kelly
Herr Babelfish der Übersetzer, he wore a whipped-cream-covered tutu for this title.
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- Jan 1, 2002
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Corda HA-1 / Corda Blue
Be forewarned: This is a somewhat strange and unusual review. First, this is actually a review of two products. One is the Corda HA-1 available from Meier-Audio. The other is the modifications designed and implemented by KurtW. I'll do my best to make clear the distinction of when I'm talking about the Corda HA-1 and when I'm talking about the modified unit, but be aware of it if you intend to skim. Second, reviews of modifications are somewhat unusual in and of themselves so this will be a bit of an experiment.
As with all my reviews, the following disclaimer must be stated. What follows are my unscientific objective opinion without the aid of any measuring devices. My opinions reflect my views alone and should not be misconstrued to represent HeadFi, HeadFi's sponsors, the moderators KurtW or Meier-Audio. Additionally, I encourage every reader to take any review with a grain of salt. One could add the following phrases to any statement made in a review like this: "to my ears", "in my system" and "in my opinion."
Associated Equipment:
Brick Wall PW8R15AUD surge protector
Sony XA777ES SACD/CD
Sony S7000 DVD/CD used as a transport
ART DI/O DAC with modifications and custom PSU by Bolder Cable
Etymotic ER-4S headphone
Grado HP-2 headphone
Sennhsier HD600 headphone
Amplifiers available for direct AB comparison of stock Corda HA-1:
ASL MG Head OTL
AudioValve RKV Mk II
Headroom Little
Headroom Max
McCormack Micro Integrated Drive
Amplifiers available for direct AB comparison of Corda Blue:
AudioValve RKV Mk II
Headroom Maxed Out Home Reference with Stepped Attenuator
Headroom Max with Stepped Attenuator
McCormack Micro Integrated Drive
Sugden Headmaster
Corda HA-1
Pictured here is the Corda HA-1 from Meier-Audio. The amplifier carries a kit price of $275 and an assembled price of $345. Meier only sells direct so this is the set price. I'm told the kit is not that difficult and the included instructions are good but Meier suggests that this project may still be a bit much for a first project. Those of you who have already built a headphone amp or two might rather save the $70 and spend the 4-5 hours enjoying another aspect of this hobby.
The amplifier measures at 6”x6.5”x2” which is small enough to be “totable” to work. Thus, the Corda instantly found a happy home with me as I could take it to work in my backpack. The image shown here is from Meier's website and is actually the kit version. For whatever reason, the kit version has silver screws while the assembled versions have black screws. It's a small thing and the black screws can be easily ordered from elsewhere if you're determined to have black.
From this photo, you can easily see my biggest pet peev of the amplifier, its inclusion of 1/8” jacks rather than 1/4” jacks. Most people only have headphones with stock cables which today are commonly terminated to 1/8”. This is the reasoning Jan Meier used to explain the decision. For my taste, I believe too many headphone enthusiasts who are involved in the hobby enough to buy a headphone amplifier are also in danger of buying after market cables and the like that are typically terminated in 1/4”. I'd also reason that if there were any quality loss, it's more likely to occur going from 1/8” to 1/4” than vice versa. To put this issue to rest, I heartily recommend the Grado 1/4” adapter cable. The cable puts less tension on the jacks than a standard adapter and seem to do the job nicely.
You'll notice there's two of these 1/8” jacks on the left side. The first is marked 120ohm while the second is marked 0ohm. Meier says the 120ohm jack is an international standard and is the reason for its inclusion. For me, I've plugged many a headphone into the Corda HA-1 and have thus far preferred only the Beyerdynamic DT931 out of the 120ohm jack. With that particular headphone, its slightly bright nature is tamed and the DT931 becomes an excellent balanced headphone. With every single other headphone I have tried, the 0ohm jack is preferred. The budget minded should take note here--Meier tends to offer a discount because of the combined shipping when more than one product is ordered and he does sell the DT931 for a good price.
Moving to right, you'll see a four position switch. This is the Meier Natural Crossfeed. The leftmost position is its “off” position and bipasses the crossfeed entirely. The other three settings are different amounts. The rightmost position has the greatest amount of crossfeed.
