FS: Conrad-Johnson LP70S: Superb power amplifier!

[Puma Cat]

For sale is my Conrad-Johnson LP70S stereo power amplifier.

Before the advent of the ART series, the C-J Linear Pentode series of amplifiers represented the very top of Conrad-Johnson's tube amplifier range. The LP70S was their stereo amplifier, rated at 70 Wpc using 6550s or KT-120s.

Cosmetically rated 7/10 to be conservative, but you can see from the photos it's in very good condition.





100% functional amplifier with with performance fully to specification. Note that because of their height, use of KT-120s obviates using the OEM tube cages, which is why they are not shown in the photos. The Tung-Sol KT-120s that provides superior sound quality to the originally specified 6550s. as well as greater tube durability, but the power output is same at 70 watts/channel because of the transformer design.

Use of KT-120s is fully supported, and more importantly, now recommended by Conrad-Johnson as the best tube to use for this amplifier.



Top View:


Rear Panel:

I've installed a ground terminal on the rear panel that makes a proper connection to chassis ground so that the amplifier can be connected to a Shunyata Altaira ground-plane noise reduction hub. This terminal is visible below the left Fuse Out LED.

Full disclosure about cosmetics: The front gold panel and top of the amplifer are virtually like new and near-flawless. There are some small marks in the texture of the wrinkle finish paint on back the transformer cover and some marks on the amplifier chassis bottom cover from the original owner placing the amplifier on StillPoints. These are minor cosmetic imperfections that can be hard to see unless viewed in exactly the right light. These imperfections are cosmetic only and do not impact the performance or sound quality of the amplifier in any way. They are not visible from from the front panel or top view. I've tried to show them here on the back of the transformer cover as best as I can in the light used for photography.


Input stage tubes are Gold Lion 6922s, which sound superb, easily available and durable. These are the same tubes used by C-J. Both tube sets are a bit over a year old, so should have a good 7-9 years of tube life remaining.

Below is the description, specification and design brief from Conrad-Johnson:
LP70S, LP140M, LP275M Vacuum Tube Power Amplifiers
These new conrad-johnson linearized-pentode amplifiers are designed to meet the needs of industry professionals and audiophiles who seek audio perfection for their reference systems. While the demand for precision and musicality is the common denominator of these systems, the power requirements can vary considerably. To meet these varying needs, we offer the LP70S stereo amplifier rated at 70 watts per channel, the LP140M monaural amplifiers rated at 140 watts and the LP275M monaural amplifiers rated at 275 watts.

The LP amplifiers share the same basic audio circuit.
This circuit consists of three stages. The input signal is amplified by a triode amplifier. The signal is then direct coupled to a cathode coupled phase-inverter. This high current, triode phase-inverter stage provides a balanced, low impedance drive to the output stage. Output power is developed by 6550 output tubes, chosen for their musical accuracy, high power, and reliability. Each channel of the LP70S uses one pair of 6550s to produce 70 watts per channel, the LP140M uses two pair to produce 140 watts per each mono chassis, and the LP275M uses four pair to produce 275 watts. The output tubes are operated in ultra-linear configuration which offers an optimal combination of high power and low distortion. The massive conrad-johnson trans-spectral output transformers have intricately interleaved windings designed for extended bandpass and high phase linearity. A small amount (about 12 dB) of loop negative feedback reduces distortion and achieves a sufficiently high damping factor to control reactive loudspeaker systems.
Separate, low impedance, discrete dc power supply regulators are provided for the input and phase-inverter stages, preventing the output stage from modulating these stages through the power supply.
These power supplies are designed to maintain a rock solid supply at all audio frequencies. The main power supply reservoir uses a bank of massive custom polypropylene capacitors. No electrolytic capacitors are used in any of these power supplies.

These amplifiers require no complicated adjustments or specialized equipment to maintain. To assure continued peak performance, the owner need only make a simple bias adjustment when new tubes are installed. Built in LED bias indicators allow the user to make this adjustment using only the supplied screwdriver.

