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Preamplifiers - Conrad Johnson Premier 10
► Commercial version and Upgraded version





Over the past years, i have a lot of excellent reviews regarding the CONRAD-JOHNSON devices, particularly about those belonging to the « Premier » serie that is the top of the line.
Nevertheless, I had never got the chance to lesson to it at home, until now...I have connected it to my
Reference System #2.
Before going deeper in the review, let remind us a few basics. A Hi-fi system must have the best possible source whatever it is CD or vynil : when this requirement is OK, the second most critical device in a system is the preamplifier.

The CONRAD-JOHNSON Premier Ten belongs to the « Premier Serie », meaning the Flagship devices of the brand. The frontplate is thick, heavy, and beautiful with its distinguish gold color.

 We precise at this point that the volume control is performed via a stepped attenuator and not a common potentiometer.


Here is a photo of the beautiful frontplate :CJ_premier10_devant.jpg

and here is a view of the rear :



Inside the Premier Ten, we see a lot of « Conrad-Johnson » branded parts, particularly for the capacitors that « look serious » with their specific white color. This may also push us to believe that these specific parts will be difficult to replace or to upgrade : we will see later that this is false.

In addition to the white CJ capacitors, there are a few SCR well known capacitors.

Here is an internal view of the Premier Ten preamplifier :



Our preamplifier is equipped with four 6GK5 tubes from GENERAL ELECTRIC, which are the best according to the afficionados.

The Premier Ten being a line preamplifier, there is no phono stage. All the parts, excluding the power transformer, are located on an unique printed board, mechanically isolated from the external vibrations.


Here is a top view of the Premier Ten :



I-2.The listening performance.


I have first lessoned to the Premier Ten without taking care about the AC phase. The listening results were as follow: it is too slow, lack of dynamics, nothing improves after 1 hour of use.

As I have a BLACK NOISE shucko multiple AC plugs allowing to easily reverse the AC phase, I have reversed the AC phase and lessened again to it: the Premier ten became a different device !

From too slow it becomes dynamic enough, the too thin and not enough consistent voices became more present and more structured.

Nevertheless, the soundstage, the beauty of the timbres, as well as the overall clarity are really good.

After a few weeks of listening, the conlusion arrives: it is a very good device with the appropriate AC phase and the GENERAL ELECTRIC tubes, but it still misses a few things to belong to the best preamplifiers out there.

What does it miss ? Its speed is still not enough, the weight of the notes and instruments is not enough, the voices could be better and the small details are not all retrieved from the source.

But we should not forget that to get all these additional quality, the price tag is most of the time over 15k€.

To be honest, we have to explain that our reference preamplifier is a (improved) JADIS JP80MC that belongs to the 5 best preamps worldwide, and the comparisons we perform against it are most of the time very difficult to the challenger...

The price of a (not improved) JADIS JP80MC is around 15.000€ whereas the Premier Ten being no longer manufactured can be bought for 1,700 to 2,500€ (the economy is evident...) and when it was still manufactured, its price was around 6,000€ (add the inflation to get an idea of its current price would be).




The Conrad-Johnson Premier Ten will be a good match wit a “mid-fi” system (according to our  standards) and can be bought below 1,500€. It will probably be too limited for a true high end system.

Its manufacturing standards, its serious design and the fact that it is very very robust belongs to the 5 stars ranking, but its sonic qualities are not high enough to get the 5 stars ranking: 4 stars is its proper ranking. We nevertheless strongly encourage you to read the second part of this article related to its upgrade, as you will see that it is possible to hire it to the 5 stars nirvana....




  • Robust and beautiful
  • No heat despite the use of 4 tubes in the chassis
  • Soundstage, beauty of the timbres and overall clarity
  • Does not require more than half an hour to reach its optimum
  • Excellent on the very high frequencies
  • Aftersale service very rare because it is very robust like a lot of the vintage devices (this is a good news because the CJ service is very expensive particularly in Europe....)




  • Dynamics are not enough
  • The Balance potentiometer is a mystery: nobody understand how it works...
  • The bass is not at its best
  • The timbres, the voices, the piano lack of weight
  • The power cable is part of the chassis and cannot be changed
  • The correct AC phase is MANDATORY
  • The CJ aftersales service prices are very high...



