL amplifier will do nothing other than play your music as loudly as you want to play it. Tube amps color the sound in a pleasing way (usually), but a good solid-state amp won't.
4. Now, to contradict point 3, the music does sound different. It's not colored in any way, but the low end (especially with my Sennheiser HD580s) has more impact. The HD580s are difficult to drive, and portable players just don't have the power to drive them properly. The JMT altoids amp drives them with authority, so they sound "right." I know you are concerned that the HD580s are hard to drive, but I can say now for sure that the CHA 47 drives them just fine.
5. I've commented previously (on another thread) about the headphone jack on my circa-1993 Onkyo Integra DX-C606 CD changer. It's one of the best headphone jacks I've ever used on a rack-style player. I can't find any specific info on what components were used for the headphone amplifier, or any specs. But it's a 1/4" gold-plated jack, and a very smooth volume pot. The 606 has always driven my HD-580s with authority -- such that I never felt the need for a dedicated headphone amplifier. I auditioned a friend's Headroom Little, and didn't notice any improvement over the headphone jack in the 606 (though unfortunately I couldn't A/B with the 606).
So, how does the JMT Altoids amp compare with the headphone jack on the 606? In a word, well. Both produce clean, detailed sound, at any listening level I want. The 606 will play louder (tested with the headphones AWAY from my ears) but the Altoids amp (built with a gain of 5, according to JMT) will drive them to uncomfortably loud, dangerous levels as well.
The sound I get from the 606 headphone jack is ever so slightly fuller and more detailed than my Panasonic 570 > JMT Altoids combo. I suspect this is due to differences in the DACs, though I suppose it could be due to differences in the opamps. It would be useful to know what opamps the 606 uses, but that will have to wait until I can find the info somewhere or open up the CD player and check for myself.
I did not have time to test the 606 into the JMT amp to eliminate the DACs as a possibility. I would not be surprised if the DAC in the 606 sounds better than the Panasonic DAC used in the 570; I remember reading about the expensive, high quality components used in the 606 when I bought it back in 1993. I have always preferred the sound of the 606's DAC to every other DAC I've tried, including the newer 24/96 DAC used in my Denon A/V receiver and the (supposedly highly-touted) Legato-Link / Pioneer DAC used in my Elite CLD-79 laserdisc player.
In any case, at home in my living room I will probably still use the headphone jack on the 606, if only because the DAC sounds better than my portable. However, I will be using the JMT Altoids amp whenever I'm not within 10 feet of the 606. It sounds great and it drives my HD580s well.
I didn't have time to do any extensive listening to the Altoids amp with my Grado SR-80s. The CHA 47 design is supposed to be optimized for low-impedance phones like the SR-80s. The brief listen I gave them was good, though I think a gain of 5 might be slightly too much for ease of use with the SR-80s. It took some playing to get the Grados set to a reasonable volume level for listening in a very quiet room... what I mean is, turning the volume pot up from no sound at all to the point where both channels play cleanly involves very little turning at all. Getting the pot into the "sweet spot" means turning it a bit further, which makes the volume too high for the SR-80s in a quiet room.
This isn't JMT's fault; I asked him to make the amp 'generic' enough to drive the Sennheisers with authority (rather than using the default CHA 47 config, which is optimized for Grados). I guess setting the gain to 5 made it work better with the Sennheisers but made it less ideal for the Grados. This isn't a big problem for me; the main reason I wanted the amp was for the Sennheisers, and my portable players can drive the Grados fine without assistance.
I'm going to be building a CMOY with crossfeed myself sometime soon, using a Hansen PCB. I'll report on its performance then, with comparisons to the Altoids amp.
Russ "The Peripatetic Audiophile"
---
I received my JMT Altoids amp (CHA 47) yesterday. I listened to it pretty much the entire evening last night. Here are my impressions:
1. Fit and finish are good. The only indication anyone would have that it's a DIY amp is the Altoids tin (there are no commercial amps available in Altoids tins, obviously).