Some of you may wonder just what crossfeed is and why anyone would want this feature. To add to the confusion, not all crossfeeds are the same. Keep this in mind when reading reviews of other amplifiers. For the Corda take on crossfeed, the circuit “simply” take the sound of the left channel and creates a very soft and slightly delayed copy of that signal to the right channel, and vice versa. With speakers, your right ear naturally hears part of what comes from the left speaker and vice versa. The crossfeed circuit mimics this behavior making the presentation more natural and less isolated to each ear.
The crossfeed is especially useful for older recording in which stereo was still somewhat experimental. Albums like the first Doors album, the Beatles' Magical Mystery Tour and the original release of the Fantasia soundtrack are great examples of recordings that had experimental stereo seperation such as putting all of the sound in the one channel briefly or putting the drums or some other instrument exclusively in one channel. For many people, this makes headphone listening less enjoyable. Sometimes it is distracting while other times, it's headache inducing. Crossfeed solves this completely. Magical Mystery Tour becomes an excellent headphone album with the crossfeed engaged.
But the crossfeed isn't perfect. For one thing, many people perceive a slight bass drop due to what Meier calls a psychoacoustic effect. In essence, this is due to most people perceiving bass exclusive to one ear as being slightly louder than bass that is heard by both ears. For me, the bass loss is minimal but it's noticable if I'm listening for it, so it's worth mentioning. The second issue is that some more modern pop recordings have a lot of special effects. With the crossfeed on a stronger setting, normal quick pans can sometimes sound “reverby” (to borrow a word from out dear Vertigo, Jpop afficionado). For this reason, I tend to leave the setting on its “low” setting for pop recordings. I use the second setting for live music, well recorded rock music, classical and jazz. The last setting for me brings the soundstage a little too far in and doesn't get much use from me. Still, it's nice to have options.
The effects of the crossfeed are very “natural” and transparent compared to Headroom's crossfeed circuit. My perception of the Corda's crossfeed leaves the image “in the head” but with a more natural pan from left to right. The Headroom crossfeed attempts to bend the image outward so that it sounds more in front of you. I haven't yet listened to the Headroom's processor enough to have a real opinion on whether I like this effect or not, but it's certainly more noticable and also seems to incur a slight high frequency rolloff and midbass boost where the Corda's frequency response is untouched.
Finally, on the far right side of the amp is a volume knob, in this case the Alps Blue that HeadFi DIYers are so familliar with and the sampe potentiometer that is found in the Sugden Headmaster. The Alps Blue is known for good tracking and has a smooth solid feel to it. This is one part is said to be a large part of the amplifiers parts cost.
The back side of the amplifier is a bit simpler. Only one pair of RCA jacks and a rocker on/off switch appear. Here, we're reminded that the Corda HA-1 is a budget amp. There aren't muliple inputs like the Headroom Max and Sugden have and there's no tape out either, meaning if you use this component in a larger rig, it has to be the component in which the signal terminates. If you were hoping to use this as a preamp, you'll have to either look elsewhere or wait for Meier Audio's next major product, a full sized preamp/headphone amp.
The case itself is a black metal case adorned with front and back anodized black faceplates. This gives the amplifier a very solid and professional look. When I first pulled my Corda out of its neatly packed box, my first thought was to be impressed by its craftsmanship.
Remember, I said this was a budget amplifier and doesn't have all the bells and whistles of the more expensive preamp/headphone amps, right? This helps the amplifier achieve its low price but sometimes one has to wonder if a low price point can hurt a products perception of value in the minds of consumers. Because the ampliefier can be had for only $345 assembled (and shipped), some want to class it with the cheaper amps. Let me put that to rest here. The Corda HA-1 does NOT belong in the same class as the CMOY, CHA47, Creek OBH-11 or Grado RA-1. It simply outclasses all of these ampliefiers in every respect.
The Headroom Little has Headroom's own version of crossfeed. If you like the Headroom crossfeed, the Little might be a consideration. The Little also has a sort of “upgrade path” in that you can buy Headroom's upgraded power supply and send the amplifier in to have its module upgraded. Its for these reasons that the Little remains a competitor. In sound alone, the base Little is also outclassed by the Corda HA-1. In comparison, the Little sounds weak and grainy. Certainly the Little is better than the headphone jacks on most components, but the Corda is a solid step up in terms of speed, accuracy, bass and high frequency extension and clarity.
