DIY audio: what are you building?

[aussievintage]

1 minute ago, andyr said:

 

Wow!  Can you possibly get a simpler circuit than that?

 

And does that count as 1 gain stage ... or 2?  (IE. does it invert the signal... or not?)

 

 

It's one, as the output stage is a voltage follower.  Yes it inverts the signal.

[muon*]

I'll likely leave the board alone and sell the pre to someone that needs the gain level.

[aussievintage]

1 minute ago, muon* said:

I'll likely leave the board alone and sell the pre to someone that needs the gain level.

Yeah fair enough.

[Bisguittin]

I've just mounted a pair of Coral 12Tx-1's onto 7-ply open baffles. Driven by @mwhouston's 71A valve amp, the results are stunning! The imaging of these things defies belief and if their efficiency isn't well, well above 100db I'd be most surprised. Teamed with an REL T9I sub, the musical presentation is remarkable. Ry Cooder has never sounded so good. WAF is another matter of course and is probably unsustainable. I've bravely put these in situ while she's not at home..............o oh??? Is that a car door I hear?

Edited April 16, 2024 by Bisguittin

[mwhouston]

4 minutes ago, Bisguittin said:

I've just mounted a pair of Coral 12Tx-1's onto 7-ply open baffles. Driven by @mwhouston's 71A valve amp, the results are stunning! The imaging of these things defies belief and if their efficiency isn't well, well above 100db I'd be most surprised. Teamed with an REL T9I sub, the musical presentation is remarkable. Ry Cooder has never sounded sp good. WAF is another matter of course and is probably unsustainable. I've bravely put these in situ while she's not at home..............o oh??? Is that a car door I hear?

You could try a coat of paint starting with a quick sandpaper, prime and top coat with a roller. May enhance WAF. 

[Bisguittin]

2 minutes ago, mwhouston said:

You could try a coat of paint starting with a quick sandpaper, prime and top coat with a roller. May enhance WAF. 

That's the plan Mark. Already poring over the Dulux decorator colour card.

[mwhouston]

Talk about efficient.

 

https://audio-database.com/CORAL/unit/12tx-1.html

 

[mwhouston]

With OBs the other thing to try is stapling thick Dacron on the back to help control rear reflections. Easy enough to pull off if you don’t like it. 

[andyr]

4 minutes ago, Bisguittin said:

That's the plan Mark. Already poring over the Dulux decorator colour card.

 

Nah - white!  (So they will fade into the background and wifey won't notice them.)

 

[muon*]

I was curious, so hard wired the power taking the switch and wires to and back from it out of the equation.

 

Less but still hum close to the speakers.

[ThirdDrawerDown]

3 hours ago, Bisguittin said:

Already poring over the Dulux decorator colour card.

 

Pink! You can always say it's a primer coat.

[stereo coffee]

3 hours ago, Bisguittin said:

I've just mounted a pair of Coral 12Tx-1's onto 7-ply open baffles. Driven by @mwhouston's 71A valve amp, the results are stunning! The imaging of these things defies belief and if their efficiency isn't well, well above 100db I'd be most surprised. Teamed with an REL T9I sub, the musical presentation is remarkable. Ry Cooder has never sounded so good. WAF is another matter of course and is probably unsustainable. I've bravely put these in situ while she's not at home..............o oh??? Is that a car door I hear?

Looking good, as long as Leo, doesn't take on Chewing Pine

[Bisguittin]

32 minutes ago, stereo coffee said:

Looking good, as long as Leo, doesn't take on Chewing Pine

Nice pick up Chris.

[aussievintage]

1 hour ago, muon* said:

I was curious, so hard wired the power taking the switch and wires to and back from it out of the equation.

 

Less but still hum close to the speakers.

 

Yeah, so probably would need a rebuild with power supply isolation/shielding etc to really fix it.  Pity.

[muon*]

Added a series resistor to the output RCAs, and this reduced gain slightly but also halved the hum/buzz.

 

See how it goes once I add a resistor in parallel.

[aussievintage]

42 minutes ago, muon* said:

Added a series resistor to the output RCAs, and this reduced gain slightly but also halved the hum/buzz.

 

See how it goes once I add a resistor in parallel.

 

Think 'voltage divider'.  This is basically what I was suggesting with the cathodee resistor of the output cathode follower.  Only difference, you are doing it externally after the output cap, so the change in loading will effect the bass response slightly (maybe insignificantly)

[muon*]

4 hours ago, aussievintage said:

 

Think 'voltage divider'.  This is basically what I was suggesting with the cathodee resistor of the output cathode follower.  Only difference, you are doing it externally after the output cap, so the change in loading will effect the bass response slightly (maybe insignificantly)

Yes.

 

Output impedance will be high, will see how it effects the response.

 

Edit: OK,

With added resistors in parallel only the slightest hum/buzz if you put ear against speaker and listen carefully

 

Most of the gain reduced, so maybe only 3 or 4db gain now.

Edited April 17, 2024 by muon*

[andyr]

3 hours ago, muon* said:

Yes.

 

Output impedance will be high, will see how it effects the response.

 

Edit: OK,

With added resistors in parallel only the slightest hum/buzz if you put ear against speaker and listen carefully

 

Most of the gain reduced, so maybe only 3 or 4db gain now.

 

But what is the Zout now?

 

[muon*]

22 minutes ago, andyr said:

 

But what is the Zout now?

 

I think about 11k

 

Zin for my amp is 10k

 

Now you are going to say it needs to be one 10th of the input impedance of the amp or less. A guess that may be true or not

 

In practice I have found the above is not necessarily true.

Edited April 17, 2024 by muon*

[andyr]

11 minutes ago, muon* said:

I think about 11k

 

That's absolutely ridiculous!

 

11 minutes ago, muon* said:

Now you are going to say it needs to be one 10th of the input impedance of the amp.

 

In practice I have found the above is not necessarily true.

 

In fact the equation is *maximum!* 1/10th.

 

I suggest the fact that you have found this 'rule' to be not necessarily true ... is simply that you were unable to hear any negatives, when you had a Zin that was <10x Zout.

I can accept that the "10x rule" may not be absolute - but I myself do not care to break it.  

 

Edited April 17, 2024 by andyr

[muon*]

23 minutes ago, andyr said:

 

That's absolutely ridiculous!

 

 

In fact the equation is *maximum!* 1/10th.

 

I suggest the fact that you have found this 'rule' to be not necessarily true ... is simply that you were unable to hear any negatives, when you had a Zin that was <10x Zout.

I can accept that the "10x rule" may not be absolute - but I myself do not care to break it.  

 

Your not a webble like I am

 

Edit: I was aiming for 10k but didn't have the resistor values at hand to get it.

Had to consider the actual Zout of the pre amp circuit going into the voltage divider.

Edited April 17, 2024 by muon*

[andyr]

16 minutes ago, muon* said:

Your not a webble like I am

 

"Webble"??

 

[muon*]

5 minutes ago, andyr said:

 

"Webble"??

 

Rebel

[andyr]

8 minutes ago, muon* said:

Rebel

 

Aah, thanks Ian.

 

(I googled it ... but no help!)

 

[Grimmie]

You know!!! 

Webble webble, you torn your dwess.

(Apologies to David)