elskardio

New 990 Discrete Opamp - 100% SMD version
« on: March 10, 2020, 11:03:27 AM »
Hi Guys,

I wanted to share my latest version of the 990 discrete opamp.

It's 100% SMD... but why?  ???
I've been building a lot of 990s lately for my Twin Servo preamp and it's pretty time-consuming. So how accelerate the assembling process without increasing the cost? SMD to the rescue! I can simultaneously build a panel of multiple opamps and a lot faster than my through hole design. No need to bend component legs or flip the pcb to solder.

All resistors are MELF. Capacitors are COG with the exact values from the original JE-990 schematic. My main concern was the heat dissipation of the output transistors. For most application, I need the 990 to be stable at +/- 16V driving a load of 600 ohm. I just finished stress testing a pair running at +/- 18V driving 150 ohm for 48 hours... I can keep my finger on the transistors  ;)

Now the big question... how does it sound? I only did a quick test between the through hole version and the SMD and I couldn't tell them apart. I sent a pair of Twin Servo to a local studio yesterday. One with a pair of the 990 SMD version and the other with the through hole version. I'll have the audio files next week to compare. If you guys are interested, I could post the files when they're available.

Cheers
Gabriel

Here's a picture:



The output transistors are mounted on the bottom.



I love how low-profile the SMD version is...
« Last Edit: May 04, 2020, 09:22:04 PM by elskardio »


fazer

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #1 on: March 10, 2020, 12:12:50 PM »
 Lean design.   Nice.   Do you sell these or are they just for your use?
« Last Edit: March 10, 2020, 04:10:35 PM by fazer »

JohnRoberts

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #2 on: March 10, 2020, 04:41:50 PM »
I seem to recall Paul Wolff converting his API DOAs over to SMD last century...

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

fazer

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #3 on: March 10, 2020, 05:54:01 PM »
Those api amps do have a hi failure rate.

john12ax7

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #4 on: March 10, 2020, 06:05:29 PM »
How many MELFS rolled away in the process of assembly?

Good idea with SMT,  I've heard multiple people say its faster to hand solder than thru hole.

Fuzz Face

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #5 on: March 10, 2020, 06:40:02 PM »
Really nice looking work as usual. I like how you thermally coupled the diodes to the output transistors, very clever.

Did you do all soldering yourself or are you able to order them with some parts already soldered on?

I want some, if only just for fun :)

pucho812

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #6 on: March 10, 2020, 06:42:59 PM »
I seem to recall Paul Wolff converting his API DOAs over to SMD last century...

JR

yes. and there are some people from last century who claim to hear a sonic difference between the smd vs thru-hole.  I don't by it but they claim it.
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

elskardio

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #7 on: March 10, 2020, 07:39:37 PM »
How many MELFS rolled away in the process of assembly?
1 or 2 haha!  :D
I pick them from the tray with a pair of tweezers and tack directly one side to the PCB.

Lean design.   Nice.   Do you sell these or are they just for your use?
I'll have the first batch of PCBs in 2-3 weeks. If some members are interested I guess I could sell a few. All the parts are available from Mouser or Digikey.

Did you do all soldering yourself or are you able to order them with some parts already soldered on?
All parts are soldered by hand.
Eventually I could have theses fully assembled by the PCB Fab house in China... but for a small run, it's overkill and out of budget.

JohnRoberts

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #8 on: March 10, 2020, 08:52:26 PM »
yes. and there are some people from last century who claim to hear a sonic difference between the smd vs thru-hole.  I don't by it but they claim it.
::)

I generally found that SMD did better than similar TH designs... same exact parts in smaller packages, work pretty much the same (or better).  ::) I found benefits from tighter component layouts with less loop area for magnetic induced noise pick up. Not sure how much of a factor that is for DOAs...(it mattered in mixer mic preamps done by my engineers, last century. )   

In my judgement Paul was a great marketer and serviceable design engineer.  I could never schmooze customers as well as he did.

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #9 on: March 11, 2020, 12:44:52 AM »
... I like how you thermally coupled the diodes to the output transistors...