This review has been written by Florent (provence13 on our Forum)


II-CONRAD-JOHNSON Premier Ten – UPGRADED VERSION (a few months later).


After having discussed with Nounours who also love the good products, we concluded that it would not be reasonable to let this Premier Ten as it is, because we have not been totally satisfied with its musical performance.

So we decided to start the study of an upgrade that would be able to hire it until the”5 stars” level...

Our previous upgrades have made us able to identify the critical parts of a device, by studying is skematics and by knowing what places are the highest importance in a given circuit...

Nounours has been in charge of performing this upgrade, like for the predecessors and the well known Threshold Fet-10He preamp upgrade.






For this upgrade we have changed the parts that we know they are are critical from a musical point of view: this is based on our experience and on our study of the schematics of the Conrad-Johnson Premier Ten preamplifier.

We have also studied the similar upgrades that have been performed by other persons on the same family of Conrad-Johnson preamps: if a part has been changed and has been reported to provide an improvement, then we study the schematics and decide if we perform an upgrade of this part.


The parts that have been upgraded on this CJ-P10 are listed herebelow:



III-1.Power Supply part:

  • Change of the power cord that was not removable from the chassis
  • Upgrade of the High Voltage rectifiers diodes (240 Vdc)
  • Upgrade of the Low Voltage rectifiers diodes (22 Vdc)
  • Upgrade of a ground cable that was going from a side of chassis to the other side


The change of the power cord has been motivated by 2 reasons:

  • it is very irritating to not have the possibility to use the power cord of our choice
  • the original power cord did not look “serious”, and my feeling was that it was of poor quality

So we made a rectangular hole in the chassis to install a standard IEC 10A connector. This connector has been installed in the right corner of the chassis, at the precise place where the original power cord arrived into the chassis (so there is not vacant residual hole in the cabinet).


Here is a view of the standard 230V IEC connector:



The upgrade of the 4 High Voltage rectifier diodes consisted by a replacement with 4 F.R.E.D. Stealth diodes from FAIRCHILD, ranked 4A 600V, delivered in a TO-220 package. No dissipator is necessary as the original ones did not use one.


Here is a photo of the original diodes, located just below the big SCR capacitor:


and the same view after the diodes upgrade (there is not a lot of available space, but it is enough):


The new diodes are bigger than the original ones, but can be located in the available space, provided that you drill a larger hole in the printed circuit board for their pins that are larger than the original holes. Be aware that the difficulty comes from the lack of space to solder them on the opposite face of the printed circuit board.


The 4 Low Voltage diodes have been replaced by the same type tan the High voltage ones. The photography shows the 8 new diodes.

We have also changed a ground cable that went accross the chassis and that did not look of a good quality...We have replaced it by a bigger Teflon OFC, 1.6mm2 cable.



III-2.Line amplification stages.


For this a deep study of the schematics is mandatory. We have decided to change the following parts:

  • The VISHAY VTA-53 resistors, 1kohm, 0,7W, located in serie with the signal at the tubes entry
  • The VISHAY VTA-53 resistors, 47.5 ohm, 0,7W, located at the tubes output
  • The VISHAY VTA-53 resistors, 324 ohm, 0,7W, located around the tubes
  • The Conrad-Johnson capacitors, 2µF 250V, located around the tubes.


The Vishay VTA-53 resistors, located just at the input of the tubes, have been replaced by two SHINKO 2kohm 2W in //. These resistors are very critical in the CJ-P10 because they are in serie with the signal path. The choice of the SHINKO is due to the unavailability of the YAMAMURA in this value.


Here is a view of the SHINKO resistors in the upper right corner; the YAMAMURA are slightly hidden by the white CJ capacitors:



The change of the resistors located at the output of the 6GK5 tubes, two VISHAY VTA-53, 47.5 ohm 0.7W , is also justified by their critical location regarding the signal path. It has not been possible to exactly find the original value, and I have replaced them by two YAMAMURA with a 39 ohm value, which is a slightly smaller value but not affecting the overall stability of the design. The quality of the Yamamura has nothing in common with the VTA-53,,,

The change of the VISHAY VTA-53 with an original value of 324 ohms have been more difficult to replace because 324 ohm is not a standard value: they have been replaced by two SHINKOH of 329 ohm, which was the closest value I received from HiFi Collective (HiFi Collective initially told me they will ship a 326 ohm, but I received 329 ohm). Of course, this very small difference between 324 and 329 ohm, around 1.5%, is in the tolerance margin and is perfectly accepted (no problem at all).

