jensenmann

Amek M2500 thread
« on: January 18, 2021, 07:02:39 AM »
Hi group

I decided to create an Amek M2500 thread to collect and preserve informations about these desks. Feel free to post whatever you think is appropriate and needs to be shared. I´m going to fill the thread with bits and pieces as time and knowledge allows.

I´ve attached a picture of my desk. It´s the broadcast version with 24 transformer balanced micpres and 12 transformer balanced stereo line channels. It´s completely torn apart since years. Initially I wanted to refurbish it, but due to moving and servicing so many other desks besides having a job I haven´t much done other than recapping. After all my controlroom in our new house is still an empty shell with nothing inside than the console frame....

A few month ago a friend called me since he bought a M2500, too. He needed some help with installation, so I passed by to have a look at his desk. It turned out that there were micpre cards and group cards missing. After getting most of the gremlins out of the desk I made a PCB layout for both cards in the original format to bring his desk back to full potential. Today the micpre PCB prototype arrived. I´ll keep you updated how they turn out.

Here´s the helpful-links department:
http://www.audiomaintenance.com Our member slenderchap stocks spareparts for Amek consoles
https://groupdiy.com/index.php?topic=52462.0 Our member sahib´s Amek based DIY projects

Here are more threads about M2500s:
https://groupdiy.com/index.php?topic=73910.msg935598#msg935598
https://groupdiy.com/index.php?topic=75137.0
https://groupdiy.com/index.php?topic=62928.msg797117#msg797117
https://groupdiy.com/index.php?topic=61152.msg774717#msg774717
https://groupdiy.com/index.php?topic=35002.0
https://groupdiy.com/index.php?topic=37078.msg457230#msg457230
https://groupdiy.com/index.php?topic=61363.0
https://groupdiy.com/index.php?topic=73147.msg926248#msg926248
https://groupdiy.com/index.php?topic=29080.0
https://groupdiy.com/index.php?topic=25238.0
https://groupdiy.com/index.php?topic=72155.0
« Last Edit: February 14, 2021, 07:07:54 AM by jensenmann »
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort


gyraf

Re: Amek M2500 thread
« Reply #1 on: January 18, 2021, 09:10:42 AM »
A piece of information:

The M2500 "Fader Reverse" card relay on the channels is not designed for being mounted vertically/on-edge like it is - so over time quite a few "intermittent" type errors develop around here. IOW, if you have something unstable in channel, you'll want to push the faderreverse-button a couple of times to get around this. Cleaning the relay works for a while, but not long. Haven't found any pin-compatible relay that will work in this position, we were once considering making a subboard with standard telecom relays to get around this..

/Jakob E.
..note to self: don't let Harman run your company..

jensenmann

Re: Amek M2500 thread
« Reply #2 on: January 18, 2021, 11:06:29 AM »
Thanks, Jakob!

I have more to add to the relay topic. Indeed the fader reverse relays are a problem, in my desk as well as in my buddy´s desk. Even worse is the price because they are obsolete. I went through a bunch of different brands and should add that you´d better stay away from Aromat brand relays. Their PCB pins are so soft that if you press the relay into spot a pin can easily get pushed inside the relay. The last few relays I had to replace cost me 3 Aromat relays which went straight into garbage because of that problem. Omron LZN4 12V of course is fine as well as NEC NF4 12V. Make sure you get sealed versions, they work longer than unsealed ones.

There´s a british company making replacement PCBs with a pair of small signal relays: https://cephosrelays.com/omron-lzn4-relay/ I have ordered a pair recently. I´ll keep you updated how they turn out. In the long run I´m going to make a replacement PCB, too, as it might be cheaper to DIY than buying them prefabbed.

The other relays are obsolete, too (Hamlin Reed Relay CCPRI/J). There are five of these on each channel. They tend to make problems but mostly the reason is that they do unsolder themselves! Resoldering often helps. Audiomaintenance.com stocks replacements, though they are not cheap. Years ago I was thinking about doing a replacement but it turned out that the problem is the coil resistance. I found only one manufacturer who´s making something similar, but they have a different footprint. That´s Pickering Electronics 101-1-C-5/3 relay. Now guess which relays AML is using... Since these relays are no stock part, you have to order >1000pcs to get a decent price from the maufacturer. That makes no sense for a single person considering that you still need an adapter PCB, etc. After calculating everything I decided to buy them from Colin (Audiomaintenance). In the end he´s offering them for a fair price.

