KurtW
500+ Head-Fier
- Joined
- Jun 26, 2001
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Note: I am posting this at both HeadWize and Head-Fi so if you read it at one place you don’t have to read it again.
This is a review of the Meier-Audio Porta-Corda (Serial number 01001), HeadRoom Total Airhead (later version, no s/n), and what I call the CHL, which is the Levallois version of the CMOY amp using the Hansen PC board. You can see the details of this amp in the HeadWize project pages at this location: http://headwize.com/projects/meier2_prj.htm The CHL has the Meier crossfeed circuit; I used the medium setting which is switchable in or out. I built mine without the bass enhance caps and used OPA2132 op amps. I don’t know if it makes a difference or not but I used Teflon coated 28 gauge silver wire. Later I’ll build another version of this with larger copper wire, since the thin solid silver wire was lots of trouble, and see if it sounds any different.
The Equipment used:
Since these are portable amps I mostly used equipment that I would normally use with these amps. The CD player was usually a Panasonic SL-SX510 and the headphones were Grado SR80, Koss KSC35 and Sony V6. I used a StraightWire cable.
The CDs used:
Schubert, Arpeggione Sonta for piano & cello, Decca 289 460 974-2
Sarah Vaughan, Crazy and Mixed Up, JVCXR-0204-2
Jose Pass, Virtuoso, XRCD2 VICJ-60256 (Japanese version)
Bob Dylan, Love and Theft
Joe Lovano, Flights of Fancy, Blue Note 72435 2761821
This last one was recorded live to 2 track analog tape and as a result of no mixing board it has very wide separation. I have a hard time hearing this on headphones without crossfeed, so this selection was used for the crossfeed tests.
The Amps:
The Porta-Corda (or PC from now on) and the Total Airhead (TA) size and weight are very close to each other. The TA is slightly smaller in front and larger in back and very slightly wider. The PC with battery weighs 5 oz and the TA just 1/4 oz less. The PC has a power LED which the TA doesn’t. The PC has all connections on the front panel whereas the input for the TA is on the side. This can be a pro or con depending on how you use it. The PC has a detachable belt clip (although it still doesn’t sit completely flat when it’s detached), and is quite attractive with it’s light colored case and blue metal faceplate. It also has a very small knob instead of the wheel type volume control on the TA. The knob is a little hard to turn; this is probably an advantage for portable use and a disadvantage for home use. They both seem to have long battery life, as does the CHL. I put the CHL in a Serpac case which is only slightly larger than the other two. I was going to put it in an Altoids tin but the switches were a little too big with everything else so it didn’t quite fit. All seem to be free of any hiss or pops.
I used two Energizer AA size batteries for the TA (Nickel Hydride also works) and a Plainview 9.6v Nickel metal Hydride batteries (one each) for the other two. Note that most Nickel hydride 9v batteries are only 7.2 volts; they’ll work, but maybe not sound quite as good so I used the high voltage ones. I also did a brief comparison with the full size Corda, and tried the PC with a regulated variable external supply up to 26 volts. In doing so I checked out Jan’s circuit to prevent damage when the supply terminals are reversed…luckily this circuitry works great! For you tweekers out there, the PC has soldered in op amps, unlike my Corda (my Corda was a kit and the PC was fully assembled, in case it matters). The PC had been run (mostly at 26v) for at least 30 hours, the CHL probably about half that. The TA is about a year old and has had at least 50 hours of use. During the testing none had been extensively warmed up, but during the course of the testing they had been on for a couple of hours.
The Sound without crossfeed:
All three amps sounded much better than the headphone output of the Panasonic directly; cleaner and much better bass. The differences between these three amps was much smaller than the differences between the three different headphones that I used. No matter what CD was playing or which headphones I used, the basic character of each amp was pretty consistent: the TA sounded more laid back and relaxed, the PC was much more aggressive and livelier. CHL was in between the two but much closer to the PC than the TA. With good sounding CDs and well balanced headphones I liked the fast, crisp sound of the PC, but there were some songs on the Dylan CD using the Koss KSC35 where the PC sounded a little bit too aggressive and was a little fatiguing after a while. There wasn’t a big difference in soundstage between the three but it seemed on occasion to be slightly wider on the PC and the least wide on the TA. The bass was very good on all three but again the PC seemed to have a slight edge with the most powerful bass, the TA the least, and as usual the CHL was in between but closer to the PC. The big Corda seemed to be more transparent and have a fuller, more open sound than any of the portables. I did try the PC briefly with higher voltages up to 26 volts from the regulated supply hooked to the battery terminals. I didn’t really notice any big difference in the sound, but maybe there would be with some harder to drive headphones. I’ll try that later.
