Critique this internet sourced Bax design...?

Peter Baxandall RIP was (is) a well respected engineer. 

Bax is easier to spell.

JR 

ruairioflaherty said:

Self has a very nice Bax implementation in this book, lower noise and with clear notes on component scaling and band interaction. 

I see no reason to favor the above design over Self's take.

Click to expand...

I love Self's books, I just order SSAD 3rd edition!, however, there is only one problem with Self's implementation, and in fact with his book in general, there is absolutely zero math on how to calculate the circuit parameters, you either take it as it is or you are basically screwed, you can fool around with a simulator trying to modify it to fit your needs, or you can try and figure out how the circuit works by doing the analysis and math by hand, but you are on your own with this. Thats the only downside I see on Self's books, if he at least included  simple formulas on how to calculate basic parameters such as cut-off frequency the book would be truly legendary.

user 37518 said:

I love Self's books, I just order SSAD 3rd edition!, however, there is only one problem with Self's implementation, and in fact with his book in general, there is absolutely zero math on how to calculate the circuit parameters, you either take it as it is or you are basically screwed, you can fool around with a simulator trying to modify it to fit your needs, or you can try and figure out how the circuit works by doing the analysis and math by hand, but you are on your own with this. Thats the only downside I see on Self's books, if he at least included  simple formulas on how to calculate basic parameters such as cut-off frequency the book would be truly legendary.

Click to expand...

I noticed back in the 1970s that college students buying my audio kits were tasked with modifying them as a course requirement for their engineering studies. To sell more kits I included some basic design equations where appropriate in my kit instructions.

JR

SWAN808 said:

I am about to pull the trigger on the BOM for this design to test on the breadboard but thought it might be sensible to check in advance it is worth pursuing from the more knowledgable types around here, seeing as it's an internet source...

Click to expand...

I've built that 3 band EQ many years ago (2004 ish)  and the interaction between the mid and the treble controls was awful.
I always thought i made a mistake somewhere until I came across a piece of equipment with 3 band EQ that had the same interaction. I took the cover off and looked inside and it was the same circuit.

I first saw it in an IC data book , page 586 and I used to drool at the pretty looking curves

mskeete said:

I've built that 3 band EQ many years ago (2004 ish)  and the interaction between the mid and the treble controls was awful.
I always thought i made a mistake somewhere until I came across a piece of equipment with 3 band EQ that had the same interaction. I took the cover off and looked inside and it was the same circuit.

I first saw it in an IC data book , page 586 and I used to drool at the pretty looking curves

Click to expand...

Never ASSume that all typical application circuits are well engineered. They are typically developed by junior engineers tasked with selling more ICs.

I learned a lot from the old National Semi applications handbooks in the 70s but I was starting from a blank sheet... Of course some senior application guys were head and shoulders above the rest (Bob Pease, Jim Williams, etc....). Dennis Bohn of RANE fame started out as a National Semi app engineer.

JR

PS: I repeated this anecdote here recently but back in the 80s when dealing with CBS I learned that one of their CX licensees copied their mistake verbatim from a typical application circuit, manufacturing tens of thousands of playback devices with an incorrect side chain time constant. 

JohnRoberts said:

Never ASSume that all typical application circuits are well engineered. They are typically developed by junior engineers tasked with selling more ICs.

Click to expand...

+1

The same is also true of eval boards. I've never quite understood why companies feel sub-par app circuits and boards is the way to help sell product.  Perhaps they feel the cost / benefit is not justified.

...talking of ICs...how specific to op amps are these type of circuits? I notice in Selfs design it just says 'IC' with no specific selected...this one recommends an OPA132....can I just use an Ne5532 (and can I power that with a 9v battery on my breadboard...)?

I need to find a pot with centre detent to fit the values of this design (100k and 500k) and/or the Douglas Self one which is 10k...which is a 6mm spline shaft and 15mm shaft length...(the Tayda unfortunately are 17mm)

question: if I used a 20k pot in the place of a 10k could this be accounted for by other resistance?

other question: in these types of EQ circuit which component value stipulates the boost amounts?