Looking for Quad Eight CA-227 Schematic

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matta

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Joined
Jan 11, 2005
Messages
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Location
Cape Town, South Africa
Hi Guys,

I'm looking to rack a pair of the Quad CA-127 line amp cards I got form Miko a few months ago but want to convert them to CA-227 mic pres. I know some have done it in the past but most I've seen just put the Cinemag input transformer on the front end and don't change any of the parts on board.

I'm assuming a few parts differ from the CA-127 and CA-227 and would love to look over the CA-227 schematic to compare them, which is proving very hard to get a hold of! I have the CA-127 and 137's.

I found this site: http://www.geocities.com/more_quad_eight/ but not sure of the accuracy as it shows a Zobel, but according to Cinemag there wasn't a need for one.

I'm mailed Ken at Orphan Audio a couple times and have not had a response, he is prob just busy, but would like to move forward if I can.

If anyone has a copy I'd love to get it, could you mail it to me @ matt(@)matt-allison(.)com (Remove brackets).

Thanks in advance

Matt
 
Those schematics look right at a glance. The only real difference between the two is the input load resistor, being 15K on the line amp and 360K on the preamp input trans secondary. The gain resistor in many installations would be fixed; you can use any variable that makes sense. I used 50K reverse log pots on mine. The Zobel is a new thing, and not original. Orphan Audio has worked out a Zobel they prefer, but I've not seen it posted.

Somewhere on the intertube is the MM-100 channel schematic; look for that. The front end is the most official version of the basic circuit I've seen in one place, and shows 3 different opamp stages in different applications. Good for comparison.

Remember, there's also a 10 transistor version from later on.
 
Yes there's a 10-transister version, CA-127a. Ken's recommendation is 360k on the input secondary, regardless of which version card you use. I tried mine with and without the 360k resistor and could not hear a difference, but went ahead and left it in. Great preamps, btw! EMRR's description is accurate, not much involved to change one into mic-amp, but there are several different versions of the line-amp, which can be confusing when looking at the different docs floating around. In the end, all you really need is an input transformer and a gain switch/pot to complete the 'mod' to a 227.

Looking at the Miko's pics in this tread,

http://www.groupdiy.com/index.php?topic=5440

appears you have ca127a's.
 
Thanks for your responses and help guys!

Emrr, thanks for the tip on the load resistor, will try that. Also the CA-127 (in may case the 127a) has a 4.7uF lytic cap on the front end, which the CA-227 doesn't should that be lifted?

So is the general consensus to just replace the load resistor and add gain as one would on the CA127/CA-127a and you have a CA-227?

I found an MM-100 schematic on Brad's site. According that info it also looked like they wired the input trafo 600Ohms on the trafo primary.

Pretty excited about getting this project going and feel they will be a great addition to my studio.

Thanks for the help

Matt
 
Gang of elk,


I caught your racking job over in that other thread:

Q8ca227insidesm.jpg


It appears that you also have the CA-127a cards like mine. Any tips on what you changed when doing the conversion? It looks like you left in the 4.7uF cap on the front end.

Cheers

Matt
 
Nice, and this may not make much diff, its not a slag or nuthin, cuase we cool, but you could stand to lose some copper on your input.
Instead of trying to receive long wave broad casts from Idi Amin's left over Hi Way patrol, why don't you make the output leads the longest and the input leads the shortest?
Or at least use RG58 unless it is already there, to lazy to look, unless you like high inductance roll off, also, the copper could be considerewd corew loss . there areHall effects going on in the wire, you lose a few Joules, who was a beer maker with a accurate thermometer,
 
It also appears that gang of elk put some Solens in place of the 2200uf 16v electrolytic next to the output transformer...

... oh wait, there's still an electrolytic there, on top of the Solens, but much smaller than the stock one.

Care to go into detail on that one, gang of elk?


I have the same cards; Miko and I bought them from the same guy on ebay back in 2003. I've got mine wired up and they sound great but if I can make them sound better, then that would be golden.
 
Matt, yes I left the 4.7uf, never thought to take it out. If it's not on the 227 schem i'd say you could take it out, unless perhaps the 227 schem shows fewer transistors, which means it's older, therefore it's possible the 4.7uf was added later for good reason to the 127a, don't know. I have several more of these cards i'm gonna rack up, maybe I'll try removing the 4.7uf on one of those and see what happens.

