M610 Microphone Pre schematic
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mitsos
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Sorry if I wasn't clear.. I meant I opened the LA610 and the preamp circuit was obviously different. Besides the tube being swapped out to do makeup gain for the comp. There were different cap values etc.AmpSim said:
About trafos: The Cinemag input is 1:7 with a CT primary, so it would run 1:14. The Altran is similar: also 1:7 with a CT primary. I wonder how they choose which one to use? (duh, price).
CJ, with a regular 4:1 output, one needs an output cap with this?
Also, if you're going to copy the LA610 schematic, keep in mind the changes made, specifically the 6072 being moved. Not that I know if any of this matters, maybe it doesn't. Ask someone who knows...
I may end up building this, but I wasn't in love with the pre of the LA610 by itself. Maybe the solo610 or 2-610 are better because of the tube difference in the pre seciton, but the LA610 I only realy like with compression... I'm leaning toward a MILA for siplicity's sake..
EDITED to correct wrong Altran trafo info.
pucho812
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Here are some solo 610 pictures....
pucho812
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your welcome. Here is some more info. The chip is for the LED's in the front. Other then that it is an all tube style signal path
mitsos
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I know this topic is getting oldish, but I traded some PMs with WO'B aka John Hinson yesterday, specifically about the schemo he drew up of the 610. I put the schemo in the group email account (see META META), along with most of this post.
There is a bit of history first, then some input trafo talk, then some interesting comments on the output trafo. (Either use an output cap or a gapped trafo is the answer, but I admit I got a bit lost with the inductance talk.)
Hopefully this will help someone here :
(the lines are there to separate PMs.)
____________________________________________________________________
The schematic you have is one I drew up from two original 1960's era 610 modules - one from Neil Young's old desk and the other that belonged to Bill Putnam. If you build a unit from that schematic, you'll have a better pre than any current UA reissue. When I did the design work for UA on the re-issue 2-610, M610 etc, there were budget and other constraints that made it not quite what I would have done had I been given a free hand.
Hope that helps Smiley
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« You have forwarded or responded to this message. »
Quote from: mitsos on April 16, 2009, 07:28:52 pm
I did a bit of searching and found there are both Cinemag (CMMI-7C) and Altran input trafos used.
You're talking about in the UA re-issues then. In the old 610's, a UTC O-1 was used.
The Cinemag doesn't have dual primaries but does have a tap on the winding for a lower impedance. It can be used for 200 ohm sources or 50 ohm sources. I don't know the Altran but if you don't need or want the option of the dual input Z then, no, it doesn't matter.
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Quote from: mitsos on April 16, 2009, 07:28:52 pm
btw, is the Cinemag also used in the REDD47?
I used it myself in about 100 that were built. I also used a different transformer in a few special units.
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Quote from: mitsos on April 16, 2009, 07:28:52 pm
Also, Ed Anderson recommended two different output trafos (both Cinemag) CM-9661A if I use an output cap, and CMO-30/600 if I don't. Is there an advantage to either one in this circuit?
If you're building from the schematic I drew rather than trying to build one like a re-issue, the issue at hand is one of there being about 7mA of current through the transformer primary.
You need to know the inductance of the primary at the current flowing through it to determine your low end limit. Inductance drops when current flows through the winding. You figure this low end limit out by knowing the source impedance coming from the tube plate and knowing the inductance of the transformer at the standing current.
The 9661 won't explode if you use it to load the plate - in other words, don't cap couple to it - but you would want to check what's happening at the low end.
If you do use a cap to block the DC from the primary (to avoid current flowing through it and thus not dealing with a lowering of inductance) then you will loose headroom if you are then loading the plate before it with a resistor. Unless, that is, you raise the H.T. for that tube plate (not the whole amp) by about a factor of 2. If you "impedance couple" with a choke loading the plate then you won't loose headroom. You just need to, again, make sure the choke has sufficient inductance for the impedance in hand.
I haven't used the CMO-30/600 but if it has a gap and the inductance is at least 60 Hy with 7mA, then it will work in the circuit.
p.s. the thought occurs to me that there may be others who are thinking of building a 610. Maybe you could copy and paste this somewhere in a thread if you think it might be useful
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Yes, it's OK to post the schematic. I think the reason it was hard to find for a while was that I had switched servers at some point and had neglected to update links etc. If it's on your server then it's your responsibility then and not mine Wink
Maybe just give me a credit for drawing it but, either way. it's good,
John
There is a bit of history first, then some input trafo talk, then some interesting comments on the output trafo. (Either use an output cap or a gapped trafo is the answer, but I admit I got a bit lost with the inductance talk.)
Hopefully this will help someone here :
(the lines are there to separate PMs.)
