Echo North
Well-known member
Please post any questions, comments, or build suggestions.
Purchase Link:
http://Hairballaudio.com/lola
Manual and Assembly Guide:
http://www.hairballaudio.com/LolaPP/LolaManual.pdf
The Story of Lola:
The Lola was conceived a few years ago during a conversation between Ed Anderson and I regarding designing a project for the then new EA-10468 and EA-1166 transformers. I worked on it sporadically in 2010 and extensively in 2011.
Rather than creating another single op amp or 2-stage pre, Ed suggested a fully differential design using two op-amps. The topology is based on the classic 3 op-amp instrumentation amplifier (in this case the output transformer is the third op-amp) and Cohen’s Double Balanced design. Though certainly not a new concept, it does allow us to see how the topology would perform with two discrete op-amps and the artfully crafted EA-10468 and EA-1166 transformers. The stock Lola includes two John Hardy 990C discrete op-amps.
The Lola maintains a completely deferential signal path from input to output. The benefits to the topology are lower noise, through use of the differential design, and a high CMRR common with this topology. It also allows us to take advantage of the excellent balance of the EA-10468 input transformer. In addition, because there are two op-amps in parallel, available output drive current is increased, lowering output impedance; improving output transformer performance and increasing the maximum undistorted gain. In this regard it’s similar to running a single op amp design on 24V rails.
The gain stage provides 65 dB of clean gain in 4.5dB steps utilizing a Grayhill rotary switch. The 600Ω Bourns t-pad on the output allows the user to fine tune the gain setting. There are three illuminated pushbutton switches to select phantom power, phase and line mode. Activating the relay controlled line mode flips the input transformer making it a step down input. This allows the user to use the Lola on line level material. A pad has not been included due to the low ratio and large adjustable gain of the Lola. A 1:1.75 ratio input means the Lola has a lowest gain setting of 16.5dB reducing the need for a pad.
The DI accepts a ¼” unbalanced cable. Inserting a cable activates a relay that controls DI/Mic in circuitry. The DI passes through 2 FET buffers creating a differential signal to feed the 10468 input.
The light pipe LED meter has selectable VU and Peak metering. Though the VU mode is actually average metering (90% of RMS), it’s calibrated to VU metering with little effect on peak mode. 0dB on the meter scale represents +4 (1.23V) in VU mode. A simple resistor change allows the user to have 0dB equal to 0dB (0.775V) if preferred. Peak mode displays the peak value of the waveform in the same scale.
The front panel and L bracket are made in the USA . As a nod to the original 10468 input transformer, the durable front panel is finished with a “hammered” powder coat. The knobs are machined aluminum and have plenty of grip for the Grayhill rotary.
The Lola comes in 3 kit options (pricing will be announced shortly):
1. Complete kit with ever part you need to complete the build including 2 John Hardy 990C op amps.
2. Complete kit without op amps
3. Bare bones metal work and PCBs only.
Internal Shot:
Simplified Block:
http://www.hairballaudio.com/diy_images/Lola-Block.jpg
Lab member Bieckmusic was kind enough to record and post sound files. They can be found here:
http://www.groupdiy.com/index.php?topic=28923.msg599577#msg599577
Some Lola related discussion can also be found here:
http://www.groupdiy.com/index.php?topic=47566.msg599814#msg599814
On a personal note I'd like to thank Ed Anderson for being a wealth of knowledge and an all around awesome guy.. I'd also like to thank Classic API Jeff for kicking in advice and wisdom and repeatedly asking me "You got that pre done yet?"
Hope you guys like it.
Mike
Hairball Audio, LLC
Seattle, WA
ps. Lola is one of my dogs.
Purchase Link:
http://Hairballaudio.com/lola
Manual and Assembly Guide:
http://www.hairballaudio.com/LolaPP/LolaManual.pdf
The Story of Lola:
The Lola was conceived a few years ago during a conversation between Ed Anderson and I regarding designing a project for the then new EA-10468 and EA-1166 transformers. I worked on it sporadically in 2010 and extensively in 2011.
Rather than creating another single op amp or 2-stage pre, Ed suggested a fully differential design using two op-amps. The topology is based on the classic 3 op-amp instrumentation amplifier (in this case the output transformer is the third op-amp) and Cohen’s Double Balanced design. Though certainly not a new concept, it does allow us to see how the topology would perform with two discrete op-amps and the artfully crafted EA-10468 and EA-1166 transformers. The stock Lola includes two John Hardy 990C discrete op-amps.
The Lola maintains a completely deferential signal path from input to output. The benefits to the topology are lower noise, through use of the differential design, and a high CMRR common with this topology. It also allows us to take advantage of the excellent balance of the EA-10468 input transformer. In addition, because there are two op-amps in parallel, available output drive current is increased, lowering output impedance; improving output transformer performance and increasing the maximum undistorted gain. In this regard it’s similar to running a single op amp design on 24V rails.
The gain stage provides 65 dB of clean gain in 4.5dB steps utilizing a Grayhill rotary switch. The 600Ω Bourns t-pad on the output allows the user to fine tune the gain setting. There are three illuminated pushbutton switches to select phantom power, phase and line mode. Activating the relay controlled line mode flips the input transformer making it a step down input. This allows the user to use the Lola on line level material. A pad has not been included due to the low ratio and large adjustable gain of the Lola. A 1:1.75 ratio input means the Lola has a lowest gain setting of 16.5dB reducing the need for a pad.
The DI accepts a ¼” unbalanced cable. Inserting a cable activates a relay that controls DI/Mic in circuitry. The DI passes through 2 FET buffers creating a differential signal to feed the 10468 input.
The light pipe LED meter has selectable VU and Peak metering. Though the VU mode is actually average metering (90% of RMS), it’s calibrated to VU metering with little effect on peak mode. 0dB on the meter scale represents +4 (1.23V) in VU mode. A simple resistor change allows the user to have 0dB equal to 0dB (0.775V) if preferred. Peak mode displays the peak value of the waveform in the same scale.
The front panel and L bracket are made in the USA . As a nod to the original 10468 input transformer, the durable front panel is finished with a “hammered” powder coat. The knobs are machined aluminum and have plenty of grip for the Grayhill rotary.
The Lola comes in 3 kit options (pricing will be announced shortly):
1. Complete kit with ever part you need to complete the build including 2 John Hardy 990C op amps.
2. Complete kit without op amps
3. Bare bones metal work and PCBs only.
Internal Shot:
Simplified Block:
http://www.hairballaudio.com/diy_images/Lola-Block.jpg
Lab member Bieckmusic was kind enough to record and post sound files. They can be found here:
http://www.groupdiy.com/index.php?topic=28923.msg599577#msg599577
Some Lola related discussion can also be found here:
http://www.groupdiy.com/index.php?topic=47566.msg599814#msg599814
On a personal note I'd like to thank Ed Anderson for being a wealth of knowledge and an all around awesome guy.. I'd also like to thank Classic API Jeff for kicking in advice and wisdom and repeatedly asking me "You got that pre done yet?"
Hope you guys like it.
Mike
Hairball Audio, LLC
Seattle, WA
ps. Lola is one of my dogs.
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