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The have the PTV09 little plastic shaft/knob pots there too which are similar to the plastic shaft Alpha 9mm pots. I think the Bourns versions are smoother and have a nicer feel than the Alpha. You have to be a bit careful with ordering them though because there are versions with various length shafts and flat or knurled tips. So, you have to look at the data sheet to get the model number you want.

I think they're useful for things like secondary knobs on 1590A type builds. I found them because I was looking for pots to use on a replacement preamp for a Godin guitar. They're perfect for that too.

Rob

Avnet are good. There are only two things I can think of when ordering from them. The first is that when you place an order with TI parts, they ship from a different warehouse. So, the website puts up some warning text that you will be charged shipping on both orders and you can't select the checkbox that says take more time and ship them together to reduce the shipping cost. So, I called their customer service number to ask about it and they said that they take this into account and only charge shipping once. This is in fact what they do. I've only been charged one shipping charge on the orders where this happens.

The second thing is that their search is a bit of a pain. When I'm price comparing, I always start on Mouser to do the searches and then put in the part number directly on the Avnet site. That said, at least all the parts they do carry are findable on their site, unlike some others.

Rob

I use the EPCOS caps too for most things. I'll note though that https://avnetexpress.avnet.com usually has them cheaper than Mouser. The two things that Avnet has a significantly better price on are EPCOS caps and TI parts. For other things, I find it's kind of a toss up who's going to have the better price/availability.

Thanks for the data points about the J201's. It's interesting that you saw the same thing on the face. The other thing I noticed was that the print wasn't quite as crisp as normal.

I understand that JET tolerances are pretty wide, but these are well outside the minimum (by about 20 times).

I didn't buy many of them, so no great loss. But, I think I'll contact the vendor and let them know and see what they think.

I've got a BBE compressor that's Ross clone with an attack knob. I like it. The OTA to make these are a bit pricey now though.

I have an EHX Black Finger compressor that I love. But, it would probably be a pain to do as a DIY. It would be cool to have the sound of the thing minus some of the EHXiness of it though.

I was testing some JFET's using the test circuit from runoffgroove and discovered that an entire batch of 2N5458 transistors I recently ordered have strange Idss readings. Before I write and notify the company, I wanted to check to see if it is likely that something else might be up (like I'm doing it wrong).

I checked several other types of transistors; J201, 2N5457, MPF102, BF245A, and 2SK117GR's. These all were within the stated specs. For the 2N5458's, the Vp was within spec but the Idss was only about 0.1 to 0.15 mA where the spec sheet lists 2.0 to 9.0 mA.

Is it likely that these are either fakes or are just bad? Or, am I missing something in measuring these?

One other thing that makes me suspicious is that the face of the transistors is a slight bit rough. I haven't seen this before.

Thanks,
Rob

I did some testing earlier with various charge pumps. There's a thread around here where I reported in a bit of detail what I found. But, the main upshot was that most of the TC1044SCPA's I tested had significantly lower oscillator frequencies than the specified typical value. Even when using the boost pin, several had audible whine.

On the other hand, the LT1054 parts all worked quite well and had no audible whine and a scope showed them to all be oscillating above 20kHz. I'm only using the LT1054's at this point.

Mouser's price on the LT1054 is pretty high, but Avnet has a much better price.
http://avnetexpress.avnet.com

Rob

For anyone who might find this useful, I ordered a few more parts to test with and they arrived today. So, here are the results:

1) I got a few of the TC7660H and tested them in a boost/overdrive circuit that was rigged to draw right at 20mA. The high frequency oscillator noise showed up at over 40kHz for each of them. So definitely useable for this situation (-9V output).

2) I got 10 more samples of the LT1054CP and put them in a circuit that was drawing about 40mA. Every one of them had the whine at over 35kHz. So, this look to be a good choice.

3) I tested driving the TC1044SCPA with a 555 timer. This works really well for setting the frequency to whatever you want it to be. I was able to drive it to 48kHz. The only problem with this is that the 555 timer does introduce noise. The CMOS version of the 555 is supposed to take care of this and I've now got a couple to test with but I haven't tried them out yet. This does look like a good path to look into if you really want to be sure the frequency is held above audible.

Once I get around to testing the CMOS 555 timer, I'll update with those results too.

Rob

Hi Corey,

Thanks for the input. I love your country. I got to spend two weeks on the South Island about 35 years ago. Absolutely beautiful!

About the scope, it's not really a scope. I have a MOTU MicroBook II. The software that comes with it has several features that are passable for this purpose. Actually, the combination of the signal generator and the FFT view have been really useful for debugging designs and builds.

I haven't tried putting a choke(s) in the circuit yet. I suppose that might help.  The opamp is an OPA2134 with the power rails bypassed using 2.2µF tantalums and 0.1µF ceramics located at the pins on the breadboard. If I have to go much farther than that with the 1044, I'll give up and stick with the LT1054. The LT1054 does work perfectly (even without the bypass caps). Really, my curiosity was piqued by how low the base frequency was for the 1044 samples I have, so I was trying to investigate what was going on.

I'm going to try an external clock on the TC1044SCP and I'm going to order some samples of the TC7660H and give them a try. I'll update with those results when I get them.

Rob

Since this is my first post, I've got to start off by saying thanks for making these PCB's available. I've built the Current Lover, Pork Barrel, and Slow Loris so far and they've all been great.

Now to the question(s). I've been playing around with a circuit that is essentially the negative voltage generation from the Road Rage. I've got a modified polarity protection scheme on the voltage input and I've changed the capacitors a bit. For the caps, I'm using low ESR electrolytics paralleled with smaller tantalums. Although, this doesn't really seem to have much to do with the issue since changing caps around doesn't fix the issue (other than changing the volume).  I'm testing with an op-amp based tone control circuit that can give about 20 dB of gain.

The issue is the oscillator frequency from the various converter chips. So far, I've tested the Microchip TC1044SCPA, Intersil ICL7660S, and the LT1054CP from TI. I've put a scope on the output and here is what I hear and see for the whine (frequency multipliers on) : TC1044SCPA 10800 Hz @ -68dB, ICL7660S fractionally below 20kHz @ -68dB, LT1054CP 38 kHz @ -64dB. I have either 2 or four samples of each of these and the numbers are pretty close.

So, the TC1044SCPA looks unusable on anything with much gain. The ICL7660S is usable but I'm a bit worried about marginal samples causing problems. The LT1054CP looks really good but is at the higher end price wise.

The TC1044SCPA's have a non-multiplied frequency of around 3kHz which is well below the spec'd typical value. So, I was wondering if anyone else had scoped any of these and had more data. 

Also, I see that Microchip has a device, the TC7660H that is spec'd at 150kHz at 20mA supply with a 10.5V limit. Has anyone tried one of these?

The last question I had was if anyone had tried using an external clock to drive the TC1044SCPA and if so what were your results?

Thanks, Rob