Mxl 770 Upgrade
MXL 770 / Monoprice 600800 Upgrade kit
Saturday, June 25, 2016
Microphone-Parts has come up with an upgrade kit for the MXL 770 and Monoprice 600800. These mics come with a small capsule surrounded with a brass “halo” like the MXL 990. They have two external switches, 10dB pad and bass cut. The electronics are entirely surface mount, so there’s no easy upgrade for the DIY enthusiast.
Microphone-Parts call the kit TL3, presumably “Transformer-Less 3-pattern”. The bass cut switch is replaced with a 3-position pattern selector for Omni, Cardioid, and Fig-8. The circuit is essentially their well-sorted Schoeps type with an adjustable bipolar capsule bias supply. You get a pair of gold plated circuit boards which go together in an “L” shape and audiophile grade parts to assemble the boards, including matched resistors and individually biased transistors as in their other kits. The instruction manual is detailed with color photos and easy to follow.
Microphone-Parts has come up with an upgrade kit for the MXL 770 and Monoprice 600800. These mics come with a small capsule surrounded with a brass “halo” like the MXL 990. They have two external switches, 10dB pad and bass cut.
Stock mic
Green normal
Yellow LF cut
Blue -10dB
Pretty good for a $100 mic, but a bit thin sounding.
Capsule
replaced.
Green Rk-12
Yellow OEM capsule
Flatter overall with fuller low end.
Headbasket
replaced.
Green Mic-Parts 2-layer wedge headbasket
Yellow OEM 3-layer cylindrical headbasket
OEM screen restricts air movement.
Electronics
replaced.
Green Mic-Parts TL3,
RK-12, & headbasket.
Yellow stock MXL 770.
‘Nuff said.
5dB more sensitivity and 6dB less noise too.
Final mic.
Green cardioid.
Yellow Omni
ruler flat below 3KHz.
Blue Fig-8. Wiggles in F.R. mostly due to pattern diff from ref. mic.
The only issue that came up was setting the capsule bias voltage. I set it with a cheap DVM which has a 1megohm impedance on DC volts. Adjusted so the meter read 60V, when I measured it with a 1 gigohm scope probe, the voltage was actually 78V, which is on the high side. I readjusted the trimpot for 65V true, which read about 50V on the cheap meter. I discussed this with Matt, and it turns out his Fluke DVM has a 10 meg impedance and is accurate since it doesn’t load the DC converter as much. He’s added an insert with an alternate way to set the voltage if your meter is like the one I used. See the next entry on measurement techniques.
So this kit isn’t really an upgrade, it’s a brand new pro quality mic which happens to use half of the body of an MXL. For around $450 you get a mic with all three basic patterns, your choice of capsules, and a well tested Schoeps style circuit. A unique feature of this kit is plug-in HF EQ for capsules which need some roll-off. You could flatten the 10K rise of the RK-12 or an ’87 type capsule by plugging in one of several supplied capacitors. Clever. A mic that will match performance with $1000+ models.
MXL or Monoprice donor mic, $85, price varies from day to day. TL3 Circuit Kit $199. Headbasket upgrade $39. RK-12 capsule $129 or RK-47, Rk-87 or capsule of choice.
I started with a new MXL 770 and made measurements. Then I swapped the capsule for a M-P RK-12 and measured again, using the OEM electronics. Big improvement, as you’d expect. Next I exchanged the stock cylindrical headbasket for one of M-P’s tapered wedge types and measured. Finally I installed the TL3 circuit kit and checked it out. As usual, the Full Monty is a real studio-quality mic. Quiet, extended response, great sense of presence without sibilance or screech.
So let’s get started. First, the stock MXL 770.