The change of the output capacitors is justified by the same reason: they are in a critical location. The original white CJ capacitors are 2µF 250V with a 10% tolerance. This value is not available actually, and the standard is 2,2µF, which is in the 10% tolerance.

As I am curious, I have asked the CJ importer about the price of a capacitors upgrade using CJ capacitors: well... just forget it ! I feel that the E.U. Importers margins are like they were in the vintage period: a bit crazy...


So I have search for top level replacement capacitors with 2 constraints:

  • I did not want to go to the Teflon capacitors such as the VH Audio ones for example (because of the price and because I am not convinced by the teflon caps)
  • The size of the replacement caps should almost identical to the CJ original ones

I have selected the CLARICAPS MR, that are the top of the line of the ClarityCaps models. They are rated 2µF 630V.

They look wonderful with their blue jacket, but … they also sound wonderful !



To implement these capacitors, it has been necessary (like for the diodes) to drill the circuit board in order to enlarge the holes: the Claritycaps have bigger legs than the CJ ones. This is not dangerous because the CJ-P10 is like most of the vintage devices: built like a Panzer...



I have hesitated to change the other white CJ caps (as they do not look of the highest quality) but they are not located at strategic locations from a signal point of view.






The preamplifier has been used for a week and is ready for a serious listening session. The parts are not yet burned in, because as usual, 50 to 200 hours are required for this, particularly for the capacitors.

But, “out of the box”, just turned on, the device is not the same at all.

Remark: my reference preamp is a JADIS JP80MC slightly modified with a better internal cabling, better capacitors at some strategic locations, mu-metal protection for the line tubes, etc... This JP80MC is a true outstanding preamplifier and we have seen a lot of preamps able to compete with it ! The only competitors that I have lessened to are the Rowland-Research, the Threshold Fet-10He upgraded and a Crimson.


My reference system #2 is still used for the reviews because I perfectly know it and it is sophisticated enough to point out the exact nature of the differences between the components.


Here is a comparison between before and after the upgrade:


Original Version Upgraded Version
Lack of dynamics (if the phase is not correctly oriented) This is a totally different device: quick and speed are present
Bass are not enough present No comparison: the bass is therefore punchy
Lack of detail The details are here ! as well as the emotion, the "taping foot syndrom" is present !
Timbres and voices are not the best available Once again the upgrade has completely transfigured the preamp; the voices are as good as with the JADIS. Congratulations for the upgrade.
Power cord attached to the chassis This has been changed and we can therefore use the power cord of our choice


Is there still any weakness ? Of course. But let us compare the two preamps: the JADIS with its current upgrades costs about 17,000€, whereas the CJ-P10 with its upgrades is less than 3,000€... But what is the most surprising, is that this CJ reaches more 95% of the JADIS performance ! So we can say that we have achieve a true challenge !!

What does the CJ-P10 still miss ? Maybe a little more sophisticated trebble, that the JADIS delivers when equipped with the (very expensive) TELEFUNKEN tubes, at a total different price...

It took a long time for me to accept that upgrading is a valuable route: I thought that the original versions, designed by qualified engineers, should not be modified... But the truth is elsewhere.


A dedicated topic has been created on our Forum, so you can discuss about it, follow
this direct link.

This article has been written by
Florent and Nounours.


Creation date : 15/05/2011 @ 17:46
Last update : 08/11/2014 @ 18:57
Category : Preamplifiers
Page read 1649 times

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Reactions to this article

Reaction #2 

by Nounours18200 10/02/2012 @ 21:14

Bonjour Pascal06: j'ai indiqué les réponses à tes questions sur notre FORUM, dans le topic dédié à ce Conrad-Johnson Premier Ten, ici:
A bientôt,

Reaction #1 

by Pascal06 06/02/2012 @ 20:44

Possesseur également d'un CJ Premier Ten, je suis très intéressé par votre article.
N'étant pas un spécialiste de l'upgrade, pourriez-vous me donner un peu plus précisément la liste et les références des composants utilisés et éventuellement les sites où les trouver.
Merci d'avance.e
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