The Sound with crossfeed:
The PC and CHL both have the Meier crossfeed so it’s no surprise that they sounded similar. What was surprising is that the PC seemed to loose some bass when the crossfeed was turned on, much more than the CHL or the big Corda where the loss is barely noticeable. This resulted in the CHL having more bass than the PC when the crossfeed was on. The TA crossfeed boosts the bass and cuts the treble, thus making a bigger impact on the sound. This is the only HeadRoom amp that doesn’t have the filter switch to bring back the treble, something I think it needs (if the filter was always switched on when the processor was on this would be fine). All seem to do an equally good job of reducing the extreme stereo effect that is on some recordings like the Joe Lovano CD.
Measurements (without crossfeed):
The PC measures flat within 0.1dB from 20 to 20kHz. The TA was down only 0.2dB at 20 Hz and had the old HeadRoom rolloff of 2.4dB at 20kHz. The CHL had no rolloff at the high end but was down 0.5dB at 20Hz. I wouldn’t expect to be able to hear any of these low frequency rolloffs, given that headphones roll off much more at 20 Hz. I also measured total harmonic distortion at typical listening levels, and all three amps were very close to the resolution of my test equipment (around 0.035%) at any frequency.
SUMMARY:
These are all very good portable amps that should improve the sound of most portable equipment, and probably a lot of home equipment too. If I had really clean sources and smooth or laidback headphones then the Porta-Corda is a good choice, or if you’re into DIY stuff then I can certainly recommend the CHL. If I had a bright source or headphones that needed a little taming, or wanted some extra bass when using crossfeed, then the TA is a good choice.
This is a review of the Meier-Audio Porta-Corda (Serial number 01001), HeadRoom Total Airhead (later version, no s/n), and what I call the CHL, which is the Levallois version of the CMOY amp using the Hansen PC board. You can see the details of this amp in the HeadWize project pages at this location: http://headwize.com/projects/meier2_prj.htm The CHL has the Meier crossfeed circuit; I used the medium setting which is switchable in or out. I built mine without the bass enhance caps and used OPA2132 op amps. I don’t know if it makes a difference or not but I used Teflon coated 28 gauge silver wire. Later I’ll build another version of this with larger copper wire, since the thin solid silver wire was lots of trouble, and see if it sounds any different.
The Equipment used:
Since these are portable amps I mostly used equipment that I would normally use with these amps. The CD player was usually a Panasonic SL-SX510 and the headphones were Grado SR80, Koss KSC35 and Sony V6. I used a StraightWire cable.
The CDs used:
Schubert, Arpeggione Sonta for piano & cello, Decca 289 460 974-2
Sarah Vaughan, Crazy and Mixed Up, JVCXR-0204-2
Jose Pass, Virtuoso, XRCD2 VICJ-60256 (Japanese version)
Bob Dylan, Love and Theft
Joe Lovano, Flights of Fancy, Blue Note 72435 2761821
This last one was recorded live to 2 track analog tape and as a result of no mixing board it has very wide separation. I have a hard time hearing this on headphones without crossfeed, so this selection was used for the crossfeed tests.
The Amps:
The Porta-Corda (or PC from now on) and the Total Airhead (TA) size and weight are very close to each other. The TA is slightly smaller in front and larger in back and very slightly wider. The PC with battery weighs 5 oz and the TA just 1/4 oz less. The PC has a power LED which the TA doesn’t. The PC has all connections on the front panel whereas the input for the TA is on the side. This can be a pro or con depending on how you use it. The PC has a detachable belt clip (although it still doesn’t sit completely flat when it’s detached), and is quite attractive with it’s light colored case and blue metal faceplate. It also has a very small knob instead of the wheel type volume control on the TA. The knob is a little hard to turn; this is probably an advantage for portable use and a disadvantage for home use. They both seem to have long battery life, as does the CHL. I put the CHL in a Serpac case which is only slightly larger than the other two. I was going to put it in an Altoids tin but the switches were a little too big with everything else so it didn’t quite fit. All seem to be free of any hiss or pops.
