[geekmacdaddy]

Cinemag FINALLY shipping! Should have it tomorrow or Sat. Will be putting it together on Sunday. I hope. Damn.

[tskguy]

Sweet!

Cant wait to hear it...

[HellfireStudios]

Just an update on my lack of a scope. I've got a customer of mine that does ham radio stuff for a hobby. Unfortunately, he is out of town until next week, and there is no guarantee he will have acces to an oscilliscope when I do hear back from him. With my patience wearing thin, I'm considering buying one myself. The only thing I need it for is transistor biasing. Can anyone recommend a dirt-cheap-but-will-get-the-job-done oscilliscope? Keep in mind, I'll only likely be biasing a few mics and preamps. I guess I could also use it to detect DC ripple in power supplies and the like. Thanks.

-James-

[0dbfs]

A simple dual channel scope is awesome for comparing signals in circuits. I bought one off clist for $50. You can get SW scopes, hw scopes, recording scopes, and newer/better/faster if you want to spend more and more. Something simple, used, and cheap works well for most general tasks.

The one I picked up is a 20mhz model which may be a little low for detecting some oscillations but works well for poking around.

Cheers,
jb

[0dbfs]

A simple dual channel scope is awesome for comparing signals in circuits. I bought one off clist for $50. You can get SW scopes, hw scopes, recording scopes, and newer/better/faster if you want to spend more and more. Something simple, used, and cheap works well for most general tasks.

The one I picked up is a 20mhz model which may be a little low for detecting some oscillations but works well for poking around.

Cheers,
jb

[kante1603]

Yes,I bought a nice used Hameg for less than 100 EUROs an evilbay.
Very usefull for most of our audio stuff.
James,maybe someone in your area from this forum can do the biasing for you.Sending just the pcbs in a flat envelope can't be too expensive,and-given the circuit is working-it's just a work of 5 minutes.

Udo.

[HellfireStudios]

Yes,I bought a nice used Hameg for less than 100 EUROs an evilbay.
Very usefull for most of our audio stuff.
James,maybe someone in your area from this forum can do the biasing for you.Sending just the pcbs in a flat envelope can't be too expensive,and-given the circuit is working-it's just a work of 5 minutes.

Udo.

I would be up for that, but my previous experience with unwilling people won't leave me holding my breath anytime soon... Not to mention I have more to bias than just the mic (two KM-84's I've yet to build, two Neve 1290 clones, and possibly a pair of Trident A-Range clones in the future). Maybe my luck will change. Thanks for the suggestions, guys.

[HellfireStudios]

Hmmm... I've been over at evilbay trying to make sense of all the oscilliscopes they have to offer. My question are:

-What is the MHz range I should be shopping in for FET biasing and the like?

-Which probe should I be using 10x or 100x?

-Is the dual channel worth the extra monetary outlay for simple electronics testing?

Sorry, if my questions are telling of my ignorance. I appreciate any help. Thanks.

-James-

[berkleystudios]

Hmmm... I've been over at evilbay trying to make sense of all the oscilliscopes they have to offer. My question are:

-What is the MHz range I should be shopping in for FET biasing and the like?

-Which probe should I be using 10x or 100x?

-Is the dual channel worth the extra monetary outlay for simple electronics testing?

Sorry, if my questions are telling of my ignorance. I appreciate any help. Thanks.

-James-

im in the market for one as well, will similar needs, and i have on good authority that this one should do us just fine, and its not to bad of a price either!
http://www.saelig.com/PSBEB100/PSBEB100009.htm

[kante1603]

-Is the dual channel worth the extra monetary outlay for simple electronics ?

Hi James,

I say yes,this way you can do comparisons pretty easy,e.g. ingoing to outgoing signal.
This way matador was able to tell us the actual gain for example.He measured the input (coming from the signal generator) on one channel and the "biasing point" (fet) and the other.You then have several informations at one time:the amplitude or gain,if the sine is looking o.k.(distortion),and others like if you have a phase shift on an eq or the frequency etc.

Cheers,

Udo.