On the tube side of things, the MG Head betters the Corda in its strength--midrange. The midrange of the Head is so smooth and sweet as to make you wonder if you're listening to a much more expensive component. But where the Corda may not take the MG Head in this way, it does have the high and low frequency extension that the Head is so sorely lacking. The Corda also has a better sense of tonal balance and speed. The Corda is not the best amplifier in all respects, but it is good at everything. For an amplifier at this cost, the Corda is just amazingly well rounded.
Suddenly, the Corda is left with nothing to compete with by amplifiers far more expensive than itself. Here is where I can make some better comments about how the Corda sounds. Compared to the Max and Maxed Out Home, the Corda has slightly better high frequency detail that leaves you with the impression that the amplifier has slightly better extension. Of course, both amps measure flat with test tones but that's still how some people would describe it. The Max family of amps still offer far better bass performance, better blackness, speed and smoothness. The Corda sounds just slightly grainy when comparing to the smoothness of the high end Headroom amps.
The Sugden Headmaster is the one real competitor to the Corda. While the Corda and Headroom amps played a little bit of give and take, the Headmaster in my brief auditions was was preferable to the Corda in every way. Unfortunately, I didn't get to AB compare the stock Corda to the Headmaster, but from my memory, the Sugden is faster, smoother, cleaner, more powerful and all of the high frequency detail, texture and ambience was left in tact. This gives one pause for thought--if you need the switching or tape out of the Sugden or can simply afford to pay over twice as much, the Sugden is probably the better amp. It's not such a bad amp to lose to, though, and Meier's forthcoming preamp/headphone amp should be closer to the Sugden's pricepoint. Rematch, anyone?
In short, the Corda HA-1 is simply an excellent value. If you're looking for a commercial amplifier under $400, it's easily the best, most well rounded and versatile amplifier you could ask for.
Corda Blue
But wait... there's more. Remember the first time you squeased a bottle of hershey's syrup over a bowl of ice cream. Oh, the ice cream was good already, but you'd found a way to make it better. As good as the Corda was, it was just begging to be upgraded. KurtW thought so too and decided to put some time into experimenting with the Corda to figure out just how it could be upgraded and which parts would really make a difference.
Kurt decided to use the name Corda Blue to distinguish his modded Corda from the stock HA-1. I'm sure this has something to do with turkey and cheese, but Kurt said it was due to the addition of the cool looking blue LED power indicator that he replaced the stock red one with.
stock Corda HA-1 (above)
Corda Blue (above)
As you can see, there are a number of differences here. As some of you already know, I'm not the world's most technical person and I'm still learning that side of the hobby. To put it frankly to those of you who are more technical, here's a list of what all was added or altered:
2x OPA637
4x BUF634
2x Avid IC heatsink + adhesive
4x Schottky diode NTE585
1x blue LED B4303F6-1
4x Resistors
2x Wima FKP2 680pF
4x Wima MKP2 220nF
2x Wima MKP2 100nF
2x Wima MKS2 1.0uF
1x Pair Cardas jacks GRFA
2x 2N5484 FET
2x 2N5486 FET
From that list, I can tell you the jacks and the LED weren't really required.
Kurt says the parts total at just under $100 and the labor is around six hours. If you're interested in having him mod yours for you, he'd prefer to be contacted directly to discuss costs. If you're interested in doing the mods yourself, one thread is already running in the DIY section here at HeadFi and Kurt seems pretty willing to lend his expertise on the matter.
But come on, you gotta do the cool stuff too if you're going to get something modded and the Cardas jacks are nice. In fact, they're the jacks the Headroom amps use. A resistor was used with the blue LED so it's not quite as bright as some components are. I have to admit, I dig it. I'm a fan of the blue LED.
That aside, the real thing you can see from this list is that the opamp has been changed to the opa637 with the 634 as a buffer and the a cascode current source of FETs was used to bias the amp into Class A. I got to hear the amplifier in direct AB comparison before the FETs were added and to tell you the truth, it wasn't all that different. The opamp was a little smoother than the LT one Meier had chosen but the differences were subtle.
