Mccurdy AT284

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Schematics always help. I see what looks like as beyer input transformer and what looks like discrete transistors. Problem is some ICs used to come in an 8 pin can that looks like a discrete transistor. Schematics always help.
 
[quote author="strangeandbouncy"]Beyer's are really tiny for good transformers![/quote]

They take less signal...

In addition: in the file that Jakob recently added I read that those Beyer TXs are toroid-like, I myself at least hadn't heard of signal-TXs like that before. It 'adds' (subtracts) to the small size as well.

http://www.gyraf.dk/schematics/Beyer_1969.pdf
 
Just curious to the ratio of input-TX T1. How is it marked ?

And another just curious, what type is FET Q1 ?

Interesting to see that this is a Hi-Z input - as is it doesn't seem to be intended directly for mics ?

Bye,

Peter
 
the input ratio of the trafo is 1:10. it is a beyerdynamic TR145BV35600.

Q1 is a fairchild 2N4416A.

i'm confused by the high impedance comment. the datasheet says the source impedance is 150ohms.

ben
 
[quote author="Brown Note"]the input ratio of the trafo is 1:10. it is a beyerdynamic TR145BV35600.

Q1 is a fairchild 2N4416A.

i'm confused by the high impedance comment. the datasheet says the source impedance is 150ohms.

ben[/quote]

Thanks for the additional info.

The input-impedance is high, as also stated in the description 4.01 (to avoid loading of the source). But does the datasheet say something like 'intended to be used with 150 sources ?

Or would that apply to the output-source impedance of this circuit ? That's unlikely though, since the output-impedance as realized by Q5,6 is much lower than that.

OK, enough for now from someone who has no practical experience with stuff from that era. People with hands-on experience with stuff like this will know what's the situation I trust.

Bye,

Peter
 
here are some specs as per the datasheet:

Gain: 62dB

Frequency Response: +/- 1dB, 30Hz to 15kHz (ref 1 kHz)

Relative Input Noise: -124 dBm, unweighted, 10 Hz to 100 kHz

Harmonic distortion: less than 0.5% 30Hz to 20kHz with -40 dBm--less than 1% at -20dBm

Source Impedance: 150ohms, balanced or unbalanced

Input Impedance: at least 10 times the source impedance

Output Impedance: less than 10ohms

Load Impedance: 600ohms balanced

Power Requirements: 48vdc regulated, 50ma
 
Looks like a nice little FET mic pre. Transformer input, Low z out, don't know what you're trying to drive with them but should have some gusto. Rack'em up. If you can't find an edge connecter just solder directly to the pads. (at least to test them anyway).

:sam:
 
A discrete, transformer-coupled pre that runs off a single 48V rail: that sounds like something that'd give a lot of people around here a hard-on. If you removed the circuit board from its little 'chassis', placed it on a scanner and took some high-res scans of both sides, you'll be a hero to the Clone Squad, I'm sure.

Do your sheets include installation and setup info, including any procedure for setting the trimmers on the circuit board?

I like that output stage; it's a throwback to tube technology, complete with "cathodyne" phase inverter.
 
No problem, +48V goes to both ends of the transformer primary (via 6.8 k resistors), so there's no DC voltage across the tranformer. You should match the phantom resistors closely, though.
 
[quote author="Brown Note"]does anybody know where i can get an edge connector?
[/quote]

Dude,
I have the Amphenol 10 ribbon contact connector you need... got any parts to trade ?

Amphenol_01.jpg



Amphenol_02.jpg


DIY projects I'm workin' on:

LA2a limiter
1176 limiter
Pultec EQ
 

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