Mccurdy AT284

[Brown Note]

hi,

i just picked up this card for cheap with a full set of data sheets. here's a pic.

http://img54.imageshack.us/img54/3248/mccurdy9dd.jpg

couple questions:

1. do you think it's worth racking?
2. does anybody know where i can get an edge connector?

if anyone else wants the schem just let me know. (i can post it if there's any sort of demand)

thanks

ben

 

[ciminosound]

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.

 

[Brown Note]

it's definitey a discrete design. all of the cans are 3-pin. the beyer seems really tiny for a good transformer. i'll post the shem later.

thanks

ben

 

[strangeandbouncy]

Beyer's are really tiny for good transformers!

 

[adrianh]

I am dying here to see that schematic!
Please...............
someone post it.

 

[The Junkshop]

Rack it. McCurdy made and still make pretty top notch gear. I'd be surprised if it wasn't at least very good sounding.

 

[clintrubber]

[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

 

[Brown Note]

here's the shematic, layout and circuit description:

http://img58.imageshack.us/img58/4566/shematic6vd.jpg
http://img59.imageshack.us/img59/7519/layout5ra.jpg
http://img59.imageshack.us/img59/1631/description6nu.jpg

i'm not sure how i can rack this without an edge connector. the infosheet specifies Amphenol 143-850 or Cannon CE9473-9202. does anyone know where i can get these connectors or an equivilent?

thanks

ben

 

[clintrubber]

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

 

[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

 

[clintrubber]

[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

 

[Brown Note]

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

 

[ciminosound]

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:

 

[NewYorkDave]

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.

 

[Brown Note]

for the clone squad...

http://img242.imageshack.us/img242/1634/traces2xt.jpg
http://img209.imageshack.us/img209/336/top7uu.jpg

 

[Brown Note]

i just noticed this on the beyer datasheet:

These transformers can however only be used in circuits where AC voltages are low and no DC loads are applied.

sooooo...does anyone know if i can safely apply phantom?

thanks

ben

 

[Rossi]

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.

 

[bALLdo]

I've got one of these sitting in a box somewhere. I'm glad to see this thread! Thanks for posting the schematics!

 

[Brown Note]

cool,

thanks rossi! it's all wired up. i just wanted to make sure before i drilled a hole for the phantom switch.

ben

 

[jetboatguy]

[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 ?

DIY projects I'm workin' on:

LA2a limiter
1176 limiter
Pultec EQ