Racking Spectra Sonics 101

[raysolinski]

Hey All,
I will be racking a 101 I bought here in the black market...anyone have any info on this? I hear the feedback circuitry can be touchy....can you drive an output attenuator to control the level? ..any info would be helpful at this point

Ray

 

[matta]

Hi Ray,

I?ve also got some 101?s on order.

Below is all the information I have gathered while doing my own research.
Most of it was gained from posts from the VERY knowledgeable Fred Forssell, who
knows ALOT about these pres and hopefully will jump in with further info.

The 101?s is a single ended +24VDC pre card, later replaced with the 110,
which is a Bi-polar Pre design (using a +24VDC/-24VDC configuration) and
inherently the 110 has a bit more headroom. The 101 was used all over the
Spectra Sonics desk in various rolls, including the famous 610 compressor.

For me it seems the 101 is to Spectra Sonics what the BA283AV is to Neve.

The pin out configuration on the 101, to my knowledge is as follows:

Pins 1,2,3 = Not Connected
Pin 4 = Input (+)
Pin 5 = Input (-)
Pin 6 = Ground
Pin 7 = Output (+)
Pin 8 = +24V
Pin 9 = Feedback out
Pin 10 = Feedback point for gain set resistor (feedback return)

You are correct in saying that it can be ?temperamental? with the gain
staging.

Fred words were:

I think you can get a limited adjustment range before the amp becomes unstable. From memory, it's pretty touchy.

The gain set resistor is connected between pins 9 and 10. The
following resistance values were give by Fred for the 110 cards, I?m not
sure how they differ from the 101, if at all.

40 dB gain Rf= 10.7k
45 dB gain Rf = 20k
50 dB gain Rf = 42.2k

The Input impedance of the 110 card is FIXED at 600 ohms (it's a grounded
base input amplifier) and the feedback return impedance is 100 ohms.

The cards originally used the Triad A-67j transformers as input transformers
and the HS (forget the model no) on output.

I would like to know how to add a pot for better gain control, this I?m
still not sure of, amongst a few other things.

Hopefully someone with more knowledge can assist you (and I) with these
questions and confirm the pin-outs.

Cheers

Matt

 

[martthie_08]

maybe you can look at the schematic for the 610 compressor, it has an output pot. I have used this compressor as a preamp, it has a 1,1 : 1 setting, in which it will act as an amp, lots of gain, pretty nice! The output iron is HS-66 on my units.

 

[JLM Audio]

It is what I worked out for another DIYer a while ago from all the documents bits we have. So not sure if it is 100% correct. Also not sure what the difference between the 110 & 101 are but the pin out seems to be the same.

The input transformer is loaded by 620ohms on the input of the card so to match 600ohm mics properly input transformer needs to be 1:1.

 

[matta]

Hi Joe,

Thanks for the great drawing. Is it possible to replace the 3 way switch
with say a 20K/22K pot to have a variable resistance and better control over
the gain (up to 45dB's)?

Thanks

Matt

 

[raysolinski]

Thanks guys,
I plan to use one of your go betweens for the mic input end Joe ...I also have 2 different 600 ohm 1:1 transformers to try as the input iron...what kind of value are we looking at for an output pot? I did notice the similarities to the BA283..same voltage...I wonder if you loaded it up with tants if it would "go Neve" on you...

Ray

 

[matta]

Ray,

There are alot of devices that run on +24VDC rails and I doubt buy swapping
out lytics for tans you would get a Neve sound. The Neve sound comes from
the design of the amp card and transformers themselves.

My reference to the similarity was more one of that fact that the BA283AV
amp card was used in different places to create different pres, channel
strips etc in the Neve consoles. In much the same way the 101 and 110?s were
used throughout the SS consoles.

Funny you mention Joe?s ?Go Between? Kits, it is exactly what I am planning
on doing with my cards.

Still unsure of what to use as an input transformer, I?ll most probably run
it unbalanced out.

Cheers

Matt

 

[raysolinski]

I was kidding about "going Neve"...A little poke at all the folks (NOT here!) who salivate at all things Rupert Neve :green: ...

Ray

 

[JLM Audio]

I plan to use one of your go betweens for the mic input end Joe ...I also have 2 different 600 ohm 1:1 transformers to try as the input iron...what kind of value are we looking at for an output pot?

If you use the Go Between kit in front of the circuit above change the 22ohm resistor to 220ohm to make it a variable 20dB pad. That way the 20dB Pad will be your output level control and with the 20dB switched pad on the GO Between you can still bring the mic pre back to unity gain for rerunning line level into the pre.

Do not add a Pad to the output as it will only reduce the maximum output level which can only just do +18dBM as it is. If you are only driving 10k loads you could use a 1:2 output transformer to get +24dBM out.

Thanks for the great drawing. Is it possible to replace the 3 way switch with say a 20K/22K pot to have a variable resistance and better control over the gain (up to 45dB's)?

The answer is Yes but you want 32k of range so maybe a 50k lin pot with 100k resistor across it with 10k in series with it should work ok.

 

[soundguy]

[quote author="JLM Audio"]If you are only driving 10k loads you could use a 1:2 output transformer to get +24dBM out. [/quote]

A 110 wont drive a 1:2 into a 600 ohm load, will it, only 1:1 right?

dave

 

[Family Hoof]

Okay people, check out this site if you haven't already. John K. told me neither the 101 or 110 can drive a stepup output transformer while sounding decent, and I've read/heard this elsewhere too. According to all of the data I've seen for the 101 and 110 amp cards they were designed with the full intention of not needing transformers at all. The common-base input has inherently low input impedance, essentially set by a single resistor, and the amps in question can accept most any input impedance because it's an entirely resistive circuit. As for output, they're spec'd to drive anything 600ohms and up, unbalanced. Why would you want a step up if it's already at 600ohm? If you ask me, the fact that it doesn't want an output transformer or kind of heavy load is self-evident in that the output transistors are TO-92 or some equivalent package - there are no power devices or heatsinking at all! If you must have isolation or balancing then try something 1:1 and easy to push on both the input and/or output. In the case of the 110, the input is already actively balanced (well, kinda) with ground isolated, and doesn't want to see a transformer at all.

As for gain, the 110 datasheet says this:
open = 35dB (??)
10.7k = 40dB
20k = 45dB
42.2k = 50dB

but I recall adjusting from unity gain to about 40dB using a 10k pot and everything seemed to be working okay.

 

[matta]

Hey Guys,

I've managed to get hold of the Spectra Sonics 101 Info/Sales Sheet (thanks to Doty)
and have it hosted up on my site. It has some great info and wiring advise, feel free to download it.

Spectra Sonics 101 (page one)
Spectra Sonics 101 (page two)
Spectra Sonics 101 (page three)
Spectra Sonics 101 (page four)
Spectra Sonics 101 (page five)

Here is the Schematic of the card it is actually of the 610 Compressor, which features a 101 card.

http://edanders.home.comcast.net/diy/ss_schem.pdf

I hope it is helpful.

Cheers

Matt

 

[jamesfei]

Hi folks. I have two SS 101 cards coming and just wanted to know what pin spacing the edge connectors are, since I'm putting an order at Digikey at the moment. I believe the pin out's are plated on both sides of the pcb? Thanks.

James

 

[matta]

I'd also like to know where to get the edge connectors. Anyone know?

The cards are single sided, here is a pic

Cheers

Matt

 

[Christian]

Edge connectors are .156 spacing / 10 position. Digi-Key part number EDC306100-ND. I believe this is for solder tails they offer two models. Brand EDAC

 

[matta]

Thanks Christian,

Have you racked up these before using those edge connectors? Any chance of some pics?

Cheers

Matt

 

[raysolinski]

Okay, with some sleuthing and piecing together of the information here and on the data sheets from doty I got the 101 up and running (kinda slapass, no edge connector, wired a mic cable right to the tranny etc...)...it sounds really good! I have the gain hard wired at 40 db with a 20k resistor in the feedback loop. I used an input transformer from an old pm1000 module that I use for parts.and ran the output unbalanced.This thing has got a HUGE bottom end that isn't muddy at all..I did a quick, unscientific A/B with an sm81 on my takamine n-10 acoustuc guitar between my mackie vlz and the 101 and the 101 SMOKED the wackie..the vlz sounded okay but the 101 has a really nice low end, smoother mids and no brittleness to the highs..there is still a little noise/hum I need to work out of the 101. For those who are interested pin 6 is the ground..I wired all the grounds there and then to the chassis. I am using a 24 volt dc walwart that could probably use a little filtering as well in the final box...I can post some sound files later in the week if someone cares to host them for me since I currently don't have any space online to host things...

Cheers,
Ray

 

[matta]

Hey Ray,

Congratulations! Glad you are up and running. I?ve got the space, so you are
most welcome to e-mail me the comparison files and I?ll host them for you
and then post the links here. My e-mail is matt(@)matt-allison.com (remove
the brackets).

Well done again, I think this resource of info will prove helpful for future
101 rackers.

Cheers

Matt

 

[PRR]

> designed with the full intention of not needing transformers at all.

The input is unbalanced. While I've had great results with unbalanced mikes, in hostile rooms you probably do want a 1:1 input transformer.

> The common-base input has inherently low input impedance

Actually, with feedback the emitter impedance is far over 2K, in parallel with a resistor of about 600Ω. Most mikes will be fine with that, though some say they want 1K or 2K load.

Noise level is not ultra-low (the common-base rigging has no special noise advantage in audio) but low enough for any normal studio work. Noise Figure may be as high as 4dB: you can find mike-amps that in practice will be a couple dB quieter IF your studio background noise does not mask mike/amp noise. Of course any condenser mike's noise level will be set by the head-amp, not by the console amp (unless it is incredibly bad).

Unlike many newer amps, the input noise level does not rise as gain is reduced. However minimum gain may be limited by stability. I assume that is why JLM suggests an input pad to accept today's hot mikes.

> output, they're spec'd to drive anything 600ohms and up, unbalanced.

Right. SS was consolidating racked tube-amp consoles into a more compact system, where most runs could be unbalanced. In those days we didn't have a lot of outboard processors. Unbalanced is cheaper, lighter, cleaner. Now we've turned back to balanced systems so we can patch-in outboard boxes randomly without ground-loops.

> the fact that it doesn't want an output transformer or kind of heavy load is self-evident in that the output transistors are TO-92 or some equivalent package

Actually, the TI epoxy blob will dissipate a Watt or more. But a conservative analysis of this output stage suggests 40mA max-peak and maybe 20mA low-strain. With just +24V supply, voltage is 10V peak. 10V/20mA is 500Ω minimum happy load. Any load reduces open-loop gain of this output; at 500Ω it runs maybe 80dB forward gain in the bass, less in the highs. So at high closed-loop gain and low load Z it will start to sound strained, especially in the highs. A 1:1.4 300Ω:600Ω step-up might be tolerable if you HAD to have isolation and over 10V peak, but in general 1:1 600Ω:600Ω is the limit and working no-iron is really the way it was meant to live. As JLM says, if all loads are over 10K, you could use a high-quality 1:2 2.5K:10K step-up to ensure full 19V peaks; darn few 10K inputs really need to be hit so hard. If you just like iron, use 1:1 and try a resistor in series so the amp doesn't try to damp-out all the iron-sound.

 

[raysolinski]

The latest update..I got rid of the hum..it requires a ton of star grounding. Each ground thru a seperate wire to the chassis since there is no common ground that runs thru the board.I recapped the input and output coupling caps and that was a big improvement. I played around with it some more and the low end still sounds HUGE without any mud. I ran a fender bass into it thru a di box and it was beautiful....It would be cool to mod it to squeeze a little more high end out of it but it has enough without being sharp..prolly good for mics that are a little bright (414's come to mind)....Definately a color for the crayola box ..now to add phantom and get a front panel...

Ray