Mini³ parts, cMoyBB boxed up

I got some of my Mini³ parts today. Also included in my shipment was a case for my cMoyBB. I bought a transparent blue Hammond enclosure (1593PTBU) with a separate battery door. After some cutting, drilling and hot glueing my first cMoyBB (red) is boxed up. Photo follows later.

I also received the 50KΩ Alps pot, a 470µF Vishay cap, two knobs, two 3.5mm jack inputs and two bass boost caps for my second cMoyBB (green). The Hammond case is too small to place the bass boost pot on the control panel too. A larger enclosure will be needed.

For future soldering of small parts I also ordered a new tip (832 SD LF) for my Ersa MultiPro soldering iron.

Operation Mini³ is a go

Went to my local electronics parts shop today. Twice. I asked if they sold miniature ⅛W resistors. They did! Bought some for my cMoyBB. John Seaber mentions using ⅛W resistors to improve performance. The shorter leads will lower inductance. So that's what I'm doing with this cMoyBB. New this time is that I will make it DC-coupled, I replaced both C2's (input caps) with 330Ω resistors as per John's modifications instructions. This too should improve performance. Bass boost resistors are 22KΩ, I couldn't get 24KΩ. Together with a 50KΩ pot it will give me a variable bass boost resistor with a maximum of ~15.3KΩ. I also bought four 0.1µF ceramic decoupling caps. I couldn't get 2KΩ resistors for R3, I opted for 1.8KΩ instead. This means an amplifier gain of 6.5. Slightly higher than the red cMoyBB.

Those ⅛W resistors are tiny! Populating the PCB with these is fiddly, but I managed. Still to buy are the jack sockets, 470µF cap, 50KΩ pot and two 0.1µF film caps.

The local availability of ⅛W resistors opens up a new possibility: making an AMB Mini³ headphone amp.

So I went back with my shopping list for Mini³ resistors and ceramic 0.1µF caps . . .

cMoyBB - small progress

The Alps pot and the AD8397 opamp I ordered from Tangentsoft.net arrived saturday. The AD8397 is going into storage, I may someday make a Mini³ headphone amp.

I just got around to measuring the DC-offset of my AD8066 equipped red PCB cMoyBB amp

• bass boost off: 0.8mV and -2.4mV
• bass boost on: 1.9mV and -5.6mV

Good, low values! Too high a DC-offset can (and will!) destroy your headphones.

I also soldered in the red LED. The green PCB cMoyBB got its opamp socket soldered in.

Green cMoyBB

My green cMoyBB PCB arrived here today. I also bought the TLE2426 voltage splitter for it and 100 grams of  0.5mm (~0.02") leaded solder for soldering small components like SO-8 form factor opamps. Still waiting for the AD8397 and Alps pot.

I emailed John Seaber (of cMoyBB fame) about using an AD8397 as the opamp in a cMoyBB. He strongly advised not to proceed in that direction. Not even with added decoupling. The AD8397 is a power hungry opamp that draws so much current at idle the TLE2426 only barely is able to supply it. Using it as an amplifier is out of the question with the cMoyBB PCB. The AD8397 requires a PCB specifically made for it and thus doesn't qualify as a drop-in replacement. Talk about cranky. John Seaber advised me to make a AMB Laboratories Mini³ if wanted to use a AD8397. The Mini³ is an interesting headphone amp... It is however not very cheap to make.

What about this cMoyBB then? Well it's gonna be a little bit different from the previous one. This one is gonna have a variable bass boost knob. The bass boost pot is gonna be a 50K linear Alps RK09. Parallel to the pot I'm gonna use a 24K resistor. This will result in a bass boost resistor of 16.6K maximum and give a maximum boost of ~7dB. Opamp-wise I would like to use a OPA2107 in it if it weren't for the price and availablility of the OPA2107. An OPA2134 will do for the time being.

cMoyBB - part two

Don't tell the missus but I'm gonna make another one... This one is gonna be a bit different from the previous one. This time I want to use an AD8397 dual opamp. The AD8397 isn't very easy to implement and might need some work to get it to operate properly. I want a variable bass boost as opposed to an off/on switch with a fixed value. This time I want to experiment with higher amplification gains. I ordered the green PCB this time as I envision this to be a green 'n' mean machine.

