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

Greetings all,

As an amplifier manufacturer, I want to tread lightly on this topic. Please bear in mind that the following are my biases. Others clearly differ. Note that I didn’t have time to get through this entire thread, so perhaps some of this has been covered. I caught a few references to PCB vs. point to point however, and some misconceptions prompted my reply. Finally, I’d consider taking a look at VAC Amplification if you’re looking for a medium to high powered tube amplifier (http://www.vac-amps.com/pages/statement.html).

Begin rant …

I’m a big fan of the turret board / tag strip construction technique. Designed correctly, it can have as short of a signal path as point to point, but with far more robust construction (immunity to shock and shipping damage), ease of maintenance, and sample to sample consistency. Know that (along with point to point) it’s much more expensive to manufacture, requiring more time and a skilled labor force, which I’ll expand on below.

If carefully designed, the signal path can be as short as point to point, although many examples of this technique don’t reflect this (short signal path) as a priority of the designer. I can understand why, because it’s tedious work. It took me over 4 months to lay out our new NiWatt amplifier, achieving a total wire length on the positive side of the circuit of only 4” from input jack to speaker binding posts. Sometimes, longer isn’t better ;-)

The term Point to point is freely bandied about by marketing departments. If you look at the Prima Luna site, you’ll note that their construction technique is in NO WAY point to point construction. It’s a mix of tag strip/turret board (I like that!) with quite a few printed circuit boards thrown in for good measure (meh!). I certainly prefer this construction to a pure PCB construction, but for my tastes, it’s not all the way “there”.

In fairness to them, an amplifier as complex as the Prima Luna would be a nightmare to manufacture and service if it were fully point to point (or tag strip/turret board) construction. This calls into question whether this complex of a design has any sonic benefits vs. sonic costs ... a discussion for another day. The fact however, is that this is not point to point construction.

Here’s a gut shot of their amplifier: http://www.primaluna-usa.com/dialogue-premium-hp-power-amplifier.

This Wikipedia page has some photos of true point to point construction: https://en.wikipedia.org/wiki/Point-to-point_construction

Here’s an example of a beautifully executed turret board/tag strip construction (a Thoress phono stage): http://www.thoeress.com/images/thoeress-phono-enhancer-03.jpg.

See the differences?

Comment: I’d like to see a shorter signal path on the Thoress, as these “ladder” (parallel) component layouts tend to add quite a few more inches of wire into the equation, but I wanted to call out the elegance and robustness of the construction technique. As I mentioned above, you can achieve a short signal path with this technique, but it won’t look quite as neat as the Thoress.

A couple of definitions and additional comments …

Point to Point:

All components are soldered to each other or to terminals (e.g. tube sockets, binding posts, input jacks, transformer terminals, etc.). An occasional wire is necessary on the hot side of the circuit (to bridge some longer distances), and some sort of ground bus (wire) is used on the negative side.

Vintage components (i.e. Marantz, Scott, Fischer, etc.) are wired this way. Looking at them, the components appear to be a chaotic rat’s nest. There’s a lot to be said for this from a sonic perspective (parallel wires are your enemy). Duplicating the construction from sample to sample can be quite difficult however, and it requires a highly skilled labor force (expensive), because lead dressing differences (component and wire length and routing) can result in sample to sample sonic differences if attention isn’t paid to this.

Tag Strip / Turret Board:

This is the evolution of point to point and the precursor to circuit boards. It’s typically a mix of some point to point wiring combined with some form of “support” for many components by use of intermediate terminals or turrets to which some components are soldered. It’s typical of vintage guitar amplifier construction and can withstand the abuse of roadies throwing the gear around carelessly. The tags/turrets tend to fix the layout quite a bit more than point to point, so it’s quite a bit easier to maintain sample to sample layout and lead-dress consistency (less QC required on the back end than pure point to point).

Circuit Board:

We all know what this is. It’s the least expensive manufacturing technique, and you can get by with a much less skilled workforce. It offers lowest manufacturing cost (by far) and a better assurance of sample to sample consistency with less QC required at the back end.

High quality circuit boards can withstand the abuse of parts replacement, but ask any tube amp tech which architecture he’d like to repair, and I’d expect them to say point to point or tag strip / turret board.

The circuit board material (glass/epoxy) is inherently capacitive (a bad thing) and you can’t control the quality of your “wire” (the circuit traces). You can’t specify silver, 6-nines copper, etc. for your circuit board traces.

Again, the above are my biases and by no means universally agreed upon.  Rant off ...

Cheers,
Thom @ Galibier Design

I noticed you said if looking for Med to High Power Tube Amp look at VAC. A lot of people can't afford VAC. What other company would you recommend looking at? Would Primaluna be a consideration?

I wish I could responsibly advise you on this. 

Most of my recent exposure has been to low power triode amplifiers - 2A3, 300B, 845 and such, and it's only serendipitous encounters with both Kevin Hayes and VAC in general that led me to bring them up.  Indeed, they occupy more of the ARC price tier and not Prima Luna's.

Prima Luna appears to make many intelligent design compromises (to meet a price point), but without hearing them I'd hesitate to say, other than to recommend an audition.

Cheers,
Thom @ Galibier Design

Thanks for the write up btw. Appreciate your time.

