insideout

Drake Electronics / Avitel mic pre schems?
« on: October 02, 2008, 03:29:17 AM »
Hi folks,
I have acquired some Drake mic pre's from a local broadcaster. part # PD7017. I have no idea what kind of quality they are, but they do contain a Lundahl LL1538 and a Sowter "type no. 4498". At the moment I don't even know how to power them up, or where the inputs and outputs are on the edge connectors at the back :?

Does anyone know have schematics for these? I have tried searching the web, found the company that bought Drake, tracked down local agents etc but no luck. No luck with the guys I got them off either
 :sad:


CJ

Drake Electronics / Avitel mic pre schems?
« Reply #1 on: October 02, 2008, 04:48:50 AM »
OK, you found a dead end, so lets back track to Drake.

What do you have on them?
Any address, for instance?
Thanks.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

insideout

as much as I know!
« Reply #2 on: October 02, 2008, 05:15:24 AM »
as far as I can tell, once upon a time there was Phillip Drake Electronics Limited in England http://www.drake-uk.com/

The details below were from www.drake-uk.com/vcs/index.asp , which now returns an error. I suspect it is well out of date, but haven't actually tried to phone or email the guy.

Contact
Tom Gittins – Director Broadcast Sales
Address
7400 Beach Drive Cambridge Research PK
Cambrdge
England UK
CB5 9TP

Telephone
+44 (0)1223 815000
Fax
+44 (0)1223 815001
Website
www.drake-uk.com/vcs/index.asp
Email
[email protected]

Drake seem to have been bought by these guys http://Clearcom.com . Their local (NZ) rep is Gencom, and I know some of the guys who work there and drew a blank.

The Drake stuff also seems tied in with Avitel, though I'm not sure how. eg these pres slot into a 3u frame that is an Avitel.

And that's about all I can find!

burdij

Drake Electronics / Avitel mic pre schems?
« Reply #3 on: October 02, 2008, 01:14:20 PM »
Did you try R.L. Drake?  http://www.rldrake.com I didn't see the model you are referring to in the obsolete equipment list but they may be able to help.

CJ

Drake Electronics / Avitel mic pre schems?
« Reply #4 on: October 03, 2008, 05:31:05 AM »
I turned up a Nick Drake studio, which is cool.
Probably no tie in.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

insideout

some pics here
« Reply #5 on: October 04, 2008, 03:57:16 AM »
I have put some pics here in case it helps: http://picasaweb.google.com/mikeinak

some closeups of the mic pre there.

Also have had a response from Clearcom.com (who also said that RLDrake aren't related to the Drake stuff I have - thx anyway burfij).

Drake Electronics / Avitel mic pre schems?
« Reply #6 on: October 05, 2008, 02:08:13 AM »
The broadcast world has changed a lot since the good (and not so old) days of analog systems.

The only UK based broadcast manufacturer of name "Drake" was originally based in Luton. The Clearcom link would appear to be the only one worthy of following.

There is compatibility between Drake modules and Avitel racks.


Have you tried reverse-engineering the pin-out data or the circuit?
Unless it's a multi-layer board with hidden inner tracks, it won't be that hard, just time consuming and requiring good concentration.

PRR

Drake Electronics / Avitel mic pre schems?
« Reply #7 on: October 06, 2008, 01:31:20 AM »
The PCB clearly says "Philip Drake Electronics Limited". I dunno if that is a clue.

> I have no idea what kind of quality they are

Appear to be very robust, well-designed, over-built, nothing sexy stuff. Just what you would sell a well-heeled broadcaster. Does the job without fuss.

> I don't even know how to power them up

There's an IEC wall-plug connector on the rack, power is already in there.

> or where the inputs and outputs are on the edge connectors at the back

Considering the function, the input surely goes to the input transformer, the output comes from the output transformer. All this wiring should be clearly visible on the side you did NOT photograph.

The input seems to be a '5534 chip, fine plan. The output is a discrete 1 Watt job capable of +30dBm though perhaps rated somewhat less for cleanliness. Output stage topology is roughly like Jensen 990 (or like an old Fisher speaker amp... it is a very flexible plan). There are a couple mystery parts on the alloy bridge, but I'm not going to puzzle them when you could just read some part numbers and maybe figure it out.

AudioJohn

Drake Electronics / Avitel mic pre schems?
« Reply #8 on: October 06, 2008, 09:12:55 AM »
From the photos everything can be worked out - if you know what you are looking for!

Nice quality components - Llundahl input transformer and Sowter output for example  - remote control of gain possible (via the reed relays on the PCB) - or from the front panel switch.

Should be easy to work out the input and output connections (work back from the transformers) - fit some XLR's - then power up and go!

