AKAI M7 M8 / Roberts 770 Mod updates

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RodC
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AKAI M7 M8 / Roberts 770 Mod updates

Post by RodC » Sun Mar 18, 2007 10:13 am

I just updated my doc for the 2 preamps in one mod. I tried to make it more detailed and document the changes all the way to the 2 in one circuit.

Ubertar done his own and I have built several for other folks. Mudcloth on this board has a pair I modded for him. There have been many threads the search should find them.

I also posted the instructions in an HTML format along with the zip file that has the updated RTF file and the schematics.

The new doc is: AkaiM7ModsRodChilders_2InOneUpdate.rtf

Just go to http://beyondsanityproductions.com/ and scroll to the bottom:

Akai M7 M8 / Roberts 770 Mods (Complete)
Akai M7 M8 / Roberts 770 Mods (HTML DOC)

EDIT: the above is in the DIY section now.
Last edited by RodC on Fri Jan 25, 2008 1:19 pm, edited 2 times in total.
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Post by buddy holly » Sun Mar 18, 2007 7:48 pm

cool! i hadn't been following this. thanks for sharing!!!

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Post by Mudcloth » Mon Mar 19, 2007 9:55 am

Thanks for the update, Rod. I've been keeping my eyes open for another set of M8's. I feel like I could tackle these mods myself now with the new updates.
I took mine to a session a few weeks ago and the engineer loved these pre's. We used them for overheads and guitar dubs. Everytime I do a session with him he asks me to bring them along.
We should start a RodMod club. Tape op Derrick was going to do his a while ago. Paging.......
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Post by RodC » Mon Mar 19, 2007 11:10 am

Mudcloth, you should be able to do your own now that you have a pair to look at. The hardest part is getting rid of all the extra stuff in there. I always pull one of mine out of the rack when doing one, just for reference.

Once you get it to this point (noted in the docs) you can begin to formulate your own input output designs.

I'm about to do some for a couple of guys in London, we are going to try some cinemag trannys with some different impedance options for ribbon mics. I'll let you know how it turns out.

Glad to hear you are liking yours, mine ends up on every project I do.
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Post by ThunderFaceWizardHead » Mon Mar 19, 2007 10:08 pm

Thanks for all your work on this Rod. I just scored an M8 for $50 shipped on the bay yesterday, and look forward to tearing into it. I was browsing through the documents and was wondering if you had found any alternatives to the M67 input transformers? Or is buying a M67 and pulling it apart the best bang for the buck?

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Post by RodC » Tue Mar 20, 2007 5:37 am

Right now the M67 and 68 are a good bang for your buck. I only tear them appart if they are in very bad shape. The Cinemags are looking real attractive, and the prices are pretty good. I will post pack when I get the ones in we are about to try.

We are trying the CMMI-7C, you can check it out here:

http://cinemag.biz/mic_input/mic_input.html
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Post by ThunderFaceWizardHead » Sun Apr 01, 2007 11:16 am

Hey Rod, I was wondering if you had any news on those Cinemags yet?

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Post by RodC » Sun Apr 01, 2007 7:11 pm

Just posted an update here.
http://messageboard.tapeop.com/viewtopic.php?t=43749

Are you trying to compete with my 'stach!!
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Post by ThunderFaceWizardHead » Fri Apr 06, 2007 10:56 pm

Thanks again Rod. I've stripped the right pre, and I'll probably be placing a parts order soon. In the latest mod, you've got a cinemag and a shure transformer in each pre, correct? I'm still debating wether to go the cheap route or just order cinemags for all the channels. Unless of course there is some other suitable transformer out there, then I'd be willing to do some guinea pigging.




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Post by RodC » Mon Apr 09, 2007 6:15 am

ThunderFaceWizardHead wrote:Thanks again Rod. I've stripped the right pre, and I'll probably be placing a parts order soon. In the latest mod, you've got a cinemag and a shure transformer in each pre, correct? I'm still debating wether to go the cheap route or just order cinemags for all the channels. Unless of course there is some other suitable transformer out there, then I'd be willing to do some guinea pigging.




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There is a Cinemag on the EF86 stage and a Shure on the 12ax7 stage. Only one tranny per channel.

Start with the cheapest, if you like it you can alwasy upgrade.
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Post by RodC » Mon Apr 16, 2007 9:02 am

Here is a draft schematic, I'm still tweaking a bit. You may want to run the input trannys through a switch on the 1/4" jacks to disconnect them when the high impedance inputs are used. Also, the output level controls are only effective in about 1/4" of their turn, I expected this and was willling to put up with it to get the rather constant 500K impedance on the output.



AkaiM7RightSchematic _MOD_BorisModel.jpg
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Post by ThunderFaceWizardHead » Tue Apr 17, 2007 9:02 pm

Thanks for getting that schematic Rod. I've got to get some transformers.

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Post by Antero » Thu Apr 19, 2007 2:54 pm

If I wound up using other transformers (say, other than the Shure type being as they require cannibalism) would I have to change anything, or just grab an appropriate transformer and make sure I had the wires going to the right places?
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Post by RodC » Thu Apr 19, 2007 3:52 pm

Antero wrote:If I wound up using other transformers (say, other than the Shure type being as they require cannibalism) would I have to change anything, or just grab an appropriate transformer and make sure I had the wires going to the right places?
Should be pretty simple, just make sure the secondary side is made for a High/Med impedance preamp imput. Find out what shunt resistor it has and this will be a pretty good indicator.

Look for one with a gain of about 15.

I know cannibalism sounds bad, but I have found these mixers in such bad shape. Worn out jacks, pots, broken meters....

I hate to tear things up but I also had a guy sell me some for $5 that he was about to pitch!
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Post by Antero » Thu Apr 19, 2007 8:52 pm

Cool, thanks.

My concern about cannibalism was less "I'll have to destroy this piece of gear," what as these Akai pres came from a tape machine to begin with, and more "Will I be able to find such a device to cannibalize? Dunno!"
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