M Jarve
Audio Geek and NGE Freak
When I first started getting into the 2-channel hobby, much of what I used was pro-gear. Indeed, for some time my main 2-channel system consisted of Peavey 1210-H speakers, a Peavey CS-400 (and later CS-800) amplifier, and a Mackie 16-channel mixer, among other things.
While much of the stuff of that sort sounded good, it was not proper hi-fi as many of us know it. Pro gear, while being unusually robust and/or powerful, often trades out the lowest levels of detail or imaging, adds noise, or is noisy itself (cooling fans, humming transformers, small ground-loops, etc). This is all perfectly acceptable for sound reinforcement duty, where it's doubtful any "critical listening" is taking place, but, in a home environment, where I really only perform critical listening, it's distracting and becomes an issue.
So, long ago I traded away my huge, powerful amps for ones that had greater finesse, if not as much power. Large, highly sensitive speakers that required only a handful of watts to fill a large room over a limited range were given over to ones that require scores of watts just to wake up, but provide 20-20k frequency response and excellent mid-field imaging.
All that said, there is still space in my heart (and rack) for something that performs well and has the power and reliability of commercial kit. Yesterday, as I was enjoying some shopping in Duluth, I stopped by the Music-Go-Round and saw that they were selling a bunch of amps for a really good price. Among them were the above mentioned Peaveys, as well as units from QSC, Crown, Crest, and Yamaha. Indeed, they even had the "commercial" version of the M-4 for sale at a mere fraction of the price of it's home hi-fi sibling. As you might expect, much of this sort of secondhand pro-gear has been around the block (or several blocks), and the trade-off can be intimidating: of course scratches and gouges are in attendance (and in abundance); often times jacks are broken or even missing; knobs are missing or broken; and sometimes the gear stinks of cigarette smoke and booze.
Out of the pile of amps they had, I chose one that seemed to have suffered less in its life than the others. The fact that it also had a good reputation for quality sound and reliability was a welcome after thought.
The Yamaha P2350 is a pretty straight-forward power amp of the sort cherished by ammeter roadies. The front has a power switch and L-Pads for each channel, accompanied by status LEDs (signal and clipping). The back is a bit busier, with both TRS 1/4" and XLR quasi-balanced input jacks (a second set of TRS 1/4" jacks are also provided for loop-through support). Output jacks are standard 5-way binding posts.
Power-wise the model number says it all: Two channels, 350 watts between the two of them (175-watts per channel). Power output boosts to 250-WPC into 4-ohms, and the amp is apparently stable into loads as low as 2-ohms, though no specification is given. Being a pro-amp as it is, the unit can be bridged for mono operation, providing 500-watts into an 8-ohm load.
Before slotting it into my system, I stopped by MarkB's place to show off my spoils (and spin up a couple LP's I bought at Electric Fetus), and, as you might expect, being a collector of all things Yamaha, he had the service manual for my unit filed neatly away. Good thing, too, as I would simply have guessed at the proper calibration of the unit.
Once I got home, before slotting it into my system, I performed my now routine series of tests on it. This mostly establishes that the thing works and won't cause a catastrophic event the first time I use it.
DC offset was admirably low (less than 20mV deviation in either channel, improving as it warmed up), and the bias was off only by a bit. Power output with a 1kHz signal into a nominally 8-ohm load peaked out at a better than spec'd 192WPC channel (39.19VRMS), both channels driven. Into 4-ohms, it was just above the rated output at ~252WPC (31.75VRMS). Not extraordinary, but decent. At 2-ohms the power hit just shy of 287WPC (23.94VRMS) before it went into protect mode. Since, during the tests, the heatsinks never became even warm (staying at abient room temp) I think that there may be a current limiting circuit that keeps the amp from dying. Additionally, the output on the o'scope showed no sign of clipping before the amp went into protect mode during the 2-ohm test, indicating that there is current limiting going into play. In any event, the amp is usefully powerful for almost any purpose. As an aside, I did not test the amp with only a single channel driven, nor did I test it in bridged mode.