[HellfireStudios]

Thanks for the suggestions. I'd like to keep the scope price between 100-200 dollars, but the PDS5022T is a great fall-back, if my endeavours to find one used don't pan out. I will be looking for a dual channel model. Is the suggested 25MHz enough, or should I try to go higher (like 100MHz)? Thanks again.

-James-

[mrc]

I bought a 100mhz 2235 dual, 2 probes, HP tone generator and 2 Fluke bench dmm's from a military surplus guy in Ft. Worth on evil bay 4 yrs ago for $300 for the whole shootin' match and every item worked/works perfectly.  Took a few weeks of looking but it paid off

[0dbfs]

I've got a 20mhz which works well for scoping audio and control signals. I would recommend higher though for the purpose of scoping and troubleshooting oscillations and such in audio circuits. I'll eventually end up with a nicer one but the used 20mhz has served quite well and is easily replaceable should it fail. Some of the digital ones have a nice small footprint which would help out on my ever-cluttered bench.

-jb

[HellfireStudios]

Since my unit MAY be oscillating, if I am to stay under budget, I will need to find a hamfest or scientific/military surplus to pick up a higher MHz scope on the cheap. Off to google I go... Wish me luck (preferably good luck this time). I may have to lurk around the internet for awhile until the next hamfest in August. Any other ideas? Thanks.

-James-

[Matador]

I finally got some time to solder some parts onto these boards.  I'm making a matched pair.

I made a few changes to the BOM:  I subbed in my favorite Nichicon UVZ electrolytic caps where appropriate (they are rater to 105C), and replaced all of the resistors with the Vishay RN55D series of epoxy coated precision 1% resistors.  I went with the Styrene caps and mica's along with Dany's recommended Wima's.



I started by labeling all of the parts by reference designation so I could keep track of where I was:



I clamped the boards into my Panavise PCB holder jaws and started soldering in all of the resistors:



I checked the values as I stuck them in to make sure Mouser didn't mess anything up when packing (totally worth the extra 15 seconds per part to save headaches later!):



Pretty simple just going part by part, soldering and clipping each pair of boards:



A little electrical tape holds in devices that want to fall right out, like the Wima caps and electrolytic caps:



And the B boards are stuffed:



For the bias resistor R11, I cut off one outside leg, then bent the other two to fit the layout, then dialed them up to 25K maximum before stuffing them in:



And finished up the rest of the components:



Somehow I messed up my Mouser order and ordered 51pF mica's instead of 560pF styrenes, so I'll have to wait until my next order comes in before I can move on to biasing and stuffing the rest of the components.

[kante1603]

Hi Matador,

Cool pics!
For building a matched pair,how will you manage to get matched capsules and transformers?
I'm quite interested in this topic.Found out that my T14s have slightly different dcr readings (not too much,but measurable).
Which parts are you going to use for these positions by the way?

Keep up the good work,maybe you should reserve some place here posting some "reserved for build pics" or so like e.g. our friend chunger does?This way your infos can be kept together....just an idea....

Cheers,

Udo.

[berkleystudios]

nice stuff matador. i cant believe i never thought of the tape for mica caps! duh! totally using that haha

and i agree with udo, we should have a reserved place for all finished builds! that would be nice

[Matador]

For building a matched pair,how will you manage to get matched capsules and transformers?
Which parts are you going to use for these positions by the way?

For matching, 90% of it is in the capsule, so I ordered a matched pair of them.  The next most important part is the 220pF cap, so I ordered 20 of them and hope to find two that are reasonably close.  Last is the FET's however different FET's of the same part number don't really sound all that different, there just might be a slight difference in volume (as opposed to frequency response).

I'll be using Cinemag CM-2480's for these.  Primary inductance is the most important part, but I think C7 is large enough that the response difference will be way down near DC, so even if they are slightly different it will be inaudible.

[kante1603]

Thanks for the infos!
I meant which capsules and transformers you will use,pardon my bad english,still learning....
O.K.,cinemags and ...?
Udo.

[HellfireStudios]

I don't know what Matador is using, but microphone parts sells matched pairs (for a little extra).

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