MountCyanide

Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« on: September 11, 2018, 09:40:24 PM »
Greetings folks. I've decided to start a white market thread for this 500 series circuit as I've sold out of my personal surplus and I've gotten more made for those who inquired. I welcome pics of finished builds here (if that's ok with forum rules). So here it is and I hope you enjoy--
Cyrus

Mount Cyanide 818 Mic and Instrumental Preamp

Made for the Jensen 918 Op Amp (gar918, BLU-18), the 818 Mic and Instrument Preamp caters to the low impedance input and feedback network that Deane Jensen spec'd for his original 918 op amp.

I initially made this mic pre for myself because I found some vintage Pacific Recorders 918 blocks with a huge non-2520 footprint. Referencing Jensen's original 918 documentation as well as the 990 application notes, I added multiple input and output transformer manufacturer options, mic input circuitry and a DI. I dug how it sounded and because I only had 2 of those vintage 918's I decided to ditch its huge footprint for the modern ones and to clear up some space for some nicer extras.
 
Relay-activated “PHD”
48v Phantom
20dB Pad
Polarity reversal

Auto-switching Transformer D.I. (unbalanced only)
Jensen JT-DB-EPC
http://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-db-epc.pdf
Cinemag DBX
http://cinemag.biz/direct_box/PDF/CM-DBX.pdf
Lundahl LL1935
http://www.lundahl.se/wp-content/uploads/datasheets/1935.pdf
Pikatron UP3096M
http://capi-gear.com/catalog/product_info.php?cPath=21_104&products_id=207

Input Transformers
Jensen JT-16PCjr
Not featured on their website but available if you contact them
Cinemag CMMI-2C
http://cinemag.biz/mic_input/PDF/CMMI-2C.pdf
Lundahl LL1570
https://www.schertler.com/public/download/1570.pdf

Output Transformers
Jensen JT-11E Series
http://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-11-emcf.pdf
Cinemag CMOB-3 or CMOQ-3
http://cinemag.biz/output/PDF/CMOB-3.pdf
Lundahl LL1517
http://www.lundahl.se/wp-content/uploads/datasheets/1517.pdf

optional snap-in THAT 1646 PCB for transformerless out

Discrete Op Amps
gar918 (from CAPI)
http://capi-gear.com/catalog/product_info.php?cPath=71_72&products_id=527
BLU-18 (from DIY Recording Equipment)
https://www.diyrecordingequipment.com/collections/parts/products/blu-18-discrete-opamp-kit

The 818 name is a slight nod to the 918 and an homage to the area code where Jensen Transformers was and continues to be headquartered (and Cinemag too) – the San Fernando Valley in California, the Silicon State.

$15 for the bare PCB
Comes with schematic, BOM and front panel design file (.fpd).
It's super easy to build. I'll put a kit together if there are requests.
$7.20 Priority shipping in the USA. International shipping depends upon quantity – inquire.

Additional info:
http://www.mountcyanide.com/shop

Email me at [email protected]
Mahalo.
« Last Edit: October 02, 2018, 01:02:23 AM by MountCyanide »


Re: Silicon State: Mic and Instrument Preamp for 918 DOA (500 Series)
« Reply #1 on: September 16, 2018, 09:55:39 PM »
Interested in a pair of full kits or close. Cheera

MountCyanide

Re: Silicon State: Mic and Instrument Preamp for 918 DOA (500 Series)
« Reply #2 on: September 17, 2018, 08:28:30 AM »
Excellent. I'm pretty sure I have enough supplies for a few of these as kits.
Give me a second to think about cost and then I'll reply.
And if more folks chime in here I'll definitely stock up.

MountCyanide

Re: Silicon State: Mic and Instrument Preamp for 918 DOA (500 Series)
« Reply #3 on: September 17, 2018, 08:29:30 AM »
Photos up
« Last Edit: September 25, 2018, 07:25:47 AM by MountCyanide »

MountCyanide

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #4 on: September 25, 2018, 01:39:27 AM »
With Lundahl in/out, Pikatron DI and gar918
« Last Edit: September 25, 2018, 06:45:21 AM by MountCyanide »

MountCyanide

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #5 on: September 25, 2018, 07:23:36 AM »
Frontin

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #6 on: September 25, 2018, 04:57:22 PM »
Just curious. How much for a kit?