Construction-wise, the amp is pretty run-of-the-mill pro-amp. Most of the chassis is heavy sheetmetal, but in an novel twist, the heatsink assemblies form about 2/3 of the bottom of the chassis. The heatsinks are not themselves exposed, and are cooled by a set of 2-speed brushless DC fans, one for each channel. Internally, the central portion of the amp is dominated by a largeish 900VA EI core transformer. Towards the center-back is the input array, protection circuit, and additional power supply elements. The transformer feeds a large bridge rectifier, and power is smoothed by a single set of 15,000uFd caps. I've noted before that pro amps tend not to have substantial power reserves in the form of large banks of high-value caps, relying instead on larger, more capable power transformers meant for more continuous, high-power output (as opposed to many home amps, which combine a somewhat less capable power transformer designed for lower continuous ouput, but large amounts of capacitance to better handle dynamic peaks).
The amp circuit for each channel is a pretty basic affair; Output devices are a triple pair of 2SA1492/2SC3856. The output board and circuit is shared with the more powerful P2700, with the addition of 4 more output devices per channel. Indeed, by completing the output circuit, and installing the larger power transformer (and filter caps) one could conceivably upgrade the P2350 to a P2700. But, given that under ordinary circumstances the P2700 only costs $50 more, the value of doing so is questionable.
While I had it on the bench, and since I had the cover removed, I decided to disconnect the cooling fans. When the unit was powered on and idling, the fans were noticeably loud (akin to having a typical desktop computer powered up). Despite the enclosed design of the heatsinks, there seems to be adequate surface area as well as venting to alow this. After 2 hours of typical usage, the temp of the heatsinks hit only about 110-degrees F, so I'm pretty sure I'm in the clear here.
After going through the amp, calibrating it, measuring it, and so on, I slotted it into my system. First I used it full- range, then in various bi-amping configurations.
Full range, the amp performed well. While it does not have the ultimate resolution of my h/k 775's, there was no area that I could really find a fault with. If anything, its performance seemed a little on the polite side, given it's pro-grade status, but it did not seem overly reserved at all. Power to the speakers seemed plentiful and solid, with little sign of anything breaking down as high levels were reached. Occasionally the clipping lights would flicker, but you would be hard pressed to say that the amp was audibly clipping at that point. Imaging was so-so. Not super terrific, spooky-good, but not as bad as many other amps I've had. Mostly there was a lack of depth of the sort that I'm used to. Depth is a hard thing for amps to get right, in many occasions, but I can forgive it. L-R spatial cuing was as good as most amps, but the image did not often journey beyond the boundaries of the speakers. Tone seems to be dead neutral, leaning neither warm nor cool, and extension on both the low and high end seems to be very good. There was indeed a wonderful sense of "air" from the amp that I've not experiened with other pro amps. Bass extension also seemed to be quite good, but in terms of impact, it did not seem to match the h/k's, which is also not my experience with other pro amps.
Switching things around a bit, I put the system into a bi-amp configuration, but not crossed over at the line level, instead continuing to use the speakers' own crossover and running the amps full-range. While this is not as theoretically optimal as a full bi-amp setup, it does alow for a bit better dynamic range.
First I setup the Yamaha to power the mid-high end of the speakers (the drivers covering from ~200Hz on up), with the h/k's powering the Watkins woofer. This configuration gave me quite a bit more headroom and impact, but the fair to good imaging capability of the P2350 quickly became apparent. When run full-range, the excuse could be made that there was a lot more going on, but in this instance, the Yamaha showed its own capabilities were the limiting factor.
Swapping things around, putting the P2350 on the Watkins and the h/k's on high, proved to be the more optimal configuration. The setup gained a bit more "slam" in the bass regions, while retaining a coherent and high-resolution performance. The most surprising thing about this configuration, though, was that the P2350 seemed to sound just like an extension of the h/k 775's. There is no sense that "this amp is doing this and that amp doing that". I was indeed quite delighted by this observation. Very coherent perfomance between the amps.
Clearly, more listening is indicated, as well as a more thorough assessment of the amp's performance at low volumes (I've been cranking the system almost constantly). Additionally, I'm going to have to get a second set of ears in to verify my observations. But, I'm very pleased with the performance nonetheless.