____________________________________________________________________
The schematic you have is one I drew up from two original 1960's era 610 modules - one from Neil Young's old desk and the other that belonged to Bill Putnam. If you build a unit from that schematic, you'll have a better pre than any current UA reissue. When I did the design work for UA on the re-issue 2-610, M610 etc, there were budget and other constraints that made it not quite what I would have done had I been given a free hand.
Hope that helps Smiley
_____________________________________________________________________
____
« You have forwarded or responded to this message. »
Quote from: mitsos on April 16, 2009, 07:28:52 pm
I did a bit of searching and found there are both Cinemag (CMMI-7C) and Altran input trafos used.
You're talking about in the UA re-issues then. In the old 610's, a UTC O-1 was used.
The Cinemag doesn't have dual primaries but does have a tap on the winding for a lower impedance. It can be used for 200 ohm sources or 50 ohm sources. I don't know the Altran but if you don't need or want the option of the dual input Z then, no, it doesn't matter.
____
Quote from: mitsos on April 16, 2009, 07:28:52 pm
btw, is the Cinemag also used in the REDD47?
I used it myself in about 100 that were built. I also used a different transformer in a few special units.
____
Quote from: mitsos on April 16, 2009, 07:28:52 pm
Also, Ed Anderson recommended two different output trafos (both Cinemag) CM-9661A if I use an output cap, and CMO-30/600 if I don't. Is there an advantage to either one in this circuit?
If you're building from the schematic I drew rather than trying to build one like a re-issue, the issue at hand is one of there being about 7mA of current through the transformer primary.
You need to know the inductance of the primary at the current flowing through it to determine your low end limit. Inductance drops when current flows through the winding. You figure this low end limit out by knowing the source impedance coming from the tube plate and knowing the inductance of the transformer at the standing current.
The 9661 won't explode if you use it to load the plate - in other words, don't cap couple to it - but you would want to check what's happening at the low end.
If you do use a cap to block the DC from the primary (to avoid current flowing through it and thus not dealing with a lowering of inductance) then you will loose headroom if you are then loading the plate before it with a resistor. Unless, that is, you raise the H.T. for that tube plate (not the whole amp) by about a factor of 2. If you "impedance couple" with a choke loading the plate then you won't loose headroom. You just need to, again, make sure the choke has sufficient inductance for the impedance in hand.
I haven't used the CMO-30/600 but if it has a gap and the inductance is at least 60 Hy with 7mA, then it will work in the circuit.
p.s. the thought occurs to me that there may be others who are thinking of building a 610. Maybe you could copy and paste this somewhere in a thread if you think it might be useful
__________________________________________________
Yes, it's OK to post the schematic. I think the reason it was hard to find for a while was that I had switched servers at some point and had neglected to update links etc. If it's on your server then it's your responsibility then and not mine Wink
Maybe just give me a credit for drawing it but, either way. it's good,
John
Winston OBoogie
Well-known member
mitsos said:
Thanks Mitos. Not necessarily saying that the transformer needs to be gapped, just that you need at least 60Hy of L with 7 - 10mA current on the winding.
Hint: the original 5946 output transformer for the 610 (For which I have full winding docs), may, or may not have been gapped
Winston OBoogie
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mitsos said:
Well, if my son doesn't want them, I could bequeath them to you in my last testament 8)
Winston OBoogie
Well-known member
rodabod said:
I probably would too.
mitsos
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OK, hopefully he wont want to have much to do with audio then. Are you old enough that I could start holding my breath?? ;DWinston O'Boogie said:
Seriously though, I am in no hurry to do this, it is a long term project, and I'm slowly gathering all the info I can.
As far as gapped or ungapped, you and Roddy are confusing me.... You said one could go ungapped and use a choke, would that be the way to go then? Or would you cap couple and raise the HT like you said before? Just checking for expert opinions...
Winston OBoogie
Well-known member
The decision is really up to you as there are lots of ways to skin small animals
Maybe I was being a bit cagey in my responses though, sorry.
You can absolutely use a transformer without a gap. I was only saying that you would need adequate L for the tube if you do. If you found that you didn't have enough L, you could still use the same transformer ( so you haven't wasted your money) and then either
1/ impedance couple with a suitable choke load and cap couple it to the transformer. or
2/ Use a resistor as the load but raise the H.T. so the signal voltage swing at the plate is the same. (Another hint: this is where the re-issue falls short)
A transformer with a gap is designed for current in the winding and will also work of course. You still need to know that the inductance will be sufficient at the current you have flowing through it.
I have zero experience with the CMO-30/600 that you mentioned and so I can't comment on it.
I do have experience with the 9661 running it as a direct load on a plate. It wasn't in a 610 type circuit (not a modified REDD type either) but it did work well for what I was doing.
I did not go for an all nickel version in that application
Hopefully less cagey?
Maybe I was being a bit cagey in my responses though, sorry.
