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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 21st Nov 2019, 3:11 pm   #41
mhennessy
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Default Re: Mullard Audio Circuit

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Which, although potentially helpful to the marketing department, is, as I alluded to in post #19, of no practical benefit whatsoever.
You did indeed Mark! And it can also be a bit more fun to stabilise again as you pointed out (been there done that - making a low-dropout voltage regulator rather than an AF amplifier).

However, in the Texan, the output stage is driven from a 741 operating with -15 / +15V rails, so the output stage has to have some voltage gain else it would be limited by the +/- 13V swing of this, irrespective of the 25V rails to the output.
Not disputing that - I made the same point earlier (output stages with gain are worth the effort as it's getting harder to get high voltage small-signal transistors. The grounded-source/Transnova circuits being the ultimate expression of that, where the small-signal circuitry can operate from tiny supply rails if you like)

But voltage efficiency as a goal is the pointless bit. Did that once when I was still at school - talk about a lesson in decibels learnt the hard way!

I did once consider building a Texan, but by that stage I'd already done a lot of my own designs and had decided to keep away from projects in the magazines, as some of them were really quite iffy in my experience thus far.

Random aside: Douglas Self did an amplifier based on a 32 NE5532s in parallel - no output transistors!. 16 watts per channel into 8 ohms at extremely low distortion, from +/-18.3V rails. Meant as a bit of fun, but interesting nonetheless
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Old 21st Nov 2019, 9:49 pm   #42
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Default Re: Mullard Audio Circuit

This talk about the Texan reminded me that many yaers ago we had a group project in our spare time at work, we were all building identical amplifiers and bulk buying the components.
The design was similar to the Texan in that it used op-amps, 741s I think, driving transistor output stages but was unusual in that it used filters to split the signal into low, mid and treble frequencies and amplified them separately to drive the tweeter, mid range and woofer speakers rather than splitting the signal with crossovers in the speaker.
I seem to recall the design was from chip a manufacturers application note.
Does anyone recall what the design might have been?

Peter
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Old 21st Nov 2019, 10:47 pm   #43
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Default Re: Mullard Audio Circuit

That was probably earlier than Siegfried Linkwitz's first active crossover system design in WW 1978, May, June and December. That used TL072 op amps. I built it in about '79 or '80.

Siegfried was designing and refining the active crossover concept until not long before he died at 82. I personally use his final and greatest design, the LX521.

https://www.linkwitzlab.com/

Craig
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Old 21st Nov 2019, 10:56 pm   #44
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Default Re: Mullard Audio Circuit

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Originally Posted by mhennessy View Post
Random aside: Douglas Self did an amplifier based on a 32 NE5532s in parallel - no output transistors!. 16 watts per channel into 8 ohms at extremely low distortion, from +/-18.3V rails. Meant as a bit of fun, but interesting nonetheless
Hope I've un-entangled all the quotes!

Nelson Pass has upstaged Self by building a power amp with several thousand complementary discrete JFET buffers in parallel http://www.firstwatt.com/pdf/art_beast.pdf

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Old 22nd Nov 2019, 2:49 am   #45
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Default Re: Mullard Audio Circuit

A fascinating thread. Just a thought, was there any clever audio circuitry employed in the "slab" type of STK output chips that were popular in the 80s and 90s?
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Old 22nd Nov 2019, 9:48 am   #46
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Default Re: Mullard Audio Circuit

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A fascinating thread. Just a thought, was there any clever audio circuitry employed in the "slab" type of STK output chips that were popular in the 80s and 90s?
Just the timer for when they self-destruct :-0

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Old 22nd Nov 2019, 2:07 pm   #47
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There is a very poor and often out of focus You Tube video of the internals of an STK here https://www.youtube.com/watch?v=m6DbeIy51tU

Seems to be a combination of conventional circuit board, thick film and discrete. This one was ripped open because (surprise surprise) it had blown up.

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Old 22nd Nov 2019, 11:37 pm   #48
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Default Re: Mullard Audio Circuit

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The design was similar to the Texan in that it used op-amps, 741s I think, driving transistor output stages but was unusual in that it used filters to split the signal into low, mid and treble frequencies and amplified them separately to drive the tweeter, mid range and woofer speakers rather than splitting the signal with crossovers in the speaker.
I seem to recall the design was from chip a manufacturers application note.
Does anyone recall what the design might have been?

Peter
I think this may have been inspired by an applications leaflet for the Plessey SL403, and I'm sure a construction article featuring the (triple SL403) design appeared in a magazine sometime around 1970. Possibly Practical Electronics?

I didn't build it, but I've no doubt that tri-amping would have enabled the three, rather low-powered, amplifiers to punch well above their weight.
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Old 23rd Nov 2019, 9:46 am   #49
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Originally Posted by m0cemdave View Post

I think this may have been inspired by an applications leaflet for the Plessey SL403, and I'm sure a construction article featuring the (triple SL403) design appeared in a magazine sometime around 1970. Possibly Practical Electronics?

I didn't build it, but I've no doubt that tri-amping would have enabled the three, rather low-powered, amplifiers to punch well above their weight.


I think you have hit the nail on the head. I think I have been confusing the Texan with the triple SL403 project.
I am pretty sure now that it was the Texan we built, I remember one of us testing and matching the ouput transistors into pairs and thinking back we each got 4 for a stereo pair not 18.

Back to the triple SL403 it would only give a sigificant increase in power if the sound to be reproduced was evenly distributed across the spectrum otherwise one channel would have to handle the lions share and that would limit the available power.

Peter
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Old 23rd Nov 2019, 2:20 pm   #50
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Default Re: Mullard Audio Circuit

The SL403 article using 3 ICs was in Practical Electronics Dec 1969 on by M J Gay of Plessey.
It can be found here if you're interested. https://www.americanradiohistory.com...cs-1969-12.pdf
I played around with several of these modules and ICs in the late 60s building stereo amps for mono record players for friends.
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