Jump to content
The Klipsch Audio Community
Chris A

Transconductance amplifiers?

Recommended Posts

Getting closer

P1020030.jpg

 The 1/4" input jacks needed to by sacrificed to accommodate the current sense resistors. Not planned but that's how it worked out. The 1/4' jacks on the D75 are unbalanced inputs unlike the D45/D75A where they are directly in parallel with the XLR inputs and therefore balanced. I will never have a need to use the unbalanced inputs.

P1020029.jpg

P1020028.jpg

Current sense resistors epoxied to chassis

P1020031.jpg

Dual push switches on left replacing original slide switch. Added 4PDT toggle on right

  • Like 2

Share this post


Link to post
Share on other sites

On the negative feedback,

do you have to change the value on the remaining resistor after the 2nd ground is removed ?

 

To maintain the same levels of attenuation on the various frequencies ?

 

Can you jump a variable attenuater around the resistor

so you can vary the input of the Negative feedback ?

Can be compared to the stock channel.....

Share this post


Link to post
Share on other sites
34 minutes ago, Bubo said:

On the negative feedback,

do you have to change the value on the remaining resistor after the 2nd ground is removed ?

The books author states the current sense resistor is so low in value that the original feedback resistor will have no effect anymore....we'll see. After all I am trying to mod an existing old Crown amp and it may not be a suitable candidate for this type of operation...again we'll see. I do not understand the question about the second ground.

Have you read the book? Or looked at the author's website?

Share this post


Link to post
Share on other sites

Got it all wired up ---you point to point wiring tube guys would be proud but.........

So far it is an EPIC fail:angry2: Appears I have built a fusing blowing oscillator.

Not giving up just yet...it will take all the circuit engineering skills I have to figure this out.

If it takes more than I possess then I will give and change it back.

So I have never used the light bulb as current limiter on the input power before. Do I just wire it in series with the AC hot?

Share this post


Link to post
Share on other sites
Posted (edited)

Just for fun...

 

Here's a simulation of my Klipschorn bass cabinet, properly loaded by a room corner, no crossover, driven by an amp with a 0.02Ω output impedance vs. a First Watt amp with an 80Ω output impedance.

 

Yellow trace is the voltage across the driver terminals and the Teal trace is the current passing through the driver. If you were to divide voltage by current, you'd get impedance c/o Ohm's Law. Since the two illustrations are very close to constant voltage (left) and constant current (right), you can see the driver/cabinet/corner impedance quite well in the other trace. I love this stuff. : )

 

1238832413_ConstantEvsI.thumb.png.41186b66a20a0423d4215320f4ae8417.png

 

It's obvious that a current source amp for audio application has a lot more to it than just a high output impedance.

 

I need to read the links provided - thanks for the fascinating thread! : )

 

God bless you and your precious family - Langston

Edited by Langston

Share this post


Link to post
Share on other sites

Meanwhile...... I need help...any and all thoughts and suggestions are appreciated.

First things first. Build a light bulb current limiter. Then I need to connectorize all the connections from the circuit board in the amp to the various points. Before it was tedious to make and remake the connections. Now with all the added parts it is darn near impossible. Once it is connectorized it will be much easier to teardown to remove or add a part to stabilize this amp(oscillator) and then re assemble.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...