DIY ACA mini

[Nelson Pass]

Currently I am having fun with cheap...

 

[Lewisknox]

Currently I am having fun with cheap...

It is not only about how to have fun cheap but how good it sounds!

 

[audiosteve]

Currently I am having fun with cheap...

And we all really appreciate that. Many thanks!

 

[nicoch58]

Currently I am having fun with cheap...

Sound really good to me , thanks a lot

 

[thomasnadeau]

look is in R8

Good catch! I bet I looked too closely at Papa's pictures in the article as all of the R's he used are green 3Ws. 🙂 I'll swap the R's this weekend though and see how that changes things.

With that in mind, the article says you can use something between .75R and 1.5R, so the 1R works within that range. Raising the value of R11 lowers the gain, but increases the 2nd harmonics which explains the very "tube" sound I am used to configuring in Papa's projects now (see the H2 for a great hands-on way to play with and listen to this if you haven't). I've also listened to this with the jumper pulled which removes R11 from the circuit and produces the effects specified, but I prefer the sound of this as built.

As I said above, I played around with the various configurations and this sounds nice - REALLY nice - as-is!

 

[nicoch58]

Good catch! I bet I looked too closely at Papa's pictures in the article as all of the R's he used are green 3Ws. 🙂 I'll swap the R's this weekend though and see how that changes things.

With that in mind, the article says you can use something between .75R and 1.5R, so the 1R works within that range. Raising the value of R11 lowers the gain, but increases the 2nd harmonics which explains the very "tube" sound I am used to configuring in Papa's projects now (see the H2 for a great hands-on way to play with and listen to this if you haven't). I've also listened to this with the jumper pulled which removes R11 from the circuit and produces the effects specified, but I prefer the sound of this as built.

As I said above, I played around with the various configurations and this sounds nice - REALLY nice - as-is!

yep we know alter the symmetry in pushpull give H2 but "we find that this results in greater bias drift with temperature."
give a look...

 

[Mark Johnson]

John Bau employs (in my opinion) the perfect countermeasure in his 3-transistor, 10 watt, class A, JLH variant: nullify temperature dependent bias drift with a servo.

 

[Nelson Pass]

Perfectly respectable approach.

 

[Franz Gysi]

John Bau employs (in my opinion) the perfect countermeasure in his 3-transistor, 10 watt, class A, JLH variant: nullify temperature dependent bias drift with a servo.

Can you post a link or a circuit?

 

[nicoch58]

John Bau employs (in my opinion) the perfect countermeasure in his 3-transistor, 10 watt, class A, JLH variant: nullify temperature dependent bias drift with a servo.

btw I like the simplicity that Nelson put in .
As is , is stable and perfect sound if one need more H2 there is the ACA /RACAM or we can add sugar having fun with caps and resistor to taste
As is I like better then vfet go figure

 

[baeijsman]

As is I like better then vfet go figure

Me too! 🤐

 

[tamra]

Thank you Nelson Papa.
I am so into aca mini sound.

 

[Dennis Hui]

Lovely build Tamra!

 

[WBS]

Nicely done Tamra. I especially like the way you mounted it in its base and added both speaker jacks and what looks like a headphone jack as well!

 

[WBS]

Here is the updated BOM from Nelson that addresses the issues mentioned in his post #1216. It reflects the changes: R2 = 200K, and R4 = 22.1K. These changes have been incorporated in the new batch of completion kits that are about to hit the shelves.

 

[sov]

ACA mini plays nicely. 🙂 I put it in same size as ACP+. The tricky part comes next, cut out the top.
It was fun assembling this tiny amp!

 

[audiosteve]

Here is the updated BOM from Nelson that addresses the issues mentioned in his post #1216. It reflects the changes: R2 = 200K, and R4 = 22.1K. These changes have been incorporated in the new batch of completion kits that are about to hit the shelves.

Hi WBS. I've searched the thread and see no mention of changing R2 to 200k anywhere. R4 is discussed in #1216 but nothing On R2 anywhere. Can you direct me to where this change is discussed?

 

[WBS]

In post #1218 Nelson suggests, "the R4 change to 22k or so."

R2 was changed by NP in the updated BOM he provided for the most recent batch of kits for the store.

 

[audiosteve]

In post #1218 Nelson suggests, "the R4 change to 22k or so."

R2 was changed by NP in the updated BOM he provided for the most recent batch of kits for the store.

Ok Thanks. But no explanation as to why?

 

[WBS]

Not to me. I'm just the trained monkey stuffing bags. 🙂

I'm sure he'll let us know.