Triaxis LDR Part Numbers?

[tbryanh]

Does anybody have manufacture names and part numbers for the light dependant resistors, LDR21, LDR29, etc. in the Mesa Boogie Triaxis? http://www.tubefreak.com/triaxis2.jpg

I am looking for the integrated circuit company name(s) and part number(s), not Mesa Boogie's in house part number.

I want to experiment with automated adjustments to guitar amps, so this would help alot.

[Don Symes]

They are (or were a couple of years ago) by Hamamatsu - a Japanese company. The dual-element ones - which you're going to need - are fiendishly difficult to get.

I talked to one of the manufacturers a while back and found that I could get them - get exactly what I wanted - if I bought them in lots of 1000.

[tbryanh]

I googled "Digital Potentiometers" a few days ago and found Maxim Integrated Products
http://www.maxim-ic.com/products/digi_pot/

They have some very interesting product that are geared to be used with Op Amps (yuck), but it might be that they can work with vacuum tubes.

It appears the Triaxis uses LDRs in the grid circuits between stages. The voltages are probably pretty reasonably low there. It might be that Maxim products will work too.

I emailed them a few days ago asking about the composition of the digital resistor, i.e are they equivalent to carbon comp, metal film, wire wound, etc. I also asked them if they could be used in vacuum tube circuits. Their response was off topic and didn't answer any of the questions. Hopefully the resistors are not silicon (yuck).

I just sent them an email asking about minimum quantities and any distributors they might have. Hopfully I will get a reply soon.

[tbryanh]

Here is Maxim's response.

Yes, we do. Although almost all users now order online from the Maxim
website. This is particularly useful to customers requiring sample
quantities or with smaller orders which do not require the distributor to
place the order for the customer.

Here is a link to the listing of North American franchised Maxim
distributors:

http://www.maxim-ic.com/company/cont...nadistributors

Here is a link to buy direct for best pricing/availability for all
quantities:

https://shop.maxim-ic.com/storefront...PartSearchLoad

[tbryanh]

Hamamatsu didn't have a distributor that would do small quantities?

[Gregg]

talked to one of the manufacturers a while back and found that I could get them - get exactly what I wanted - if I bought them in lots of 1000

If not a secret what was the price they offered?

One thing bothers me however - how come no other company came to the idea of designing an all tube programmable preamp? For example all Marshall tube preamps in 1U rack case /instead of the JMP-1/. Are there only marketing reasons behind that or other not so obvious reasons?

[Don Symes]

Hamamatsu didn't have a distributor that would do small quantities?

Not that I found - at least not for the dual-element ones.

[Don Symes]

If not a secret what was the price they offered?

Sorry, I don't really remember. In the $2 to $5 range, I think.

One thing bothers me however - how come no other company came to the idea of designing an all tube programmable preamp? For example all Marshall tube preamps in 1U rack case /instead of the JMP-1/. Are there only marketing reasons behind that or other not so obvious reasons?

The main one is this fiendishly difficult problem of controlling high voltages with digital stuff. Randall Smith (Mesa) patented his method (US PAT 05208548), and I'm sure he declined to license that technology to his competition ... as is his right. He's also known as somewhat sue-happy.

tbryanh may want to search this site for our previous conversation on this subject - I think I use the word PhotoPot, which should keep the search focused.

[Gregg]

This is the thread Don mentions:

http://music-electronics-forum.com//...ead.php?t=1015

Randall Smith (Mesa) patented his method (US PAT 05208548), and I'm sure he declined to license that technology to his competition ... as is his right. He's also known as somewhat sue-happy.

Does this mean that nobody else can use LDRs as pots /did he patent the whole idea/ or they can't use them the way described in his patent. If for example I use a DAC instead of fixed value resistors is this a patent violation?
I'm sorry I'm not very much in patents and stuff.

We know that Randall is sue-happy but does he know that in some countries nobody gives a damn about Randall and his patents? I would like to see him sue a company in China or Russia.

[tbryanh]

Does this mean that nobody else can use LDRs as pots /did he patent the whole idea/ or they can't use them the way described in his patent. If for example I use a DAC instead of fixed value resistors is this a patent violation?

An idea cannot be patented, only your method of doing it can.

