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Compactron - Wikipedia, the free encyclopedia I would doubt you'll find many testers that test these. They weren't made for very long, so testers would need to be from the same era. They were basically a way to cram a bunch of tubes into one to take up a little less space. I've never seen a commercial amp that uses these. They are good for DIY since they are super cheap, but they are otherwise nothing special. At any rate, with a couple of clip leads, a multimeter, and a bench power supply, you can measure everything a tube tester can -- in fact more, and more accurately.

When you see that a manufacturer specs a certain amount of distortion, this is typically total harmonic distortion, the aggregation of several harmonic components, at a particular frequency. However, while THD doesn't show it, different components influence the sound differently. 10% 2nd harmonic distortion will be barely noticed, while 0.1% 17th will sound horrible. Additionally, while distortion might be one thing at one frequency, it can be totally different at another. So, what I am saying is that two different DACs that both measure "flat" and that both have similar THD specs might not actually be very similar at all. Here's a good article that covers this, and some other stuff: http://passlabs.com/pdf/articles/distortion_and_feedback.pdf

It doesn't sound like an EQ issue to me. It sounds like a particular distortion characteristic.

This is, to my ear, what NOS dac's based on the AD1865N-K sound like. See if you can borrow somebody's AudioNote to play with -- I think you'll like it.

Indeed

My wife has written/worked on software to do this. She uses it to compare sound waves against brainwaves generated from listening to said sounds. I'll find out what format she needs the waves to be in to do the comparison. http://www.soc.northwestern.edu/brainvolts/documents/Lee_et_al_JofNeuro2009.pdf

Many years ago ... well, about 7 years ago, I had a Pentium 1, 150, running FreeBSD and acting as a headless music player. I basically wrote (in Python) a socket server that would serve up some basic HTML to give me a list of tracks and that would control mpg123 when I clicked one of them. I think it also had a crude queue for track lists. All in all, it was about 100 lines of code, and actually worked reasonably well. The point is that mpg123 might do what you need.

Actually the LL1674. Similar transformer (Kevin at K&K says they are virtually sonically indistinguishable) but on a larger core than can handle higher dBu. I think if you look around that Lynn Olson did some measurements on it, or maybe the LL1676.

Some of the knocks on transformers are deserved, but some are hyperbole. For instance, low Z transformers, such as the ones Neko uses, are relatively easy to make and are extremely linear. Even a cheap one with a steel core can perform quite well. Use a 50% or 80% nickel core and they are staggeringly good. Distortion is very low, and it is all low even harmonics and barely noticeable. Input trandsformers are a lot harder as they require a lot more inductance and care in design. As such, they tend to impart their character a lot more. Steel cores tend to sound very warm and lack a bit of detail. Nickel is a lot better w/r/t/ detail, and they are less syrupy. However, something like the Lundahl amorphous core input transformers are utterly transparent. I've used them quite a bit and often can't tell whether they are in a circuit or not -- as close to wire with gain (sort of literally) as I've experienced. Note that input transformers also impart the benefit of eliminating common mode noise which is often (usually) a big enough advantage that it overshadows any possible drawbacks. Finally, it might be noted that studio work is often more about tuning the sound than it is about recreating it perfectly. As such, studio people will use transformers expressly for this purpose. For instance, if you want your band to sound like it was recorded in 1972, use an Edcor steel core. If you want your violin to sound like a violin, use the Lundahl amorphous. The fact that transformer manufacturers are not always trying to make a perfectly accurate device means that choosing what to use in neutral audio equipment must be done with some care. For a good example, Cinemag has a transformer comparison on their site -- you can download the files and listen to the transformer tuning -- Cinemag Audio Transformers

Just swapping parts is probably OK. I ran into issues when I tried to put a choke in the PS and it started oscillating. I could have just left it out, but I think the benefits of a choke are sufficient that I was interested in getting to the bottom of what was oscillating. This led to the PS rebuild and regulator replacement. My sense is that this does more good than just swapping caps -- better to get a circuit right in the first place than to add the band-aid of audiophile boutique parts. It is less expensive in terms of parts, though it is probably more expensive in terms of time. And, I happened to have the little PCBs around.

For shielded tubes, you can AC or DC couple the shield to ground. I've done both, and both seem to work OK. So, you could just AC couple it (100n is fine) and then it should be fine with CT or not CT tubes. For a more complicated solution, use an 18.9V supply and a 42R resistor in series with the heater. Then, 12.6V/150mA tubes (12**7) will drop 6.3V across the resistor while 6.3V/300mA tubes will drop 12.6V across it. You could add a relay, as well, that would connect the CT to ground in the event that it is supplied with 12.6V. The drawback here is that you are limited to 12.6/150 and 6.3/300 tubes, which may be a limitation you are unwilling to make. There is only one 12V non-ct only tube that I know of, but it is a secret. Send me a PM and I'll tell you about it.

Looks to me like 1/4" minus the thickness of the extruded bottom which I'd guess to be about 1/16".

So long as you don't drop them, they are fine. The biggest issue is that the mercury condensates and settles over time, so the first time you turn them on, you have to just power the filament and let them sit for a while (~30 minutes or so I think) to re-evaporate the vapor. There is also the issue of PS input caps, and they are really meant for choke input supplies. Choke input supplies are fine, but they are more expensive to implement and often hum unless you really oversize the choke. They also glow real pretty. That said, I won't use them. Other than the light show, there isn't any real benefit to them (if you can hear the difference from one rectifier to another, you have a poorly designed power supply ...) and while the risk is small, it is there and I prefer to keep the toxins out of my living room when I can. I have broken enough tubes in my life to not want to deal with it. Other things that may expose you to mercury ...

