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Parasound JC2 Preamplifier Review

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PeteL

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Is there a use case for a simple pre-amp in this day and age without the DAC functionality, just wondering :confused:

Unless it's Phono > Preamp > Poweramp
Yes, for me definitely, typically the dacs become obsolete much faster than a simple preamp, and most DAC/preamps combinations I know of don't have many analog inputs. FM radio, turntable... they are still quite common devices in this day and age.
 
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amirm

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Also, the preamplifier has a gain of 14dB. Even with the gain pots backed right off (-10dB) there is still a gain of 4dB. How then did you test at 4V in and 4V out without winding back the master volume pot from maximum?
??? I had the volume set to the middle or so to get unity gain.
 
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amirm

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amirm

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To be fair, the preamplifier has a rated output of 1V and is clearly designed to achieve its lowest THD at levels typical for power amplifier sensitivities of 1-2V (as was/is the norm). The Stereophile plots also show this to be perfectly true. You are testing it at 4V, 4 times its rated specification. Of course the THD rises at 400% of rated spec.
??? What I measured matched the spec:

index.php


Spec is 0.003% and I got 0.0025% which is even better. Unity gain should not be hard for a pre-amp. And higher voltages help with sign to noise ratio.

Since just about any external DAC will output 4 volts over XLR, I don't see the merit of testing at lower voltages on the input.

But sure, I will continue my battler to get audio manufacturers to proper output voltages not the anemic ones they make up on their own. :)
 

restorer-john

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??? What I measured matched the spec:

Absolutely. At 1KHz. But the distortion rises with frequency, but much more so with a 4V in and out. Yours and Stereophile's result correlate except you are pushing the preamplifier past its ratings and it still did extremely well IMO.

I get it, you like 4V. :) But asking a preamp rated for 1V to drive 4V into a 300R load and then calling it out for HF THD is a bit harsh wouldn't you say?

1595126220740.png
 

jaykay77

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When I drop off my Yamaha MX-1 with @amirm, I'm happy to bring along my Parasound P5 with it. Currently, pulled both out of my system to try out a Soncoz SGD1 fed straight into an Icepower 1200AS2 based amp.

The P5 is an odd bird in their line-up. It's very "not audiophile" if you take a look inside.
That Mx1 will probably surprise a lot of people. Excited for results. I’d love to see an mx1000 tested!
 
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amirm

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I get it, you like 4V. :) But asking a preamp rated for 1V to drive 4V into a 300R load and then calling it out for HF THD is a bit harsh wouldn't you say?
Oops. Sorry that title is wrong. I pulled that template from headphone test, modified the load but forgot to change the graph text. Here is the specs for the very test:

1595128538068.png


1595128615971.png


As you see, the load is 200 kilo ohms. The THX headphone amp though was running at 300 ohm which is remarkable given its performance.

I actually don't like that stereophile uses 600 ohm load because it is too severe for a pre-amp. So definitely would not use 300 ohm myself.
 

restorer-john

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I actually don't like that stereophile uses 600 ohm load because it is too severe for a pre-amp. So definitely would not use 300 ohm myself.

@amirm Thought it was an unusually harsh load, thanks for clearing it up. I'd decided after lunch to see what 300R would do the HF distortion of some of my preamps- now I don't have to. :)
 

zelig

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Conclusions
This preamplifier was measured by stereophile which stated it had exceptional performance. I am not seeing any signs of that, ...
Oh dear! I have to say as a consumer I am really enjoying the roasting of Stereophile. They represent the bullshit side of the home audio industry and not long ago that was the only side there was. I bet there are literally 100's of Stereophile reviews that could be shredded now. Poor poor Stereophile! :cool:

Maybe they should just yank all their old reviews and claim there was a data breach?
 

restorer-john

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Is it possible that preamplifiers cannot be independently tested and compared as "apples to apples" because different companies use different parameters for performance standards?