A large number of patents are bogus.

The patent office is mostly a record-keeping office. They generally let industry fight it out to see if a patent is valid, otherwise it sits there uncontested.

The patent office generally does not decide if a patent is valid unless it is extremely obvious that it was already invented or is not novel.

Take the wheel for example.

If the patent office already recorded a patent for someone for inventing the wheel, they would not record a patent for you for this. It would be extremely obvious that the wheel was already invented. And, it they hadn't recorded a patent for someone else yet, they still would not do it for you. It would be extremely obvious that inventing the wheel is not novel.

A patent search to see if the "invention" already exists or is similar to one that already exists is required before a patent can be issued. But the patent office does not do the search. They require that the person applying for the patent to do the search.

Bottom line: If you are not "inventing" the wheel, you fill the paperwork out correctly, and you pay the fee, you get your "patent."

Most of the protection for electronic circuits comes from copyrights, not patents. The foil patern on a printed-circuit board is unique and can be copyrighted as art. Most companies copyright their artwork on their PC boards because it is easy to prosecute someone who copies it. When someone duplicates their PC boards, it is blatently obvious.

Feel free to use LDR pots anyway you want. If you cause a big enough stir doing it, you'll have the money to fight Mesa Boogie and prove their "patent" is bogus.

[Gregg]

Thanks for the explanation. However I'm still somewhat puzzled why /except for Triaxis/ similar products are not available.

[tbryanh]

I think two-terminal LDRs are available in small quantities from various vendors.

It appears that three-terminal LDRs are available only directly from the LDR manufactuer and only in quantities of 1000.

It appears Mesa Boogie buys quatities of 1000 directly from the manufactuer.

[Gregg]

It appears that three-terminal LDRs are available only directly from the LDR manufactuer and only in quantities of 1000.

Maybe you meant 4-terminal LDRs because 3-terminal are readiliy available.
You can easily and cheaply build your own 4-terminal /or even more terminal/ LDR - that's what I did for one of my next projects. The software is another story.

[tbryanh]

Maybe you meant 4-terminal LDRs because 3-terminal are readiliy available.
You can easily and cheaply build your own 4-terminal /or even more terminal/ LDR - that's what I did for one of my next projects. The software is another story.

When I was mentioning terminals, I was refering to the resistor. I was in a little bit of a hury. Sorry. I actually have not looked at any of the devices, so it might be some of the terminals are connected together inside and do not make it to the ouside or the LDR.

To make sure I understand you correctly,
1. There are LDRs that have an LED and a resistor. Lets call them LDRs.
2. There are LDRs that have an LED and a potentiometer. Lets call them LDPs.
3. LDRs are used in a variety of products, street lamps, security devices, camera shutters, etc. This makes them available in small quantities at a cheap price.
4. LDPs are used in Mesa Boogie products only. Mesa convinced the LDR manufactuer to make LDPs by being willing to by quantities of 1000. This make LDPs expensive and available in large quantities only.
5. LDRs can be used in some situations to control vacuum tube circuits.
6. LDPs can be used in any situation where LDRs are used, and they can be used in many more situations where a potentiometer is needed rather than a resistor.
7. It does not appear possible to use 2 or more LDRs to make an LDP.
8. Not having access to LDPs at a cheap price in small quantities appears to be a big stumbling block.

[Gregg]

The thread I pointed to contains interesting information on this subject.
Concerning the LDRs there are what I call regular LDRs and custom made. I call regular all those that you can buy freely from various web sites. They include:

1/ 2-terminal LDRs /the photocell terminals are interesting only/ built from one LED and one photocell.
2/ 3-terminal LDRs built from one LED and one center tapped photocell /or two photocells sharing a common terminal/.

2/ can be used in vacuum tube circuits as Middle and Presence control in a regular passive tone stack and amp. For the Bass you'll need a 4-terminal LDR /one LED and two independent photocells/. To imitate a regular pot with a taper however you'll need 2 of those 4-terminal LDRs. Since they're available only in wholesale quantities for DIY projects you'll have to build them yourself by using regular LEDs and photocells available online. This way they'll cost you $2 the piece and you can forget about the wholesaler.

Enjoy!