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March 26, 2019, 10:58:47 PM
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News: In order for you to be able to post a new thread in the "For Sale" board, you need at least 10 posts in the rest of the forum, however you'll be able to reply to any topic in the forum even if you dont have the 10 post count. Any posts in the "For Sale" board will not appear in your total post counter.

Any ads, should be posted in the "For Sale" or "Looking to Buy" forums ONLY, and they should be MCI or MCI-related. Please do not advertise your item on someone else's thread (hijack).

If you have any questions, feel free to contact me.

Thanks!

Dualflip

+  MCI Console and Tape Machine Forum
|-+  Recent Posts
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 1 
 on: March 14, 2019, 05:53:15 PM 
Started by rennywilson - Last post by Rob
Nothing too exciting.  Just needed to wake the console up.  A bit of reseatiing the channels.
I've been thinking of ways to get the automation working again.

 2 
 on: March 09, 2019, 10:17:34 PM 
Started by rennywilson - Last post by rennywilson
What sort of problems are you having, Rob?

 3 
 on: February 18, 2019, 07:08:53 PM 
Started by rennywilson - Last post by Rob
Just switched my console on for the first time in a while & need to sort a few channels too.

 4 
 on: February 10, 2019, 05:33:02 PM 
Started by rennywilson - Last post by rennywilson
For whatever reason I tried accessing this page a while ago and it was gone, the domain was for sale etc. Maybe I went to the wrong place but I thought this place was gone!

Glad it's still here, got plenty of mci issues to keep this forum afloat.

 5 
 on: February 10, 2019, 04:22:33 PM 
Started by rennywilson - Last post by Rob
I'm still here.

 6 
 on: February 09, 2019, 03:56:03 PM 
Started by rennywilson - Last post by rennywilson
Vote Now!

 7 
 on: January 01, 2019, 06:16:26 PM 
Started by LDS - Last post by LDS


Hi everyone,

I have a whole lot of parts from a spare JH-600 console up for sale. They are located in Sydney, Australia. Please drop me a PM if you are interested in anything. 

- Channel Strips
- Master Section
- Power Supplies
- Meters
- Faders
- Motherboards
- Patchbay components.


 8 
 on: October 26, 2018, 06:08:17 AM 
Started by TonesOnTail - Last post by Fenris
After doing the mod I recalibrated the EQ, bias, and record level so it's still recording at +9/185. The purpose of the mod is to eliminate clipping on the transients. The rest of the circuit has plenty of headroom.

I don't know the specs of Studer record heads, but the impedance is swamped by the loading resistors anyway. The efficiency (relationship between voltage drive and nW/m) is more relevant. It's probably about the same as MCI heads, but I don't have any data.

I imagine the headroom was less of an issue in the 80's when most machines were 24-track, +9 tape didn't exist, and most people used NR and conservative recording levels.

 9 
 on: October 25, 2018, 05:10:47 PM 
Started by TonesOnTail - Last post by W1DAN
Hi Fenris:

Good info, thanks. I am not concerned about record headroom as I use my JH110B as a player. But for education, I am following your efforts.  My only concern would be the possibility of opening the record head winding with too much current, which you stated that Mr. French says you are safe. So much the better!

I would assume that the Woelke JH110B and C record heads have the same construction (I bet they are the same part number), and thus the same DC resistance and AC inductance? With the Studer, do their heads have similar inductance and resistance values as the Woelke ones?

When you now set your new standard operating record level, do you set to a particular third harmonic distortion level on tape? Is tape headroom affected with the higher recorded flux level?

I have seen a patent where someone takes a current sample from the record path and sends that back to the driving amp for negative feedback to help linearity a bit. They key here is your bias signal has to pass through the amp.

Maximum flux ahead!

Thanks,
Dan

 10 
 on: October 21, 2018, 01:26:16 AM 
Started by TonesOnTail - Last post by Fenris
The audio electronics of the JH24 and the JH110B/C are largely copied from the Studer A800. For some reason lost to history, MCI doubled the value of the two series resistors after the record amp. This results in half the voltage and 6 dB less output.

The JH110C has two resistors in series, one on the record card and one on the motherboard. I bypassed the resistor on the record card, R46, and left the resistor on the motherboard in place.

On the stock machine, 1" 8-track, aligned for Quantegy 499 at +9/185, 15 ips. IEQ equalization, the record amp has approximately 6 dB of headroom. The mod increases it to approximately 12 dB. You should check the output of the record amp with an oscilloscope before and after the mod, determine the clipping point, and make sure you get the same results.

Wider trackwidths such as 1/2" 2-track are more efficient and the headroom is much greater.

Based on information from John French, the record head can handle the extra currrent with a comfortable margin. However, nobody really knows the specs for original MCI heads or whether they all use the same wire gauge. This mod should only be done if you're a qualified tech, you're not happy with the performance of the machine, and you're willing to risk the possibility of burning out the record head.

Some people will dispute this information. Anyone who is interested can do the relevant measurements on their own machine in about five minutes.

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