After the FETs were added--the amplifier had been transformed. The final amp sounds much different from the stock amplifier. Texture and ambient detail are brought to a level that made me unwilling to hang on to my stock McCormack Micro Integrated, an amp I formerly considered a champion of texture and detail. And the grain? Gone. The Corda Blue now exceeds the Max family of amplifiers even in smoothness--yet without giving up that edge in detail.
The bass response of the modded unit is also improved dramatically. Of course, the Corda still doesn't catch the Max or RKV in this department but it's much better than the stock unit, which was already besting the McCormack and all of the other budget amps. The Corda still couldn't get there in terms of speed and blackness either. I'm inclined to believe the Max's power supply and dual circuitry can be credited for these qualities in the Max, though I really have nothing to base such a belief in. Just call it a hunch.
And finally... the Sugden Headmaster. Amazingly, the Sugden is still smoother, faster, and more powerful sounding than the Corda. The Corda Blue and Headmaster have slightly different personalities meaning it'd not be hard for me to believe that someone could prefer the modded Corda, but I'd have trouble putting my finger on what that quality would be to win someone over right now. For my taste, the Headmaster is still ahead of the Corda Blue. Kurt described the Corda Blue as being at a midpoint between the stock Corda and the Headmaster and I'd have to agree. Still, the Corda had a good showing and manages to do what it does in a case far less than half the size of the Headmaster.
For me, the Corda Blue is the ultimate in “totable” amps. It's made my work place a lot more fun place to be and I love having an amp of such high quality that I can take with me. The modded unit is incredible, but I'm still open to exploring a few more things before laying it to rest. Notably, one has to wonder what could be done in terms of upgrading the power supply. Maybe it won't make a difference. I have a feeling you'll hear me rambling on about it either way.
Meanwhile, Jan Meier would do well to take note of Kurt's findings. While the overpriced jacks and blue LED may not fit in with Meier Audio's current business philosophy, FET driven cascode current source seems to good an improvement to not look into. Researching the different opamps available and applying some of these techniques could really push the next product in the Meier line into the high end realm. Hopefully it'll work out. For me, I'll look forward to hearing anything from either of these guys.
Photos provided by Jan Meier and KurtW.
Be forewarned: This is a somewhat strange and unusual review. First, this is actually a review of two products. One is the Corda HA-1 available from Meier-Audio. The other is the modifications designed and implemented by KurtW. I'll do my best to make clear the distinction of when I'm talking about the Corda HA-1 and when I'm talking about the modified unit, but be aware of it if you intend to skim. Second, reviews of modifications are somewhat unusual in and of themselves so this will be a bit of an experiment.
As with all my reviews, the following disclaimer must be stated. What follows are my unscientific objective opinion without the aid of any measuring devices. My opinions reflect my views alone and should not be misconstrued to represent HeadFi, HeadFi's sponsors, the moderators KurtW or Meier-Audio. Additionally, I encourage every reader to take any review with a grain of salt. One could add the following phrases to any statement made in a review like this: "to my ears", "in my system" and "in my opinion."
Associated Equipment:
Brick Wall PW8R15AUD surge protector
Sony XA777ES SACD/CD
Sony S7000 DVD/CD used as a transport
ART DI/O DAC with modifications and custom PSU by Bolder Cable
Etymotic ER-4S headphone
Grado HP-2 headphone
Sennhsier HD600 headphone
Amplifiers available for direct AB comparison of stock Corda HA-1:
ASL MG Head OTL
AudioValve RKV Mk II
Headroom Little
Headroom Max
McCormack Micro Integrated Drive
Amplifiers available for direct AB comparison of Corda Blue:
AudioValve RKV Mk II
Headroom Maxed Out Home Reference with Stepped Attenuator
Headroom Max with Stepped Attenuator
McCormack Micro Integrated Drive
Sugden Headmaster
Corda HA-1
Pictured here is the Corda HA-1 from Meier-Audio. The amplifier carries a kit price of $275 and an assembled price of $345. Meier only sells direct so this is the set price. I'm told the kit is not that difficult and the included instructions are good but Meier suggests that this project may still be a bit much for a first project. Those of you who have already built a headphone amp or two might rather save the $70 and spend the 4-5 hours enjoying another aspect of this hobby.
