یه برند خوب
https://parttimeaudiophile.com/2015/09/18/caf-2015-borderpatrol-triode-wire-labs-and-living-voice/
طراح بلندگوي 2way شركت ليوينگ وويس تو كل مراحل طراحي و ساخت اين بلندگو از پوش پول 300b شركت kondo audionote استفاده كرده و چون قيمت kondo ربطي به قيمت اين بلندگو نداره طبيعتا بايد براي Kondo دنبال جايگزيني مي گشتم كه به اين آمپلي فاير BorderPatrol P20 رسيدم.
Each PSU contains three independent tube rectified, choke input filter high voltage supplies to independently feed the 300B’s, the input/driver tubes and the negative bias supply, together with filament supplies for the 300B’s and small signal tubes. The use of choke input filtering is a critical difference and is unique to BorderPatrol power amplifiers. Other brands use tube rectification and choke smoothing but do so in the cheaper, smaller and easier to implement capacitor input filter configuration. A choke input filter design has far superior voltage regulation (stiffness) and noise rejection. The PSU’s stiffness explains why the BorderPatrol amplifiers have bass performance and dynamics unlike any other 300B amplifiers.
Why design a 300B amplifier in push-pull rather than single-ended-triode (SET) mode?
“A push-pull 300B design will typically have 20Wpc, which allows it to work with a wider range of loudspeakers,” Dews said. “Push-pull amps typically have tighter, punchier bass than SETs, can drive much more difficult speaker loads, and play a wider selection of music. A stiff power supply, like the ones used with BorderPatrol SETs, addresses the SET dynamic and bass issues significantly, but a similarly executed push-pull like the P21 will still be superior in those areas.”
Note Dews’s description of the typical sound of 300B SET amplifiers: “[They] are often charming and beguiling but have low power, are limited dynamically, and have poor bass performance. They need to be partnered with loudspeakers that have very high sensitivity, and a high and uniform impedance characteristic. Complex music with heavy bass is best avoided. SETs predominantly generate even-order harmonic distortion, which gives them the characteristic open, airy, romantic sound. It’s not accurate, but it can be nice. Push-pull amplifiers predominantly generate odd[-order] harmonic distortion, which leads to a sharper, less romantic sound, but one that is still engaging.”
Read more at https://www.stereophile.com/content/borderpatrol-p21-exd-power-amplifier#D2dUPjlQXWjQWIxL.99