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valves in a Farfisa pre amp

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Re: valves in a Farfisa pre amp

Postby Martin Walker » Wed Mar 06, 2019 5:54 pm

Adam Inglis wrote:Learning all the time, as Benny Hill used to say.

My local emporium didn't have any cartridge pickups of course, but it did stock some cheap little piezo transducers they called "buzzers" so I grabbed a couple. One type only responded to DC, so that was no good, but I had more luck with the other one. I had to crack the case to get to the transducer

If you're prepared to go mail order, you don't have to crack the cases ;)

I've bought some of these in the past:

http://spiratronics.com/product-39448.html

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Re: valves in a Farfisa pre amp

Postby James Perrett » Wed Mar 06, 2019 9:50 pm

Folderol wrote:Have you thought of trying to get hold of another ceramic PU? That one looks like it suffered moisture damage, whereas one in an old record player will likely still be clean.

I realise that I'm a bit late to this but I thought I'd mention that obtaining working crystal/ceramic pickups is becoming a big problem for the vintage record player fraternity. High output types are especially rare. The only new ones available are the ubiquitous red ones seen in the cheap record players which can be obtained very cheaply if you can wait for them to arrive from China.
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Re: valves in a Farfisa pre amp

Postby Sam Spoons » Wed Mar 06, 2019 11:34 pm

Martin Walker wrote:If you're prepared to go mail order, you don't have to crack the cases ;)

I've bought some of these in the past:

http://spiratronics.com/product-39448.html

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Maplin was the goto for those but I'd expect them to be easily available elsewhere.
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Re: valves in a Farfisa pre amp

Postby Martin Walker » Thu Mar 07, 2019 1:49 am

True, but I've actually since remembered that I bought mine via Ebay, via this link:

https://www.ebay.co.uk/itm/360719728982 ... rsta=en_GB

The different sizes have differing resonance frequencies.


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Re: valves in a Farfisa pre amp

Postby Adam Inglis » Mon Mar 25, 2019 4:46 am

Thanks Martin.
That vendor quotes a "resonant impedance" as measured in watts. Not sure what that is... but those larger 35 mm ones with resonant frequency around 2 kHz could be well worth experimenting with.

A couple of observations:
messing around with the current setup, I found several "sweet spots" for the transducer, in contact with the aluminium baseplate (this is isolated by foam blocks inside the aluminium chassis of the tank). I suppose there is probably some amount of "plate" resonance going on here along with the spring vibration (some will recall the DIY plate reverb on youtube recently using piezos).
In addition to the reverberation, there is also quite a bit of "direct" sound, which, I guess because of two state changes and a bit of metal in between, has a rather distorted edgy sound.
The overall effect has buckets of character!
I’m enjoying it so much that I’m going to look at installing an external input to the circuit so that I can use it as a send from the mixer.
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Re: valves in a Farfisa pre amp

Postby Folderol » Mon Mar 25, 2019 9:26 am

Adam Inglis wrote:The overall effect has buckets of character!
I’m enjoying it so much that I’m going to look at installing an external input to the circuit so that I can use it as a send from the mixer.
That's what I like to hear :bouncy:
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Re: valves in a Farfisa pre amp

Postby Wonks » Mon Mar 25, 2019 1:51 pm

Just discovered that Vox did the same thing in their mid-60s hybrid solid state/tube amps to avoid the cost of the Hammond reverb or paying $1 royalty per unit for a copy.

"One delay spring between two 1 volt output Sonotone 2T crystal phono cartridges."

Reverb described in the paragraphs towards the lower part of the footswitch picture.

http://www.voxshowroom.com/uk/amp/730.html
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Re: valves in a Farfisa pre amp

Postby Hugh Robjohns » Mon Mar 25, 2019 2:15 pm

Interesting article, but I always baulk at the phrase 'resented paying the royalty' in the context of patented devices -- like the Hammond Accutronics spring reverb.

The whole point of a patent is so that an engineer/company can protect it's intellectual property and generate profit from it for a reasonable period of time. It's a concept that lies at the very bedrock of Western commercialism.

So to 'feel bitterness or indignation' -- the dictionary definition if resentment -- at that, especially from another manufacturer who endeavours to protect its own unique designs, too -- seems rather inappropriate, to say the least.

Sure, I understand that Vox might not want to have to load their products with the extra $1 royalty... but having made that business decision their challenge is to come up with a viable independent alternative... not be resentful that someone else beat them to it with a better idea!

And they did come up with a (borderline patent-avoiding) alternative, which did work to a reasonable degree -- although in retrospect it might have been better to cough up the $1! :-)
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Re: valves in a Farfisa pre amp

Postby ef37a » Tue Mar 26, 2019 7:44 am

Now I do not pretend to understand patent law Hugh but there have been cases in the past where a fairly simple circuit technique for example has been seized upon and a company lodged a patent on it.

I recall a push pull valve amplifier circuit that originally had a simple switch that cut the output power by two thirds but the amps had not been on the market barely a month when the company was told they were infringing on a USA patent.

Now, I do not know the ramifications but assume the holder of a patent can refuse its use? Claiming I suppose that they feel it would impact their sales? The other possibility was that the cost of paying the royalty was judged excessive (they were top grade amps so that proverbial $1 would easily have been absorbed).