Do you have a pic of how they came out? I am thinking about using them for this but am a little unsure of the quality.

How about FPE? It costs a little more, but you can make them any size you want. If it is only for a few, it seems like a decent deal.

Not one to leave well enough alone, I thought I'd tinker a little more. The obvious next thing to do was to swap out the last PS cap. I had used a Blackgate Std, but these aren't my favorite caps, and I figured a film cap would be better. To that end, I removed the Blackgate and added a big Motor Run film cap. These are just big polypropylene caps dipped in oil of some sort. This improved clarity a little, but unfortunately it also lost some bass. The usual solution to not enough bass is bigger caps. So, I got a bigger cap.

I used to work at a used camera dealer (let me tell you about the stack of Nikon S1's we had ...) and AE-1's were everywhere. I always found the frame advance felt like it was grinding the film to shreds, and the FD lens mount was awkward. Consequently, we couldn't sell them. We didn't see all that many Nikons, but the old OM stuff was some of my favorite. Personally, I like to use either Olympus Pen stuff now, or else my Contax G which was really cool when it came out, but not so cool now that Contax is once again extinct

In general, in a standard single ended "300B" amp, assuming that everything is reasonably done, the things that influence the overall sound from most important to least important are ... 1. topology (including the power supply) 2. quality of passives and iron 3. quality of driver tubes 4. the 300B's Western Electrics may well sound a lot better than Valve Arts, but I'd take a well designed amp with good iron and caps and cheap tubes over a run of the mill amp with WE outputs any day. As a matter of fact, I have 300b amps with good iron, a good topology, and extra cheap tubes. They sound great.

Isn't this what insurance is for? You can get some big output caps for cheap to put between it and the speakers for testing if you are concerned that it will spew DC. Or, get some 8R 5W resistors and put those across the speaker terminals (instead of speakers). Then, assuming no smoke comes out upon turn on, use a cheap multimeter to measure across the resistor for DC. If there is none, download a 60Hz tone, play this through the amp, and measure for AC across the resistor. if you get AC but no DC, then hook it up and give it a listen. 70's solid state gear that's even worth $2K? I am having trouble envisioning it. I agree with Nate that I'd open it first and see if anything looks corroded.

The design uses a balanced dac chip, has balanced outputs, and uses a single tube. That tube only has two grids, two circuits, which means that these numbers don't add up. This suggests that either the tube is not actually part of the signal, of that the output is converted from balanced to single ended and then the tube is being used as a cathodyne phase splitter to make it balanced again. Also, the headphone out looks like a single opamp.

That's what mine are. I have soldered and modified a fair number of things in my life, yet cutting the end off my headphones still made me nervous.

What standards are people using for reterminating these? I'm planning on a single 4-pin XLR rather than 2 3-pin as it is less cumbersome. Does a male connector on the phones with pin 1 for R+, 2 for R-, 3 for L-, and pin 4 for L+, and 2 and 3 connected together for use in single ended amps sound right? Also, anyone know the stock Grado wire colors before I cut this thing apart? If it matters, these are RS-1's bought about 6 years ago.

Why is the power button not centered top to bottom? It looks awkward where it is. Also, does it need to say "power"? Are you going to forget what it does?

In theory, theory and practice are the same, but in practice ... Yes, I basically like a high load for a tube and no cap in the cathode. The design is clever in a lot of respects, and there is much about it to like, but in a cost for sound calculation, I'm not sure I agree with their choices. Here are some issues ... Chokes present a load to the tube that is 2*pi*Frequency*Inductance. There are two things to note about that. The first is that the load is rising with frequency. This is not necessarilly a problem so long as the choke is sufficiently large, but at the margins it can be an issue, particularly with high rp tubes. The second is that the choke is just too small for the tube in the first stage. They are loading a 6J5 with a 200H choke. The 6J5 has a rp of ~7K. The higher the load on a tube the better, but you really want it to be at least 4 to 5x rp. At 60 Hz, that choke gives a load of ~75K which seems pretty good. However, at 20Hz, it is only 25K which is a lot less good. Moreover, that diode has an impedance of around 200 ohms at these currents. This, as you know, is multiplied by mu and added to rp. So, rather than 7K, rp is actually ~11K meaning that that 25K load is really on the borderline, and deep bass is likely to suffer considerably. In contrast, the LEDs in yours (which are diodes as well) have an impedance or about 8 ohms, and the load that we put on the tubes is about 10M, even at 20Hz. In fact, the limit to yours comes fro the Miller capacitance of the output tube which is a different issue altogether. Anyhow, this really comes down to the 6J5 being a poor choice of valve -- a D3a, for instance, solves much of this. The advantage of a choke over a CCS is that it can swing above B+, but that does not seem to be the issue here, at least in the first stage, as the grid will hit cutoff long before that point. So, a CCS on the first stage with a better biasing scheme would likely be a good thing. Oh, and the PS has a little more ripple and a lot more sag than I think you'd want -- and in simulations, it might destroy the rectifier. Why they didn't use damper diodes there instead of in the cathodes is a bit of a mystery. Edit: I should also add that iron resonates, and that much iron is likely to resonate in unpredictable ways. It may not be an issue, but it is likely not an amp that you could just build as drawn without some sophisticated measurement equipment and just expect it to work.

It's a big topic. These are probably as good as anywhere to get started: [url=http://www.sixmoons.com/industryfeatures/distortion/distortion.html]6moons.com - industry features: "Distortion &