bluebird

peerless/altec 15356 600:600?
« on: October 02, 2004, 07:02:09 PM »
Anyone have the specs. for this?


ciminosound

peerless/altec 15356 600:600?
« Reply #1 on: October 03, 2004, 11:48:56 AM »
Line matching transformer.

Primary
600 Conn 7-8 strap 3-4
150 Conn 7-8 strap 3-8 4-7

Secondary
600 Conn 1-6 ground 2

Can't seem to find level or freq response info but I believe I saw it on the old Altec site, before the sale of the company a few years ago, as being +15dbm and 30Hz-20000Hz. I'm 99% sure about the level but not the freq response. Earlier ones may have been speced to 15000Hz.

bluebird

peerless/altec 15356 600:600?
« Reply #2 on: October 03, 2004, 02:11:42 PM »
thanks ciminosound,

yea, the impedance is on the can. I was interested in the frequency response.

it would be cool if it was 30hz to 20Khz.
I'v seen these on E*BA*Y for pretty cheap so it might be only 15Khz.

when a transformer is rated at 30hz to 15Khz it means its flat between those frequencys.

but a few db drop after those frequencys isn't really a BAD thing right? its not like you can't hear anything above 15K right? I mean people don't always NEED a compleatly flat frequency response.....

uggg just talking to my self now,

bannana coffee face plant on jupiter bus stop egg.

rafafredd

peerless/altec 15356 600:600?
« Reply #3 on: October 03, 2004, 02:41:42 PM »
I have tried transformers rated at 40-15k Hz that sounded really good.
There was no bass and no highs missing for my ears, even if compared to FLAT rated transformers.

Sometimes, they are talking +-0.5dB 40-15k, but in fact you have a +-1dB 20-20k, and this is a nice response. I think that even +-2dB or +-3dB isn´t that bad, and still usefull, depending on what you are tracking and what you want. Many people uses low or hi cut in almost every track, and if you are missing a little high or low end, you have that marvellous six channel EQ for that...  :green:

But any audio transformer can be usefull. I´ve heard people using those 150-10k UTC as mic input and loving it. Probably they ended with a lot better freqeuncy response. Some trannies, like those UTC H series are rated for line levels, so, when you use it with mic levels, the FR is a lot better.  You gota try to know.

bluebird

peerless/altec 15356 600:600?
« Reply #4 on: October 04, 2004, 03:39:35 AM »
WORD.

so Rafa,

I know you've been messin with some Langevin stuff. I got a couple of these line amps:


got this pic from you I think :grin:

I want to make them low gain mic pres...well they already are kind of.

can I just stick an input transformer on the front of this going right into the .1mf cap? maybe the altec wired as 150:600? or is that way to low an impedance for this circuit?

rafafredd

peerless/altec 15356 600:600?
« Reply #5 on: October 04, 2004, 11:53:56 AM »
I would put a 1:10. This will give you more gain and lowest noise.

NewYorkDave

peerless/altec 15356 600:600?
« Reply #6 on: October 04, 2004, 12:03:54 PM »
As shown, that circuit has about 32dB of gain. Impedance issues aside, a 1:10 input xfmr (with 20dB voltage gain) might result in too much gain unless you're using weak mics.

rafafredd

peerless/altec 15356 600:600?
« Reply #7 on: October 04, 2004, 12:09:53 PM »
You know, 52dB is generally what you get from most mic preamps at max gain setting.

I would pad the inputs and outputs for less gain, or maybe implementing a gain control. I can´t really point how, exactly, but I guess this feedback loop could be changed with the addition of a pot for gain control. Ask Dave about this possibility. He will know.

NewYorkDave

peerless/altec 15356 600:600?
« Reply #8 on: October 04, 2004, 12:15:58 PM »
Mic preamps range in gain from 30dB to 60dB and more. 40dB used to be very common. I don't know if I could give a specific figure that suits "most" preamps.

Before you pick an input transformer, you have to figure out the impedance at the base of Q1 so that you'll know what's being reflected back to your mic. You'll also need to know the base-emitter voltage of Q1 to figure out your input clipping point, since that will help to determine what ratio transformer is suitable to use. And we're not even getting into OSI. I notice the schematic doesn't give any voltages...

rafafredd

peerless/altec 15356 600:600?
« Reply #9 on: October 04, 2004, 12:21:01 PM »
As Dave said, that´s the right way.