Pictures (Inside and Out) possibly to follow.
While much of the stuff of that sort sounded good, it was not proper hi-fi as many of us know it. Pro gear, while being unusually robust and/or powerful, often trades out the lowest levels of detail or imaging, adds noise, or is noisy itself (cooling fans, humming transformers, small ground-loops, etc). This is all perfectly acceptable for sound reinforcement duty, where it's doubtful any "critical listening" is taking place, but, in a home environment, where I really only perform critical listening, it's distracting and becomes an issue.
So, long ago I traded away my huge, powerful amps for ones that had greater finesse, if not as much power. Large, highly sensitive speakers that required only a handful of watts to fill a large room over a limited range were given over to ones that require scores of watts just to wake up, but provide 20-20k frequency response and excellent mid-field imaging.
All that said, there is still space in my heart (and rack) for something that performs well and has the power and reliability of commercial kit. Yesterday, as I was enjoying some shopping in Duluth, I stopped by the Music-Go-Round and saw that they were selling a bunch of amps for a really good price. Among them were the above mentioned Peaveys, as well as units from QSC, Crown, Crest, and Yamaha. Indeed, they even had the "commercial" version of the M-4 for sale at a mere fraction of the price of it's home hi-fi sibling. As you might expect, much of this sort of secondhand pro-gear has been around the block (or several blocks), and the trade-off can be intimidating: of course scratches and gouges are in attendance (and in abundance); often times jacks are broken or even missing; knobs are missing or broken; and sometimes the gear stinks of cigarette smoke and booze.
Out of the pile of amps they had, I chose one that seemed to have suffered less in its life than the others. The fact that it also had a good reputation for quality sound and reliability was a welcome after thought.
The Yamaha P2350 is a pretty straight-forward power amp of the sort cherished by ammeter roadies. The front has a power switch and L-Pads for each channel, accompanied by status LEDs (signal and clipping). The back is a bit busier, with both TRS 1/4" and XLR quasi-balanced input jacks (a second set of TRS 1/4" jacks are also provided for loop-through support). Output jacks are standard 5-way binding posts.
Power-wise the model number says it all: Two channels, 350 watts between the two of them (175-watts per channel). Power output boosts to 250-WPC into 4-ohms, and the amp is apparently stable into loads as low as 2-ohms, though no specification is given. Being a pro-amp as it is, the unit can be bridged for mono operation, providing 500-watts into an 8-ohm load.
Before slotting it into my system, I stopped by MarkB's place to show off my spoils (and spin up a couple LP's I bought at Electric Fetus), and, as you might expect, being a collector of all things Yamaha, he had the service manual for my unit filed neatly away. Good thing, too, as I would simply have guessed at the proper calibration of the unit.
Once I got home, before slotting it into my system, I performed my now routine series of tests on it. This mostly establishes that the thing works and won't cause a catastrophic event the first time I use it.
DC offset was admirably low (less than 20mV deviation in either channel, improving as it warmed up), and the bias was off only by a bit. Power output with a 1kHz signal into a nominally 8-ohm load peaked out at a better than spec'd 192WPC channel (39.19VRMS), both channels driven. Into 4-ohms, it was just above the rated output at ~252WPC (31.75VRMS). Not extraordinary, but decent. At 2-ohms the power hit just shy of 287WPC (23.94VRMS) before it went into protect mode. Since, during the tests, the heatsinks never became even warm (staying at abient room temp) I think that there may be a current limiting circuit that keeps the amp from dying. Additionally, the output on the o'scope showed no sign of clipping before the amp went into protect mode during the 2-ohm test, indicating that there is current limiting going into play. In any event, the amp is usefully powerful for almost any purpose. As an aside, I did not test the amp with only a single channel driven, nor did I test it in bridged mode.
