Merren Audio

First and foremost I would like to pay tribute to Mike Battle and Les Paul for thier pioneering work in the echo reproduction for guitars... RIP

ECHOPLEX EP-3 IN FOR SERVICE

Echoplex units can be quite troublesome due to the age of these units.

Many Echo units claiming to be in "perfect working condition" or "recently serviced" when purchased are usually still in need of plenty of work to get them running properly .

Typical complaints:

1. Poor Erase: The erase head may still work, but there is still some faint signal still remaining when you stop playing. Your band-mates and or possibly your audience may be looking at you funny when they hear your solo playing back after you have finished the song...

The Erase head may not have enough AC bias current to print over the recorded signal. In this case the bias circuit may need modification to increase the bias current and or adjust bias frequency to the erase head.... The quality of the erase depth is measure in dB.

In many cases the Record level is simply too high for the Erase head signal to erase from the tape and can be resolved by adjusting the RECORD level to a sensible amplitude. The trade off is between Signal to Noise ratio and saturating the tape...If the record signal is too low you will need to turn your mix level higher and your echo signal may sound thin. Too strong a RECORD level will saturate the tape and sound murky and bloomy. An optimum RECORD level is to match the DRY signal level or be slightly higher.

2. ECHO WOW & FLUTTER: This is the ability of the tape unit to faithfully reproduce the original signal without frequency modulation. Major sources stem from mechanical rigidness of transport,
frame, motor mounting, belt slippage, motor speed. Typically the rubber pinch roller is dried up and causes tape slippage against the capstan. Some famous musicains prefered the flaws of the echoplex for it's chorusing effect from wow & flutter. Dried up rubber pinch-rollers can be sent to Terry's Rubber Rollers, which is top quality work: http://www.terrysrubberrollers.com

3. Poor Quality Echo Signal: This can have a long list of reasons. Head alignment is typically the main reason for poor echo frequency response. Heads need to be adjusted in 3 dimensions for proper alignment, not just head height. There is AZIMUTH, ZENITH, WRAP, Tape-to-Head contact and Head Height.

Another issue is the coupling caps in the playback and record circuits can be leaky as well as the bypass caps...This can affect the fidelity of both the ECHO and DRY signals. Another source of trouble is the AC bias frequency. A high bias frequency is usually prefered but is limited by tape speed and the gap length in the RECORD head. One way to optimize the AC bias frequency is to set it case-by-case. Tube units can vary from 50kHz to 70kHz depending on the year of the model and component tolerance, where C16 setting the resonant tank with either a .001uF or .002uF, while most Solid-State echo-plex units were about 70kHz. When setting the AC bias frequency, we adjust it to optimize the high frequency response right when it peaks...This is right at the point where the gap length is equal to the signal wavelength. The quality of the AC bias current waveform is significant in that it should have minimal distortions.

4. BIASING:  Tape biasing is essentially LINEARIZATION of the tape's magnetic BH curve by way of mixing an AC bias current with the Audio signal when recording. Although there are several theories to how bias works, it is impericaly known to work. My belief is that the high frequency bias current rate of change on the ferromagnetic domains greatly reduces the incremental Barkhausen effect that the audio signal will encounter. This AC bias current will have a frequency higher than the audio range, typicaly a minimum of 4 to 5 times higher than the highest audio signal frequency to prevent beat frequency. Monkeying with the bias trim pot to obtain maximum peak reproduction signal is not always optimum and in many cases will produce more distortions. The bias adjustment is used to obtain the optimum balance of highest signal amplitude vs best distortion performance vs high frequency response...  Tape speed, Bias frequency, head gap and tape thickness, quality all play a role in biasing. Some of the high performance Mastering tapes re-wound in echoplex cartridges may not bias properly due to the limited bias range of the circuit. Bias circuit modification is needed in some cases to extend bias range, resulting in some extended dynamic range. This may allow for higher RECORD levels prior to saturating, thus resulting in erase issues, since the erase bias current will now need to be increased to properly erase tape to certain erase depth. The erase circuit has limitations especially with respect to the erase head impedance. Too high a bias current can be risky to the erase head windings and will have diminshed returns since the efficiency of the erase head diminishes with higher frequency, therefore a optimum balance must be made. High quality machines will have erase depths of about 80dB....

5. HIGH LEVEL OF NOISE: There are a number of mods we do to lower the noise floor of both the DRY signal and ECHO signal. There are some key locations in the signal path that have significant contribution to noise.

6. BLOWN HEADS: This is an issue that is only resolved by replacing the head, since they are internally potted with epoxy and repair of winding is next to impossible on some models, while some models can be repaired.

For additional Echoplex info there is a terrific site by Regis: http://www.regiscoyne.com/echoplex/

                  KLEMT ECHOLETTE  NG-51 IN FOR SERVICING

3-Record Heads & 2-Play back heads make this unit heavenly.

Built in the tradition of High Quality German Engineering.

The repeat/regen knob is also push-pull switch for activating the second play-back head.

I especially enjoy restoring these Echolette units.

 This unit had a dead play head upon arrival.

Head was repaired and now functioning like new.  

Check out the 3 Record Heads and 2 Play-Back Heads. 
Very Cool Tape Cover EP-3    Photo below is the more rare EP-2 unit with the Sound-On-Sound feature:Notice extra play head as well as SOS toggle switch located in what would normaly be input 2      Photo Below is the early EP-1 model in for servicing. The volume control makes for some interesting over-drive effect.     

Roland Chorus Echo RE-201 and RE-301

  Ampex 351 restoration and servicing  
    REVOX PR77 SERVICING
    STUDER B67 SERVICING  
 
 STUDER G36 SERVICINGThese tube units are amazing and a blast to work on....Look at all those Valvo and Telefunken tubes !!!! 
   

Merren Audio has over 25 years experience in the repair and modifications for all tape echo units including Echoplex, Rickenbacker, Roland Space Echo, Klemt Echolette units.

Including tape recording equipment such as Studer, Revox, Ampex...ect..