Galaxy Maggiorato

Two Hifi 2000/ModuShop enclosures from Italy arrived yesterday. The left one (Galaxy Maggiorato GX383) is for my B1 buffer preamp, the one on the right (Galaxy Maggiorato GX183) is for my K272 tube preamp. The B1 comes first. I've got almost all the parts needed to complete it, it's only lacking a suitable transformer. Now it's time to layout the pot, switches and RCA sockets onto the front and rear panel.

William Kennedy

I just discovered this bit on yellowjackets.com:

"We want to wish Marcus Baylor all the very best as he embarks on a new musical path after 10 years as a member of Yellowjackets. We are deeply grateful to him for his profound musical contributions to the band...

At the same time we are excited to announce that William Kennedy will be back in the drum chair for Yellowjackets as we move forward with our live performances and prepare for a new CD to be recorded this spring."

William Kenndy back in the drum chair, that's the best news for me as a Yellowjackets fan. Marcus is a fine drummer but if I may choose my vote goes to William. The prospect of a new CD is good news too. Can hardly wait.

cMoyBB - Hot glue

Since there's no strain relief on the battery clip leads. John Seaber suggested using hot glue to insulated the PCB from the metal casing. Would hot glue also work for securing those leads? This afternoon I applied a blob of hot glue to the leads, effectively glueing them to the PCB. Works OK. 

Harry Brown - Krasse Knar

I just saw the movie trailer of Harry Brown starring Michael Caine. This is a must-see IMO. Move over Paul Kersey, Harry Brown is in town!

cMoyBB - It's alive

I got my Alps pot today. I soldered it in, hooked up the battery clip. Inserted the OPA2134 into its socket. Connected a 9 volt battery and switched it on. Measured DC offset: a few millivolts. That's good. Switched it off, connected my iPod, inserted my PX-100's and turned on the amp. No noise at all just silence, just like John Seaber promised. Turn the volume up and there's music! Woohoo, it works!

The bass boost kicks in a hefty amount of low end. Some music will really benefit from the extra bass. Roxy Music's Avalon CD is a bit lean on bass and really benefits from it. Other music is best enjoyed pure, without bass boost. John Mayer's cover of Bold As Love doesn't need it at all. The Still Warm CD from John Scofield sounds much better with bass boost on, now Darryl Jones' bass lines really come to life. Don't switch it on on Erykah Badu's Baduizm Live. I could go on (and on, and on) but you'll get the idea.

Bass boost is a really useful feature to have, but don't have it switched on permanently, unless of course you're a bass head. Remember that the default bass boost is ~9 dB, I opted for a slightly lower bass boost of ~6 dB and I'm glad I did.

I built my cMoyBB with an amp gain of 6, enough for my PX-100's. The overall sound is very good and can be tweaked to taste with a whole range of different opamps. Currently I've got a Burr Brown OPA2134 in it. I also have an Analog Devices AD8066 opamp for it. 

It will have to burn-in for a few hours, and I'll have to box it up too. 

The cMoyBB is fun to build and a great little project if you want to get started in DIY audio (gewoon doen Boudewijn!). It's easy to build, the assembly guide is clear. Apart from the Alps pot and jack-inputs, parts are fairly generic and shouldn't be too difficult too source. Run some simulations before ordering/buying parts to get the frequency response you want. If it's all gibberish to you, you'd better stick to default values. John Seaber is very responsive to emailed questions should you have some.

It's highly rewarding when this cool little amp you built actually works and sounds great. Highly recommended!