Amp for Vandersteen 2ci

I had the Signature 2ce and they were very power hungry, my Hegel H100 needed to be at 85/100 to achieve 80db. You need some power, 150w @ 8ohm that doubles at 4ohm would be my suggestion 

@gdnrbob  

Amps with Zero Feedback tend to make the Vandy's shine.

Interesting.  Based on my limited knowledge, the neg. feedback (NFB) of the amp. usually reduces distortion and improves both input and output impedances of the amp.  For example, it makes the output imp. lower and enhances the damping factor.  Could you elaborate on why technically the zero NFB makes this particular speaker shine? Thx.

@lanx0003 ,

I don't have the technical knowledge to describe why, but here are some posts on another forum.

Mr. V. wrote on his forum:

It's not complicated.  Feedback is time distortion.  Vandersteen's are Time and Phase Correct.

Ralph Karsten (Atmasphere) gave a more detailed explanation on feedback:

There are several reasons feedback has a bad rap in high end audio.

The main reason has to do with where the feedback is applied. In most tube amps its the cathode of the input tube. In many solid state amps is the input of a transistor that is part of the differential input of the amp.

In both cases these devices aren't linear. As a result, the feedback signal gets distorted prior to being able to do its job! So of course its going to add distortion as a result.

The distortion added is IMD and higher ordered harmonics. A lot of the innate distortion of the circuit does get suppressed.

If the resulting distortion profile lacks the 2nd and 3rd harmonics in sufficient amount, the higher orders will be audible as they are not masked by the lower orders. This will cause harshness and brightness. We've all heard it!

There are two solutions. One approach is to make the feedback node as linear as possible. Thus the feedback isn't as distorted as it would be otherwise. Here are two examples of that- the feedback used in an opamp, where the feedback is entirely external to the opamp itself, instead being mixed with the incoming audio thru a restive divider network. The other way is to use a really linear tube like a 12AX7 section to receive the feedback. In this way you might not have to use a lot of feedback and the circuit might still sound quite good. The Dynaco ST35 is a good example of that in practice. The ST70 is not.

The other solution is to use a lot of feedback. Like over 35dB; this can overcome the non-linearity of the feedback node. The problem here is that you have several things that can stop you in the circuit. One is that the circuit might not have the gain or bandwidth to support the feedback. If this happens distortion will rise above a certain frequency. Distortion rising with frequency isn't a good thing- its a clue that the amp might sound bright and harsh although the bass might be just fine (since the feedback is supported at the lower frequency).

The second problem you can have with this approach is circuit stability. Because of frequency poles in the circuit, feedback at audio frequencies might be negative, while at some ultrasonic frequency it can become positive due to phase shift associated with the frequency pole(s). Sources of a frequency pole might be a coupling capacitor, a coupling transformer, Miller effects in the active devices (tube or transistor), stray capacitance and the like. If the feedback loop isn't properly designed, the amp could go into oscillation if a signal of high enough frequency can get through the feedback loop and phase shifted enough to be positive feedback.

Class D amplifiers offer a way around both of these problems. They are particularly easy to develop the gain/bandwidth product that is needed to support a constant +35dB or more  of feedback at audio frequencies. If the amp is of the self-oscillating variety, you can add so much feedback that the amp goes into oscillation, but then the oscillation is used as the switching frequency. The feedback network can be designed so that the amp will always find the same switching frequency, killing two birds with one stone.

A large amount of feedback can compensate for phase shift that might otherwise be present if no feedback is used and bandwidth is limited. It also allows the amplifier to reject AC noise problems. So there's a lot of advantage to this if you can pull it off.

Mind you, we've been building zero feedback amplifiers for nearly 50 years so I'm not saying this idly. A zero feedback amplifier will not have the dreaded rising distortion with frequency and if designed properly, will not exhibit harshness and brightness since the higher ordered harmonics are masked. So this can be a very musical amplifier, but also can be load sensitive, so the choice of speaker used can be critical to really getting this kind of amp to show off its stuff.

A very high feedback amp gets you to the same place if designed properly and has the advantage of being usable on a wider range of speaker loads.

HTH

Bob

@highend64 i have had all sorts of amp on a 2C.

• PSE (SS)
• VTL compact 100 (EL34)
• NAD 3040 (SS)
• PrimaLuna (EL 34)
• AIYAMA Class-D)

They all sounded pretty good… even the $70 AIYAMA was good enough.

The PrimaLuna Dialogue Premium HP was $2k used, and the main thing I don’t like is that the Mrs has to turn it on with a tie poke of the switch… and a trigger, and balanced XLR.

But I have been considering Class-D (Like the Atmasphere amp which is beyond the $2k budget) or a Purifi derivative.

Your speaker is easy to drive… any in your list will likely sing fine.

Looking at your RC-995 preamp, the balanced output is in name only BTW because it’s clearly not a fully-balanced preamp so paying up for an amp with balanced inputs really doesn’t get you anything (except higher cost).  Frankly, I don’t think the RC-995 is doing you any favors sonically so I’d seriously consider selling it and buying a good integrated.  Here are a couple good examples FWIW…

https://www.usaudiomart.com/details/649933972-hegel-h190/

https://www.audiogon.com/listings/lisb2666-plinius-hautonga-solid-state

Just another potential avenue to ponder, and best of luck in your search.