The 47 pole Elma's (7.5 degree indexing) are really nice, but not cheap. In the UK >£200 for a two gang one for stereo. So >£1200 in switches for the filter functions alone. There is a serious step change in price going from 24 way (from Blore Edwards) to 48 way Elma - like an order of magnitude.
I've used 4-gang 24 way ones in stereo balanced volume application, and two mono ones side by side in another.
Craig
I've used 4-gang 24 way ones in stereo balanced volume application, and two mono ones side by side in another.
Craig
Of course the question is, would Colangelo/Jayson have designed custom switches if the 7.5 indexed ELMA, or 6 degree indexed Seiden or Shallco units have been available?
Even though the commercial switches seem prohibitively expensive in small numbers in a hobby unit, in a commercial high end or studio product the buy vs build decision is down to overall cost effectiveness.
FWIW John Curl used Shallco switches for input select and phase invert in the Blowtorch. And these as the volume controls http://www.tkd-corp.com/en/products/att/stepatt.html
Craig
Even though the commercial switches seem prohibitively expensive in small numbers in a hobby unit, in a commercial high end or studio product the buy vs build decision is down to overall cost effectiveness.
FWIW John Curl used Shallco switches for input select and phase invert in the Blowtorch. And these as the volume controls http://www.tkd-corp.com/en/products/att/stepatt.html
Craig
Poking around the web, the stereo version of the TKD switched attenuator is around UKP500. There is no free lunch. Unless you use linear pots such as were used in the Palette Preamp, and Charles uses in his own version - these are cheap as chips.
Craig
Craig
Rearding the Burwen LF/HF shelving - I was careless and didn't look beforehand at your plot.
Does appear to be like the old Bass/Treble controls, which "way back when" were in most tubed preamps, I used AND liked their effect.
Charles
Does appear to be like the old Bass/Treble controls, which "way back when" were in most tubed preamps, I used AND liked their effect.
Charles
Yeah. I guess that is why Cello abandoned that, and incorporated all the filters the same way. Burwen seems to be a real fan of mixing different sorts of program EQ, based on his practical experience,
Whatever I build, I'll probably use plug in modules - then I can try out different arrangements of Cello-like and shelving filters. Or even make it switchable.
Well, IF YOU ASK ME, having 1.5 dB, 0.7dB and 0.35dB steps and +/- 16dB/8dB/4dB and using 23-Positions is just fine. But I would probably not replace them with pots.
Thor
If only it were that easy. The controls are far from linear, so you cannot just divide the range up. In general they are S shaped, some of them quite markedly so. The attached is the characteristic of the 15Hz filter. You could get away with a linear control with small error in the middle +/-12dB range. The 500 and 2kHz controls are quite linear though, and can probably be divided up per your suggestion. 15Hz and 25kHz ones are the worst. 120Hz and 5kHz are also quite non-linear.
Craig
Craig
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Given the shelving section of Burwen's Audio Palette prototype, why does he describe them as 120Hz and 5kHz?
Having looked at the curves for the shelving responses, those frequencies are at 6dB below the upper and lower asymptote at maximum boost and cut.
I guess he had to describe them in some way, and that was as good as any.
Incidentally, Douglas Self in his book Small Signal Audio Design (2nd Ed) shows on pp422-403 a two opamp schematic, figure 15.43, that can be switched between a peak resonant mode and shelving response.
Having looked at the curves for the shelving responses, those frequencies are at 6dB below the upper and lower asymptote at maximum boost and cut.
I guess he had to describe them in some way, and that was as good as any.
Incidentally, Douglas Self in his book Small Signal Audio Design (2nd Ed) shows on pp422-403 a two opamp schematic, figure 15.43, that can be switched between a peak resonant mode and shelving response.
I know what he meant - these https://www.hificollective.co.uk/components/switches/elma-jumbo-a47-switch-2-pole-47way.html .
It IS that easy. Calculating the relevant resistors is a job for Excel. And yes, I'm aware you need appx S-Shaped controls.
Thor
All the resistor chains are worked out already; either supplied by Charles or worked out by me. Both for Burwen or Cello. All on this thread.
