Adcom GTP-500 II Stereo Pre-amp/Tuner - *Sold*

[japosey]

Up for sale is a nearly mint Adcom Pre-amp and Tuner. The item has been tested and works like a charm. Cosmetically, it is in excellent condition. It features 6 inputs, including phono and 2 outputs, plus an AM/FM tuner. No remote included

Below is a review from Ken Rockwell.

ADCOM GTP-500 II

Rear, ADCOM GTP-500 II (about $150 used). enlarge. This free website's biggest source of support is when you use these links, especially this link directly to the ADCOM GTP-500 II at eBay (see How to Win at eBay), when you get anything, regardless of the country in which you live. Thanks! Ken.

August 2014

The ADCOM GTP-500 II is an analog preamplifier with a built-in AM-FM stereo tuner. Use it as your control center on your desk, add a remote power amp and speakers, and you've got a first-rate hi-fi system.

A pleasant feature of this all-analog preamp is a remote control. The tuner is a quartz synthesizer, the volume control is a motorized potentiometer, and input switching is electronic. Put this in your rack, retire to your chair with the remote, and enjoy it in your music room.

Plug your power amps and the rest of your system into the switched outlets on the back, and with the optional remote control you can turn everything on and off from across the room.

ADCOM pitched these in the 1990s as "the cure for the common receiver," because when teamed up with any power amp, like ADCOM's own, you have a complete AM-FM stereo receiver.

Unusual is true DC-coupling. The GTP-500 II amplifies and controls audio flat down to DC, unless you switch-in the Tone Controls or use the AC ("Normal") preamp outputs.

The ADCOM GTP-500 II has a high-output, zero output-source-impedance (less than 0.2 Ω!) dedicated headphone amplifier with a professional ¼" socket.

This is a 2011 test of an unmodified unit built 20 years ago.

Sound

Its sound is neutral, however colored by some channel imbalance from the relatively inexpensive ganged potentiometer used to control volume. More serious preamps like the Apt Holman Preamp and the Quad 34 use genuine laser-trimmed stepped attenuators instead of pots. The ganged pot in preamps like the ADCOM GTP-500 II wholesale for about 30¢, while stepped attenuators wholesale for about $30. This is the biggest audible limitation of most analog preamps.

The balance control is a typical attenuate-one-channel-at-a-time type.

With low-impedance, high-sensitivity headphones like the Ultrasone Edition 8 there is some slightly audible noise from the headphone amplifier.

The Contour (loudness) control is excellent: it's not boomy and doesn't boost the treble. The Contour control is at least as good as those on 1950s and 1960s integrated tube amplifiers that boosted the deep bass and left the rest alone. The GTP-500 II's contour control is uncanny in bringing out astonishing levels of very deep bass when a full-range system is played at very low levels. Likewise, the Bass control also works great, never making the bass boomy. The treble control affects only the higher treble. The tone circuit doesn't degrade the sound -- and is bypassed unless deliberately engaged anyway.

All of the Bass, Treble and Balance controls are center click-stopped.

The input selectors are reasonably click-free as inputs are selected. Since the remote makes it easy to select between alternate inputs with dedicated buttons, it's easy to compare different input sources, like your Krell SACD player at the CD input and the CD on the same hybrid disc ripped into iTunes and played remotely from the iPod Touch in your hands via AirPlay with an Apple AirPort Express connected to the TAPE 1 input.

I do lab reports first to make sure that this 20-year-old piece of used gear gotten from a stranger over eBay isn't going to go unstable and blow my ears or tweeters, so you'll see an extensive lab report below. I'll be adding more about how it actually sounds as I spend more time with it.

As I do spend more time with it, it sounds smooth, with a perfect combination of warmth and sweetness, especially when listening at low levels with the Contour engaged. At all levels except those loud enough to duplicate a live performance, the Contour control works fantastically to replace the very deep bass that otherwise goes unheard.

Mechanical

The case is sheet metal, the front panel is anodized aluminum and the knobs and buttons are plastic. The four feet are hard plastic. All markings are painted.

Electrical

It's got a fat 16 AWG power cord, with plenty of extra insulation to impress the innocent, but it's only 5½ feet long.

It has two switched and an unswitched polarized outlet.

It draws about 16 watts as I measured it, and draws 5 watts even when turned-off to keep the remote control receiver alive.

Ergonomics

The real volume control knob works great, and so does the motor controlling it remotely.

The click-stops on Bass, Treble and Balance are wonderful, as are their knobs. It's sad how many other preamps make this difficult with either screwy knobs, or skipping the zero detents.

The black push buttons don't make their positions obvious when viewed any further away than a foot.

Input selectors are debounced: you have to tap them for more than a millisecond or they ignore you. I'd prefer direct-entry buttons to having to run through all the options each time, but tough.

The remote control controls most functions, except for Balance, Bass and Treble, which are analog controls without motors. The remote also lacks the MONO switch, which is a real analog switch on the GTP-500 II, which would have been handy for speaker and head positioning.

The remote only controls the Listening selection. It cannot control the Recording selection, so forget trying to use a tape look as an external-processor loop and then being able to select Listening inputs remotely. (When a tape loop is used as an EPL, the Listen input is set to Tape 1 or Tape 2, and the Listening inputs are selected with the Recording control.)

The motorized remote-controlled Volume pot runs at just the right speed via the remote control. I wished its LED blinked as it moved as it does on my Sony CDP-X303ES, but tough, and that the Volume LED were visible from all angles and that the faceplate indices were illuminated, but tough.

Tuners

The tuners are surprisingly great for real-world use.

Most people never use more than a crappy FM dipole antenna, and with that, the ADCOM GTP-500 II is much freer from distortion and noise than more advanced tuners like the Kenwood KT-917 to which I compared it. Even with a dipole, this ADCOM brings in more cleaner than any of the other tuners I've tried. I haven't tried it with a proper roof-mounted directional FM antenna on a rotor.

The AM tuner, with the included loop antenna, was also quite a surprise. While its frequency response is as crappy as almost every other AM radio, it was far more free from birdies, whistles, static and interference than all of my other AM tuners.

The tuner uses a non-multiplexed vacuum fluorescent display.

It's set back into the case, so the top becomes hidden when viewed from above about a 40° vertical viewing angle.

It's easy to tune, with your easy selection of either Scan or Manual modes for the up/down buttons.

Scan works great, stopping right where I want it to -- but it only scans on FM.

The tuner's bright, real-time, 5-red-LED S meter also works much better than the delayed and coarse indications of most other tuners. The 5 segments are well calibrated to show meaningful differences between stations, both AM and FM.

The tuner combines the UNMUTE and HI-BLEND button. It has no automatic hi-blend on weak stations, so if you want to hear weak stations, the strong stations will be hi-blended, or the weak stations will be muted. This isn't as big a deal as it seems, because the hi0blend is much milder than other tuners and this tuner has much less noise when used with crappy antennas in real-world reception than other tuners.

The tuner stores its memory settings with an internal capacitor. It stores its settings for at least 11 days when left unplugged.

Specifications:

Inputs

Line

35 kΩ.

320 mV for 2V rated output (15.9 dB gain).

Phono

47kΩ, 100 pF .

4 mV for 2V rated output (54.0 dB gain).

Outputs

Two MAIN outputs, one DC coupled ("LAB") and one AC coupled ("NORMAL", AC-coupled from the DC output).

100 Ω source impedance.

Two tape outputs: 475 Ω source impedance.

One ¼" headphone output from a separate amplifier.

Output Levels

2 V RMS rated.

10 V RMS maximum.

Frequency Response

Line

5 - 65,000 Hz ±0.5 dB.

Phono (RIAA EQ)

10 - 50,000 Hz ±0.5 dB.

Distortion

Line

Less than 0.004% THD+Noise at rated output (2V).

Less than 0.005% SMPTE intermodulation distortion (60/7k Hz 4:1) at rated output (2V).

Phono

Less than 0.025% THD+Noise at rated output (2V).

Less than 0.006% SMPTE intermodulation distortion (60/7k Hz 4:1) at rated output (2V).

Noise (A-weighted RMS referred to 2V RMS)

Line

-100 dB.

Phono

-84 dB.

Crosstalk

-80 dB at 1 kHz.

Tuners

FM

87.5 ~ 108.0 MHz in 0.1 MHz steps, 75 µS de-emphasis, USA (internal jumpers can set to European 50 µS de-emphasis).

AM

530 ~ 1600 kHz in 10 kHz steps, USA (internal jumpers can set to European channel spacing).

Power

120V AC, 50-60 Hz.

0.5A 250V rear fuse.

Rated 20 W power consumption.

I measure 15.45 watts power consumption, up to a maximum of 18.5W when driving a 37.5 Ω load at maximum sinewave output level.

I measure 4.8 watts power consumption when off; the GTP-500 II's infrared remote receiver is always on, waiting for the remote control signal to wake up the rest of the circuitry.

5.5 foot, 16 AWG polarized power cord.

Two switched outlets rated 500 VA. I tried, and a 200 WPC ADCOM GFA-555 II seems perfectly happy running from the switched outlet.

One unswitched outlet rated 800 VA maximum.

Edited April 9, 2016 by japosey

[ryanm84]

Pm sent

[LochbuieLife]

If it is not sold, I will buy it..

Thanks, Mark

Text: 303 960 4042

 

[japosey]

If it is not sold, I will buy it..

Thanks, Mark

Text: 303 960 4042

Sorry, Ryan above you purchased it.