I had a conversation with Graham Langley about the relays years ago and he told me that the brands were chosen for lowest current. Esp. if you replace the Hamlin relays with current type 12V relays you´ll run into problems on the 12V (actually 11V) rail. My buddy´s M2500 has all CCPRI/J relays replaced with currently available relays on adapter PCBs, done by the last owner. He  blows the 8A fuse on the 11V rail every few weeks. It makes sense to stick with the AML solution as those Pickering relays are nearly the same resistance as the original Hamlins.
« Last Edit: January 18, 2021, 11:09:49 AM by jensenmann »
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

jensenmann

Re: Amek M2500 thread
« Reply #3 on: January 21, 2021, 01:16:07 PM »
The first preamp card is working. I had to modify the layout a quite bit for being able to add bypass caps to the electrolytics and rails. It´s pretty tight on that board, anyway. The Zetex ZTX214 transistors are obsolete, so I replaced them with BC560C. And for benchtesting I made a small jig on perfboard with all connections and the gain pot. That makes testing a lot easier without using the desk.
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

jensenmann

Re: Amek M2500 thread
« Reply #4 on: February 11, 2021, 02:32:33 PM »
Next one is a replacement for the bus amp card. Again as above, the layout is modified to accept bypasscaps for rails and electrolytics. The new board contains more space for both the input and output caps. They can be doubled in value which is a huge improvement for the lowend response of the desk. Instead of TL072 I´m using OPA2134 because they have lower selfnoise.
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

ilfungo

Re: Amek M2500 thread
« Reply #5 on: February 13, 2021, 09:09:26 AM »
Hi this discussion is a great news!!!
I'm working on a Amek M2000 PSU to rebuilt.
I have 2 psu
one in good condition
and the second ready to rebuilt.
I'm working on GL48 redraw because the boards are in very bad shape...
Can someone suggest me some advices or upgrades for   this board?
Thanks!
« Last Edit: February 13, 2021, 10:10:26 AM by ilfungo »

jensenmann

Re: Amek M2500 thread
« Reply #6 on: February 13, 2021, 01:16:00 PM »
Increase C3 and use low ESR long life electrolytics with high ripple current rating here. Add a 100nF ceramic bypass cap parallel to C3.

Make sure that the power resistors are mounted with a distance to the PCB to prevent browning and overheating the PCB. E.g. use standoffs. It won´t do no harm if you increase their wattage. In theory wirewound resistors with bifilar winding are the best solution in this spot.

Use a thyristor in the crowbar circuit with higher current rating. In case of PSU failure it has to drain a huge current (short circuit current of the transformer winding + discharge current of the big electrolytics). The original part has 4A/20Apeak current rating which is not enough. 8A is more appropriate and a heatsink won´t do no harm either.

Often the TO3 sockets have contact problems with age. Maybe you can find another solution to mount these....

Make the PCB traces wider for better current handling.
« Last Edit: February 13, 2021, 01:56:35 PM by jensenmann »
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

jensenmann

Re: Amek M2500 thread
« Reply #7 on: February 17, 2021, 07:03:07 AM »
The sliderails break easily after all these years. Their plastic has hardened hence it breaks like glass if you slide a channel in with too much force. I broke a bunch of them in my desk already. A friend with a 3D-printer made me spare parts. If you guys need some spares, too, then feel free to contact him and say hi from me: https://audiosohn.com
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort

gyraf

Re: Amek M2500 thread
« Reply #8 on: February 18, 2021, 03:33:14 AM »
Aah, der Felix. Say hello from here!!
..note to self: don't let Harman run your company..

ilfungo

Re: Amek M2500 thread
« Reply #9 on: February 19, 2021, 03:41:38 PM »
The sliderails break easily after all these years. Their plastic has hardened hence it breaks like glass if you slide a channel in with too much force. I broke a bunch of them in my desk already. A friend with a 3D-printer made me spare parts. If you guys need some spares, too, then feel free to contact him and say hi from me: https://audiosohn.com


Hi
there is another fader  part that create the same problem over the years...
With a friend we have redesigned it , if someone need the solid work file ready for 3D print,just ask...


 

Related Topics

  Subject / Started by Replies Last post
27 Replies
12528 Views
Last post November 29, 2007, 01:09:23 PM
by tonebucket
9 Replies
5034 Views
Last post August 25, 2008, 02:40:15 PM
by 12afael
36 Replies
9411 Views
Last post November 21, 2020, 04:33:56 AM
by ipindalieson
4 Replies
4851 Views
Last post January 12, 2010, 05:42:42 PM
by sahib