Lightspeed attenuator with a Clarinet?

schubert · « **on:** 8 Nov 2010, 02:45 am »

I just finished building a Clarinet for my brother, and now I'm tempted to keep it (pics below). That's not the brotherly thing to do, alas, so it looks like I'll have to build one for myself.

I've been intrigued by the glowing descriptions I've read of the Lightspeed attenuator - does anyone out there have any opinions as to whether such a marriage would work?

Here's the pics - I know I'm no great shakes at case work, but I was inordinately proud of myself that it turned out as good as it did. The ugly box on the back is for the power relay, which my brother wanted so he could turn off the unit with a remote control. There's also a mute relay, and both are contolled by a Dantimax kit (nice kit, by the way) - it's the small board in the front.

Clio09 · « **Reply #1 on:** 8 Nov 2010, 03:01 am »

I'm not sure I understand the question. Both the Clarinet and Lightspeed are preamps (technically the Lightspeed is just a passive attenuator). Personally, if you have the passive friendly amp I'd give the Clarinet to you brother and just use the Lightspeed on its own in your system.

schubert · « **Reply #2 on:** 8 Nov 2010, 03:21 am »

The Lightspeed is basically just a volume control, and it would replace the volume control in the Clarinet. I would build just the volume control part of it myself, without the in/out jacks of the "preamp" version. I was just wondering if the loading would work OK. I'll try it on its own without the Clarinet too.

JDUBS · « **Reply #3 on:** 8 Nov 2010, 04:41 am »

Interesting idea. I think there are a number of folks using the lightspeed in place of a "regular" volume pot with success (not sure about in the Clarinet, specifically).

-Jim

Clio09 · « **Reply #4 on:** 8 Nov 2010, 04:49 am »

That's kind of what I assumed so glad that you could clarify. As mentioned, a number of people use LDRs in preamps in place of the stock control. Melos and Dartzeel are two companies that have incorporated them into their active preamp designs. I think you'll find the LDR design to be very flexible in the application you described.

david62 · « **Reply #5 on:** 8 Nov 2010, 11:57 am »

How did you produce the lettering on the front panel of the case?

schubert · « **Reply #6 on:** 8 Nov 2010, 03:16 pm »

The front panel is from Front Panel Express (http://www.frontpanelexpress.com/) - they supply a very nifty design program, you make the design and send it to them, and voila! a very professional-looking front panel appears in the mail. This one ran just under $60.

schubert · « **Reply #7 on:** 8 Nov 2010, 03:22 pm »

Thanks for the replies, gentlemen. I'll definitely consider trying it.

Maybe a little explanation is in order as to why I want to do this. I've built a couple of high-quality passive buffer preamps (Pass B-1 and a Musical Fidelity knockoff), then I did the Clarinet at my brother's request. In comparing the Clarinet to the passives I felt that there was a certain "aliveness" (sorry for the subjective term) that the buffers lacked, as good as they were. So, I am hoping that the combination of the Lightspeed and the Clarinet will prove unbeatable!

Bill Epstein · « **Reply #8 on:** 9 Nov 2010, 01:47 am »

Franz, old man, looking at what you have brilliantly done you must be aware that, altho' the spec'd Panasonic volume control is 50Kohms, the acceptable range is probably from 10K to 100K. Hard to think of a pot or attenuator that wouldn't fit, no? So full Light Speed ahead!

I'm a volume control snob and couldn't wait to replace the "cheesy" Panasonic with my favorite $25 discrete attenuator from Taiwan, or perhaps a TKD. Funny thing is, I just never got around to it because the Clarinet kept showing me stuff I didn't expect in tone and texture.

What do you enjoy more, the braiding or the finger cramps?

schubert · « **Reply #9 on:** 9 Nov 2010, 03:11 am »

Oh, the braiding is especially fun with stiff solid core wire....

tubesurf · « **Reply #10 on:** 10 Nov 2010, 01:20 am »

I had the same question. I have a clarinet kit and have ordered the lighter note kit from buildanamp.com but haven't assembled either yet. I have listened to passives as well an enjoy the sound but do miss some body or fullness. I guess what you call "aliveness".

poty · « **Reply #11 on:** 10 Nov 2010, 01:34 pm »

In my opinion the Lightspeed attenuator is a bad idea for Clarinet. From the description of the attenuator (found at http://diyaudioprojects.com/Solid/DIY-Lightspeed-Passive-Attenuator/) I have learnt that it has very small input impedance (<100 Ohm) which is not suitable for all sources. It may be preferable to use it with a buffer or after the Clarinet, but who knows...
The idea of the attenuator is very simple and elegant by nature, but it brings several problems too. The first problem is the quality of resitors in the optocouplers. I doubt they are better than in some inexpensive pots (then they will bring more noise and even possibility of distortions - they are non-linear really). The second problem is linearity of regulation and fine matches of characteristics - it is almost unachievable (mentioned in the above description) - then we have channel disbalances and unstability of volume. The third problem - unknown sensitivity of the resisors to noise (from the power supply ripples, regulating circuits and LEDs). The fourth problem - despite of mentioned in the description - the input and output impedances changes greatly (it can be easily counted) which brings problems to both source and amplifier.
I think a volume control based on FETs is easier, more stable and predictable than the Lightspeed (maybe more expensive though). And if you don't want to add some distance control - the switched volume control with carefully chosen resistors and switch will be far better approach to best circuit for this need.