2. When there's no source signal, this thing is SILENT. No hum, hiss, or noise, even with the volume turned up much louder than I would use to listen to actual music. I know that was a concern of yours after your bad experience with the Boosteroo.
3. It's pretty darn neutral -- i.e. it does not color the sound at all. Exactly what a solid state amp should do. One thing other people I've spoken with about amps said is that their first decent amp didn't "blow them away" -- as if the amp should somehow make the music sound different. You have to keep in mind that an IDEAL amplifier will do nothing other than play your music as loudly as you want to play it. Tube amps color the sound in a pleasing way (usually), but a good solid-state amp won't.
4. Now, to contradict point 3, the music does sound different. It's not colored in any way, but the low end (especially with my Sennheiser HD580s) has more impact. The HD580s are difficult to drive, and portable players just don't have the power to drive them properly. The JMT altoids amp drives them with authority, so they sound "right." I know you are concerned that the HD580s are hard to drive, but I can say now for sure that the CHA 47 drives them just fine.
5. I've commented previously (on another thread) about the headphone jack on my circa-1993 Onkyo Integra DX-C606 CD changer. It's one of the best headphone jacks I've ever used on a rack-style player. I can't find any specific info on what components were used for the headphone amplifier, or any specs. But it's a 1/4" gold-plated jack, and a very smooth volume pot. The 606 has always driven my HD-580s with authority -- such that I never felt the need for a dedicated headphone amplifier. I auditioned a friend's Headroom Little, and didn't notice any improvement over the headphone jack in the 606 (though unfortunately I couldn't A/B with the 606).
So, how does the JMT Altoids amp compare with the headphone jack on the 606? In a word, well. Both produce clean, detailed sound, at any listening level I want. The 606 will play louder (tested with the headphones AWAY from my ears) but the Altoids amp (built with a gain of 5, according to JMT) will drive them to uncomfortably loud, dangerous levels as well.
The sound I get from the 606 headphone jack is ever so slightly fuller and more detailed than my Panasonic 570 > JMT Altoids combo. I suspect this is due to differences in the DACs, though I suppose it could be due to differences in the opamps. It would be useful to know what opamps the 606 uses, but that will have to wait until I can find the info somewhere or open up the CD player and check for myself.
I did not have time to test the 606 into the JMT amp to eliminate the DACs as a possibility. I would not be surprised if the DAC in the 606 sounds better than the Panasonic DAC used in the 570; I remember reading about the expensive, high quality components used in the 606 when I bought it back in 1993. I have always preferred the sound of the 606's DAC to every other DAC I've tried, including the newer 24/96 DAC used in my Denon A/V receiver and the (supposedly highly-touted) Legato-Link / Pioneer DAC used in my Elite CLD-79 laserdisc player.
In any case, at home in my living room I will probably still use the headphone jack on the 606, if only because the DAC sounds better than my portable. However, I will be using the JMT Altoids amp whenever I'm not within 10 feet of the 606. It sounds great and it drives my HD580s well.
I didn't have time to do any extensive listening to the Altoids amp with my Grado SR-80s. The CHA 47 design is supposed to be optimized for low-impedance phones like the SR-80s. The brief listen I gave them was good, though I think a gain of 5 might be slightly too much for ease of use with the SR-80s. It took some playing to get the Grados set to a reasonable volume level for listening in a very quiet room... what I mean is, turning the volume pot up from no sound at all to the point where both channels play cleanly involves very little turning at all. Getting the pot into the "sweet spot" means turning it a bit further, which makes the volume too high for the SR-80s in a quiet room.
This isn't JMT's fault; I asked him to make the amp 'generic' enough to drive the Sennheisers with authority (rather than using the default CHA 47 config, which is optimized for Grados). I guess setting the gain to 5 made it work better with the Sennheisers but made it less ideal for the Grados. This isn't a big problem for me; the main reason I wanted the amp was for the Sennheisers, and my portable players can drive the Grados fine without assistance.
I'm going to be building a CMOY with crossfeed myself sometime soon, using a Hansen PCB. I'll report on its performance then, with comparisons to the Altoids amp.
Russ "The Peripatetic Audiophile"
