Considering switching from Audio Research to PrimaLuna, troube with VS115 amp

Hi Kevin (@upscaleaudio),

John Atwood (One Electron, Artemis Labs, etc.) has a fairly concise commentary on some of the design considerations you mention (post #2 of this thread in DIYaudio: http://www.diyaudio.com/forums/tubes-valves/132233-fixed-vs-cathode-bias.html).

I'm thinking that the hot running cathode-biased amps you've experienced were more of a design choice for maximum power than anything else.

There are certainly different issues at play with a cathode biased amp from that of fixed bias.  For example, the quality of the cathode resistor's bypass capacitor can have a noticeable effect on the amplifier's sound.  Typically (due to the required value), they're electrolytics, although bypassing them with a high quality cap can work.

I'm not arguing in favor of one technique over another, but one serendipitous attribute of cathode bias is that you might loose fewer (or no) parts if a tube shorts out (a plate or screen to cathode short).

Of course you can build protection into a fixed bias amp to address this.  I think the Prima Lunas do this.  It's a nice feature.

I think that sonic considerations for fixed/auto bias are more evident in guitar amps where the output stage is pushed very hard.  At this point, the time constant in a cathode biased amplifier (the recovery time) John refers to in his post comes into play, and cathode biased guitar amps have a slightly softer edge to them as a result.

My thinking about audio in general, is that as design architectures "mature" (move higher up the sonic food chain), their sound converges ... toward reality.

And so it goes ...

Cheers,
Thom @ Galibier Design

Hey folks I'm getting on a plane now and may be out of touch for a bit. My wife is cool and loves audio but I better be present if you know what I mean. Vacation time.

Update for everyone and a great big thanks to Kevin,
Been listening to my ARC system for awhile now and no problems to report. Sounds great. Very impressed with the low noise floor of the preamp. I can turn down the volume to zero while music is playing and the sound goes to zero. Can't hear a thing. Back when I had the Vincent amp hooked up, I could not do that. You could still hear the music a little.
In a earlier post, Kevin stated he had a PS Audio Direct Stream Digital DAC for sale. I looked into that and could not believe all the great reviews about it. Watched videos on it when it was unveiled back in 2014. Was going to purchase the Sony HAP-Z1ES but could not pass up the incredible deal Kevin had on the PS Audio DAC. I knew at some point down the road I would go with an external DAC but figured it would be awhile before I could afford that option. With the price Kevin had on the PS Audio DAC, I couldn't pass on it. Kevin was very helpful in answering all my questions which helped me decide what to do. Thanks Kevin.
Anybody out there have any experience with that DAC? Some people say it compares to the dCS line of DACs.
FYI, PS Audio is planning on coming out with a new product this Fall to go along with that DAC. It will store digital files on a SSD and come with an app for use on a tablet to manage the music. They hope to unveil it at the Rocky Mountain Audio Fest this October. No word yet on what it will go for.

Interesting to see this as I also have the Vivid 1.5 and am looking to upgrade amplifier. Presently have CARY SLI-80 Sig F1. Thinking of the Primaluna as well. Wondering if it is worth going to the Dialogue Premium HP with the standard EL34 vs the Dialogue Premium but putting in KT 150 tubes. The HP has 8 tubes, so it will be pricey when time to retube as compared to the regular premium with 4 output tubes. It does have significantly more power, and if it runs cooler, the tubes could last longer.

Hey Skyhawk. I own a Primaluna Dialogue Premium HP Integrated Amplifier and I  love it. I'm 57, an ex night club DJ of many years. I've loved Valve amps since I was a kid and I own a Leak Stereo 20 fully restored. Kevin Deal was reluctant initially to put his name to an amp that couldn't be made totally in the states! I live in Melbourne Victoria Australia by the way. The build quality of the Primaluna Dialogue Premium HP Integrated is beyond reproach. Point to point wiring, toroidal hand made transformers, an Alps motorised volume control, a remote control that weighs about half a kilo......it has everything. No printed circuit boards here and you have a switch on the side to select either EL34s or KT88, KT120 or KT150 tubes. It has 6 12AU7s for the input and 8 power tubes with fully ventilated sockets. They're mounted to the chassis so theres no flexing unlike circuit boards which will eventually fail. The big thing here is full automatic bias. No multi meters here. As the tubes age this circuit which is not in the signal path keeps the push pull mode in its perfect sweet spot which minimizes noise by at least 50% more. It has AC offset to kill unwanted mains noise. It also has hermetically sealed relays controlled by the selector knob to kill input crosstalk which can stand being switched open and closed 50 thousand times. The headphone socket is selected by another switch to stop the socket from being a weak link in the audio chain. The speaker binding posts have no hole to insert cable to improve sound quality and all RCA inputs are gold plated. I'm running a turntable but even though you could've had a preamp installed, I bought a Cambridge Audio preamp to keep the unit stock. Vinyl sound through this amp is stunning and CDs are clean and warm. If a tube fails, a red LED lights up telling you which tube is faulty. Replace it, turn the power back on and forget about bias adjustment! I'm running a pair of Wharfedale speakers and using the stock EL34s, this amplifier just sings whether it's Enya, Pink Floyd or dance music. It has a Home Theatre through selector and it handles this function well. It's a heavy amp 30 kilos, but there was no compromise on build quality......10 out of 10. You can get them as stereo power amps or mono blocks and boy they kick some serious arse. Primaluna have just released a 5AR4 tube rectified stereo preamp and even though I don't need one, I will be getting one as soon as I can order it. The only downside is that if you want to run KT150 tubes, you can't fit the protective cage over them because those tubes are  too high but 88s or 120s provide plenty of power but you can use KT150s without the cage! Primaluna are a young company but man their gear makes you drool. Google their internal pictures. No cheap components here. I love my Primaluna amplifier. Both them and Macintosh are my favourite amps but the Primaluna Dialogue Premium HP Integrated wins hands down! Cheers Andrew Peter Collins, Melbourne Victoria Australia!