The Optometrist - and so it begins. . .

[Jim Williams]

Whenever I need to rush out and pick up a guided missle controller or spare nose cone, Apex has me covered.

It's also used heavily by Hollywood set designers. You can outfit a 50's scifi movie for a couple thousand bucks.

The glory days were the 1970's and 1980's, lots of audio companies sold off their excess inventory to Apex, including Fender. I would buy Fender amp power and output transformers for 5 bucks.

[mjrippe]

Geez, I thought this was a post about another member with failing eyesight trying to read component values. Been putting off that optometrist visit for a while now...But I am glad to see it is a new preamp project instead!

[KAB]

very cool...

[alcoyot]

Awesome! So many choices would be confusing for me though. Anyone know of a similar scrap yard in the NYC area?

[rvwainscott]

Originally Posted by Jim Williams

Whenever I need to rush out and pick up a guided missle controller or spare nose cone, Apex has me covered.

It's also used heavily by Hollywood set designers. You can outfit a 50's scifi movie for a couple thousand bucks.

The glory days were the 1970's and 1980's, lots of audio companies sold off their excess inventory to Apex, including Fender. I would buy Fender amp power and output transformers for 5 bucks.

You are 100% correct about all that. The sad thing is is that the place has been pretty well picked clean. It takes hours of scrounging around to find really cool things there. I went back there again today looking for some things. Here is what it looks like on the inside. For those of you that don't know, imagine a large supermarket but with row after row of this. . .




After APEX I went to get some metal work done and talk to the powdercoater. I noticed this sticker on the box which seemed to be the last time the unit was serviced - 1967!


I picked my colors which I want to look like hospital colors from the early '70's. They are the top two colors (Ral 1000, Ral 8008. The dark color will be on the bottom. I think those are pretty classy looking and will really look good with the white jewel and I'm going to put white led's in the vu meter.



I'm still not sure about the faceplate layout but I was sure about where I want to put the VU meter so I had my metal guy punch out the faceplate to I could get a better idea.



It is going to take a week or more for my custom colors to arrive by mail so that gives me a little time to properly lay out the faceplate. Also, I've decided to leather wrap the two metal handles and I've either got to figure out how to do that or find someone that can do that. Any thoughts anyone?

[Jim Williams]

Yes. Just drive up San Fernando Road to San Fernando. On the side of the road you will see several auto re-upolstry shops that do leather too. They will fab anything you want there. I've even had console armrests re-done there before. Spanish speaking skills are a plus.

[rvwainscott]

Originally Posted by Jim Williams

Yes. Just drive up San Fernando Road to San Fernando. On the side of the road you will see several auto re-upolstry shops that do leather too. They will fab anything you want there. I've even had console armrests re-done there before. Spanish speaking skills are a plus.

Wow, sounds like you know that neighborhood well. I will follow your advice and look for them the next time I am there.

OK, I only had a little bit of time to work today so I make up a point to point little circuit on some copper clad board.



I also started gathering up some of the parts I'm going to need. I also realize that I'm going to need another copper clad "circuit" board and I really need to take some time to figure out how many "functions" I want to put in this thing.
I'm thinking that more than 10 different ways to change tone and response (remember, I will not put an eq in this pre but get my different responses by voicing the tubes differently) may overwhelm the user. Here are the options I"m considering so far but I'm open to more suggestions.

Input Transformer Selector
Input Impedance Selector
Output Transformer Selector
Phantom
Phase
Bright Boost 1 & 2 (based off of the cathode bypass capacitor)
Boost (based off of the cathode bypass capacitor)
Presence
Triode 1 2 or 3
5 Position High Pass Filter
Triode Bypass
5 Position Asymmetrical Frequency Dependent Clipping
4 Position Blocking Capacitor Selector (polystyrene, compressed ceramic, Polyester film, possibly transformer coupled)
Bass Boost (I suspect that I can do this by loading the input transformer but I'm not positive)

Anyway, here are the parts that I've gathered up so far.




Geeks should feel free to ask me any questions, offer suggestions or just mock me for my endeavors. Enjoy.