Construction-wise, the amp is pretty run-of-the-mill pro-amp. Most of the chassis is heavy sheetmetal, but in an novel twist, the heatsink assemblies form about 2/3 of the bottom of the chassis. The heatsinks are not themselves exposed, and are cooled by a set of 2-speed brushless DC fans, one for each channel. Internally, the central portion of the amp is dominated by a largeish 900VA EI core transformer. Towards the center-back is the input array, protection circuit, and additional power supply elements. The transformer feeds a large bridge rectifier, and power is smoothed by a single set of 15,000uFd caps. I've noted before that pro amps tend not to have substantial power reserves in the form of large banks of high-value caps, relying instead on larger, more capable power transformers meant for more continuous, high-power output (as opposed to many home amps, which combine a somewhat less capable power transformer designed for lower continuous ouput, but large amounts of capacitance to better handle dynamic peaks).
The amp circuit for each channel is a pretty basic affair; Output devices are a triple pair of 2SA1492/2SC3856. The output board and circuit is shared with the more powerful P2700, with the addition of 4 more output devices per channel. Indeed, by completing the output circuit, and installing the larger power transformer (and filter caps) one could conceivably upgrade the P2350 to a P2700. But, given that under ordinary circumstances the P2700 only costs $50 more, the value of doing so is questionable.
While I had it on the bench, and since I had the cover removed, I decided to disconnect the cooling fans. When the unit was powered on and idling, the fans were noticeably loud (akin to having a typical desktop computer powered up). Despite the enclosed design of the heatsinks, there seems to be adequate surface area as well as venting to alow this. After 2 hours of typical usage, the temp of the heatsinks hit only about 110-degrees F, so I'm pretty sure I'm in the clear here.
After going through the amp, calibrating it, measuring it, and so on, I slotted it into my system. First I used it full- range, then in various bi-amping configurations.
Full range, the amp performed well. While it does not have the ultimate resolution of my h/k 775's, there was no area that I could really find a fault with. If anything, its performance seemed a little on the polite side, given it's pro-grade status, but it did not seem overly reserved at all. Power to the speakers seemed plentiful and solid, with little sign of anything breaking down as high levels were reached. Occasionally the clipping lights would flicker, but you would be hard pressed to say that the amp was audibly clipping at that point. Imaging was so-so. Not super terrific, spooky-good, but not as bad as many other amps I've had. Mostly there was a lack of depth of the sort that I'm used to. Depth is a hard thing for amps to get right, in many occasions, but I can forgive it. L-R spatial cuing was as good as most amps, but the image did not often journey beyond the boundaries of the speakers. Tone seems to be dead neutral, leaning neither warm nor cool, and extension on both the low and high end seems to be very good. There was indeed a wonderful sense of "air" from the amp that I've not experiened with other pro amps. Bass extension also seemed to be quite good, but in terms of impact, it did not seem to match the h/k's, which is also not my experience with other pro amps.
Switching things around a bit, I put the system into a bi-amp configuration, but not crossed over at the line level, instead continuing to use the speakers' own crossover and running the amps full-range. While this is not as theoretically optimal as a full bi-amp setup, it does alow for a bit better dynamic range.
First I setup the Yamaha to power the mid-high end of the speakers (the drivers covering from ~200Hz on up), with the h/k's powering the Watkins woofer. This configuration gave me quite a bit more headroom and impact, but the fair to good imaging capability of the P2350 quickly became apparent. When run full-range, the excuse could be made that there was a lot more going on, but in this instance, the Yamaha showed its own capabilities were the limiting factor.
Swapping things around, putting the P2350 on the Watkins and the h/k's on high, proved to be the more optimal configuration. The setup gained a bit more "slam" in the bass regions, while retaining a coherent and high-resolution performance. The most surprising thing about this configuration, though, was that the P2350 seemed to sound just like an extension of the h/k 775's. There is no sense that "this amp is doing this and that amp doing that". I was indeed quite delighted by this observation. Very coherent perfomance between the amps.
Clearly, more listening is indicated, as well as a more thorough assessment of the amp's performance at low volumes (I've been cranking the system almost constantly). Additionally, I'm going to have to get a second set of ears in to verify my observations. But, I'm very pleased with the performance nonetheless.
Pictures (Inside and Out) possibly to follow.
Last edited:
