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Q: The ‘C’ positions on my attack switch does not turn off compression.
A: When the attack control, if switched to ‘C’ will not allow ADDITIONAL compression if the level goes up, it will not bypass the compressor and pop your level back to non compressed. This was done to prevent large levels being sent to the speakers when great amounts of compression are being used.
If you turn the input control all the way down while the attack control is in the ‘C’ position, and then back up, the compressor will not compress signal. To allow the compressor to drop back to zero compression via the attack control, you need to switch to another numbered position.
The ‘C’ function is putting the compressor into hold, without allowing additional signal increases to increase the amount of compression; “hold” on the recovery control does the same thing but allows increased level to increase the compression amount.
Q: How do I set up the gain structure to use my compressor with a console or DAW?
A: 1: After the compressor is wired into your system, send it a zero VU,1KHz, sine wave tone.
2: Set the input control to the number ‘3’.
3: Set the attack control to any of the ‘C’ positions. (This will turn the compression circuit off.)
4: Set the output attenuator control to ’15’.
5: You are now outputting approximately +4dB at the output connector of the compressor.
Setting up your compressor in this way will insure that you have not overloaded the compressor. You will have adequate range on the input control and you have adequate adjustment range on your output control. Due to the higher levels entering the compressor during normal use, the input control is usually positioned lower than ‘3’. Program material will vary the input control as well as the threshold controls position.
Q: How do I get the “best” sound from my compressor?
A: The input control has a dual function. It is used to adjust the input level and to provide the desired compression. As you increase the input, the amount of compression increases. When compression starts is determined by the threshold and how far the input control is advanced.
The input tube has a limit as to how far it can be pushed before distortion. You can use distortion creatively by turning up the Input and turning down the Output while using very little or no compression.
The recovery control determines how quickly the signal rebounds after the input signal has fallen below the threshold.
The Hold function is a unique feature of the compressor. It is the “jewel” of this compressor and should be used in situations when large amounts of gain reduction are being applied.
When processing the initial attack of an audio track, the slow attack of the compressor will cause an audible thump to be produced. In addition, it will allow the audio to rise back up, based upon the Recovery switch setting. The Hold function can be used to “prime” the compressor with the required amount of gain reduction and prevent the thump from occurring. It will also “hold” the signal at the compressed value instead of allowing the level to move up and down during the song.
To set this process up you playback the track, setting the controls as required and then moving the Recovery control to one of the adjacent Hold positions. This would prevent the compressor release from taking place and maintain the amount of gain reduction. Cymbals can be processed without the familiar “swish” and everything from vocals to guitar and bass tracks will produce a consistent, signature sound.
Q: What do I need to do when I replace the 6BC8/6BZ8 tube in my LIVERPOOL compressor?
A: You must balance the cathode and the anode of the tube. Here is how:
To adjust the cathode balance, turn the trim pot fully CW and then fully CCW, then to the middle position. Connect the negative lead of a digital multi meter to ground and the other one to test pin 3 of the tube socket and note the DC voltage, then measure the DC voltage at test pin 8 of the same socket. Adjust the pot until the voltage at pin 3 and 8 are equal.
To adjust the anode balance, turn the trim pot fully CW and then fully CCW, and then to the middle position. Connect the negative lead of a digital multi meter to ground and the other one to test pin 1 of the 6BC8 tube socket and note the DC voltage, them measure the DC voltage at test pin 6 of the same socket. Adjust the pot until the voltage at pin I and 6 are equal.
Q: What do I have to do to LINK two units together for stereo compression?
A: 1)- LINK two units together with a standard 1/4 inch mono or stereo cable. 2)- Check to see that the 6BC8 tubes in each unit are gain matched, if they are not, contact us and we will assist you in getting a *closer match, for a nominal charge.
DO NOT LINK THE TWO UNITS TOGETHER FOR THIS TEST.
Set the attack and recovery switches to ‘1’. Set the threshold pot to ‘0’
Send the compressor a sine wave from a test generator with the level set to ‘0 dB’ at 1kHz and turn the input pot to ’10’.
The compression meter will indicate a value. Both compressors, running as separate. mono units should read close to the same value. If they do not, record the levels on each unit and contact us. We will send you the tube(s) to get the units more closely matched to operate in stereo.
* Close matching of tubes is acceptable in most all musical situations. We will be happy to supply closely matched tubes for our customers. Many tubes were no longer produced after 1960’s. The manufacturing capability 50 years ago did not allow tubes to be made identically. On complex waveform music, excellent results can be obtained with closely matched tubes.
Audio tube performance may be readily gauged by listening when matching two Liverpool Compressors linked together.
Since the operating conditions imposed upon a tube such as the 6BC8 are complex and may vary within wide limits of operation, the 6BC8, and all tubes as a matter of fact, are difficult to evaluate their full performance capabilities. For this reason we suggest doing a listening test when trying to get as close to a match as possible. A tube tester cannot be looked upon as the final authority. We hope this information is useful.
If more exact matching is desired, we encourage users to obtain a quantity of tubes and match test them until a satisfactory result is achieved.
NOTE: If changing the 6BC8 tube is required, only A QUALIFIED TECHNICIAN should perform this task, following the balancing procedure in the manual.
Q: What was the inspiration to build the Liverpool Compressor?
A: I have owned an Altec 436c for many years. While performing mandatory studio gear maintenance (cleaning and re-capping various pieces of vintage gear), the Altec was next on the bench. My 436c never really sounded that great and was only used on occasion as an effect. While refurbishing it, I decided to apply some modifications and component upgrades. We returned it to the studio to take a listen and determine if the effort was worth it. Jason (our studio engineer/owner) and I patched in the Altec and sent a female vocal track through the 436c. To our surprise the old funky sounding Altec was transformed and sounded great! We continued to run a wide variety of vocalists and instruments through the Altec with very nice results. It’s one of our favorite compressors in our collection.
Although the Altec sounded great, it lacked some features found on a typical compressor. This inspired Brian and I to revisit the technical notes of the EMI modified Altec compressors of the 60’s and apply some of the useful features to our Liverpool prototypes. After several tweaks and critical listening, we found some of the EMI mods were cool but decided to enhance them. We really wanted a version that was hot rodded and worked well in today’s modern recording environment. We paid special attention to the signal path components, transformers and the power supply.
Philosophically, the Liverpool design had to be a little different (not a clone) and also a great sounding creative tool.
The criteria for the Liverpool design were that “the sound” had to be “right”. It had to stand on its own and compliment vintage and modern recording gear alike. The quality had to meet professional standards with low noise, wide bandwidth and suitable for modern recording techniques. The final version became a unique iteration of the original Altec 436 and the Abbey Road compressor. It now has a modern twist which extends beyond the specifications of the old 60’s gear.
Of equal importance, the street price had to be within reach of the larger recording arts community. Vintage gear prices are out of reach for many. Our view is that the young talented artists worthy of great equipment should be able experience the sound and features of premium gear. We were determined to offer the Liverpool at a price accessible to the larger recording arts community and meet the standards of professional studios. Achieving this was a challenge. Nevertheless, we found a way to produce the Liverpool within our guidelines. It was a team effort and we are thankful to our many friends that helped us bring the Liverpool to fruition. We wish all of our users many years of enjoyment.