UA 610 Microphone Preamplifier Help thread
« on: June 20, 2019, 09:09:12 AM »
HI,

following John Hinson's drawing, I got to let you know this thing sounds really nice. Using a humble OEP mic transformer and a gapped output transformer I'm getting  nicely distorted Doors / Neil Young  sounds. The PSU is a modification of the G9 PSU .

The High shelf EQ is perfect, however the +6 dB bass boost does not work. Is there something wrong with the drawing around the LF switch?  I can get the bass cut to engage , however the bass boost just stays flat.

Many thanks to John Hinson for the drawing, which I gather was derived from an early 610 console.

Michael

« Last Edit: June 20, 2019, 10:35:26 AM by muffy1975 »


Re: UA 610 Microphone Preamplifier Help thread
« Reply #1 on: June 21, 2019, 07:43:29 AM »
Glad you got it sorted Michael. 
Even though it's correct as drawn, I think the schematic could have been a little clearer, sorry for that.
Enjoy ☺
« Last Edit: June 21, 2019, 10:15:55 AM by Winston O'Boogie »
Note to self:  Don't let c**ts wind you up

letterbeacon

Re: UA 610 Microphone Preamplifier Help thread
« Reply #2 on: June 23, 2019, 05:27:36 AM »
What voltage did you use for your B+?

letterbeacon

Re: UA 610 Microphone Preamplifier Help thread
« Reply #3 on: June 23, 2019, 03:02:18 PM »
Congratulations! Sounds like a success! Out of interest, what are the transformers you used?

ruffrecords

Re: UA 610 Microphone Preamplifier Help thread
« Reply #4 on: June 23, 2019, 05:16:00 PM »
For clarity, it is worth saying you do need a gapped transformer because the primary carries the plate current of the output stage.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: UA 610 Microphone Preamplifier Help thread
« Reply #5 on: June 24, 2019, 04:00:37 PM »
Hey Michael,
I think B+ was around the 275V range on the original desk but, as you discovered, the operating points don't really change much from 250 to 300V so you're good to go. 
Your description is exactly how I would describe the tone too, the 12AX7 stages supplying the hair that you hear 👍.  The main difference between this and a current UA box will be that your output stage now won't crap out early since it can swing more volts.

Yep, I think gain is a bit north of 60dB with your transformer set, would have been a bit more with a UTC O1 input like the original but 60dB is more than respectable I think

Anyway, it's really great to know someone built this and likes it, thanks 😊
Note to self:  Don't let c**ts wind you up

rackmonkey

Re: UA 610 Microphone Preamplifier Help thread
« Reply #6 on: June 25, 2019, 12:19:24 AM »
John’s annual post.  ;) Glad to see you staying on schedule, man.

You’ve probably answered this at some point, but what off the shelf OPT comes closest to the original, in your opinion (assuming you have one on that)?


thanks,
BT
« Last Edit: June 25, 2019, 12:30:13 AM by rackmonkey »
Whether you think you can or you think you can't, you're probably right.

Re: UA 610 Microphone Preamplifier Help thread
« Reply #7 on: June 25, 2019, 12:53:55 AM »
John’s annual post.  ;) Glad to see you staying on schedule, man.

You’ve probably answered this at some point, but what off the shelf OPT comes closest to the original, in your opinion (assuming you have one on that)?

😀

Stateside, taking a peek at Cinemag's site, looks like the  CMO-30/600 would work.  Just let them know there'd be about 7mA single-ended current through the primary. 
Over here in the UK, I would just ask Sowter what they have similar in 30K/600  7:1 ratio. 
Lundahl will also have something but would no doubt be a bit cleaner sounding, which may not be what you want? 

I shoved a Cinemag  CM-9661A  50% nickel in a proto many years ago.  It isn't gapped but I had no problems with it.  Best check with David over @ Cinemag though if you went that route.

Cheers mate 👍
Note to self:  Don't let c**ts wind you up

rackmonkey

Re: UA 610 Microphone Preamplifier Help thread
« Reply #8 on: June 25, 2019, 10:43:09 AM »
Thanks, John.

Looks like the Sowter 9980 designed for the REDD47 would fit the bill if Sowter will gap it appropriately. Only off-the shelf 7:1 I saw on their site.

Cinemag also has the CM-27101, which is close. It doesn't mention it in the datasheet, but they do a gapped version. I have that one but haven't experimented with it.

Whether you think you can or you think you can't, you're probably right.

ruffrecords

Re: UA 610 Microphone Preamplifier Help thread
« Reply #9 on: June 25, 2019, 04:13:24 PM »
what about a UTC A26?

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


Re: UA 610 Microphone Preamplifier Help thread
« Reply #10 on: June 25, 2019, 08:34:38 PM »
what about a UTC A26?

Forgot about that one, yes 30K to multiple line.   

Lundahl ll1630/5mA looks OK too,  data sheet here: 
https://www.lundahltransformers.com/wp-content/uploads/datasheets/1630.pdf
Note to self:  Don't let c**ts wind you up

EmRR

Re: UA 610 Microphone Preamplifier Help thread
« Reply #11 on: June 25, 2019, 09:29:39 PM »
what about a UTC A26?

Not meant for unbalanced DC in primary. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

Re: UA 610 Microphone Preamplifier Help thread
« Reply #12 on: June 26, 2019, 04:39:48 PM »
Not meant for unbalanced DC in primary.

Hadn't noticed that Doug.  Then again, neither was the UTC PA-5496 used on the original 610 so... ?
Note to self:  Don't let c**ts wind you up


 

Related Topics

  Subject / Started by Replies Last post
70 Replies
34625 Views
Last post March 01, 2007, 04:22:51 PM
by buschfsu
35 Replies
8819 Views
Last post September 20, 2009, 06:42:28 PM
by Svart
78 Replies
22101 Views
Last post December 26, 2019, 05:55:40 PM
by Rochey
24 Replies
895 Views
Last post June 02, 2020, 08:11:46 PM
by FarisElek