The amplifier measures at 6”x6.5”x2” which is small enough to be “totable” to work. Thus, the Corda instantly found a happy home with me as I could take it to work in my backpack. The image shown here is from Meier's website and is actually the kit version. For whatever reason, the kit version has silver screws while the assembled versions have black screws. It's a small thing and the black screws can be easily ordered from elsewhere if you're determined to have black.
From this photo, you can easily see my biggest pet peev of the amplifier, its inclusion of 1/8” jacks rather than 1/4” jacks. Most people only have headphones with stock cables which today are commonly terminated to 1/8”. This is the reasoning Jan Meier used to explain the decision. For my taste, I believe too many headphone enthusiasts who are involved in the hobby enough to buy a headphone amplifier are also in danger of buying after market cables and the like that are typically terminated in 1/4”. I'd also reason that if there were any quality loss, it's more likely to occur going from 1/8” to 1/4” than vice versa. To put this issue to rest, I heartily recommend the Grado 1/4” adapter cable. The cable puts less tension on the jacks than a standard adapter and seem to do the job nicely.
You'll notice there's two of these 1/8” jacks on the left side. The first is marked 120ohm while the second is marked 0ohm. Meier says the 120ohm jack is an international standard and is the reason for its inclusion. For me, I've plugged many a headphone into the Corda HA-1 and have thus far preferred only the Beyerdynamic DT931 out of the 120ohm jack. With that particular headphone, its slightly bright nature is tamed and the DT931 becomes an excellent balanced headphone. With every single other headphone I have tried, the 0ohm jack is preferred. The budget minded should take note here--Meier tends to offer a discount because of the combined shipping when more than one product is ordered and he does sell the DT931 for a good price.
Moving to right, you'll see a four position switch. This is the Meier Natural Crossfeed. The leftmost position is its “off” position and bipasses the crossfeed entirely. The other three settings are different amounts. The rightmost position has the greatest amount of crossfeed.
Some of you may wonder just what crossfeed is and why anyone would want this feature. To add to the confusion, not all crossfeeds are the same. Keep this in mind when reading reviews of other amplifiers. For the Corda take on crossfeed, the circuit “simply” take the sound of the left channel and creates a very soft and slightly delayed copy of that signal to the right channel, and vice versa. With speakers, your right ear naturally hears part of what comes from the left speaker and vice versa. The crossfeed circuit mimics this behavior making the presentation more natural and less isolated to each ear.
The crossfeed is especially useful for older recording in which stereo was still somewhat experimental. Albums like the first Doors album, the Beatles' Magical Mystery Tour and the original release of the Fantasia soundtrack are great examples of recordings that had experimental stereo seperation such as putting all of the sound in the one channel briefly or putting the drums or some other instrument exclusively in one channel. For many people, this makes headphone listening less enjoyable. Sometimes it is distracting while other times, it's headache inducing. Crossfeed solves this completely. Magical Mystery Tour becomes an excellent headphone album with the crossfeed engaged.
But the crossfeed isn't perfect. For one thing, many people perceive a slight bass drop due to what Meier calls a psychoacoustic effect. In essence, this is due to most people perceiving bass exclusive to one ear as being slightly louder than bass that is heard by both ears. For me, the bass loss is minimal but it's noticable if I'm listening for it, so it's worth mentioning. The second issue is that some more modern pop recordings have a lot of special effects. With the crossfeed on a stronger setting, normal quick pans can sometimes sound “reverby” (to borrow a word from out dear Vertigo, Jpop afficionado). For this reason, I tend to leave the setting on its “low” setting for pop recordings. I use the second setting for live music, well recorded rock music, classical and jazz. The last setting for me brings the soundstage a little too far in and doesn't get much use from me. Still, it's nice to have options.
The effects of the crossfeed are very “natural” and transparent compared to Headroom's crossfeed circuit. My perception of the Corda's crossfeed leaves the image “in the head” but with a more natural pan from left to right. The Headroom crossfeed attempts to bend the image outward so that it sounds more in front of you. I haven't yet listened to the Headroom's processor enough to have a real opinion on whether I like this effect or not, but it's certainly more noticable and also seems to incur a slight high frequency rolloff and midbass boost where the Corda's frequency response is untouched.