Should Amir, in your opinion, change his preamp testing standards/parameters?

Amir is between a rock and a hard place. His tests can be consistent and therefore fair to each thing he tests. That is good.

However, testing things at significantly different levels to rated figures means certain conclusions can be hard to draw and may not be fair or a level playing field from one product to another. If we drag everything back to older levels (150mV-200mV and 1-2V out), the SOTA figures would be become less so and differences wouldn't be so obvious.

I think Amir does his best to be fair. If it were me doing the testing, there would be way more people complaining for sure. :)
 

bigguyca

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Absolutely. At 1KHz. But the distortion rises with frequency, but much more so with a 4V in and out. Yours and Stereophile's result correlate except you are pushing the preamplifier past its ratings and it still did extremely well IMO.

I get it, you like 4V. :) But asking a preamp rated for 1V to drive 4V into a 300R load and then calling it out for HF THD is a bit harsh wouldn't you say?

- Graph omitted -


From the Owner's Guide the rated maximum output is 8V. The Distortion specification is a separate area in the Owner's Guide from the Input Specification, which includes the gain information (.2V in, 1V out) and maximum output (8V). If one wants to defend the JC-2 these numbers can be mixed and matched, but at least in the Owner's Guide, the absolute claims are unclear.

https://parasound.com/pdfs/JC2Manual.pdf

Discrete transistors are used and the rail voltages are +/- 25V so the headroom should be available.

As with Parasound power amplifiers the JC-2 uses JFET's which have a much lower transconductance than bi-polar transistors. In the Parasound power amplifiers this lead to 10dB to 20dB more distortion since less open-loop gain, and thus less feedback, is available. It's hard to see the offsetting benefit from use of the JFET's.
 

restorer-john

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but at least in the Owner's Guide, the absolute claims are unclear.

No, they are perfectly clear. The preamplifier is rated as 14dB gain, 200mV for 1.0V output. Maximum output is generally quoted for preamps, but the THD, FR etc is generally referenced to the rated output. Never the maximum.

typical example:
1595133232628.png


similar example:
1595133567213.png
 
Last edited:

bigguyca

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To be fair, the preamplifier has a rated output of 1V and is clearly designed to achieve its lowest THD at levels typical for power amplifier sensitivities of 1-2V (as was/is the norm). The Stereophile plots also show this to be perfectly true. You are testing it at 4V, 4 times its rated specification. Of course the THD rises at 400% of rated spec.

(1) Specification is 200mV for 1V out. You are feeding in 4V. 20 times its rated sensitivity for full rated output. A CD at full level is 2V.

Also, the preamplifier has a gain of 14dB. Even with the gain pots backed right off (-10dB) there is still a gain of 4dB. How then did you test at 4V in and 4V out without winding back the master volume pot from maximum? Once the master volume pot is not at maximum, your tests cannot be compared to Stereophile's (vol max (as is standard testing protocol), input shorted etc). The Stereophile 1:1 (unity) 2nd plot shows the FR deviations, but all other tests are at full volume position and adjusting the input level.

Also, just as an aside, why a 300ohm load? It's not a headphone amplifier- why compare it to one? The line outs are 60ohm rated per leg for the balanced and 60ohm for the single ended. A typical load would surely be several k ohm.

The Stereophile tests do show exceptional performance in my opinion.

(1) As noted in a previous post, per the owner's manual the maximum rated output is 8V.

You've raised a really interesting question concerning setting the volume control. The JC-2 uses a multi-gang pot before the gain stage. In this case the lowest noise reading is obtained by using the maximum volume setting since then little to none of the resistance in the volume control is in the circuit and Johnson noise, which is amplified by the gain stage, is minimized. This would not be the case with a volume control that includes an opamp such as those used by D/M and Yamaha. Reducing the gain to 0dB would like increase noise and reduce the S/N ratio.