The alternative would have been to say **** you! And just stay with the circuit but the company was in no position to fight a protracted case in America!

Fortunately there was another solution. You cannot patent the mode or class a valve works in or if you could once it has long expired.

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Re: valves in a Farfisa pre amp

Postby Adam Inglis » Tue Mar 26, 2019 8:44 am

Wonks wrote:Just discovered that Vox did the same thing in their mid-60s hybrid solid state/tube amps to avoid the cost of the Hammond reverb or paying $1 royalty per unit for a copy.

"One delay spring between two 1 volt output Sonotone 2T crystal phono cartridges."

Reverb described in the paragraphs towards the lower part of the footswitch picture.

http://www.voxshowroom.com/uk/amp/730.html

Thanks Wonks. That "reverb pan" in the picture looks an awful lot like the one in this Farfisa! I wonder who really invented it? I think mine is circa 1966.
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Re: valves in a Farfisa pre amp

Postby Hugh Robjohns » Tue Mar 26, 2019 10:50 am

ef37a wrote:Now I do not pretend to understand patent law...

You and me both... and I've held a couple of patents in the past (now expired)!

The concept is straightforward, but the practice is anything but... because it relies on the specific writing and interpretation of the documentation. And it's an industry infested with specialist lawyers (no offence intended to specialist lawyers BTW! ;-) ).

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Re: valves in a Farfisa pre amp

Postby blinddrew » Tue Mar 26, 2019 11:24 am

The US Patent Office has been under a lot of political pressure over the last few years to approve patents - they're seen as a measure of innovation and they have to keep up with the Chinese... :roll:
A lot of stuff that shouldn't be patentable ends up getting locked up until someone with a big enough wallet comes along to litigate it. :(
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Re: valves in a Farfisa pre amp

Postby Hugh Robjohns » Tue Mar 26, 2019 12:06 pm

Very true. Had some experiences of American companies railroading through patents that shouldn't have been permitted, and then litigating other companies to cease and desist their own legitimate designs! Grrr...

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Re: valves in a Farfisa pre amp

Postby ef37a » Tue Mar 26, 2019 2:58 pm

I had read that if you have a good idea for a gizmo and publish the details in a decently widely read place such as SOS it is "in the public domain" and could not be patented?

You do not earn money off the idea but at least giant b****d company can't either?

There is a (apocryphal?) story that P Walker never patented his ELS because it was SUCH bugger to get right that he simply had to keep the processes secret?

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Re: valves in a Farfisa pre amp

Postby blinddrew » Tue Mar 26, 2019 4:14 pm

Think it's a bit more complex than that Dave. Speaking from a US point of view (because I have a better understanding of the law there - which is weird but a separate conversation), patents, like copyrights, can't be assigned to an idea; it has to be the execution of an idea.
So I can't apply for a patent that says, "I've got an idea for a gizmo that does X." I'd need to submit an application that says, "Here is the design for a gizmo that does X," and part of the submission is the details of how that gizmo works.
As a result I could have a load of discussions online about the idea but that wouldn't prejudice the patent application, unless the concept had reached the point where it was no longer an original idea and was simply a logical enhancement of an existing product.
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Re: valves in a Farfisa pre amp

Postby ef37a » Tue Mar 26, 2019 4:24 pm

Ah! But I did not mean just an idea in a magazine Drew. I was thinking of a full blown article about a gadget complete with schematics and a working prototype sent to the magazine to test. (done this* but not to SOS)

My idea is, if you show in detail, "this is how you make a Splatterblatter pedal it is done and dusted?

*No, no interest at all but MAYBE I'll make my million before I am 80?

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Re: valves in a Farfisa pre amp

Postby Wonks » Tue Mar 26, 2019 4:29 pm

Thanks, Dave. You've just reminded me to get my lottery ticket!
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Re: valves in a Farfisa pre amp

Postby Hugh Robjohns » Tue Mar 26, 2019 4:36 pm

ef37a wrote:I had read that if you have a good idea for a gizmo and publish the details in a decently widely read place such as SOS it is "in the public domain" and could not be patented?

I think the whole thing is quite complicated and, as I mentioned earlier, subject to legal interpretation... But as Drew says, patents apply to the physical implementation of the idea, not the idea itself. You have to show that it can be made to work, and how.

And that's why it is often argued that it's better not to apply for patents, because by doing so you educate your competitors about how your innovative product works, and they can then find a way to circumvent your patent -- like by using piezo transducers in the reverb tank. Instead, just make the thing and hope you establish a market and make money from large sales quickly, before the competition catch on and do their own version.

But as you say, if a product is revealed in detail in public it is difficult then subsequently to get a patent granted, and just as hard to prevent a competitor from making something very similar.

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Re: valves in a Farfisa pre amp

Postby Wonks » Tue Mar 26, 2019 5:05 pm

I once bought some 'patent' leather shoes, and found that everyone else also had some! So much for the so called 'patent' and exclusivity! ;)
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Re: valves in a Farfisa pre amp

Postby Hugh Robjohns » Tue Mar 26, 2019 5:10 pm

:lol:
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