A Battery-Powered Low Distortion "Pocket" Audio Oscillator With Auto Off

[mediatechnology]

Here's the assembled gizmo:



The DC power and TRS connectors will be insulated from the chassis.

This is the FFT:

[AnalogJoe]

Are you using an amp to send it to the Focusrite or what are you using as you sound interface?

[mediatechnology]

The output, at 0 dBu, is being fed to the balanced input of the Focusrite 2i2.

On the FFT the stated 796Ω load impedance is the differential input impedance of the pad and the captioned level (+18 dBu) is the differential level feeding the pad.

(Some earlier measurements had slightly different load impedance since I hadn't found the 348Ω resistors.)

The actual distortion may be higher or lower than the reading since it may add or subtract from the A/D's.
To get the actual number I'll use the notch filter.
Earlier measurements on the Protoboard using the notch filter were around 0.00025% attributable to the oscillator.

[AnalogJoe]

I find it quite amazing that the 2i2 can be used to measure such low levels of THD.

[Tubetec]

There was a guy locally who had intended to set up a studio using an MCI console but in the end he abandoned the idea and headed off to the US to work in live sound .Not sure what happened to that console in the end . Damn +-thing was built like the proverbial brick shit house . Reminds me a bit of API , although Im not sure if the two brands are connected in their lineage . There was also a couple of US producers who came to work at the studio I was in later who spoke very highly of MCI .
Wasnt it Sony took it over in the end .

[AnalogJoe]

There was a guy locally who had intended to set up a studio using an MCI console but in the end he abandoned the idea and headed off to the US to work in live sound .Not sure what happened to that console in the end . Damn +-thing was built like the proverbial brick shit house . Reminds me a bit of API , although Im not sure if the two brands are connected in their lineage . There was also a couple of US producers who came to work at the studio I was in later who spoke very highly of MCI .
Wasnt it Sony took it over in the end .

MCI JH-500 consoles sound amazing.

I completely restored a JH-528C for a client back in 2012. This console was set in a studio/rehearsal room. A few months later the owners opened up a studio at another location, and they decided to buy a brand new API console for it. After a few months of use they ended up ditching the API and replacing it with the MCI. They mentioned that they loved the headroom and grit that the MCI had compared with the API. This is a famous, multi Grammy-award winning rock band who loves distortion with a "brit" kind of sound. They told me several times that they loved how they could push the MCI very hard but the sound wouldn't be completely destroyed as compared to the API. I guess that those +/- 32V rails in the MCI are the ones responsible for what they love to hear. Their studio is still standing and the MCI is still there. It is a maintenance nightmare, which, fortunately, is no longer my responsibility. I know the tech who is now taking care of it, hes a good guy.

The biggest downside of the MCI is, in my opinion, contacts and switches. Switches didn't have gold contact plating (only the rotary switches for the EQ section had gold contacts), that, plus the notoriously infamous Molex connectors that were scattered all over the console, are the main culprits for intermittencies, clicks, pops, and just plain old scratching your head as to why channel 15, or whatever, suddenly stopped working properly. There are 32 bus switches, plus the ones in the EQ, aux, and automation per channel, plus the ones in the master section. It is an insane amount of money to replace them all, never mind the amount of work required to do it. That is one of the reasons why, back in the day and even still today, MCI is referred to as "Munchy Crunchy Intermittent". You definitely can't argue about the "intermittent" part, though.

Also, those 32V rails made the console heat up bad! the thing would eat up in no time the 85 °C rated axial electrolytic capacitors it had inside, and they would spill goo all over the modules. That goo is next to impossible to remove. I tried everything with the exception of sinking the whole module into an ultrasonic cleaner. Each module is 1m long, so finding an ultrasonic cleaner of that size wasn't easy nor cheap. I would clean the PCB's with CRC contact cleaner, isopropyl alcohol, you name it. After a while, a layer of greasy goo would reappear. Also, you had to replace every single cap in it (IIRC, around 2500 caps in a 28 ch console), and replace them with 105 °C rated ones, otherwise, they wouldn't last too long. The heat that thing radiates is insane.

P.S. Regarding the console being built like a tank. I had a conversation with one of the JH-500 designers and I asked why they designed the console to be used as a bomb shelter. He mentioned that its older brother, the JH-400, had a metal frame but had some sort of wood beam or panel under it. After some time, the console would bend and they would receive lots of complaints from clients about it. After that, they said: "never again", so when they designed the JH-500 they built it to last till Armageddon.

[Tubetec]

The beige coloured modules ring a bell ,so I think it might have been a 500 series .
I lost contact with the guy after he went to the states .
A thick slab of oak subject to all that heat will do as it pleases , the metal frames will yeild

[AnalogJoe]

The beige coloured modules ring a bell ,so I think it might have been a 500 series .
I lost contact with the guy after he went to the states .
A thick slab of oak subject to all that heat will do as it pleases , the metal frames will yeild

There were 4 revisions for the MCI-JH500. The A and B had beige/cream modules, the A is very rare, but the B is more available. The C and D rev versions are brown. The most common of all revisions is C, although the B is usually more coveted due to still having line-input transformers, while the C had differential amplifiers instead. The D rev had the options of transformers or diff amps, most come with diff amps, but you can still find some with iron. Also, the D rev was the first one to offer a transformless mic input, although transformers were still an option.

The main difference between revisions is the opamps inside. The A and B use an MCI rebranded opamp called the MCI-2002, which is a high-voltage opamp from Intersil that it is now very difficult to find. The C rev used a mixture of MCI-2002 and MCI-2003 opamps, but mostly 2003. The MCI-2003 opamp was no other than a rebranded NE5534. The D rev, IIRC, only used 2003, with perhaps one or two 2002s, but I believe it was all 2003.

Up to the C rev the MCI consoles had a serious downside, that is, the insert point before the EQ was postfader. So if you inserted a compressor and moved the fader, you would be also changing the level feeding the compressor. They fixed it in the D rev, and placed the insert point were it should be. Also, the auxiliary send faders had a problem, due to some grounding issues and after the faders were worn out, signal would leak into the bus even with the faders all the way down. In the D rev they added mute switches to avoid this problem. So, overall, a D rev was much better.

[ruffrecords]

So, I have just two questions:

Can I get hold of the PCB? And what would be a suitable box to house it in?

Cheers

Ian

[mediatechnology]

Ian -

Not sure I have the answer yet to the second question yet. I was going to look at some of the Hammond boxes.

As to the first question I'm sending you a PM.

Wayne