You can absolutely use a transformer without a gap. I was only saying that you would need adequate L for the tube if you do. If you found that you didn't have enough L, you could still use the same transformer ( so you haven't wasted your money) and then either
1/ impedance couple with a suitable choke load and cap couple it to the transformer. or
2/ Use a resistor as the load but raise the H.T. so the signal voltage swing at the plate is the same. (Another hint: this is where the re-issue falls short)
A transformer with a gap is designed for current in the winding and will also work of course. You still need to know that the inductance will be sufficient at the current you have flowing through it.
I have zero experience with the CMO-30/600 that you mentioned and so I can't comment on it.
I do have experience with the 9661 running it as a direct load on a plate. It wasn't in a 610 type circuit (not a modified REDD type either) but it did work well for what I was doing.
I did not go for an all nickel version in that application
Hopefully less cagey?
edanderson
Well-known member
with a large enough steel core, 10ma flowing in the primary might not lower the inductance too much. i suppose you could also probably "over-wind" on a smaller core and let the inductance drop a little once the DC starts flowing, so that you hit the spec-ed target. but on a small core, the resistive losses could be problematic. 10ma isn't so much current... with a decent size steel core and possibly some creative lam stacking (not gapped, but interleaved in stacks of 2 or 3) you could probably hit the target without gapping the core.
as for using a choke and cap, or a gapped (or DC tolerant) transformer, either way you've got a custom wound component (the type of choke needed is not a common item), so i'd say just get a custom output.
i'm certain that if you went to cinemag with the spec of 60H with 7ma, they could gap one of their standard output transformers and it would work. would it sound exactly the same? who knows, without trying.
ed
as for using a choke and cap, or a gapped (or DC tolerant) transformer, either way you've got a custom wound component (the type of choke needed is not a common item), so i'd say just get a custom output.
i'm certain that if you went to cinemag with the spec of 60H with 7ma, they could gap one of their standard output transformers and it would work. would it sound exactly the same? who knows, without trying.
ed
Winston O'Boogie said:
Hi Mr. O'Boogie, good to have you back in the Lab!
I have an LA-610, which is certainly not a bad piece of gear, but somehow it doesn't thrill me that much (I prefer the sound of my A-Designs MP-2). Is there any easy mod that would enhance the UA circuit? Add a choke, maybe? Or would it be a lot more complicated than just adding/replacing a few components?
Winston OBoogie
Well-known member
God damn it! I keep posting responses when my generous host and friend is logged into the forum on this computer and I end up posting under his name and then having to remove them and try and remember what I wrote!
Hi Rossi
I didn't do the LA-610, just the 2-610 and M610. I think the LA has things swapped about a bit and I don't have a schematic to check.
I would hesitate to make recommendations without knowing what is going on in there but I don't doubt that it could be made to sound better.
Sorry
I think that's what I said? Time to borrow a laptop I think!
Hi Rossi
I didn't do the LA-610, just the 2-610 and M610. I think the LA has things swapped about a bit and I don't have a schematic to check.
I would hesitate to make recommendations without knowing what is going on in there but I don't doubt that it could be made to sound better.
Sorry
I think that's what I said? Time to borrow a laptop I think!
mitsos
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Ed, as you can see I haven't gotten much further since those emails months ago.... Did I say this was a long term project?
Winston and Ed, thanks for the explanations. Cinemag's site states "butt stack optional" for the 30/600 trafo. I guess that means gapped? (sorry, I'm more familiar with butt STEAK) Anyway, it sounds as if the easiest route would be Winston's #2, a standard output trafo with resistor load and double HT. That way, it sounds like I won't have to worry about the inductance of the primary? Should be a large-ish core?
BTW, what kind of voltages/current should this thing see?
Rossi, the LA-610 is a different beast, indeed. There was a review in Mix which described the differences.
http://mixonline.com/mag/audio_universal_audio_la/
Thank you all for the contributions!
Winston and Ed, thanks for the explanations. Cinemag's site states "butt stack optional" for the 30/600 trafo. I guess that means gapped? (sorry, I'm more familiar with butt STEAK) Anyway, it sounds as if the easiest route would be Winston's #2, a standard output trafo with resistor load and double HT. That way, it sounds like I won't have to worry about the inductance of the primary? Should be a large-ish core?
BTW, what kind of voltages/current should this thing see?
Rossi, the LA-610 is a different beast, indeed. There was a review in Mix which described the differences.
http://mixonline.com/mag/audio_universal_audio_la/
Thank you all for the contributions!
mitsos
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Just bumping this because I made a mistake on the specs of the Altran input trafo, which may cause confusion. The Altran C-3799-8 does, in fact, have a center-tapped primary, allowing for 1:7 or 1:14 ratios, and consequenty, 50 or 200 Ohm input impedances, like the Cinemag. This is according to an email from Ed, which I don't know how I did not read correctly, but there you have it. I corrected my previous post.
EDIT: spelling
EDIT: spelling