Bet it will work fine.

insideout

Drake Electronics / Avitel mic pre schems?
« Reply #9 on: October 14, 2008, 02:41:41 PM »
a very helpful guy at Cleracom has sent me schematics  :cool:
As soon as I get a chance I'll put them up somewhere handy.
- Mike


insideout

schematic posted
« Reply #10 on: October 16, 2008, 12:49:13 AM »
Hi folks,
I have uploaded the PD7017 mic pre manual/schematic to
http://twin-x.com/groupdiy/displayimage.php?album=random&cat=10301&pos=-2666

would be very interested to get thoughts on the design, what it might be good/not-so-good for, or if there are any useful improvements that could be made.

thanks
Mike

AudioJohn

Drake Electronics / Avitel mic pre schems?
« Reply #11 on: October 16, 2008, 03:24:49 AM »
Looks like a very nice design - fairly typical for its time - and will still give good performance for sure! (Excellent transformers.......).

The only aspect I would change is the Phantom feed - I prefer genuine 48 volts - this design has only 12 volt feed.

Nice find!

CJ

Drake Electronics / Avitel mic pre schems?
« Reply #12 on: October 16, 2008, 05:40:43 AM »
And maybe add two phantom resistors instead of running the Phantom Power thru the transformer winding.
No two windings are exactly the same, but 6.81 K resistors can be matched pretty good.

Looks like they changed the output to a model that features a tertiary winding in 83. (engineers rev  box)
This provides negative feedback?
Too lazy to plot phase diagrams.
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

PRR

Drake Electronics / Avitel mic pre schems?
« Reply #13 on: October 16, 2008, 10:26:08 PM »
http://twin-x.com/groupdiy/albums/userpics/pd7017.pdf

Gain-range 40dB-80dB is rather frightening for rock-n-roll.

Input iron is connected 1:5. NE5534 feedback minimum gain is 5. Total gain 25 minimum. Rails are +/-12V, peak output say 10V, 7V RMS. 7/25= 280mV maximum input at 5534 clip (I dunno if the iron will take 280mV heavy bass). It will be widely useful, but for all-purpose use you want a 20dB pad in front of the transformer.

VR1 or external pot give a +/-5dB gain swing. This is fine for set-forget work. For general tracking work in modern studios, I'd max VR1, use external pot, but ground it to pin 19 instead of through the 3K9 at pin 35. Then gain and output can be faded to zero.

The output stage from pin 34 to pins 20-21 must work at gain of 4. So if external pot is turned-down past 4:1 the signal clips in 5534 rather than at output. So use LINear extrenal pot. If you must turn-down below "3" (on 0-10 scale), reduce 5534 gain or add a pad. (or overdrive the 5534 and fuzz-it-up; but it's plan harsh clipping, no magic color.)

You can break between pin 33 and 34 (ground at 19) to insert unbalanced FX.

Link "A" comes out so you can apply a different Phantom Supply at pin 8.

Rack pin numbers appear to be different from amp-card pin numbers. Be sure it makes sense before you smoke-test.

I said it was a +30dBm output, perhaps rated less. The spec says +16dBu but into 50 ohms, which is +26.8dBm.

It will drive ten real-600-ohm loads. If there is heavy loud sex-action in studio A, and the mike is on, studios B through K can tap-in with 600R loads and listen without any signal drop. If they use 22K bridging inputs, up to 200 loads can take the one mike signal (though you will need more Y-cords or loop-thru patchbays).

CJ

Drake Electronics / Avitel mic pre schems?
« Reply #14 on: October 17, 2008, 01:44:09 AM »
What about studios K>Y?
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

insideout

Drake pre pad
« Reply #15 on: November 03, 2008, 12:23:11 AM »
Quote from: "PRR"
http://twin-x.com/groupdiy/albums/userpics/pd7017.pdf

Gain-range 40dB-80dB is rather frightening for rock-n-roll.

Input iron is connected 1:5. NE5534 feedback minimum gain is 5. Total gain 25 minimum. Rails are +/-12V, peak output say 10V, 7V RMS. 7/25= 280mV maximum input at 5534 clip (I dunno if the iron will take 280mV heavy bass). It will be widely useful, but for all-purpose use you want a 20dB pad in front of the transformer.


Indeed, tried one very briefly, output was too hot for my DAW and I had to revert to a baby animal.
/edited/
Now am I right in saying that to optimise the noise in the signal path that pad should go before the output transformer, not the input? Otherwise I would be padding down a perfectly ok signal, then amplifying an unnecessarily low signal = more noise.

Can I just use something like the left hand diagram at JLM's http://www.jlmaudio.com/PAD.gif ie 1k on the signal and 100R to ground? Do the values need to be different because of the location in the circuit? reading http://www.uneeda-audio.com/pads/ indicates I should know the input and output impedances on either side of the pad?

rafafredd

Re: Drake Electronics / Avitel mic pre schems?
« Reply #16 on: November 14, 2008, 09:42:29 AM »
No. You want the pad in front of the transformers, as normally done. With 40dB minimum gain, you will be clipping that 5534 with a hot source, and the output pad will save your converters but won't make clippng distortwed sound any better. Also, it won't impart much more noise, specially in a hot source and hot mic. Noise is a problem with mic preamps when you have ribbons or dinamics and quiet sources.

