Editing Echoplex (section)

===EP-4===
[[File:Maestro Echoplex EP-4 with analog meter (edit1).jpg|thumb|EP4]]
In the mid-1970s Market created an upgrade to the EP-3, designated the EP-4, adding features such as an LED input meter and tone controls and dropping the sound-on-sound feature. The EP-4 has an added output buffer to help improve impedance matching with other equipment. A compressor board based on the CA3080 [[Operational transconductance amplifier|transconductance amplifier]] was added to the record circuit of both the EP-3 and EP-4 models for a short while after the EP-4 model was introduced and then the compressor board was dropped from both the EP-3 and EP-4 models. The EP-3 model was also offered for sale alongside the EP-4 model after the EP-4 was introduced.<ref>{{cite news|title=Echoplex: Roots of Echo, part IV|last=Teagle|first=John|date=7 December 2004|work=[[Vintage Guitar (magazine)|Vintage Guitar]]|accessdate=10 May 2012}}</ref>

Battle's final consulting with Market yielded the EM-1 Groupmaster, which offered a four-channel input mixer section and a mono output section. Dissatisfied with the transistor-minded direction Maestro was taking, Butts left the company.<ref name=dregni/> In the mid-1970s Maestro also created the ES-1 Sireko (pronounced "Sir-Echo"), a simplified, echo-only unit with a bin-loop cartridge system.{{Citation needed|date=September 2010}}