New racked preamps. 1108 and AM-16

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jho-audio

Well-known member
Joined
Oct 17, 2004
Messages
118
Location
London, Ontario, Canada
Hello,

Time to show off my newest rack jobs and my messy work area. I have had all of this stuff sitting for a few years and finally got around to racking it up.

1108:
http://www.twin-x.com/groupdiy/albums/userpics/1108-front2007-02-04.JPG

1108 inside:
http://www.twin-x.com/groupdiy/albums/userpics/1108-topdown2007-02-04.JPG

AM-16:
http://www.twin-x.com/groupdiy/albums/userpics/am16-front2007-02-03.JPG

AM-16 inside:
http://www.twin-x.com/groupdiy/albums/userpics/am162007-02-03.JPG

They both sound so good, but so different. I definitely prefer the 1108 over the AM-16 and am going to consider getting rid of the AM-16 rack.

Now I need to stop procrastinating my patchbay wiring.

Jason
 
Looks good!

Reminds me I have an 1108 sitting here that needs to be racked.

How's that gain control working out? Or is that an output fader?
 
Thanks!

I have not had a chance to extensively test these out. No drums through either just yet.

The "Gain" is mis-labeled, it should read "Pad" or "Atten". I had the front panels done up in January 2006 and have since learned a lot from this place. These are input attenuators using JLM's dual 1k scheme. They work great as do the JLM DI's. Going forward I will be using the full suite of JLM racking products available as these really simplify a rack job.

Gang of elk, I highly recommend that you get around to racking your 1108. It is an amazing preamp.
 
Thanks guys! Big thanks to Miko for hooking me up with the AM-16's years ago now. Took a while but I'm glad to get those into a working state :thumb:

Not sure about the 1108 input trannies. Ed Anderson may know.

I have started to do up a pcb for the 1108's now that we have a cinemag UA5002 equivalent. I will offer these pcb's up to the group soon if all goes well. I would love to build up another four or eight channels of this pre.
 
bermp
I hear tell the 2108 used a custom input xfmr still used in the 610 and 2-610, which I believe is a cinemag creation , Maybe they can do another run .
I had a chance to use a pair of the originals last weekend and thought they had a lovely low end .
:guinness: :sam: :guinness: :sam:
 
i don't know much about the guts of the 2108. a former forum member did once tell us that the input transformer for the current 610 series pres were cinemag recreations of the input transformer from another piece of vintage gear (not UTC O-1s as used in the original 610). cinemag now sells those inputs as the CMMI-7c, which i don't think is, strictly speaking, the same as what you'd find in an original 1108. then again, i believe the 2108 has an extra amplifier stage before the 1108 line output stage, so a different input transformer could work. and the 2108 lit does tout the input transformer as having multiple ratios. the CMMI-7c certainly is a very nice transformer.

ed
 
holy shit i cna't belive you are thinkng of getting rid of the am16's,... they are incredible...i've gota four pack of htem and they are incredible for durums and gtrs.

oh christ I am drunk! :guinness: :sam: :guinness: :sam: :guinness: :sam:
 
[quote author="edanderson"]i don't know much about the guts of the 2108. a former forum member did once tell us that the input transformer for the current 610 series pres were cinemag recreations of the input transformer from another piece of vintage gear (not UTC O-1s as used in the original 610). cinemag now sells those inputs as the CMMI-7c, which i don't think is, strictly speaking, the same as what you'd find in an original 1108. then again, i believe the 2108 has an extra amplifier stage before the 1108 line output stage, so a different input transformer could work. and the 2108 lit does tout the input transformer as having multiple ratios. the CMMI-7c certainly is a very nice transformer.

ed[/quote]

thanks ed
I know the new 2108 has the selectable input inpedance just like the 610/2-610 . 1K and 4K input options I believe .
It would be great to try and design some preamp with the 1108 line amp .JHO hows that pcb !!
 
Thanks guys!

I have been trying to fix my house to sell for a while and have put many projects on hold. I am going to try to get some time in on this today, this week at very least.
 
hi jason,
great builds. i'm still working on Chae's Bellerophon 4 channel and would also like to try and build an 1108.
i would love to see an 1108 pcb! i was thinking the same thing, with the availability of ed's output xfrmr and the cinemag CMMI-7C equivalent to the input this might be possible now. since the 1108 was originally intended as a line amp, does anyone know what the pre-section of the 2108 is? schematic? :green:
regards,
grant
 
Thanks Grant!

I got some time in tonight to play with the layout. I am going to look at additional FET front ends for the extra gain stage as well. This is going to take me a while yet as it is really my first time at eagle pcb layouts and I'll be trying out the boards before I publish anything. Lots to learn yet but it is starting to take form.
 
hi jason,
i'm glad you're still working on them! :green: i'm patient, heck, i've got a LOT of other builds to do anyway. I wonder if the scott hampton pre section would work? of course if we could find out how the real 2108 front end is like then we'd get a little closer which would be really cool. thanks for taking this on jason! :thumb:
BTW, does your 1108 pres have the 45dB of gain as suggested in the manual? i'm also curious how you connect the input trim (looks like the pot is between pin 1 and the output connectors)? what value/type of pot did you use?
cheers,
grant
 
Hey Grant,

Dual 1k linear pot. Half way down this page is a diagram of the hookup:

http://www.groupdiy.com/index.php?topic=173025&highlight=jlm+am16#173025

I did wire them up for 45dB and it works like a charm. Good enough for my condensers and dynamics.

I'm leaning towards separate PCBs for the 1108 section and a front end to offer up more choices. The FETBloak is going to be my first choice for the front end mainly because I've got some hanging around. Was thinking that a DOA footprint with a simple API circuit would be a good candidate. Thoughts on this?
 
hi jason,
thanks for the info on the pot!
i'm sure the fetbloak front end would be great, though i think you need a very lean step-up (TK suggests a 1:4 on input) xfrmr. i have a feeling this would be a very clean front end with a little sizzle and fast. reviews seem to indicate that the 2108 dirties up quite a bit if you push it, though i don't know if this is due to the front end or the line amp. does your 1108 build get dirty when you push it (meaning the output wide open)?
regards,
grant
 
It sure does get nice and dirty. Leaving the 1108 section as a stand alone or back end (separate PCBs) will give us the option of experimenting. It will also let me get it finished sooner as I'm almost there already. Also, allows for people to use it as a straight line amp, a 45dB mic pre or wide open to other configurations. It's going to be a simple build for the 1108 section as there are not so many parts. I'll try to finish up the design this week or early next.

It would be really nice to get a peak at the 2108 jfet front end, just a bit concerned that a straight copy may cause issues with the manufacturer (even though it is no longer a production unit, it is a recent one).

I'll work on the front end and power supply as soon as the 1108 PCB is ready to go into production.

I'd like to get to the point where this PCB has a supporting front end, EQ and comp section (1176 separate PCBs) so that we can get many projects out of the 1108 PCB.

I'm thinking I'll approach things in this order:
- 1108 (output)
- power supply
- mic pre front end (maybe a few options)
- mic front panel board (relays or switches - should be able to use an existing design for this)
- EQ (inductor)
- 1176 GR, meter and front end PCBs
 

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