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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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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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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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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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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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Help with technics se-m100 rebuild!

Posted 3rd November 2009 at 07:24 AM by Jo90

Hi, I hope I have this right- I am new to this! I am dusting off my electronics by rebuilding an old technics se-m100 power amplifier (1989) as a practice run (before upgrading my marantx cd-80). I bought this very cheaply, but it sounds rather thin compared to my old sugden's! I have had difficulty getting exact capacitor matches for the electrolytics in terms of voltage (not capacitance). I have ended up having to use 10v or 16v capacitors, in place of originals rated at 6.3v. Equally I have had to replace capacitors rated at 25v with those at 35v. They are nearly all in the signal path, and so I have used elna cerafines or silmics. Is this going to be OK?- I couldn't see why not, but, am I missing something obvious? In principle it is quite a nice amp (dual mono, big power supplies), so even though this is a practice run, I don't want to break it! Apologies for the ignorance of the question and thanks for any help!
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The Truly Unexpected -

Posted 2nd November 2009 at 06:51 PM by tomtt
Updated 8th January 2010 at 07:41 PM by tomtt (320)

Click the image to open in full size.Click the image to open in full size.

Maybe i should have thanked Her,

Sooner, than i have,

for those Unexpected Presents.

Of Things, I really liked.

the kind that make life worth living ...





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Last Activity: Today 02:49 PM
Current Activity: Deleting Visitor Message

(one of mine)

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some propaganda in here -

The Story of the Moffat & Company Gold Coins
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K2-wj

Posted 2nd November 2009 at 04:32 AM by jimn1

OPAMP History
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Tube Voltage Regulator, Is it worth the effort

Posted 27th October 2009 at 10:31 PM by DougL
Updated 13th January 2010 at 08:53 PM by DougL

This thread has some good, solid information and very little bravado.

http://www.diyaudio.com/forums/tubes...th-effort.html

Special Mention to:
janneman
Tubelab
kevinkr
Allen Wright
Bas Horneman
SY

For their interesting contributions.

IMHO, There are several ways to make an adequate Power supply. And several ways to totally botch the job.

In the 1980's, I was totally against using solid state in a tube preamp. However, this was more about not using low voltage devices in high voltage circuits than anything else.
Now that high voltage transistors are available this is not a major consideration.
My first tube amp is going to be a platform to play with some of the discussions.
I want to try unregulated and regulated power supplies. I will probably start out with unregulated choke input supplies.

It...
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In Need of plate amplifier under $40 for 8" sub!

Posted 27th October 2009 at 01:32 AM by Skywalker2012

Hi I'm in need of a plate amplifier for a 8" sub if anyone has one preferrably under $40
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