All about electronic valves and hi-fi
Some of you may be a bit fed up already with these slew rate posts, however I find this fascinating as is taking me through different routes of experimentation.
On my last tests, I abused the DN2540 to an extent which meant the dead of it. So I ended up adding the appropriate back to back protection zeners on the gate:
Continue reading “Slew Rate (Part IV) and the Tale of the three Source Followers”
Are you writing again about the “Slew” thing? There is a lot to be said about the slew rate still. In fact, this post is about some real life measurements and experiences had in the past few days.
This week I went to my friend’s (Tony) place to listen to his 01a with the additional follower discussed previously. Tony complained about that the addition of the follower changed the sound of the 01a. Something was lost, detail on the treble, airiness. I brought up again my test gear and surprisingly we found some H3 level which wasn’t there on the previous preamp. Odd, could that be the FET follower? In the end after several tests, I checked the operating point (you should never assume they should be as expected) and found that the follower wasn’t operating at the optimal level, source current was low and also the 01a was running out of place. I recalibrated the gyrator and voila. The sound of the 01a, came back!
Unfortunately we ran out of time and I did not take any measurements again after re-calibration.
Merry Christmas to all!
When I was still a teenager and learning saxophone I came across this wonderful version of “Get thy bearings” by King Crimson. The power of the electrified alto sax blew me out my mind. Ian McDonald clearly found a way to drive the saxophone there and bring a new sound to the 1969’s progressive rock. Surely he didn’t experience any of this slew rate thing 🙂
In my previous post, I explored the slew rate challenge of the 01a preamp:
You may probably already asked yourself: what is this “slew rate” business? Has this guy lost his mind? Probably I have, but not due to this interesting phenomenon. The second question that should have probably popped in your brain is: why? Well, writing about this stuff came up by sheer coincidence.
We tested my friend Tony’s 01a preamp which has an older gyrator board I made for him about 3 or 4 years ago. The preamp (as well as his system) sounds extremely good in my opinion and the 01a has brought a new clarity which is what you’d expect as a result of the introduction of a DHT stage. We decided to run some frequency response tests since Tony has made some interesting mods to his Push-Pull amp. We encountered an unexpected challenge as I didn’t have the right XLR connectors for my testing gear so we run the FR tests on the power amp with the 01a.
The 01a preamp measured as expected with a flat response up until 40kHz before the sound card rolloff kicked in – I’m aware of this and this is the limited bandwidth of my current portable measurement gear. The distortion was also really low (H2 predominantly ) with less than 0.02% for 2 Vrms output signal. This test was done with Pete Millett’s interface which has an input impedance of 100kΩ: Continue reading “Slew Rate in Preamps”