+1.   Nice layout and soldering dude


evil grill

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #10 on: March 11, 2020, 02:54:45 AM »
::)

I generally found that SMD did better than similar TH designs... same exact parts in smaller packages, work pretty much the same (or better).  ::) I found benefits from tighter component layouts with less loop area for magnetic induced noise pick up. Not sure how much of a factor that is for DOAs...(it mattered in mixer mic preamps done by my engineers, last century. )   

In my judgement Paul was a great marketer and serviceable design engineer.  I could never schmooze customers as well as he did.

JR

Interesting.  I immediately came to think of this: www.davehilldesigns.com/smt_resistror_distortion_rev1.pdf

Tekay

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #11 on: March 11, 2020, 03:26:00 AM »
What did you use instead of the LM394 on the input?
Thomas "TK" Kristiansson
----------------------------------
"The Sound Is In The Iron"
www.vintagedesign.se  www.tkaudio.se

gyraf

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #12 on: March 11, 2020, 04:15:21 AM »
..beautiful work, that..
..note to self: don't let Harman run your company..

living sounds

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #13 on: March 11, 2020, 06:19:46 AM »
Looks great! How about a DIP8 version?  8)

Dan Kennedy

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #14 on: March 11, 2020, 09:19:56 AM »
Very nice work. I'm guessing SSM2212 input pair?

JohnRoberts

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #15 on: March 11, 2020, 09:27:35 AM »
Interesting.  I immediately came to think of this: www.davehilldesigns.com/smt_resistror_distortion_rev1.pdf
The semiconductors are generally the exact same parts just in different packages.

"Small" resistors can be problematic even in through hole packages. The problem with small resistors expresses with higher voltages. I've seen compromised linearity (measurable distortion) in audio power amplifier feedback networks that can have tens of AC volts across them.

More recently when I was designing my outlet tester design, that used smd parts, I found that to realize high resistances at high voltage (tested at 500V) I had to avoid using too small SMD resistor packages.   [edit- I used a 1206 for the 100M resistor /edit[



In my judgement it is not a SMD issue but a size issue, while I doubt you will ever find a leaded through hole resistor as tiny as an 0204 smd.

Considering all these sundry factors is what design engineers do...

JR
« Last Edit: March 11, 2020, 04:31:26 PM by JohnRoberts »
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

elskardio

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #16 on: March 11, 2020, 10:30:09 AM »
+1.   Nice layout and soldering dude
..beautiful work, that..
Thank you guys

------------------------------------------------------
What did you use instead of the LM394 on the input?
Very nice work. I'm guessing SSM2212 input pair?
Yes SSM2212 on the input. I guess it's the official replacement now... John Hardy is using the same.

------------------------------------------------------
Looks great! How about a DIP8 version?  8)
hummmm... Why not  ;)

------------------------------------------------------

Interesting.  I immediately came to think of this: www.davehilldesigns.com/smt_resistror_distortion_rev1.pdf
Thanks for sharing that. I remember reading a comment from a wise guru somewhere (can't remember who) about choosing SMD resistors for audio. His conclusion was, choosing thin films with the lowest temperature coefficient in size 0805 or bigger yielded to lower distortion. If you need high power rating, you parallel multiple resistors.

moamps

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #17 on: March 11, 2020, 07:00:27 PM »
Nice design, but I will suggest for next version moving output transistors on top and soldering small heatsinks around.

elskardio

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #18 on: March 21, 2020, 01:11:12 PM »
Hi Guys,

next week I'm assembling a full panel of the latest revision of my SMD 990.

If you want one, PM me. $30 USD each + shipping.

Cheers

Re: New 990 Discrete Opamp - 100% SMD version
« Reply #19 on: March 22, 2020, 04:19:37 PM »
Can your variation on the 990 drive 75ohm at +/- 24VDC?


 

Related Topics

  Subject / Started by Replies Last post
4 Replies
2758 Views
Last post March 02, 2006, 01:57:09 PM
by Samuel Groner
4 Replies
1690 Views
Last post July 21, 2007, 01:59:53 PM
by mikep
18 Replies
10031 Views
Last post April 11, 2008, 04:25:27 PM
by Samuel Groner
9 Replies
6204 Views
Last post September 27, 2011, 06:46:35 AM
by Harpo