Low Noise Measurement Pre-Amplifier – 0.8nV/rt(Hz) LNA

This post will discuss a Low-Noise-Amplifier (LNA) for measurement of voltage regulators and other low noise low impedance sources. The design target had a few requirements, including:
– High gain (X1000/60dB as a minimum)
– High BW (1MHz)
– Low input referred voltage noise (<1nV/rt(Hz))

There are multiple approaches to designing such an instrument, and each designer has his own preferences based on his requirements and experience. I chose to design something that would fit my needs, which would also be discussed in this post.

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Hantek CC-65 Current Clamp Probe – Part 3 – Signal Chain, Improving BW and Noise

This is the 3rd (and final) part of a series of posts on the Hantek CC-65 current clamp probe. In part 1 we went over the probe structure and circuit operation, and discussed possible issues and improvements. In part 2 we’ve started measurements and modifications of the probe, focusing on the power-supply (PS) and the sensor bias circuit. That allowed us to achieve lower noise on the supplies and sensor bias, as well as extend the circuit operation down to lower battery voltage.
In this post I’d like to go into modifications of the actual signal chain. This consists of the amplifier structure at the heart of the probe, but will also touch on the offset cancellation circuit. The main goal from my point of view is to both extend its bandwidth (BW) by at least an order of magnitude, and reduce the equivalent input noise density so that limited BW measurements can be made on lower amplitude signals.

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Hantek CC-65 Current Clamp Probe – Part 2 – Basic Measurements, Power-Supply Modifications

In the previous post we’ve gone over the CC-65 probe structure and schematic, and noted a few things that can be done to improve its performance. Other than modifying the probe with higher spec parts, there were a few design decisions and potential issues that were discussed. In this post I plan translate the previous discussion into actual measurements and modifications to the probe. I will cover only part of the circuit in this post, and will cover the rest in a follow up post. This time we’ll have a look at the power-supply and biasing circuit, while the actual amplifier/signal path will be covered in the next post.

I should start by saying that the parts shortage observed nowadays is affecting this project too, it is one of the reasons it took such a long time to get something done. In fact, even now, I’ve had to opt for some replacement parts which weren’t my preferred option, or else it would call for months of wait for parts to be back in stock. With that said, lets move on to some actual measurements.

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Hantek CC-65 Current Clamp Probe – Part 1 – Probe Analysis and Discussion

This post will discuss the Hantek CC-65 current clamp probe, a cheap and useful tool. I’ve ordered this probe because of its low cost, and reasonable performance. I was happy to see there’s even a schematic for it available online as drawn in a post on the EEVblog forum. Looking at the schematic made it clear there’s a lot that can be done to improve it fairly easily. Due to the length of the post, and the fact I’m still waiting for the parts to arrive, I’m going to split this post into a few parts. In this part we’ll go over the operation of the probe and its schematic, and then discuss possible modification that can be made to it. There are quite a few tradeoffs to be made in the selection of parts and which mods to do, based on the requirements out of the probe. I will detail some of these considerations, and in the next parts will present results based on the mods I’ve decided to implement according to my preferences.
This part turned out to be quite long with a lot of text and little pictures/results. I think this is of value and will serve as good background and reference in the next parts on this topic where measurement data will be presented. There, it will be possible to simply point to the relevant part of the current post, to explain the reasoning behind chosen components for mods, and measurement results explanations.

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Compact Stereo Dummy Load for Amplifier Testing

In a past post, I’ve attached a picture of the load I was using for speaker amplifier testing. I have a box full of these 50W wire-wound resistors and a heatsink (HS) I’ve tapped to be able to attach these resistors easily. I was simply connecting as needed for the specific case. In practice, I rarely change the default 8×2-ohm resistors which are split into 2 loads of 8-ohm each. When I needed to dissipate significant power I would normally point a fan at that HS and be done with it. However, this wasn’t very convenient, and I wanted something more “user friendly” to replace it, this is what will be described in this post.

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Control Program for BK Precision 8500 DC Electronic Load

This post will be somewhat different to others, but I consider it interesting enough and useful enough to share on the blog. Over the past years I have used MATLAB quite a lot for communicating with instrumentation/test boards I’ve designed. Due to a number of reasons I’ve recently decided that gradually transitioning to use of Python instead is a good idea. My needs are typically quite basic, some communication with external instrumentation/test boards, data recording, data analysis, and finally generating some nice looking figures to summarize the results. Since the best way to learn is do, I’ve decided writing a control software for a DC electronic load I own would be a nice first project. The code is finally complete, so I’ve decided to share it with others so that anyone who owns an instrument from this series could use it.

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AKG K1000 Headphones Repair

The AKG K1000’s have a somewhat of a legendary status as a unique pair of headphones. They are more like “floating” speakers than typical headphones. These are a fairly old model which was produced for a fairly long time, but it was discontinued some years ago. Many people still own these, but as all things, they do need some TLC over the years. In this post I’d like to briefly share my comments on these headphones along with some pictures to describe the work that was needed keep my pair of K1000’s in proper working condition.

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Audio Measurement Pre-Amplifier – Part 5 – Updated Ver1.1

Over the past year and a half since posting the series of pages about the measurement pre-amplifier I’ve designed and built, I’ve received emails from multiple people who were interested in building the pre-amp. I’ve happily shared with them the remaining boards I’ve had from that first batch I ordered at the time. These few boards were all given out, and I’ve therefore ordered a few extra boards to be able to keep offering these boards to people who would like to build such an instrument for themselves. Unlike the first batch, this time I’ve printed boards that fixed the issues I’ve reported when building my own unit and were fixed by a “bodge” over the original board. These modifications to the board design (and the writing of this post) were all done well over a year a go when I’ve originally assembled my unit, but I didn’t see a need to post them until this point in time.

This post is meant to share the updated schematic, as well as to offer additional information that can be of help to people who would like to assemble such an instrument.  I didn’t make any functional changes to the pre-amp at this revision, therefore I will offer no additional measurements in this post.

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Hafler 9505/9300 Power Amplifiers Repair and Measurements

Over the past few months a few different Hafler amplifiers passed through my bench. First it was a combo of a 915 pre-amplifier with a 9300 power-amplifier to accompany it, and some time later I got a 9505 power-amplifier. If you’ll have a look at the schematic you will see that while the pre-amp isn’t too exciting, the power amplifier has a few interesting points in its schematic. So I’ve decided these amplifiers are interesting enough to warrant a short post about them with some pictures and measurement results.

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Kenwood KA-7100 Vintage Amplifier Revisited

One of the amplifiers I own is a Kenwood KA-7100 stereo amplifier. It is a fairly old amplifier (late 70’s), with a modest 60WPC into 8ohm specification. I was a fan of the KA-XXXX amplifier series and its siblings from the moment I first heard its smaller brother (KA-601). While that KA-601 was in fairly bad shape, I was amazed at the time by how much better it sounded than my (back then) modern Denon AVR HT receiver. I’ve since had an opportunity to listen to quite a few amplifiers from this series including the KA-7300, KA-8100, KA-9100, and others. Therefore, when I’ve had the chance (more than a decade ago) to get my hands on a KA-7100 I grabbed it right away. It wasn’t in bad shape, but it has seen better days, no doubt. As I learned a bit more about electronics, that amplifier became one of my first projects.
I have recently had the opportunity to revisit this amplifier by doing another small modification, which gave me an opportunity to write something about it, and add some measurement results while at it.

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