Extensive compressor reviews and FAQ

Aphex 651: This is the predecessor of their 661 model, so be sure to read that review for the details. The primary difference is that the 661 includes a tube gain stage and the older 651 has no tube. The audible difference is small, however. The tube in the 661 may add a bit of subtle richness to the signal, but the 661 is known more for transparency than coloration; the 651 is even a little more transparent yet--it's one of the most transparent compressors I've heard. Playing through it I do not lose any of the subtle nuances of tone or texture that some other compressors may dampen or muddy up. The HFX expander especially helps with this. One other difference compared to the 661 is that the 651 does not run hot, so it is much more suited to use in a gig rack with minimal ventilation. For effective limiting, smooth natural compression, and transparency of sound there is pretty much nothing better available, for the low price at which these can be found.
 
Be aware that as with all old gear, there is always a chance that the unit you buy will have problems. As much as I praise this unit, odds are good that it will need a recap or other servicing for best results. There are companies such as Audio Upgrades and Revive Music that will go further and replace a number of components for even lower noise and better fidelity, so that's another option. I had intended to send this one I tested off to one of them for the mods, and report back about the results; but between the price of the service and shipping both ways, and the price of buying a second unmodded unit for A/B comparison, I just couldn't justify the cost yet. I'll try to do this at some point in the future--and I'll write about it here just as soon as that happens.
 
Price in USD: used $100-$300 depending on condition, source, and modifications/upgrades. No longer available new.
 

 

 
 
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