Use the second pad, the balanced one in that JLM picture. In a minimum 40dB gain micpre, I would change that 470R resistor for a bigger one (have to calculate) for 15dB/30dB attenuator instead of 10dB/20dB one... Will make it more useful if you really use hot with hot, like chinese transformerless condenser mics in a snare... Also, higher resistor in there makes the load for the mic higher, and better than the aprox 1k load in that pic, when the pad is engaged. Otherwise, making the shunt resistors lower instead of messing with the 470R series resistor, will have the same effect on total pad attenuation and will present a lower impedance to the mic transformer, and should yeld to better results depending on the transformer used, specially when using he 270R lower attenuation pad. I think 270 is a little high for a 150ohms rated winding if the mic transformer is not a top quality one...

As an example, after many tests with mics and different transformers, I've found 820R series and 180R shunt the best values for a balanced 20dB mic preamp pad for general studio purposes. You could work your 15dB/30dB pad from there. If you can use a 6x2 switch like a cheap lorlin, you could go crazy on a pad, and make it 0/6/12/18/24/30 dB pads... Now, that would be nice and perfect for that preamp.
« Last Edit: November 14, 2008, 09:56:19 AM by rafafredd »

insideout

Re: Drake Electronics / Avitel mic pre schems?
« Reply #17 on: November 14, 2008, 12:30:50 PM »
awesome, thanks for that. I am diverted p2p'ing a hamptone at the moment but will return to these soon!
- Mike

BerrylandsSound

Re: Drake Electronics / Avitel mic pre schems?
« Reply #18 on: January 26, 2009, 06:59:58 AM »
Hi Folks,

Sorry I'm a bit late on this thread but for any other late readers here is some more details which may be of interest. Back in the late 1970s / early 1980s Avitel produced video products and Phillip Drake Electronics audio DAs and talkback systems, mostly for the broadcast and live venue markets. Around this time they combined their efforts to provide a standard frame format which would take either company's products. This meant that they could concentrate on what they did best but the customer could fill a frame with both audio and video cards. A "card" in this instance actually consisted of module, as in this mic amp, and a back connector which fitted to the rear of the frame giving options of transformer or resistive isolation for the distribution amplifiers, for example.

I think the two companies did eventually merge and have recently been taken over by Clearcom.

The mic amp module was really designed for venue istallation, hence the high gain and remote control, for ambient mics, show relay and that sort of thing. The BBC (British Broadcasting Corporation), I believe, had a hand in the design or specification. I remeber the output stage was marked as being licenced from the BBC and was to drive long lines from the roof! Many BBC installs used dynamic or ribbon mics, or mics with their own PSU and remote control such as the Neumann SM69, hence the lack of propper 48volt phantom power.

To answer a few other questions and comments:

PRR (reply #7) the mystery components are the voltage regulators 7812 / 7912.

CJ (reply #12) the tertiary windings are for feedback. I have come across similar arangements on other line driving circuits from manufacturers such as Neve.

CJ (reply #14) no problem. There is space in the frame for more Drake DAs to send to the other studios!

As I recall these were nice mic amps and other Drake cards often come up on E-bay which may be of use to you. Remember to ensure there is a matching back connector though because they can be a pain to connect without them.

Cheers,

Andy

abbey road d enfer

Re: Drake pre pad
« Reply #19 on: January 26, 2009, 07:38:24 AM »
Quote from: PRR
http://twin-x.com/groupdiy/albums/userpics/pd7017.pdf

Gain-range 40dB-80dB is rather frightening for rock-n-roll.

Input iron is connected 1:5. NE5534 feedback minimum gain is 5. Total gain 25 minimum. Rails are +/-12V, peak output say 10V, 7V RMS. 7/25= 280mV maximum input at 5534 clip (I dunno if the iron will take 280mV heavy bass). It will be widely useful, but for all-purpose use you want a 20dB pad in front of the transformer.

Indeed, tried one very briefly, output was too hot for my DAW and I had to revert to a baby animal.
/edited/
Now am I right in saying that to optimise the noise in the signal path that pad should go before the output transformer, not the input? Otherwise I would be padding down a perfectly ok signal, then amplifying an unnecessarily low signal = more noise.

Can I just use something like the left hand diagram at JLM's http://www.jlmaudio.com/PAD.gif ie 1k on the signal and 100R to ground? Do the values need to be different because of the location in the circuit? reading http://www.uneeda-audio.com/pads/ indicates I should know the input and output impedances on either side of the pad?
I think that you should first decrease the gain of both sections. I reckon there is no reason why the first section gain could not be reduced by at least a factor of 5 (that's already 14dB), by reducing R11 to 22k and increasing the values of resistors R5, 6, 7, 8, 9. In fact, you may start by increasing only R7, to Meg, and the rest should be acceptable.
Then the output section gain can be reduced by increasing R32 (suggest 470R). You should end up with a max gain of ca. 50 dB, which should be ok for most of your work.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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