CJ, thanks for the tip. Not too proud of this wiring job, these are the first cards I ever racked up. Not pretty but they're quiet as a mouse, been working great for the last 2-3 years, dragged all over the place doing mobile recording! I do hear ya on the copper reduction/inductance front, will work on that. :thumb:
 
Well looking at the cards and schematics it seems most of us have the CA-127a cards and since they are all recapped with similar caps/values (higher than the originals) my guess is they all came from the same guy :shock:

From further investigation it seems out cards have the Quad Eight AM-10 discrete opamps on them.

It seems that really all that may be needed is the Rload resistor be changed to a higher value as Emrr suggested and the addition of the Cinemag QE input trafo, seems most like it wired 150 Ohms?

It seems that the 4.7uF can could be removed as well between pin 14 and 15? I'm ignorant as to why it was/is there in the line amp as opposed to the mic pre?

Thanks for all the input/creative thought. I'm looking forward to racking these buggers!

Cheers

Matt
 
[quote author="b3groover"]It also appears that gang of elk put some Solens in place of the 2200uf 16v electrolytic next to the output transformer...

... oh wait, there's still an electrolytic there, on top of the Solens, but much smaller than the stock one.

Care to go into detail on that one, gang of elk?


I have the same cards; Miko and I bought them from the same guy on ebay back in 2003. I've got mine wired up and they sound great but if I can make them sound better, then that would be golden.[/quote]

It's a bypass cap, the 'lytic is the same value as before, just newer, so it's smaller.

The Solen bypass cap is one of those things I tried, as recommended by a hi-fi guy and i must admit I'm not sure if it's doing anything.
 
the cap blocks DC on the input. So does the transformer. Both is using a double-bagged condom.

The output cap as seen on the MM-100 stages is 100 mfd, which is what I've seen on earlier cards too. Pretty common change seen across products from most manufacturers.

the input is series connected, but the input connections are the two winding center taps (the inner taps before the total center), which is not 600, as that would be the outside taps. It would be 150 I believe. Just a different path to the same solution, and gives 600 option with a simpler re-tap.

Notice the wacky voltage divider on the transformer secondary as part of the gain changing structure. That position would affect high frequency response to some degree.
 
[quote author="emrr"]the cap blocks DC on the input. So does the transformer. Both is using a double-bagged condom.
[/quote]

You're referring to the 4.7uf cap, right?
 
better yet:

connect to 15 and 13 to bypass the cap, no? And change R1 on that website CA127 schematic to 360K for QEE-3440A transformer input. His Zobel is hopefully for the UTC O iron he used instead.

connect to 14 and 13 to use the cap for transformerless line input.


Damn, hold the phone! That sucker has 6 transistors rather than 5. First time I've seen that version. So there's 5, 6, and 10 transistor variations.
 
Both is using a double-bagged condom.

While it might be safer it sure doesn't sound too sexy :shock:

I heard back from Orphan Audio and it seems they have a document pack with full size scans of the various cards which can be had for $50 ex shipping, just waiting for clarification, it might be worth investing it if it has all the original scans/cards etc, other wise I'll just wing it from these on-line schematics and your input/insight.

Damn, hold the phone! That sucker has 6 transistors rather than 5. First time I've seen that version. So there's 5, 6, and 10 transistor variations.

I get 6, not 5? Which schematic are you looking at? Or are you looking at the card photo, I see the 6th Q, it just looks different from the others. Unless you mean the MM100, which seems to have 5?

Cheers

Matt
 
If you have a transformer that's passing DC then that cap ain't gonna help the sound any in the first place.


I'm looking at every other Quad Eight schematic I can come up with, which are all either 5 or 10 transistor versions. The CA-27 and CA-727 cards I have are all 5 transistor versions like the MM-100 amp stages, and the schematic I have for the CA-27 is the 5 transistor version also. That site has the first 6 versions I've seen.
 
Well the schemo's I've manged to find for the CA127 are 6 Q's, CA-127a and CA-137 are 10, which if I'm not mistaken is the AM-10 opamp.

We seem to be starting a Quad Eight club here, LOL

Matt
 
hello,
it could be the next project .. :roll:
About input and output transformer, where can I find the original?
Or can I use Sowter, Jensen or other ones with identical values ?
Thank you by advance :wink:
 
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