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PREAMP technology shift? - Class A/ balanced/ dual-mono/ zero feedback vs. op-amp preamps

Hi all,

Even ten years ago, it seemed that the gold standard for solid-state pre's was some combination of the following: Class A/ balanced/ dual-mono/ zero feedback or local feedback. Recently, I'm seeing a range of well-reviewed preamps, from Schiit to Rowland, that use new, high-quality op-amps in their circuitry, to the extent that I wonder if op-amp technology, and chip manufacture in general, has gotten so good that some of the tried and true markers of quality (MOSFETs, Class A circuits) are not in the market except at the highest end, and even then, see also Jeff Rowland. Or is it that manufacturers are looking to less power hungry designs (I know that Rowland was concerned with meeting EU efficiency requirements in its latest designs) and so avoid Class A, for example? Does balanced/ dual mono seem less popular because separates are now less popular than integrateds? Have we reached a tipping point with op amps?

Here's a more focused question. I have invested in a 90s era Aragon 8008BB dual mono balanced amp, but i have an early 90s B&K PRO10-MC that I want to upgrade. Is a Schiit Freya a significant step up, or should I save my pennies for a used, more recent example of the old school: Classe CP500, Pass Labs Aleph or X2.5, or a good example of a newer approach, the Rowland Capri. Speakers are Vandersteen 2CE Sigs. Input impedance of the Aragon is 44 kOhms. 

The tube route is always possible, but I like the idea of a no-fuss, very clean ss, valuing sound stage and detail over warmth, which makes me think I'd be wasting my time with the Freya (any shoutouts for its JFET stage?)

Thanks for letting me wonder aloud!

Paul


paulburnett
auxinput
1,538 posts
 

You have so many questions, I’m not entirely sure what you really want answered here. Though, it seems you are looking for a good preamp. In general op amp technology has really advanced with opamps that have come out in the last 10 years. However, usage of op amps versus discrete or Class A is entirely dependent on your application and what source you have. If you have a very laid back analog or tube source (such as a tube DAC), then a high-speed accurate bipolar preamp may be a good match. Or maybe go with a passive preamp with a higher impedance attenuator (like 100k ohms).

If you have a very solid-state DAC source that only uses op amps, then you probably want to have some sort of Class A preamp. But be aware of what you are using as some op amp sources are engineered to sound warm (like NAD or Adcom or even Emotiva XDA dacs). Many use the OPA2134 FET based op amp for this purpose (the lm49720 / lm4562 op amp is also used somewhat like this). In my opinion OPA2134 is a really poor op amp that smears the sound to make it warm sounding and you also lose resolution.

You have purchased an Aragon 8008BB, which is a very nice amplifier. It is biased high into Class A (the initial 26 watts if I remember right). Also, this was designed by D’Agostino and he likes the warm/rich FET type of sonic signature. I have heard this amp and it is very warm and rich sounding. However, as a byproduct of the warm signature with the Class A bias, it is definitely on the warm/slow side and you can sense a slight smearing of the sound. Nothing wrong with this -- it’s part of its sonic signature.

So, based on that, I would look for a very fast accurate bipolar-based preamp, such as the Rowland Capri you mentioned. The OPA1632 is a bipolar opamp with very good specs. It is going to be very clean and very fast. I would avoid Class A or tube preamps with your Aragon because there is going to be too much smoothing of the waveforms going through several Class A circuits and you will have a slower sound and the high frequencies may start to roll off. But if that’s what you want, then great.

I remember the older B&K stuff being very warm. It is actually too warm for me. You might want to look for a transparent/clean type of preamp. Cambridge Audio Azure 840E-B? Or the Wyred 4 Sound STP-SE?

The Freya uses a JFET solid-state stage which will add a warm/rich signature.

georgehifi's avatar
georgehifi
4,966 posts
 
The Freya uses discrete J-fets as it's output stage, the opamps you see are most probably for dc servo duties because it's dc coupled, which even the $$$$$$K discrete preamps have.

From Schiit:
"JFET Buffer
Gain: 1
Frequency Response: 20Hz-20Khz, -0.2db, 3Hz-500KHz, -3dB
THD: <0.001%, 20Hz-20KHz, at 2V RMS
IMD: <0.0015%, CCIR
SNR: >110db, A-weighted, referenced to 1V RMS
Output Impedance: 75 ohms SE, 600 ohms balanced
Topology: Single pair JFET per phase with passive distortion cancellation, DC coupled"

Cheers George
soix
2,133 posts
 
"I like the idea of a no-fuss, very clean ss, valuing sound stage and detail over warmth"

There's a Bryston BP26 for sale here now that nails this in spades.

audioman58's avatar
audioman58
1,219 posts
 
There are many different types . I have had many in my day .Currently I have which is considered the purest preamp type, Single ended . Which has several unique features . It is a Direct Heated Triode type completely Lundahl Transformer coupled 5 transformers,and 3 chokes and the little known 4P1L Vacuum tube 
which is very Linear, plenty of gain to eliminate the need of another tube for additional gain stage like many indirect Heated tubes. A very detailed and 
well balanced tube .it can be a bit microphonic in vibration if the builder does not 
isolate the tubes and isolate and damp the power from the Audio output section properly .modern technologies like relay remote and 63 step Shunt attenuated- Khozmo type. just another  twist for another Audiophile dilemma.

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