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The problem with wanting to get the best performance

Posted 14th November 2009 at 09:28 AM by wintermute (Wintermutes Rantings)
Updated 25th November 2009 at 11:15 AM by wintermute (added o category misc)

Well for me anyway I think I must be borderline obsessive compulsive! It happens every time I start a project (or even before I start it). I spend hours and hours and hours deliberating on whether this would be better or that would be better. Honestly in some ways I wish I'd never become "aware" of alternatives to the kits that were available from the local electronics shops Dick Smith and Jaycar

I got the jfets for my B1 a few weeks ago. I finally started matching them earlier this week, I hadn't started because I was obsessing over the fact I needed a 100 ohm precision resistor and a transistor socket. I hadn't got those because I wanted to order all the other bits as well and only pay for one lot of shipping. But do you think I could make a decision on what parts to get?

First off I obsessed over the resistors (yeah I know).. wanted vishay RN60D's but local sources are 5 - 10 times the price of mouser, problem with mouser is unless...
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Old

Tweaking

Posted 12th November 2009 at 08:53 AM by aaaron
Updated 12th November 2009 at 09:03 AM by aaaron (wrong word)

Iam into the tweaking of marantz cd 94 MK2 (just repaced the output op amp with OPA 627,and the buffer stage with BUF 634 T and balance output *****(need to mention Special Thanks to Subash from FARNELL INDIA chennai branch for the wonderfull support rendered throughout the tweaking ***can be contacted at subashb@farnell.com for any elctronic components and the related )
the result is good and there is nice improvement in sound and sonic stage.

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Old

Too late

Posted 12th November 2009 at 01:56 AM by relder (Rob's active 3way with transconductance chipamps build blog)

The day or two after I start a blog here they take the blogs off the main diyaudio home page. Figures.
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Old

3 way post #5 - the drivers

Posted 11th November 2009 at 01:37 AM by relder (Rob's active 3way with transconductance chipamps build blog)

The drivers chosen were somewhat dictated by what I had lying around.

Tweeter: Fountek NeoCD3.0 - I've been wanting to use a ribbon for a while. I have fond memories of hearing old Apogees in the 80's. I bought the prior version (JP1?) quite a while ago. (I'm good at buying drivers for projects and then not building them when I get some other bright idea) When I opened them to use them one of the unit's magnets had delaminated/disintegrated. Big bummer. Madisound came through with great service though and gave me the current model at no cost and no hassle.

Mid: Tangband W4-1337S - The Statement guys seemed to have success with this mid with the Fountek, so I figured why not.

Woofer: Peerless 850146 - I bought these a while ago. Supposedly one of the few woofers appropriate for sealed enclosures. One reason to go sealed is the double hump in the impedance for a vented enclosure would cause the frequency response to rise at both...
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Old

Useful link

Posted 10th November 2009 at 11:41 AM by robocow

http://ampslab.com/vifa62.htm
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Old

Blog Starter

Posted 10th November 2009 at 11:22 AM by robocow
Updated 10th November 2009 at 11:23 AM by robocow (Insert Title)

I have been insipred by PMC to create my own Trasmission Line design. I say inspired, as clearly I'm not going to match their acheivement on a private scale!

So to date I have chosen my drivers, the Vifa PL18 WO09 and the SEAS 27TFFC(H0881).

I'd love to hear if any one has had any experience with these drivers!
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Old

3 way post #4 - power supply

Posted 9th November 2009 at 09:27 PM by relder (Rob's active 3way with transconductance chipamps build blog)

Here's the power supply brick for all amps. A toroid with a CLC. -35V-0V-+35V

Note the color coded terminals on the right so I don't roach another LM4780! (see last post)
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Old

3 way post #3 - the circuit boards

Posted 9th November 2009 at 09:20 PM by relder (Rob's active 3way with transconductance chipamps build blog)
Updated 9th November 2009 at 09:28 PM by relder (Update title)

Here are two of the assembled boards. A mono one for the woofer on the left and a stereo on the right for mid and tweet. I designed the PCB to do both.

Originally I did two in point-2-point, which I found tedious, especially for the LM4780 which has tiny pins with little room for error. And after I blew up the LM4780 board (I hooked up the power supply backwards - poof!) I decided to go PCB, since there was no way to replace the chip given how close the pins were to each other.

The ExpressPCB software is pretty easy to use. Eagle, for how often I attempt PCB's, had too many annoyances for me when creating new objects, etc. The service is pretty quick too, ordered on a Tues and received them on a Fri. They give you 3 boards in their low cost service - so I'll use the one P2P LM3886 and 3 PCB boards.
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Old

3 way post #2 - the amp circuit

Posted 9th November 2009 at 07:59 PM by relder (Rob's active 3way with transconductance chipamps build blog)
Updated 9th November 2009 at 09:29 PM by relder (Update title)

Here is the basic circuit for the amps. Turn the pot in one direction and it acts like a current source. Turn it the other direction and it behaves like a voltage source -- almost, you still have that 0.5 ohm series resistor there, so output impedance will always be at least that.

It's stable on the bench with a fixed R and with real speakers.

The adjustability will allow me to:
  1. Tone things down at woofer resonance (you'd have a big peak at Fs if driven totally like a current source)
  2. Act somewhat like an adjustable Linkwitz transform for the woofer (around that resonance peak again)
  3. Control phase somewhat (if I recall right there is a 90deg phase change between current and voltage driven)
  4. Adjust frequency response somewhat, depending on the impedance plot
  5. Adjust distortion (less is better but compromises with the above must be made)
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Old

3 way post #1 - intro

Posted 9th November 2009 at 07:34 PM by relder (Rob's active 3way with transconductance chipamps build blog)
Updated 9th November 2009 at 09:30 PM by relder (Update title/cat)

I figured I'd do this as a blog rather than a new thread somewhere.

My goals were:
1) Play with the distortion reducing effects of transconductance amps (voltage in - current out.) I think it was likely Nelson (via the F1/F2 papers) that really turned me on to Hawksford's paper that described the benefits of driving voice coils with current rather than voltage.
2) More bass than the 2 ways I built, so 3 way w/ a 10" it will be.
3) Given #1 and #2 building a FirstWatt F1/F2 per driver is a bit much, and given this is an experiment we'll go with chip amps (LM3886/LM4780)
4) I've always wanted to play with a ribbon, despite Zaph's warnings.

I've been working on these slowly for quite a while - so a flurry of posts on the various parts will follow quickly.
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