[Griff]

On another note : I haven’t been able to use the “FetHead” with the VC7. It worked great on the VC3, gave me a clean extra 15dB, much needed with the RE20 mic. On the VC7 however, it totally changes the tone depending on the impedence setting. None of them sound any good, so I’ve been using just the VC7’s own gain. I’m up around 55 which does raise the noise floor a bit.

I noticed use of the TL074 and MC33078. I’m sure much has changed in IC op-amp design since the VC7 was designed (as well as pricing and availability). I imagine there’s some value in upgrading these. Perhaps with less nose and/or more gain?

Is that feasible? Maybe wishfull thinking.

Or else , just any recommendations based on what you may have learned lately while working on the new voice channel? (Sorry, I do like to tinker )

[Griff]

Hi Ted,

Sorry for the late response, and thanks for the offer of the manual, I will drop you an email after this post!

I just wanted to feed back on my recent findings with hum on Ch2. I had observed before that the AC wire for the bulbs were twist-tied in place, so that they were laid right across Ch2 circuit (which looks tidy, for sure, but maybe not a great idea technically). As I had some crackling pots and was in there anyway, I decided to re-route the wires. There was enough slack to raise the black bulb wiring so that it was well clear of the circuit.

Well, guess what? The hum has almost entirely gone. There’s still a tiny amount more than Ch1, I suspect that is either due to the proximity of the mains transformer or the already discussed problem with input tranny 2 going microphonic.

I guess there was probably a change in wire routing between your final design, and how that was interpreted in production. 🙄

So I hope this helps anyone else with a VC7 and who notices a hum on Ch2!

And by the way – I used DeOxIt spray for the pots. Amazing stuff!!

EDIT : added a couple of pics to show the routing of the bulb lead.

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[Griff]

Thanks Ted, I’ll give it CH2 go in my next session and see how I get on!

Another question: I don’t suppose you have any user manual for the VC7? I think I’ve figured most of it out, but it’s always nice to read what you had to say about the design and function.

[Griff]

Thanks for the advice Ted!

I used it in the session this weekend and ran it nice and hot, sounded much better and didn’t even notice the noise floor

As for the EQ. 3.5KHz is close enough, so maybe no need to tweak it to expand the range (although that would be useful).

Thanks again,

Griff.

[Griff]

Thanks for the swift response Ted!

I took some brave pills and popped the lid off this evening. (The catches on those Switch Craft plugs had be vexed for a few minutes! But I worked it out eventually).

I had a tap around the board with an eraser pencil, and for sure, there’s microphonics on both channels like you say. But CH2 is much louder.

I’m fairly confident the microphonics are from the transformers, it’s loudest if I tap on them or the immediate vicinity.

But like you say, I can live with microphonics to a certain extent, it’s the 50 Hz hum which is the real concern.

I did notice that the AC for both lamps runs right long the top of CH2 input circuit and is tied to the various wires coming from that area, so I wonder if CH2 is simply amplifying AC from there. I guess a few minutes with a soldering iron could test that theory.

Finally, the only thing visually amiss are the four output caps, they are all slightly domed, so it could be they need replacing. But conversely, the input caps look just fine.

I did try the sum and difference outputs too. I can hear the hum on both, although it’s far quieter. Given all the output caps look suspect, it possibly proves nothing.

At least channel 1 is good, so I can crack on with the vocal session booked for this weekend

P.S. This reminds me of another similar issue on another bit of kit….I’ll start a new thread

[Griff]

There seem to be quite a few variations. The “square” edged model I think you found, seems to be the latest. Earlier models include one running on batteries and one requiring phantom power.

This one appear to have a “proper” capsule. I suspect this is the model we’re seeing on eBay as BM-700 (even though this video says BM-800)

https://www.youtube.com/watch?v=EqR0os3r_2Q

I guess there’s only one way I’m going to find out

[Griff]

I believe that’s the version made by Feilo and sold by PMI and is essentially a repackaged MXL V67.

There were also some made by 797 audio which made the JM47 a repackaged MXL 2001.

The original JM47 (I believe made by Soundking) is very similar to the one posted, but doesn’t have the tapered top. There is a picture of it in the SOS article : JoeMeek JM47 Meekrophone

Keep your eye open for an original JM47 as designed by Ted, it’s a nice mic for your locker and a piece of history. They occasionally come up on eBay.

DISCLAIMER: This is information I’ve scavenged from various forums over the years, so you never know how accurate that is! Feel free to set me straight Ted!

[Griff]

I have seen these Ted! In fact, every time I go onto by eBay bookmark, one of these is at the top of the list. At just over £22 and looking miniature. I wouldn’t have given them a second thought. I’m half tempted to give one a go now just for a bit of fun. Perhaps good for miking up a guitar cab?

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