McIntosh C2600 Tubed Preamplifier Review – Page 2

Q&A with John Henkel, Sr. Electronic Design Engineer, and Ron Cornelius, Product Manager

Rafe Arnott: What was the precis for change going from the C2500 to the C2600?

McIntosh Labs: “The main reason was to upgrade the Digital Audio section to include DXD, DSD, and our proprietary MCT signal handling.”  

RA: What improvements/updates was the company looking to make? The website notes the addition of HXD (Headphone Crossfeed Director) to the headphone amplifier, upgraded tube circuitry and “[an] advanced digital audio section.” Can you discuss these and other changes made in the new C2600?

ML: “The McIntosh HXD Circuitry restores the directionality component of the spatial sound stage normally heard with loudspeaker listening. The ‘advanced digital section’ is discussed above.”  

RA: The internal DAC lists support for up 32-bit/384kHz resolution PCM files, up to DSD256 and DXD 352.8kHz and DXD 384kHz. Can you discuss what type of DAC the company ended up using and why? And is the DSD transmission over USB DoP? Or is the stream being software converted to PCM before delivery to the DAC, or is PCM being converted to DSD like those DACs utilized by PS Audio, EMM Labs, Meitner, etc.? 

ML: “The Digital Audio PCB comes with an upgraded ESS9016 SABRE Ultra eight-channel, 32-bit Digital-to-Analog Converter (DAC) used in Quad-Balanced mode and six digital inputs consisting of two coax, three optical, one USB and one MCT for use with our MCT500 SACD/CD Transport. We don’t use a separate external re-clocking circuit before the DAC. Instead, to reduce jitter, we use a feature (ESS patented 32-bit Hyperstream DAC architecture and Time Domain Jitter Eliminator) that is built into the DAC (DNR of 124dB and THD+N of –110dB). The Digital section of the C2600 is fully-capable of native DSD decoding when used with a music program that supports this such as JRiver 24. It will also decode DoP files if that is how the files are received.”

 RA: The balanced design section of the C2600 is not entirely differential, i.e.; fully balanced, end-to-end, is the single-ended conversion happening internally via transformer or amplifier? And why was the choice made to not make the design fully balanced?

ML: “The single-ended conversion happens in the amplifier. The fully-balanced circuit size, the required doubling of parts count, and its related complexity was implemented in the top of the line C1100. Since the C2600 has very high specifications compared to competing designs, we feel it is the correct choice at this price point in our lineup. The balanced phase conversion is performed by a simple transistor as it is not required to change gain in any way.”  

RA: Can you talk to me about the design of the dual-chassis architecture and how critical that is for separating the analog and digital sections in the C2600?

ML: “The split-chassis design is another way to increase signal-to-noise ratio. Since we build all of our chassis, we have adopted this design throughout many products. Shielding of the analog section from hum and buzz is a primary design goal.”  

RA: What was the biggest design challenge that faced the C2600 engineering design team during R&D, tooling and final production?

ML: Each model is controlled by digital logic circuits for switching and programable features like naming inputs, volume offsets between sources, cartridge loading, etc. The C2600 has specific operational software that takes some time to perfect to our desired feel and function.”  

RA: What type of tubes does McIntosh use in the C2600? And did the designers do a number of listening tests with different tube suppliers before settling on the final brand? 

ML: “McIntosh tube products are designed to work with any properly operating tube of the type the circuit is designed to use. Since all power supply and voltage regulation is handled by transistors, the job of the tube is simplified to only audio. The C2600 will meet performance goals with fairly worn tubes and it is also easy on tube life as we do not stress the tubes close to their design limits. Long tube life has always been a McIntosh engineering goal. We use JJ tubes at this time as they perform well and can meet our requirements.”

McIntosh Laboratory Inc.
2 Chambers Street - Binghamton, NY 13903-2699

Everclear's picture

May be Rafe could also review Schiit Audio Freya pre-amp $699 .......... Yes, it has tubes :-) .........