[Matt Syson]

Hi
Having a coupling cap feeding an output tranformer that is too low in capacitance can provide a dB or two 'LF boost' but it will get flattened again if you load the transformer hard.
Otherwise you are into 'cut everything but LF' territory, like the bottom end of ye olde Pultec (and so many others).
It keeps you off the street corners so go for it!
Matt S

[rvwainscott]

Originally Posted by Matt Syson

Hi
Having a coupling cap feeding an output tranformer that is too low in capacitance can provide a dB or two 'LF boost' but it will get flattened again if you load the transformer hard.
Otherwise you are into 'cut everything but LF' territory, like the bottom end of ye olde Pultec (and so many others).
It keeps you off the street corners so go for it!
Matt S

Matt,

Actually, I was looking through an old hand book for audio engineers from the 1960's. I came across a schematic that achieved a bass boost by using a 1 meg resistor between the high and low sides of the secondaries of the input transformer. I am not too sure as to why that would give a bass boost but I do plan to do a mock up and see what happens. Also, if it does work then why not use a variable resistor to control it.

Also, those old audio engineer handbooks hurt my head. I can't help but wonder if that kind of knowledge was expected of an audio engineer in the 1960's.

Finally, you are correct in that it is easier to play with the high end as I can think of three places just off the top of my head to achieve a top end boost.

I'll let you know how my "experiment" turns out.

[dogma]

I love you

Subscribing - I'm all for keeping kids off the streets and its real nice to see Jim back -

Hi Jim, Matt. This MCA SP1's are soo nice, thank you

I'm nowhere near smart of knowledgeable to do something like this but I'll learn what I can.

[Matt Syson]

Hi
I have a radio constructors encyclopaedia from around 1910 - 1920 sort of era (sadly not mentioned in the fly leaf as it would be now) with all manner of interesting 'stuff'. Audio distortion was probably 'less than about 30 percent' on a good day!
Make your own capacitors using a glass jar with foil on the inside and outside kind of stuff.
I can only think that having a 1 meg resistor would help 'flatten' HF resonance. Any chance of posting the schematic?
Matt S

[rvwainscott]

Originally Posted by Matt Syson

Hi
I have a radio constructors encyclopaedia from around 1910 - 1920 sort of era (sadly not mentioned in the fly leaf as it would be now) with all manner of interesting 'stuff'. Audio distortion was probably 'less than about 30 percent' on a good day!
Make your own capacitors using a glass jar with foil on the inside and outside kind of stuff.
I can only think that having a 1 meg resistor would help 'flatten' HF resonance. Any chance of posting the schematic?
Matt S

Matt,

Sure, I will scan the page from that book. If I remember correctly, it featured about 12 different places in a tube circuit where frequency response could be attenuated or boosted.

Finally, I realize that there are modern active designs that would easily do these things but I really enjoy the passive components and the happy surprises that come with using them.

[Matt Syson]

Hi
All EQ is 'cutting' using passive parts. If you have a 'boost' circuit it is 'simply' an amplifier with passive parts before, during or after, cutting the amplified signal at some fequency or other.
Matt S

[rvwainscott]

Originally Posted by Matt Syson

Hi
All EQ is 'cutting' using passive parts. If you have a 'boost' circuit it is 'simply' an amplifier with passive parts before, during or after, cutting the amplified signal at some fequency or other.
Matt S

Matt,

Couldn't agree with you more. The reality is is that I'm hacking away at something - sometimes before the tube, sometimes after. Given that the input transformer is a 1:7 step up transformer, I can get some response out of that as well.

Really, frequency response can be tweak by changing the input impedance, plate resistor size, grid stop resistor, etc, etc, etc.

Oh yeah, I was wrong as that resistor is on the primary of the input transformer. I'm curious to see what that does. I'll post some images from the scope when I get around to it.

[12ax7]

Originally Posted by rvwainscott

[...]

OK, I only had a little bit of time to work today so I make up a point to point little circuit on some copper clad board.

[...]

.

Mmmmmm...

...Copper!!!

.

[MrMegaEli]

This is beautiful! Where’d you get the copper clad board?

[rvwainscott]

Originally Posted by MrMegaEli

This is beautiful! Where’d you get the copper clad board?

Greetings,

Apex in Los Angeles. The stuff is just laying around. It isn't at all hard to cut.

[rvwainscott]

Taking the Black Box Mic Pre to AES in New York sidetracked me for a bit but I'm back working on the Optometrist. I finally got my custom colors so check out today's work.

