I own a pair of Audiopax 88 monoblocks. It is either the best amp overall I've ever heard or at least in the top 3. Certainly it is on objective music fidelity the best power amp solution I've owned. The designer has several highly distinctive innovations in his circuit but part of the beauty of the Audiopax is that it models SET behavior using a commodity tetrode/pentode tube. These amps take some break-in to sound convincing as "best" amps, and you must take your time to find the right TimbreLock setting to dial them in to their sweet spot. They also respond to tube rolling, so top-grade tubes are well worthwhile. I wasn't won over out-of-the-box, but six weeks later I couldn't bear to part with them.
Prior to this I owned other single-ended KT88 amps, the Acoustic Masterpiece M101, which when it has been reviewed has been very highly regarded, and the Audion Sterling ETSE KT88. The Audiopax takes the SEP approach with KT88s further than anyone so far, with fabulous results within their 30w capability.
The common thread trait shared by all the single-ended KT88 amps I've owned (and heard elsewhere) has been transient speed, objective clarity, meaty tone, excellent bass discipline and spacious soundstaging. Big-T TONE, as guitar players think of tone, has been excellent in the way a very high quality 300B can do it.
The Audiopax TimbreLock circuit is elemental to those amps' ability to surpass other similar SEP designs. It is unusual. In the 88s, each monoblock has 2 single-ended KT88 amps, one output tube each. These twin amps are paralleled at the input and are internally wired in series at the outputs, if I recall correctly. The dual output transformers differ in their winding in a small but undisclosed way. The TimbreLock controls are bias controls for each of the twin amps in the monoblock. Any setting in the range keeps the respective KT88 within its operating range. You use trial and error listening to find the best differential in the two control settings on each monoblock, first, and then refine your setting by finding the best absolute settings on each dial while maintaining the gap or differential between the two. The setting is influenced by your speaker load so you must dial them in for your specific system. When the TimbreLock sweet spot is found, there's sensational focus, transparency and realism.
Now, I also have a pair of unusual 300B amps that have a similar cost to the Audiopax 88s. They are on another system but I've compared the two on same systems. On balance the cost-peer 300B is fully competitive with the Audiopax but they are different. The 300B has extremely rich midrange density that exceeds what the Apax 88s can deliver. The two designs are comparable on what they can reveal. The 300B amps, which are Audion Golden Dreams Level 6, have very fine bass but not as quick and objective as the 88s, and the 88s do not contribute the last bit of high-frequency "spray" common to 300B designs, most of which has been wrung out of the Audion GDs, but not quite all.
It takes an exceedingly clean amp to work well with Avantgarde horns. It has to be dynamic and emotional too. The Audiopax has the right balance and emphasis on accuracy with tone. A commensurate 300B amp, like the Audion GDs will dial in a little warmth and body over the 88s. The 88s will tip a bit lean in body but give you very uniform transient character up and down its frequency range.
One caveat on the Audiopax 88s: gain is low, only 18 db. There is only a single 12AT7 ahead of the power tube in each of the twin amps within each monoblock. These amps are relatively input insensitive, so you need robust output from sources or some extra gain in your preamp for average material to drive full power from the amps. Choose your source/input combination to mate with the reality of an 18db gain design.
There have been many excellent KT88 amps over the past few decades. Google Acoustic Masterpiece M101 and you'll find an audio musing / positive feedback review that gives you a sense of what a simple SEP design can do with outstanding Tamura transformers.
Phil
Prior to this I owned other single-ended KT88 amps, the Acoustic Masterpiece M101, which when it has been reviewed has been very highly regarded, and the Audion Sterling ETSE KT88. The Audiopax takes the SEP approach with KT88s further than anyone so far, with fabulous results within their 30w capability.
The common thread trait shared by all the single-ended KT88 amps I've owned (and heard elsewhere) has been transient speed, objective clarity, meaty tone, excellent bass discipline and spacious soundstaging. Big-T TONE, as guitar players think of tone, has been excellent in the way a very high quality 300B can do it.
The Audiopax TimbreLock circuit is elemental to those amps' ability to surpass other similar SEP designs. It is unusual. In the 88s, each monoblock has 2 single-ended KT88 amps, one output tube each. These twin amps are paralleled at the input and are internally wired in series at the outputs, if I recall correctly. The dual output transformers differ in their winding in a small but undisclosed way. The TimbreLock controls are bias controls for each of the twin amps in the monoblock. Any setting in the range keeps the respective KT88 within its operating range. You use trial and error listening to find the best differential in the two control settings on each monoblock, first, and then refine your setting by finding the best absolute settings on each dial while maintaining the gap or differential between the two. The setting is influenced by your speaker load so you must dial them in for your specific system. When the TimbreLock sweet spot is found, there's sensational focus, transparency and realism.
Now, I also have a pair of unusual 300B amps that have a similar cost to the Audiopax 88s. They are on another system but I've compared the two on same systems. On balance the cost-peer 300B is fully competitive with the Audiopax but they are different. The 300B has extremely rich midrange density that exceeds what the Apax 88s can deliver. The two designs are comparable on what they can reveal. The 300B amps, which are Audion Golden Dreams Level 6, have very fine bass but not as quick and objective as the 88s, and the 88s do not contribute the last bit of high-frequency "spray" common to 300B designs, most of which has been wrung out of the Audion GDs, but not quite all.
It takes an exceedingly clean amp to work well with Avantgarde horns. It has to be dynamic and emotional too. The Audiopax has the right balance and emphasis on accuracy with tone. A commensurate 300B amp, like the Audion GDs will dial in a little warmth and body over the 88s. The 88s will tip a bit lean in body but give you very uniform transient character up and down its frequency range.
One caveat on the Audiopax 88s: gain is low, only 18 db. There is only a single 12AT7 ahead of the power tube in each of the twin amps within each monoblock. These amps are relatively input insensitive, so you need robust output from sources or some extra gain in your preamp for average material to drive full power from the amps. Choose your source/input combination to mate with the reality of an 18db gain design.
There have been many excellent KT88 amps over the past few decades. Google Acoustic Masterpiece M101 and you'll find an audio musing / positive feedback review that gives you a sense of what a simple SEP design can do with outstanding Tamura transformers.
Phil