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Tweakers' Asylum: REVIEW: Borbely Audio Servo-50 Amplifier (SS) by ccd

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REVIEW: Borbely Audio Servo-50 Amplifier (SS) Review by ccd at Audio Asylum

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Part 1

You have probably seen ads for Borbely amps in Audio Electronics or Speaker Builder and wondered about them. Well, here is the story:

Borbely makes high-end kit amps, preamps and crossovers, both tube and SS.
The amp I'm building is a variation on the Servo-50 amp which was published in Audio Amatuer in 1993 or 1994. Erno Borbely has been designing amps for 20 or 30 years and is a widely respected amp designer. The consults and/or designs amps for commercial manufacturers such as Hafler.

Borbely kits are for the experienced kit builder ONLY. There are NO step-by-step instructions. At a minimum, you need to know how to wire a PCB from a stuffing guide and the ability to read schematics is preferable. If you want to modify the amp with Borbely's help, the ability to read schematics will be required. You will need a drill with various size bits to drill out holes that may not be large enough on the PCB. At some points in the instructions, an attachment will be indicated, but it will be left to you to figure out/decide on how it is going to be done. The cabinets are of high quality, but generally come UNDRILLED. A fair amount of drilling is required on a Borbely amp and there is no indication of the precise location of the hole. For example, the instructions for the Servo-50 will tell you to drill holes to attach 5 pairs of output devices both above and below the output board. The exact placement of these holes as well as the drilling is left to the builder. In addition to a drill, you will need a soldering iron, a variac, a digital volt meter, and preferably an oscilloscope. Also be advised that these are not simple amps; their complexity exceed that of many commercial designs. There are a lot of parts to be stuffed on the PCBs. You will need to test components before soldering them; we found several "dead" LEDs.

On the plus side: the fit and finish of the cabinets I order (Fisher) is excellent and the quality of parts used by Borbely is excellent as well. We are using some poly caps instead of the electrolytics provided in the kit, but we are using everything else. For example, 1% resistors are used and they have been within spec so far.

Borbely speaks excellent English and is VERY responsive to questions. He is also willing to adapt his products for the customer's use. We exchanged emails for several weeks regarding amp design changes for my particular use. I never felt rushed into a decision; he seems to really care about his customers getting the right amp for their application. For example, my system is bi-amped and I needed a powerful amp for my woofers. He agreed with me that BJTs generally produce better bass response and re-biased the driver board for BJTs and provided a schematic of the changes required on the driver board. He also provided significant input into my decision to build a 4 channel amp bridged to two channel to get at least 400wpc @ 4 ohms and provided a schematic for the bridging circuitry as well as showing the necessary modifications to make the amp balanced. However, it was left to me to implement the changes indicated in his schematics. Also, you may be able to incorporate future improvements made to the amp by Borbely.

The amp is still in the construction phase and in Part II, I will talk about how the amp sounds. In retrospect, the value presented by a Borbely amp really depends on its application. As a bass amp, the Borbely amp probably doesn't represent a great value. There are a number of amps on the used market which can do this duty. The one new amp which could do the job, the Krell KAV 250 is a $3500 amp with a street price of $2600 and even less used. The cost differential between the Borbely amp and the Krell really isn't enough to justify the hassle of building the Borbeley. There are two other factors to keep in mind: 1) you can audition commercial amps and find one you like unlike the Borbely which cannot be auditioned; and 2) kits have little or no resale value whereas an amp like the Krell would have a good resale value (generally 50% of retail).

The places where Borbely kits are a better value is for a preamp and as a high-end full-range (or upper range) amp. Personally, I am skeptical that preamps have any sound, so not being able to audition a preamp does not bother me that much. While Borbely amps are not cheap, his Millenium amp at about $2,000 for a 75wpc Class A design IS inexpensive compared to the cost of most Class A designs. If Borbely's claim is true that the Ribbon and Millenium amps can compete with other amps, regardless of price, then these amps are a true bargain. But again, you won't know how much you like (or dislike) the amp until you turn it on. By then your money will be spent on a product that cannot be returned and has little resale value. The sad fact of life is that the used market values equipment by the name on the product, and refuses to use their ears to make an independent judgment.

However, if you like to build amps and want input into the design you end up building, then Borbely could be the ticket. If all goes well with this amp, I'll probably build Borbely's Millenium amp.

Given the length of this review, I guess you now know why I'm breaking it into two parts.


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Topic - REVIEW: Borbely Audio Servo-50 Amplifier (SS) Review by ccd at Audio Asylum - ccd 09:58:00 04/26/00 ( 14)