Mount Cyanide's 323 Discrete Opamp and 500 Series Mic Preamp

[MountCyanide]

Mount Cyanide 323 Discrete Op Amp
An original circuit - clone of none! 9 transistor amplifier utilizing both vintage style transistors and modern SMD transistors. Designed in Spice then modded out on the breadboard and finalized with tons of PCB revisions. I love this thing.
$40 fully (and meticulously) built.
https://www.mountcyanide.shop/product-page/323-discrete-opamp

818 Mic and Instrumental Preamp
Made for the large vintage Jensen 918 Op Amp  or modern clones (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. Jensen, Cinemag or Lundahl transformer footprints available, please specify when ordering.

Build Documents: https://www.dropbox.com/sh/7p7kpmq2t2qy7e2/AACDvFmxVK91qSeTbVn9c6f5a?dl=0
Mouser Carts:
MTC-818 Mic Preamp
https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=d2e3665e15
MB5 LED Meter Board
https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=3202237879

$20 for the bare PCB
$7.50 Priority shipping in the USA. International shipping depends upon quantity – inquire.

http://www.mountcyanide.shop

Email me at [email protected]
Mahalo.

 

[MasterTheSound]

Interested in a pair of full kits or close. Cheera

 

[MountCyanide]

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]

Photos up

 

[MountCyanide]

With Lundahl in/out, Pikatron DI and gar918

 

[MountCyanide]

Frontin

 

[Wordsushi]

Just curious. How much for a kit?

 

[MountCyanide]

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.

 

[iturnknobs]

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]

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]

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]

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]

and from the frontside

 

[MountCyanide]

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]

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 !

 

[iturnknobs]

I have assembled 2 different preamps, one with all Lundahl transformers and one with all Jensen transformers. Everything seems to work on each except for the 1K trim pot. I have soldered it directly to the PCB. The only way I can get audio is to use jumpers between the output transformer at the provided locations right near the edge connector.  It seems to make no difference what I do with the jumpers near the trim pot on the PCB. I can use them as if there is no output trim pot, but would like to figure out what I have looked over.

 

[MountCyanide]

Hey there -
Wires need to be installed from the output pads to the pot. They're labelled accordingly. JP+1 to JP+1, JP+1 to JP+1, JP-1 to JP-1 and JP-2 to JP-2.  Keep the wires under the board for tidiness as opposed to this photo. Also as opposed to the photo, try to use shielded wire.

 

[iturnknobs]

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.

I am wondering if the same would apply for the Jensen trafos. It seems by looking at the schematic as if this Zobel network(I think)just dumps to ground, so omitting it wouldn't create an open circuit. Also, when purchasing the 16-PCJR direct through Jensen, they provided me with a 680pf WIMA cap. I am guessing this is for the 620pf cap in the Zobel network from your schematic. Any idea why there is a difference?

...thanks for the JP +/- wiring response in previous post.

 

[MountCyanide]

Yep, go ahead and omit it and see if you like it.
620pf is the Jensen recommended cap but definitely an "ideal" value and a more exotic one too. 680 is the standard and readily available nearest value. I've also done 680 in my builds too.

 

[MountCyanide]

The following updates added to the 1st post at the top

The latest version of the 818 (v4.4) now includes an LM3915 based 5 LED Meter. Yes, you can still easily find those.  Input transformer is no longer limited to 1:2 and now includes the footprint for the JT-110K, CMMI-8C, CMMI10C, EA2622 if you want to get creative. The output transformer is now the bigger sized Jensen D, Cinemag 2 and CAPI 2503. All Lundahls removed.

323 Op Amp
I've been working on a completely original discrete op amp for the past year and after tons of revisions I've got it to where I want it. It is a clone of nothing and was created in LTSpice and my breadboard. Research references came from Hans Camenzind, Douglas Self, Nelson Pass, various Google searches and of course the GroupDIY message board. Utilizing vintage style metal hat transistors in the long tail pair and voltage amplifier stage, modern SMD pairs as a current mirror and constant current sources, and the standard TO-126 BD139/140 in the output, the 323 is a hybrid of old school and new school. I'd really love some feedback and reviews so just to get this ball rolling I'm throwing an assembled one in if you buy at least 2 PCB's from me.

I've put some Mouser carts together:
MTC-818 Mic Preamp
https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=d2e3665e15
MB5 LED Meter Board
https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=3202237879