Finally, on the far right side of the amp is a volume knob, in this case the Alps Blue that HeadFi DIYers are so familliar with and the sampe potentiometer that is found in the Sugden Headmaster. The Alps Blue is known for good tracking and has a smooth solid feel to it. This is one part is said to be a large part of the amplifiers parts cost.
The back side of the amplifier is a bit simpler. Only one pair of RCA jacks and a rocker on/off switch appear. Here, we're reminded that the Corda HA-1 is a budget amp. There aren't muliple inputs like the Headroom Max and Sugden have and there's no tape out either, meaning if you use this component in a larger rig, it has to be the component in which the signal terminates. If you were hoping to use this as a preamp, you'll have to either look elsewhere or wait for Meier Audio's next major product, a full sized preamp/headphone amp.
The case itself is a black metal case adorned with front and back anodized black faceplates. This gives the amplifier a very solid and professional look. When I first pulled my Corda out of its neatly packed box, my first thought was to be impressed by its craftsmanship.
Remember, I said this was a budget amplifier and doesn't have all the bells and whistles of the more expensive preamp/headphone amps, right? This helps the amplifier achieve its low price but sometimes one has to wonder if a low price point can hurt a products perception of value in the minds of consumers. Because the ampliefier can be had for only $345 assembled (and shipped), some want to class it with the cheaper amps. Let me put that to rest here. The Corda HA-1 does NOT belong in the same class as the CMOY, CHA47, Creek OBH-11 or Grado RA-1. It simply outclasses all of these ampliefiers in every respect.
The Headroom Little has Headroom's own version of crossfeed. If you like the Headroom crossfeed, the Little might be a consideration. The Little also has a sort of “upgrade path” in that you can buy Headroom's upgraded power supply and send the amplifier in to have its module upgraded. Its for these reasons that the Little remains a competitor. In sound alone, the base Little is also outclassed by the Corda HA-1. In comparison, the Little sounds weak and grainy. Certainly the Little is better than the headphone jacks on most components, but the Corda is a solid step up in terms of speed, accuracy, bass and high frequency extension and clarity.
On the tube side of things, the MG Head betters the Corda in its strength--midrange. The midrange of the Head is so smooth and sweet as to make you wonder if you're listening to a much more expensive component. But where the Corda may not take the MG Head in this way, it does have the high and low frequency extension that the Head is so sorely lacking. The Corda also has a better sense of tonal balance and speed. The Corda is not the best amplifier in all respects, but it is good at everything. For an amplifier at this cost, the Corda is just amazingly well rounded.
Suddenly, the Corda is left with nothing to compete with by amplifiers far more expensive than itself. Here is where I can make some better comments about how the Corda sounds. Compared to the Max and Maxed Out Home, the Corda has slightly better high frequency detail that leaves you with the impression that the amplifier has slightly better extension. Of course, both amps measure flat with test tones but that's still how some people would describe it. The Max family of amps still offer far better bass performance, better blackness, speed and smoothness. The Corda sounds just slightly grainy when comparing to the smoothness of the high end Headroom amps.
The Sugden Headmaster is the one real competitor to the Corda. While the Corda and Headroom amps played a little bit of give and take, the Headmaster in my brief auditions was was preferable to the Corda in every way. Unfortunately, I didn't get to AB compare the stock Corda to the Headmaster, but from my memory, the Sugden is faster, smoother, cleaner, more powerful and all of the high frequency detail, texture and ambience was left in tact. This gives one pause for thought--if you need the switching or tape out of the Sugden or can simply afford to pay over twice as much, the Sugden is probably the better amp. It's not such a bad amp to lose to, though, and Meier's forthcoming preamp/headphone amp should be closer to the Sugden's pricepoint. Rematch, anyone?
In short, the Corda HA-1 is simply an excellent value. If you're looking for a commercial amplifier under $400, it's easily the best, most well rounded and versatile amplifier you could ask for.
Corda Blue
But wait... there's more. Remember the first time you squeased a bottle of hershey's syrup over a bowl of ice cream. Oh, the ice cream was good already, but you'd found a way to make it better. As good as the Corda was, it was just begging to be upgraded. KurtW thought so too and decided to put some time into experimenting with the Corda to figure out just how it could be upgraded and which parts would really make a difference.