Hey Dave how would you go to determine the input impedance of the base of the first transistor?

Bluebird, try to take some voltage readings. This is a very good thing to learn, if we can folloqw and if Dave have the time to guide us.


owel

peerless/altec 15356 600:600?
« Reply #10 on: October 04, 2004, 12:34:58 PM »
What is the supply voltage for that schematic? +/-18???

rafafredd

peerless/altec 15356 600:600?
« Reply #11 on: October 04, 2004, 03:58:27 PM »
it´s +42v -0v

bluebird

peerless/altec 15356 600:600?
« Reply #12 on: October 04, 2004, 05:12:14 PM »
I have tryed one of my geoformers on the front of it and had a switch select between different taps on the primary.

the geoformer goes from about 1:3 to 1:9

it seemed when recording kick and snare the line amp compressed the signal a bit on all transformer settings. it actually sounded really good like a bit of limiting. BUT something is being over loaded. you can tell by seeing the waves on the computer.

I'll check the voltages on the transistor. I guessing this will need a buffer.

PRR said there really is no way to change the gain on circuit. except of course for input padding.

bluebird

peerless/altec 15356 600:600?
« Reply #13 on: October 04, 2004, 05:12:34 PM »
I have tryed one of my geoformers on the front of it and had a switch select between different taps on the primary.

the geoformer goes from about 1:3 to 1:9

it seemed when recording kick and snare the line amp compressed the signal a bit on all transformer settings. it actually sounded really good like a bit of limiting. BUT something is being over loaded. you can tell by seeing the waves on the computer.

I'll check the voltages on the transistor. I guessing this will need a buffer.

PRR said there really is no way to change the gain on circuit. except of course for input padding.

NewYorkDave

peerless/altec 15356 600:600?
« Reply #14 on: October 04, 2004, 05:27:37 PM »
I agree with PRR. This is a good example of the "ring of three" circuit I've mentioned earlier and since the feedback network also sets DC conditions, there's no easy way to change the gain. Better to treat it as a fixed-gain block and adjust input and output levels accordingly...

NewYorkDave

peerless/altec 15356 600:600?
« Reply #15 on: October 04, 2004, 05:27:59 PM »
I agree with PRR. This is a good example of the "ring of three" circuit I've mentioned earlier and since the feedback network also sets DC conditions, there's no easy way to change the gain. Better to treat it as a fixed-gain block and adjust input and output levels accordingly...

bluebird

peerless/altec 15356 600:600?
« Reply #16 on: October 04, 2004, 05:44:56 PM »
I chose to use this for a pre because micing drums always seems to require a pad. I wanted someting low gain and simple for kick and snare.

I suppose you do need to amplify the signal just a bit more than a transformer will alone to interface with the line amp.

this goes beyond my knowledge.

rafafredd

peerless/altec 15356 600:600?
« Reply #17 on: October 04, 2004, 06:17:51 PM »
I think it should be able to drive low impedance inputs with this. I don´t think you would need a buffer even if you are driving real 600 ohms inputs. Are you connecting this to a 600ohms input?

If you want low gain, you could try the 1:3 on the input and listen if the noise performance is nice enought...

bluebird

peerless/altec 15356 600:600?
« Reply #18 on: October 04, 2004, 06:55:20 PM »
Oh...what I ment was to drive the actuall line amp (langevin). yea the Langevin can drive my sound card fine.

thats the thing... Using the 1:3. AND even a bit of pad after the transformer I still get this overloading or kind of squaring off of the waves.

I'm sure its and input impedance mis match.

I should just stick some 1/4 jacks on the front and use it as a stand alone line amp.

rafafredd

peerless/altec 15356 600:600?
« Reply #19 on: October 04, 2004, 07:05:38 PM »
I cannot find my Langevin book right now, but I don´t think the input impedance is lower than 10k. Didn´t I passed you the specs also?

You can try a 1:1 in any case, just to see how it goes...


 

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