Craig
Craig
But these are not for 24-position switches, so the would need re-scaling... Right?
Thor
I clearly misunderstood your mail - the way you worded it looked like you intended to have switchable attenuation. I now realise what you actually meant!
The switches are actually 23 way - there has to be a rotation stop. So center position is zero, then 11 steps each way. So 1.5db/step would give +/-16.5dB etc.
Craig
The switches are actually 23 way - there has to be a rotation stop. So center position is zero, then 11 steps each way. So 1.5db/step would give +/-16.5dB etc.
Craig
From an article I saved at some point or another by Burwen:
"I hate to admit it, but even I have been deceived by expectation. For many years I used a hand-held tone control prototype of my own design. This device was never produced, but became the predecessor of the Cello Audio Palette. It had 6 tone controls working in different parts of the audio frequency range. Instead of using expensive, custom made, two-gang, 60-position switches with 120 1% resistors for each 2-channel tone control, my prototype used a cheap pair of 3-inch linear potentiometer sliders for the left and right channels. Two fingers operated one closely spaced pair of sliders. 2 One day I was standing up, intently listening to my sound system while operating the tone sliders at waist level. Having spent much of my life designing tone controls and feedback systems, I knew exactly how each control sounded when boosting or attenuating. As I carefully moved the sliders to refine the sound of the music, I clearly heard the improvement in sound and left the sliders at my preferred position. When I looked down, I discovered the tone controls were actually switched out. I had done nothing. My self-deception did not happen just once, but perhaps 2 or 3 times a year during a period of 10 years."
"I hate to admit it, but even I have been deceived by expectation. For many years I used a hand-held tone control prototype of my own design. This device was never produced, but became the predecessor of the Cello Audio Palette. It had 6 tone controls working in different parts of the audio frequency range. Instead of using expensive, custom made, two-gang, 60-position switches with 120 1% resistors for each 2-channel tone control, my prototype used a cheap pair of 3-inch linear potentiometer sliders for the left and right channels. Two fingers operated one closely spaced pair of sliders. 2 One day I was standing up, intently listening to my sound system while operating the tone sliders at waist level. Having spent much of my life designing tone controls and feedback systems, I knew exactly how each control sounded when boosting or attenuating. As I carefully moved the sliders to refine the sound of the music, I clearly heard the improvement in sound and left the sliders at my preferred position. When I looked down, I discovered the tone controls were actually switched out. I had done nothing. My self-deception did not happen just once, but perhaps 2 or 3 times a year during a period of 10 years."
Happened to me before.
I asked the roadie on stage during soundcheck to move microphones. I heard the expected changes.
Later I checked the stage and found the mic's had not been moved as directed. Went back, tested again and it sounded wrong, went up, adjusted mic's and the sound went to "right".
I had the opposite experience too.
Having to my mind changed nothing the lead vocals were "out", not huge but just audible and it threw me off bugged me for weeks and many shows. I eventually traced it to the microphone cable (this was before the industry went wireless) which had been made from a "star quad" PTFE insulated silver plated copper cable, instead my usual twin & screen in PVC. Put the generic cable back and the sound went back to "normal".
Thor
I asked the roadie on stage during soundcheck to move microphones. I heard the expected changes.
Later I checked the stage and found the mic's had not been moved as directed. Went back, tested again and it sounded wrong, went up, adjusted mic's and the sound went to "right".
I had the opposite experience too.
Having to my mind changed nothing the lead vocals were "out", not huge but just audible and it threw me off bugged me for weeks and many shows. I eventually traced it to the microphone cable (this was before the industry went wireless) which had been made from a "star quad" PTFE insulated silver plated copper cable, instead my usual twin & screen in PVC. Put the generic cable back and the sound went back to "normal".
Thor
Yes, things of that nature happened to me as well.
OTOH, many times I made circuit or component changes expecting an improvement and it got worse, and I'm not talking about errors.
OTOH, many times I made circuit or component changes expecting an improvement and it got worse, and I'm not talking about errors.
Yes, I had the same experience.
It is just very easy to fool ourselves and hard to really listen and hear what is going on.
Thor
It is just very easy to fool ourselves and hard to really listen and hear what is going on.
Thor