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Discrete Op Amp PCB Build

Posted 25th May 2017 at 10:18 PM by googlyone

Well I am home again, and the PCBs for the discrete op amp beat me home.

I used PCBcart, who have a very competitive prototype PCB service -it is certainly not worth your time to make fiddly double sided boards like these at home!

They came out like this...

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And no, I don't have a finger the size of a baguette...

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and thru the microscope which I had to use to solder the bits on:

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There are parts on both sides of these PCBs.

A this point I am yet to mount the miller cap, as I want to play with this a bit. On the schematics there is a "guaranteed to work" value. I want to measure the phase margin and stability into some odd loads - as overcooking this will directly affect...
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Views 268 Comments 4 googlyone is offline

Superlux HD668B SE classA amp

Posted 23rd May 2017 at 09:58 AM by abraxalito
Updated 8th June 2017 at 03:38 PM by abraxalito

My Superlux HD668Bs are the best value purchase I've ever made in headphone kit, far and away the best bang for the buck at their very modest price-point. If any pair of cans is worth designing a specific amp for, they are most certainly on the short-list. The amp I designed specifically for my AT MSR-7s doesn't have enough ooomph for these as the impedance is appreciably higher and the efficiency lower.

So here is my attempt at a dedicated HD668B amp with no corners cut in SQ while still being cheaper to buy the parts for than the cans themselves. I've designed it to run from a single lithium ion cell - a Panasonic 18650 would work fine and give around 60hrs of listening time. Its a single-ended classA topology driven by a single current-source loaded MOSFET. And naturally enough it sounds like no amplifier at all - a straight wire without gain, seeing as its just a buffer.

In actual fact it certainly does have gain, but only current gain. And no shortage of...
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JFET Amplifer and Filter Project

Posted 17th May 2017 at 10:37 PM by SyncTronX
Updated 17th May 2017 at 11:36 PM by SyncTronX (add images)

JFET Amplifier and Filter Project.


A lab was developed with something a little bit more hands on for participants than just blindly doing the NIDA labs. We would benefit from making an N-Channel JFET amplifier and asked if we would be interested. Of course, we werent told the JFET type or gain and didnt know wed also include a bandpass filter. These parameters wed have a drawing from which to choose. Finally, wed have to document and report the entire process in APA format.

Each project is unique and provided on two stapled pages placed upside down in a mixed pile at the front of the room. Each participant was asked to come up and draw their project. I drew project labeled E on the upper right corner of the second page. Included were the following: JFET 2N5485 or 2N5458, Gain set to 22, the Bandpass to be 15kHz 30kHz, and Total Circuit DC Power as Calculated/Measured.
Other resources were...
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Discrete OpAmp - Replaces Dual Channel DIP8 - design and PCB

Posted 11th May 2017 at 06:28 PM by googlyone

Well here I am travelling again, and this time stuck for an extra week away from home. The design bug has bit, and this time I tried keeping things small rather than crazy.

I have built a number of discrete operational amplifiers in the past. Usually integrating everything onto the board so that they wind up being preamplifiers rather than operational amplifiers.

If that confuses you - the difference is that an operational amplifier needs to be plugged into a circuit to be useful, a preamp is a standalone PCB.

The inspiration was seeing a burson amp on ebay. I looked and thought to myself "I keep starting that, and keep ending up with a preamp". Then I thought "Do it right for once".

The resultant goals:
- Dual channel op amp
- DIP8 pinout
- Good perfromance
- Class A (vs class AB which many are)
- Minimum size, whilst
- Sticking to 0805 SMD resistors caps, and...
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Attached Files
File Type: pdf Composite CH1.pdf (11.6 KB, 74 views)
File Type: pdf Composite CH2.pdf (13.5 KB, 47 views)
File Type: pdf Schematic CH1.pdf (24.6 KB, 130 views)
File Type: pdf Schematic CH2.pdf (24.8 KB, 78 views)
File Type: pdf Final Artwork CH1.pdf (21.2 KB, 56 views)
File Type: pdf Final Artwork CH2.pdf (22.9 KB, 43 views)
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Tweeter passive XO based on a transformer

Posted 1st May 2017 at 01:04 PM by abraxalito

As avid readers of my blog over the years may well know, I've modded quite a few active speakers. Mainly Swan/Hivi D1010s and D1080s of various generations along with some 3Nods. The entry level Swans are super-cheap on Taobao nowadays with pairs of older generation D1010s going for about 375rmb.

As a result of all these mods and my learning by doing I haven't got a single pair of actives in working condition, primarily because the mods I currently want to do (including fitting transformers inside and swapping out the classAB chipamps on bass/mid to replace with classD) won't fit in the available space. All the amp and active XO parts have been hacked about almost beyond recognition and are of very dubious reliability. So I have come up with a plan - I've thrown all the electronics boards away and will convert the carcasses into passive speakers. Since I also prefer to feed speakers via step-down transformers for better dynamics, I wanted to explore the possibilities of using...
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