MountCyanide

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #7 on: September 26, 2018, 05:05:42 AM »
Hi. Here's what I've got.
Kits being available will be contingent on if we can get folks to sign up for at least 10 kits.
So please sign up here if you're interested and then I'll research further and refine to get the best price.

Quick tentative estimates:
$210 - semi-kit (everything except for transformers)
$390 - Jensen full kit (includes 3, count em 3, Jensen Transformers)
I could do a Cinemag kit instead and that would be less dough.

Here's how I've saved dough on my builds:
- scavenged Jensen JT-123's from eBay (25 bucks!)  It's why I used the E size in the first place.
- Lundahls from GroupDIY's Andre Tchmil
- Cinemags. Period. One of the best bargains in premium iron.
- Pikatron DI (from CAPI)
- EA-2623 - I haven't tried yet but I'm pretty sure it fits.


Also, I'm down to 8 bare PCB's left. When I get down to 4 I'll order more.
« Last Edit: September 26, 2018, 08:36:36 AM by MountCyanide »

iturnknobs

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #8 on: September 26, 2018, 10:01:51 AM »
Cyrus-

Thanks for the product/project and assistance thus far.  Is there any chance I could ask you to increase your front panel order by 4 for me if and when you get 10 kit orders together? I'll obviously pay for all costs involved. If that is a hassle, could you possibly provide the company's contact info so that myself and others can get theirs fabricated?
-Brian

MountCyanide

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #9 on: September 26, 2018, 07:08:13 PM »
Hey Brian ,
Not so sure when we get to 10 here so I'll recommend you to go ahead and order.
The .fpd file I sent is from Front Panel Express in Seattle.
Download their software and open up the file
http://www.frontpanelexpress.com/downloads/front_panel_designer
Go to the "Pricing" tab under the file menu and you can order directly from within the app.
A snap! Enjoy.


MountCyanide

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #10 on: October 10, 2018, 08:37:13 AM »
Just wanted to add that Per Lundahl said this regarding the zobel in this circuit -
"I am more and more inclined to think that often in audio the purpose of a zobel network is to please the eye more than to please the ear. In my opinion, with a zobel network the square wave response looks good, but often sounds dull...
However, of course you can try the 2.8k + 0.7nF suggested in the LL1570 data sheet"
Sounds to me  like a vote for OMIT from the man himself.

TillM

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #11 on: October 14, 2018, 06:30:29 PM »
Just want to show your guys a EQ Prototyp from Cyrus.
This was planned as 500-Series EQ, but I decided to build it in a 1u Rack.
Just have some small issues with noise, when i touch the screws from the sliders.
Should be a ground issue, I hope I will find the mistake.

TillM

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #12 on: October 14, 2018, 06:31:11 PM »
and from the frontside


MountCyanide

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #13 on: October 15, 2018, 06:54:27 AM »
Fresh!!!!!
If you haven't, be sure to drill a star point on the rear of the chassis where you'll connect all of your chassis ground connections.
The pin 1 of input (only) XLR's should connect there.
Also, be sure to insulate the top right mount pad of the pcb's. Those are connected to chassis ground (Pin 1 of the edge connector).
There should be a total of 5 wires going to the star point.
- (2) XLR input Pin 1
- (2) Edge Connector Pin 1
- (1) IEC inlet Safety Ground
And if there are any pads or conductors that are exposed on the pot pcb- be sure to cover them up with non-conductive electrical tape.

I'm really glad you did this and like it.
The new version of this circuit is totally different now- I'll send them to you when they're done.

Thanks Till!

Cyrus

TillM

Re: Mount Cyanide's Mic Pre for the 918 DOA (500 Series)
« Reply #14 on: October 15, 2018, 06:20:49 PM »
Thanks Cyrus !
Your advice was just gold.
Now the unit is silent as it should.
Test it on my Snare and kick drum and it sounded awesome !

I really appreciate it, that you will send me some new revision PCBs. Thank you !