Kurt decided to use the name Corda Blue to distinguish his modded Corda from the stock HA-1. I'm sure this has something to do with turkey and cheese, but Kurt said it was due to the addition of the cool looking blue LED power indicator that he replaced the stock red one with.
stock Corda HA-1 (above)
Corda Blue (above)
As you can see, there are a number of differences here. As some of you already know, I'm not the world's most technical person and I'm still learning that side of the hobby. To put it frankly to those of you who are more technical, here's a list of what all was added or altered:
2x OPA637
4x BUF634
2x Avid IC heatsink + adhesive
4x Schottky diode NTE585
1x blue LED B4303F6-1
4x Resistors
2x Wima FKP2 680pF
4x Wima MKP2 220nF
2x Wima MKP2 100nF
2x Wima MKS2 1.0uF
1x Pair Cardas jacks GRFA
2x 2N5484 FET
2x 2N5486 FET
From that list, I can tell you the jacks and the LED weren't really required.
Kurt says the parts total at just under $100 and the labor is around six hours. If you're interested in having him mod yours for you, he'd prefer to be contacted directly to discuss costs. If you're interested in doing the mods yourself, one thread is already running in the DIY section here at HeadFi and Kurt seems pretty willing to lend his expertise on the matter.
But come on, you gotta do the cool stuff too if you're going to get something modded and the Cardas jacks are nice. In fact, they're the jacks the Headroom amps use. A resistor was used with the blue LED so it's not quite as bright as some components are. I have to admit, I dig it. I'm a fan of the blue LED.
That aside, the real thing you can see from this list is that the opamp has been changed to the opa637 with the 634 as a buffer and the a cascode current source of FETs was used to bias the amp into Class A. I got to hear the amplifier in direct AB comparison before the FETs were added and to tell you the truth, it wasn't all that different. The opamp was a little smoother than the LT one Meier had chosen but the differences were subtle.
After the FETs were added--the amplifier had been transformed. The final amp sounds much different from the stock amplifier. Texture and ambient detail are brought to a level that made me unwilling to hang on to my stock McCormack Micro Integrated, an amp I formerly considered a champion of texture and detail. And the grain? Gone. The Corda Blue now exceeds the Max family of amplifiers even in smoothness--yet without giving up that edge in detail.
The bass response of the modded unit is also improved dramatically. Of course, the Corda still doesn't catch the Max or RKV in this department but it's much better than the stock unit, which was already besting the McCormack and all of the other budget amps. The Corda still couldn't get there in terms of speed and blackness either. I'm inclined to believe the Max's power supply and dual circuitry can be credited for these qualities in the Max, though I really have nothing to base such a belief in. Just call it a hunch.
And finally... the Sugden Headmaster. Amazingly, the Sugden is still smoother, faster, and more powerful sounding than the Corda. The Corda Blue and Headmaster have slightly different personalities meaning it'd not be hard for me to believe that someone could prefer the modded Corda, but I'd have trouble putting my finger on what that quality would be to win someone over right now. For my taste, the Headmaster is still ahead of the Corda Blue. Kurt described the Corda Blue as being at a midpoint between the stock Corda and the Headmaster and I'd have to agree. Still, the Corda had a good showing and manages to do what it does in a case far less than half the size of the Headmaster.
For me, the Corda Blue is the ultimate in “totable” amps. It's made my work place a lot more fun place to be and I love having an amp of such high quality that I can take with me. The modded unit is incredible, but I'm still open to exploring a few more things before laying it to rest. Notably, one has to wonder what could be done in terms of upgrading the power supply. Maybe it won't make a difference. I have a feeling you'll hear me rambling on about it either way.
Meanwhile, Jan Meier would do well to take note of Kurt's findings. While the overpriced jacks and blue LED may not fit in with Meier Audio's current business philosophy, FET driven cascode current source seems to good an improvement to not look into. Researching the different opamps available and applying some of these techniques could really push the next product in the Meier line into the high end realm. Hopefully it'll work out. For me, I'll look forward to hearing anything from either of these guys.
Photos provided by Jan Meier and KurtW.