analog97 · « **Reply #12 on:** 10 Nov 2010, 03:54 pm »

Poty raises the key point IMO. The low input impedance is a potential killer. For me, I would not attempt this, given the risks. Yes, I am pretty conservative on experimentation because I have a stock + Auricapped Cornet2 and Clarinet. Good luck if you go forward and post your impressions of the sound. Best wishes.

schubert · « **Reply #13 on:** 10 Nov 2010, 04:28 pm »

Thanks, gentlemen. The fact that the lightspeed prefers low source output impedance was what I was worried about, to tell the truth, though I did read a post where the inventor claimed that the lightspeed was relatively insensitive to loading. My sources (Chime and Cornet2) have output impedances of 220 ohm, as far as I can tell (can somebody correct me if I'm wrong?). If input impedance is a problem with the lightspeed in a Clarinet it will be a problem without it too, so I'm going to build one separately and see how it works in my system. Then I'll try it in the Clarinet - if it doesn't work I can always use PEC carbon pots, which are my next choice (one for each channel, w/no balance control a la the Pass B1).

poty, can you supply a link for a descrption of a FET based volume control? It sounds interesting.

Brinkman · « **Reply #14 on:** 10 Nov 2010, 05:27 pm »

Quote from: Bill Epstein on 9 Nov 2010, 01:47 am

I'm a volume control snob and couldn't wait to replace the "cheesy" Panasonic with my favorite $25 discrete attenuator from Taiwan, or perhaps a TKD. Funny thing is, I just never got around to it because the Clarinet kept showing me stuff I didn't expect in tone and texture.

I had initially purchased a Goldpoint stepped attenuator for my Clarinet that I ended up using in my Castanet build. I was a little bothered at this as I was now short an expensive "boutique" component for my Clarinet build. As fate would have it, I don't use the volume control on my Castanet (I leave it full throttle), so the Goldpoint will be removed and the volume control eyelets will be jumpered on the Castanet. Funny thing is, after all this effort I'm not really convinced that a stock volume pot would have degraded things noticeably. I imagine I'd still be pulled in, as Bill hints above.

I suppose my point is that a stepped attenuator is an elegant and versatile alternative for those of us who are scared of blade and wiper volume pots, even if that fear is more superstition than anything else. It's also much easier to get in "stereo-balanced" configurations for more ambitious DIYers. Considering the complication, the "lightspeed" attenuator sounds like a solution in search of a problem.

schubert · « **Reply #15 on:** 10 Nov 2010, 07:34 pm »

A solution in search of a problem? Perhaps - but I like to think of it as just one more thing to play with!

poty · « **Reply #16 on:** 11 Nov 2010, 11:36 am »

Quote from: schubert on 10 Nov 2010, 04:28 pm

poty, can you supply a link for a descrption of a FET based volume control? It sounds interesting.

It's a pity I haven't build any such FET-volume-control by himself (just because they also - like Lightspeed - rise some questions in my head) but read a lot about them on Russian forums, so I can't give you exactly the link to working device. But every manufacturer who sells FETs have some papers about this usage (for example: http://www.vishay.com/docs/70598/70598.pdf). In the Internet there are some offers of DIY kits based on FETs, but I can't prove are they good or not.

hagtech · « **Reply #17 on:** 14 Nov 2010, 04:54 am »

Do you have any "buzz" or hum with this CLARINET? The input and volume control wiring gets a bit close to the AC wires and rectifier. You may need more distance or shielding.

jh

schubert · « **Reply #18 on:** 14 Nov 2010, 04:58 pm »

I had a terrific problem with buzz/hum for a while but it turned out to be caused by an overstressed interconnect. That corrected, I still had a little residual buzz in an earlier configuration that had the power relay too close to the output wiring; I then mounted it outside the case and the problem went away. Now the noise is only low level hiss which is pretty tube dependent, and occasional whistling with an older set of RCA cleartops (from a Conn organ). The 5814's I ended up with are pretty quiet, though, and the unit sounds absolutely smashing with them. Thanks for a great design - I'm definitely building another for myself!

audioray · « **Reply #19 on:** 23 Nov 2010, 11:06 pm »

WHAT POINTS TO GET POWER FOR LIGHSPEED. I MEAN WHERE TO TAP ON BD.