Audio Asylum Thread Printer
Get a view of an entire thread on one page
|For Sale Ads|
which one is your favorite 6SN7 preamp circuit? Mine is Aikido. What about your choice?
The 6SN7 is a linearity champion. There's more than 1 good way to exploit that linearity.
The cathode coupled (LTP) hybrid design I'm uploading is non-inverting and comparatively low gain. Given today's 2 VRMS digital sources, lowish gain is a definite plus. The O/P impedance of the setup is below 100 Ω, without resorting to costly step down transformers.
low gain? How low? Less than 10db?
I said comparatively low gain. The max. theoretical gain for a 1 grid driven LTP is μ/2. 6SN7 μ = 20. As drawn, the hybrid exhibits approx. 17 dB. of gain. If that's too much, lift the non-inverting grid's stopper from ground and connect it to a tap on the 1 Mohm resistance across the O/P jack. That portion of the resistance between the "hot" O/P and tap should be non-inductive. Meter matched carbon comp. parts (for good channel to channel balance) is the cost effective method, but (naturally) Mills NIWW or Caddock film are the "super/duper" way.
This one is pretty good
Do you think Aikido better than the Ultra-path?
Different. It really helps to understand what you need the circuit to do. If you need 10 to 20 db of gain to drive your amp to full volume and your preamp is 20 feet from your amps then either one will work. The Aikido injects B+ power supply noise out of phase into the signal to cancel. The Electra Print uses a step down transformer which accomplishes a noise reduction as well. Output transformers like this transfer voltage to current which makes for very good drive capabilities. The cathode follower aspect of the Aikido lowers the output impedance.
I happen to like transformers. Building a great power supply is key to either one.
If all you need to do is to attenuate a signal before your amp, the Autoformer volume control is really hard to beat.
What about Eric babour Brute Force? However, it has 6BL7 othee than 6SN7.
I like line amps that don't invert. The Blue Velvet topology is one of the few that provides this functionality without either an IT or an overabundance of gain. I've worked out a slightly modified version on paper that will probably be my next line amp.
Buy Chinese. Bury freedom.
I'd be interested in your BV 6SN7 preamp since it is non-inverting.
Can you post the schematic here?
I worked out two schematics in SPICE. Both feature significantly less distortion and more typical tube loads than the original. Output Z of the first is about 4K Ohms. The second version adds a cathode follower to provide an output Z around 450 0hms. The follower is biased such that an additional coupling cap is not required. It will easily swing 50V p-p.
Now that I'm thinking about using 6W6s in triode mode instead of 6SN7s, the follower probably isn't needed. Wish I had a SPICE model for the 6W6!
Buy Chinese. Bury freedom.
The SRPP as gain stage is not too bad, but it inverts and has a higher output Z.
These look like a better option for a preamp.
That's a nice circuit. I had looked at the Blue Velvet some time back and considered building it, but alas my system gain is such that I don't need to run a preamp - well at least for now. The only thing that I'm a bit hesitant about, is that the input tube is running into a 11.2K impedance as presented by the next stage.
The effective load for the first stage is at 3K which is kind of low. The 15dB of NFB will cancel distortion at the second stage but the input tube has only the degenerative current feedback from the unbypassed Rk to do some HD reduction. This may, or may not be enough (I'm just thinking out loud here, not saying that this is actually the case). I'm wondering if a bit of cathode feedback at the input tube might be of some benefit.
I agree, the impedances in the circuit are too low. I've changed that (on paper), as well as modifying the feedback network to reduce output Z and gain. Lately I've also been thinking about using different tubes. The 6SN7 is an excellent choice, but the 6W6 in triode mode is extremely linear and offers an even lower output Z. The only downside is heater power, which would be almost 5A for four tubes.
Buy Chinese. Bury freedom.
I like the 6W6 tube myself and think it'd be an excellent choice. As a matter of fact I was the one that suggested its use (along with the 6V6) in a preamp thread of yours a few months back, if I remember correctly.
When I was looking into the BV preamp, I thought that instead of using around 15dB of local NFB at the output section only, it would be a good idea to cascade two anode followers each having around 10-12 db of local feedback. I ran some numbers at the time but couldn't get the input impedance of the first stage high enough to my liking and didn't want to transfer the burden of driving the preamp to the source ahead of it.
I didn't spent too much time on that exercise, but now that I think about it, maybe a high mu tube such as the 6SL7 at the input position, configured as an anode follower with a gain of ~2 driving another AF, say a 6w6, wouldn't be a bad idea. But then you're moving completely away from the 6SN7 which you probably don't want to do.
Anyway, thanks for reminding me of this circuit, I now might take another look at it.
Have Fun and Enjoy the Music
"Still Working the Problem"
Post a Message!
This post is made possible by the generous support of people like you and our sponsors: