Finished- Spectra Sonics 110 mic pre

;D

I have to make a comment about JLM's wiring diagrams (which I ignored and went with Mr. Forssell's recommendations as found below):

http://www.groupdiy.com/index.php?topic=5374.0

As mentioned elsewheres - the 110, unlike the 101 (which I suspect the JLM diagrams are mislabelled to be 110) requires a dual rail of 24 volts DC (i.e. + and - 24 volts are required, NOT a single +24V; which is for the 101). 

I found some Triad HS-66's and A67-J's...keeping consistent with the 110's 600 ohm input impedance the A67-J is wired 600:600, rather than 150:600.

Five Fish Studios 2448 power supply is internal to the case of the 110, and there ain't no issues regarding noise.

I wired a 12 position Grayhill switch to adjust from 40dB to 51dB, and have a hand-wired -20dB pad switch (that is pre-trafo)- but GAIN adjusting can now be made from 20dB to 51dB- and the turning the GAIN switch has a subtle "click" rather than the "pop" I've read about (likely from smaller gain increments from 40dB to 51dB). 

I have three SS110 cards- and all had 2 x 250 uF caps (contrary to the recommended 200uf and 250uf)- since one was purchased from a different seller- I decided to stick with 2 x 250 uF caps and haven't had any issues.  TVA/Atom series from Vishay/Sprague (I used 25 volt, although some of the cards I have are using 6V, 16V, and 35V).

Also, I think Five Fish Studios MIGHT have the LED wiring backwards in the assembly instructions for the 2448, like with the 1848 I used for my MAP/Melcor rack-job, the reverse wiring for the LEDs worked (and the position that's in the instructions causes no light).   


Alls well with this build, now... and I'm lovin' the Spectra Sonics sound, yo!
8)

Hi,

Thanks for sharing the various info.

May I ask what transistor-types are on the card you used ?
IIRC the patent mentioned Germanium or a blend of Si & Ge, but cards 'usually' seem to have all Si as I understood it.

Enjoy the pre !

  Peter

I'm not sure whether Silicon or germanium is used; however the datasheet for the 110 pictures traditional transistors with heatsyncs (i think that's what they are- they look like plastic hoops that are at the legs of the transistor); while some of the other 110 cards I have are using only button-top type transistors.  The card in the build uses the heatsynced transistors and button-top types but I'm not sure what element is used for them.  I hope somebody else can share what they know as to the type of transistors are used (composition-wise). 

All the best.

bxt

Five Fish Studios 2448 power supply is internal to the case of the 110, and there ain't no issues regarding noise.

Click to expand...

Thumbs up! Of course

the reverse wiring for the LEDs worked (and the position that's in the instructions causes no light). 

Click to expand...

Thanks for the headsup... I'll check on it.

I think some of my RED LEDs got mixed up. I found out one part# has the polarity of the long/short legs backwards compared to another part#.  In my instructions, I just tell the user where the long leg goes in.

Nice project!

Correction!

I just noticed a stamp on one of my other cards (from the same batch)- and the card used in this build is actually a 110A!  ;D

Both the 110 and 110A seem to be almost exactly the same- except for one resistor value and also the 110A has a wider spacing for one of the electrolytics.  I opened up the case and it seems the "110A" stamp is barely visible.     

Jim at Matrix Audio told me (in an old email that I've just now dug up) that 110A cards can handle higher input impedance-- up to 2.5k on the secondary.

My SS pres are based on regular 110 cards though. I used the JLM diagram labeled 110A and it works great-- I think the straight 110 diagram is meant to be 101 as you indicate.

Hi,

Thanks for the info.

bxt403 said:

I hope somebody else can share what they know as to the type of transistors are used (composition-wise). 

Click to expand...

Are the type-numbers visible ? Then we should be able to know Si and/or Ge.

Bye,

  Peter

Okay- I'm too lazy to open up the case for the one channel unit- but from the other build I've JUST completed (that has one 110 card and one 110A card) BOTH are using button top transistors: 2N3566 & 2N3645...


;D

I had to gut the single channel unit as the previous dual version had a bad input trafo...the single channel unit is going to get an OEP mic trafo installed (on order)...

bxt403 said:

Okay- I'm too lazy to open up the case for the one channel unit- but from the other build I've JUST completed (that has one 110 card and one 110A card) BOTH are using button top transistors: 2N3566 & 2N3645...

Click to expand...

Awesome! nice build.

I have a bunch of these cards and transformers myself (some that I'm selling in the Black Market).  Anyway, some of the 110A's have the black button type and some have TO-92 type transistors.  TheTO-92's are original, ie not been replaced at some time.  Both types have the same numbers as you indicated:  2N3566 & 2N3645. 

I'm defo keeping a few sets with the triad transformers for myself, I think these are great pres.  I like 'em more than I do API but don't tell anyone I said that 

Thanks for showing us your build 

Aardman said:

Anyway, some of the 110A's have the black button type and some have TO-92 type transistors.  TheTO-92's are original, ie not been replaced at some time.   Both types have the same numbers as you indicated:  2N3566 & 2N3645. 

Click to expand...

Thanks & hmm, these are both Si.
No problem, but it makes one wondering if anyone has actually ever seen Ge-types in real cards.

Bye,

  Peter

John L.

Trying to PM you, but your box is full.

Chris

Update:

So I sorta gave up on a single channel unit so the HS-66's and A67-J's are a matched pair...






Also- not pictured is the re-done point to point wiring of the 48v,phase, and -20pads. 

Since my initial post:

I replaced the cards with NOS 110 cards that needed repair/refurbishment from the Spectra Sonics factory. They also went ahead and converted them to 110As.

I also switched the Grayhill switch that would cause a loud "thump" when switched. If I remember correctly, you need a "make before break" type of switch. I ended up using a Philmore one that's identical to the ones that came with my Orphan Audio CA 727 kits. I even implemented them in my Melcor AML-27 rack up.

I went ahead and solved the equation in the 110 manual for R_f and determined the various GAIN resistor values such that:
dB: resistance value
40: 10730 Ohm
41: 12199 Ohm
42: 13894 Ohm
43: 15858 Ohm
44: 18144 Ohm
45: 20819 Ohm
46: 23968 Ohm
47: 27703 Ohm
48: 32170 Ohm
49: 37570 Ohm
50: 44180 Ohm
51: 52395 Ohm
52: 62804 Ohm
53: 76315 Ohm
54: 94419 Ohm
55: 119734 Ohm

I double-checked the "dummy" values for 40.0 dB~10.7K and 44.6dB ~20K but the values above are accurate to the precise dB value (rather than the nearest resistor value).

I implemented the 12 position switch, instead of the 3 position one with logarithmic pot layout that JLM uses.