At conrad-johnson we are fully aware that component parts contribute importantly to the sonic performance of any circuit design.
The LP amplifiers maintain the exacting quality standards for which con-rad-johnson is internationally known. Resistors are precision laser-trimmed metal foil types. Coupling capacitors are the new Teflon CJD caps and all other audio-circuit capacitors are polystyrene, while the power supplies use large value polypropylene in parallel with polystyrene capacitors. There are no electrolytic capacitors in the audio circuits or in the related power supplies. Proprietary wide-bandwidth output transformers contribute to excellent high frequency performance. Even the machined gold plated OFC connectors and the internal wiring have been carefully selected for optimal sonic performance. Attention to details of this kind enable us to extract the full potential from our circuit designs and ensure that our products will perform to this potential for years to come. Visit a conrad-johnson dealer soon to hear for yourself just how true to the music an amplifier can be.


I also had the $19,500 ART150 stereo amplifier in for review*, the current TOTL stereo amplifier in C-J's lineup, and I can unequivocally state that the LP70S sounds very, very nearly identical to the ART150, the only difference being the ART150 having ~twice the power output and very slightly quieter due to the use of Vishay bulk-metal foil resistors rather than "standard" Vishay metal-film resistors used in the older LP70S. The only way to hear any difference between them at all is to hear them side-by-side in the same room on the same day in the same conditions. Other than that, and double the power of the ART150, these amplifiers sound IDENTICAL in the "real world" for audio performance and quality attributes. That is to say, it sounds SUPERB for any and all audio attributes one would care to discuss, and with true ART-level peroformance, is a bargain at this price. Want an ART 70? Well, this is it.

Comes with the 6550 tube covers (I'll post a photo with them), a full set of tubes and a 1M Wireworld Stratus 5 power cord with IEC C15 connector. I can include the standard, generic black PC if requested, but the WW is much better with silver-plated conductors.

Asking $3000 plus buyer pays shipping (and insurance if requested). Amplifier weighs 70 lbs and comes in the original CJ box and packing materials, and an outer, exterior, box, so I'd estimate that the ground shipping costs could be in the $200-$300 range, depending on destination and insurance coverage. Shipping via UPS Ground or FEDEX Ground to CONUS destinations.

Please reach out via PM if interested or any questions. I'll also provide some very useful additional info about this amplifier's circuit topology vs the ART 150 stereo amplifier (I've got schematics for both). Thanks for taking a look at this beauty. Cheers.

[Formerly YB-2]

As it makes 70wpc assume it is wired as UL (or triode)?
Thanks.

[Robert_Anderson]

Good luck, awesome amp.

[Puma Cat]

Originally Posted by Formerly YB-2

As it makes 70wpc assume it is wired as UL (or triode)?
Thanks.

It's a "linear pentode ampliifer", hence the LP designation.

[Puma Cat]

I got a message from US Audio Mart, asking me to prove that the amplifier I posted an ad for was actually in my possession! Ha!

My guess is the photos looked a little "too good" (? ) and perhaps they thought they were professional shots from a product photographer or magazine review of another LP70S. So, I had to write a handwritten note, take a pic of it on the amp and upload it to the ad's set of photos.

Little do they know...I'm also a professional photographer! Nyuk, nyuk, nyuk...

A Porsche GT2 RS I shot while I was on a real estate assignment because, well you know..it was a Porsche!

[clpetersen]

That is funny. And the Porsche looks stunning too.

[Puma Cat]

Yeah, the Porsche was stunning.

The owner also had a Ferrari 488 and a Bentley, but it was the Porsche that had me at hello...

[Famester V1]

Wow, that is a beautiful Porsche
Great photography too!

[Puma Cat]

Originally Posted by Famester V1

Wow, that is a beautiful Porsche
Great photography too!

Thanks!

[2bornot2bop]

Originally Posted by Puma Cat

Yeah, the Porsche was stunning.

The owner also had a Ferrari 488 and a Bentley, but it was the Porsche that had me at hello...

PC, you’ve got mad skills!