You’re welcome @aniwolfe

I don’t think I need to address build quality. Or how they are built, or what "qualifies" as point to point.

I don’t mean to be a stickler, but respectfully Kevin, I think you do, since it’s in your advertising collateral.

BTW, my philosophy (others may differ) is that if a component is inside the box, it's in the signal path.  Then again, I also think that power cords make a difference ;-)

None of this is meant to cast aspersions on what is very likely a fine product (I recommended its audition). Benefiting from offshore manufacture, the Prima Luna’s construction looks like that of an amplifier costing three times its price.

My earlier post grew long, and I only implied another reason for PCB construction (apart from addressing circuit complexity) - to bring a product into a more affordable price class. If done intelligently, you can produce a very fine product.

One such component using PCB construction (which I heartily endorse) is Keith Herron’s VTPH-2 phono stage. If it were entirely hand-wired, its price would likely triple. I’d love to hear Keith’s original breadboard prototype of this phono stage. I’ll bet it’s quite special.

Congratulations on carrying a product with such value!

Cheers,
Thom @ Galibier Design

Your points are well taken, Kevin and I see that we’re basically counting angels on the head of a pin.

I agree with you about the arbitrariness of pricing in many instances, and would love to see Prima Luna whup some of the big names (withheld to protect the guilty).

High end audio prices are arbitrary and in many cases have zero to do with engineering and build costs.  Some big names charge as high a price as they can without losing sales, others that are new hope to build credibility by having a price so high it defies logic.  Wow!  It's expensive.  It must be good.  That, my friends, is the absolute truth.

This is a touchy subject I’d rather stay away from, because it’s something that really makes me grumpy.  Early in Galibier's history, we weren't taken seriously due to our value pricing.  Of course, that was a time when we were learning the ropes - priced far too low to make a profit with our turntables.  We had no clue as to the real cost of running a business ;-)

Quicksilver is another one of those brands which should be applauded for their value. Some of it is a matter of Mike Sanders pricing fairly, and the rest of it is due to him being a master at procurement (cost containment).

The VAC gear is circuit board is it not?

Hi @grannyring, I know they use at least some turret boards in his construction. I haven’t peeked under the hood in a while however.

Cheers,
Thom @ Galibier Design

Thom_mackris : I like your thinking. What’s your take on Rogers then? Cathode bias, and I suspect they run the tubes hot. Yet they say this on their website. It’s all true, except I’ve not seen a cathode bias amp with "the longest tube life". :

• Auto Bias Circuit– For long tube life and ease of operation. Self Bias circuit for adjustment free operation and longest tube life. Customer does not need to adjust tube bias. As the tubes age, they adjust for bias changes automatically. The customer can change tubes at any time or replace a single tube rather than the full set of 4 and the amp will automatically re-bias for the change.

Hi Kevin (@upscaleaudio),

The first box I look to check off when considering a product is reliability and ease of service. My earlier rant was partially based on this prerequisite. Obviously, great construction doesn’t mean you have a stable design, or good sound, but any component that doesn’t pass this test is immediately eliminated from further consideration. It’s a big trigger point for me.

For a vacuum tube product, you should be able to go to any reliable tube vendor and pick up replacements that won’t blow up your gear. Others are free to disagree.

People tend to forget that back in the day, vacuum tube gear wasn’t considered unreliable – when our “greatest generation” depended on military radios working reliably in the field because lives were at stake. Unfortunately, a segment of our industry has gone off the rails with respect to this, and it hurts all of us – the consumer as well as the manufacturer who honors this tradition.

Some manufacturers will have you believe that a component being on the knife edge of instability is an entry point into the inner sanctum of world class sound – that theirs is a finely tuned, thoroughbred circuit and this is the price of admission. My opinion about this can’t be repeated in polite company.

I haven’t had the opportunity to listen to any of Rogers’ products but it’s clear that he checks off this very important (to me) box. His thermal stress testing is impressive. One could conclude (correctly?) that his circuit designs are stable. Great engineering doesn’t necessarily mean great sound, but that’s what auditioning is about.

Of course, cathode bias means that you run a slightly higher B+ in order to achieve the same plate to cathode voltage, but it’s the quiescent current in conjunction with the plate to cathode voltage (not plate to ground voltage, which includes the voltage drop of the cathode resistor) which sets the plate dissipation of the tube. I’ve never heard anyone relate tube life to choice of biasing (fixed vs. cathode), but rather to operating points (plate dissipation).

This reliability pain point reminds me of a customer’s experience – something I think all too many people can’t or won’t admit to (a bit of Stockholm Syndrome, methinks) …

I had a customer who was looking to break in a Hagerman Trumpet phono stage. Jim Hagerman used to supply a small, inverse RIAA circuit that also dropped the signal by 40dB. The idea was that you could run your digital source into this small board and then into your phono stage. Playing on repeat, you could quickly log 25-50 hours on your phono stage.

He called me up to ask: “do I have to run my power amp in order to do this?” Well, his big amplifier (4 KT-88’s per side) had a penchant for blowing screen resistors, and every time he powered it up, he experienced angst. It’s that sort of thing that (in my opinion) is ruining the industry.

People shouldn’t be afraid to power up their gear. This hobby is supposed to be fun. Now, it’s my turn to start chasing kids off my lawn ;-)

Cheers,
Thom @ Galibier Design

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