I used two Energizer AA size batteries for the TA (Nickel Hydride also works) and a Plainview 9.6v Nickel metal Hydride batteries (one each) for the other two. Note that most Nickel hydride 9v batteries are only 7.2 volts; they’ll work, but maybe not sound quite as good so I used the high voltage ones. I also did a brief comparison with the full size Corda, and tried the PC with a regulated variable external supply up to 26 volts. In doing so I checked out Jan’s circuit to prevent damage when the supply terminals are reversed…luckily this circuitry works great! For you tweekers out there, the PC has soldered in op amps, unlike my Corda (my Corda was a kit and the PC was fully assembled, in case it matters). The PC had been run (mostly at 26v) for at least 30 hours, the CHL probably about half that. The TA is about a year old and has had at least 50 hours of use. During the testing none had been extensively warmed up, but during the course of the testing they had been on for a couple of hours.
The Sound without crossfeed:
All three amps sounded much better than the headphone output of the Panasonic directly; cleaner and much better bass. The differences between these three amps was much smaller than the differences between the three different headphones that I used. No matter what CD was playing or which headphones I used, the basic character of each amp was pretty consistent: the TA sounded more laid back and relaxed, the PC was much more aggressive and livelier. CHL was in between the two but much closer to the PC than the TA. With good sounding CDs and well balanced headphones I liked the fast, crisp sound of the PC, but there were some songs on the Dylan CD using the Koss KSC35 where the PC sounded a little bit too aggressive and was a little fatiguing after a while. There wasn’t a big difference in soundstage between the three but it seemed on occasion to be slightly wider on the PC and the least wide on the TA. The bass was very good on all three but again the PC seemed to have a slight edge with the most powerful bass, the TA the least, and as usual the CHL was in between but closer to the PC. The big Corda seemed to be more transparent and have a fuller, more open sound than any of the portables. I did try the PC briefly with higher voltages up to 26 volts from the regulated supply hooked to the battery terminals. I didn’t really notice any big difference in the sound, but maybe there would be with some harder to drive headphones. I’ll try that later.
The Sound with crossfeed:
The PC and CHL both have the Meier crossfeed so it’s no surprise that they sounded similar. What was surprising is that the PC seemed to loose some bass when the crossfeed was turned on, much more than the CHL or the big Corda where the loss is barely noticeable. This resulted in the CHL having more bass than the PC when the crossfeed was on. The TA crossfeed boosts the bass and cuts the treble, thus making a bigger impact on the sound. This is the only HeadRoom amp that doesn’t have the filter switch to bring back the treble, something I think it needs (if the filter was always switched on when the processor was on this would be fine). All seem to do an equally good job of reducing the extreme stereo effect that is on some recordings like the Joe Lovano CD.
Measurements (without crossfeed):
The PC measures flat within 0.1dB from 20 to 20kHz. The TA was down only 0.2dB at 20 Hz and had the old HeadRoom rolloff of 2.4dB at 20kHz. The CHL had no rolloff at the high end but was down 0.5dB at 20Hz. I wouldn’t expect to be able to hear any of these low frequency rolloffs, given that headphones roll off much more at 20 Hz. I also measured total harmonic distortion at typical listening levels, and all three amps were very close to the resolution of my test equipment (around 0.035%) at any frequency.
SUMMARY:
These are all very good portable amps that should improve the sound of most portable equipment, and probably a lot of home equipment too. If I had really clean sources and smooth or laidback headphones then the Porta-Corda is a good choice, or if you’re into DIY stuff then I can certainly recommend the CHL. If I had a bright source or headphones that needed a little taming, or wanted some extra bass when using crossfeed, then the TA is a good choice.