I'm going to sandblast the box. Well, glass beads actually but you know what I mean.



Got the faceplate, box and xlr connector panel all sandblasted and ready to go.



Mike is using the plasma cutter to trim my xlr connector panel.






The box is getting its first round of powder. This is the sickly beige/green color for the top.




Now we're doing the chocolate/green color. We do this after we bake the beige for 19 minutes in the walkin oven.





Here it is fresh out of the oven.





I hope to complete this box in the next few weeks provided I have all the bits I need. Let me know what you guys think.

[rvwainscott]

Starting to layout the faceplate. I want to see which knobs look the best.

[Jim Williams]

I used to do stuff like this. Once I had a Gibson L6-S, with the 6 way rotary switch that got every combo of pickups. It wasn't enough, so I installed 2 more of them, one for each pickup. I had some 250~300 pickup combinations on that guitar.

I now use 2.

Once you hear all the permutations of preamp sounds, don't be suprized if you also find only one or two that you will use.

Of couse, you will need to do this to learn that.

[S2udio]

Originally Posted by Jim Williams

Once you hear all the permutations of preamp sounds, don't be suprized if you also find only one or two that you will use.

Of couse, you will need to do this to learn that.

"Less is more" It matures with age,
Just like a good wine .

[rvwainscott]

Jim, I have other reasons for making this box as I plan to use it to produce custom tube pre's for artists and producers here in LA. Give me a singer and his or her favorite mic and I will quickly dial in the settings and features necessary to build a custom pre for that person.

My past pre's have been shown to be wildly versitile but it isnt reasonable to offer the public so many features. But to find the right fit for the client I'm going to need everything available to me in a big silly box.

Not only that, but I will build the thing to look like anything you want.

[Jim Williams]

Originally Posted by rvwainscott

But to find the right fit for the client I'm going to need everything available to me in a big silly box.

Better include some silicon too, most preamps are made that way and you will need all of those too to have everything available to you in a big silly box.

[rvwainscott]

Originally Posted by Jim Williams

Better include some silicon too, most preamps are made that way and you will need all of those too to have everything available to you in a big silly box.

If you are talking about opamps and transistors then I would have to say "no".

Solid state is fine for people that are into that kind of thing and I have nothing but respect for designers that figure out how to make it sound good but it just isnt for me.

I prefer something that I can really mess with and do extreme things with. A 50 cent opamp that can be destroyed by static electricity is, frankly, boring. I'll take a tube over that any day.

[Jim Williams]

Too bad all your hard work will eventually be force fed into one of those boring opamps. Maybe if you spend more than 50 cent on one you might find one you could live with, but I don't think so.

So, what happens after the tube?

Answer: Silicon.

[Paul Gold]

But hopefully not gear that has been destroyed by installing video opamps. They really suck for audio.

BTW the project is great. Sort of like a salesman's product sample kit of yore. Apex and Apex Jr. are a must when I'm in LA. I'm jealous that you have someone who will do one off metal work and powder coating.

[rvwainscott]

Originally Posted by Jim Williams

Too bad all your hard work will eventually be force fed into one of those boring opamps. Maybe if you spend more than 50 cent on one you might find one you could live with, but I don't think so.

So, what happens after the tube?

Answer: Silicon.

I refuse to debate the issue of solid state vs vacuum tube. They are great for what they do and it is now cheaper to produce one than to grow a grain of rice (fact). That said, I have no desire to work with them as I prefer the character of a vacuum tube. My preferance isnt open to debate.

There are people that still appreciate the DIY approach that I take and I make these posts to encourage others to raid the junk yards and scrap heaps and do the same as we are fast approaching a time when few of the products we use wont be produced by a machine in Asia.

[rvwainscott]

Originally Posted by Paul Gold

But hopefully not gear that has been destroyed by installing video opamps. They really suck for audio.

BTW the project is great. Sort of like a salesman's product sample kit of yore. Apex and Apex Jr. are a must when I'm in LA. I'm jealous that you have someone who will do one off metal work and powder coating.

Paul, you hit the nail on the head as a "salesmen's product kit of yore" is exactly what I'm going for. I also get a kick out of saving many of my parts from the trash bin.
of