That more resistance is in the circuit at 0dB gain is shown by the frequency response graphs in Fig 1. A 0dB gain setting reduces the bandwidth at high frequencies. This is because the added resistance at 0dB vs. +14dB forms a low pass filter with capacitance to ground later in the circuitry. It is likely that further reducing the volume control setting will further reduce the bandwidth. IMO hardly a great design.

Hopefully JA used 0dB gain for the rest of his tests. Setting the volume control for maximum gain and driving the JC-2 with a low impedance (low resistor noise), low noise, source such as the AP test gear will overstate the performance of the JC-2. In normal use at less than 0dB settings on the volume control, the pot is adding noise, which is multiplied by the gain stage, and the bandwidth is greatly reduced.

Does this analysis seem correct?
 

hapnermw

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For those that only require digital inputs, a D90/A90 combo provides SOTA DAC, preamp and headphone amp for <%20 the price of this product (in 2020 $'s).

It is interesting to see what performance these legacy audio components actually delivered. Even at the time, this preamp was not all that great. There were likely other preamps in its price range that were better engineered and provided better performance. It's a shame that the reviews of the day were not revealing enough to expose this. There were many preamps of the time that provided 15db or higher gain. It is inexcusable for this preamp to have delivered its best performance at 1V output.
 

bigguyca

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No, they are perfectly clear. The preamplifier is rated as 14dB gain, 200mV for 1.0V output. Maximum output is generally quoted for preamps, but the THD, FR etc is generally referenced to the rated output. Never the maximum.

typical example:
View attachment 74092

similar example:
View attachment 74093

In your High Level Amplifier example:

Rated output is 1V
Total High Level Harmonic Distortion in the next line is given at 5V.
1V does not equal 5V

In the next example
Rated output is 2V
The specs for distortion are given at 8.0V, which is also given as the maximum output.

The examples you have included don't support your claim. The 3rd example doesn't support the "never" claim.

It's always good to take a deep breath or two, when someone disagrees with one of your posts, before you reply.
 

restorer-john

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In your High Level Amplifier example:

Rated output is 1V
Total High Level Harmonic Distortion in the next line is given at 5V.
1V does not equal 5V

In the next example
Rated output is 2V
The specs for distortion are given at 8.0V, which is also given as the maximum output.

The examples you have included don't support your claim. The 3rd example doesn't support the "never" claim.

It's always good to take a deep breath or two, when someone disagrees with one of your posts, before you reply.

It's probably a good idea, to take that breath and perhaps go read, say a few hundred listed specifications/service manuals for preamplifiers and then come back with your findings on consistency and truth in specifications.

Rated outputs are one thing, maximum outputs are another. The examples I listed above are just excerpts from considerably more comprehensive specifications for the two preamplifiers concerned. Comprehensive, in that they separate the high level, low level stages and specify them individually. Both preamplifiers I have sitting right here, should you have any more queries.

The rated output of the first example preamplifier is 1.0V. quite clear (as is the JC-2).
The rated output of the second example preamplifier is 2.0V, again, quite clear.

The frequency response, signal to noise and other parameters are referenced to the rated outputs. Where they are not, it is specified.

The second example THD <0.005% is referenced to the rated output of 2.0V on any inputs (Accuphase guarantee a worst case figure for any input) and, as a bonus, it also is achieved at 5V out on the RIAA EQ and Line stage.

So, if you want a discussion on specifications, truth in specifications and ratings, start a thread on it- I'll be happy to add my two cents. :)
 

YSC

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With those low feedback myth applied and still gets 90db of SINAD is kind of ok to me already, some ppl just buy into those myths and at least John don’t create monsters like the audiogd no?
 

Robbo99999

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OMG! Knock me over with a feather...a Schiit preamplifier recommended over a Parasound John Curl unit?

View attachment 74059
Severely off-topic, but what's wrong with that cat, you've got a cat avatar too so I'm thinking you know all things 'cat'!?
 
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