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JamieOxford
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#1
7th April 2012
Old 7th April 2012
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UA 610 Schematic

Has anyone here built a 610 preamp before? Or is there a company in the deepest darkest corner of the internet making them?

I know the originals are rare but with the amount of 1176 and Neve/API preamp clones being made , I'm surprised no ones had a go at a 610.
Supposedly UA has a no schematic policy but I've found a few dotted round the web including one for the Urei 1108 pre?

Thoughts/comments? Or am I missing something?
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8th April 2012
Old 8th April 2012
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I know of one individual who made some 610B units complete with custom wound output transformers, however he does not offer them for sale commercially. A studio I tech at has six of his modules and six original UA 610s. The engineer says they sound different, but we have yet to do a technical comparison.

In the Group DIY email account there is a bit of info about original 610s, but the schematic attachment is missing.
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8th April 2012
Old 8th April 2012
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I checked on the Group DIY site, couldn't find the original post but I did find a link to this of the 610-A - schematic attached: UA 610-A Schematic
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8th April 2012
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Actually the info is in their gmail archive. I've copied it into a .pdf attached here. Mostly info about transformers.
Attached Files
File Type: pdf 610 Notes.pdf (71.6 KB, 883 views)
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28th November 2012
Old 28th November 2012
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Does anyone know the value for the B+ rail in that diagram?
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27th May 2013
Old 27th May 2013
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PSU?

I would also love to know the voltage for the B+ rail. Anyone who knows where to find info on the PSU in general, please let me know! I've just finished two channels on a prototyping board and would like to order the parts necessary to get a proper power supply built for them.
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28th May 2013
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Welllllll, not exactly. It is between 250 and 300vdc. It's been a while since I worked on those modules and it depends on whether you are talking about original 610s or a modern "clone". "Typical operating" plate voltage for these tubes is 250v so hook up your B+ supply and measure at the plates.
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26th June 2013
Old 26th June 2013
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Quote:
Originally Posted by mjrippe View Post
Welllllll, not exactly. It is between 250 and 300vdc. It's been a while since I worked on those modules and it depends on whether you are talking about original 610s or a modern "clone". "Typical operating" plate voltage for these tubes is 250v so hook up your B+ supply and measure at the plates.
Just read this. Good to know! Since my mains is 240, it'd probably be easiest to use a 1:1 trafo and bring the B+ down to 300V.

Now for some other annoying questions. I assume R9 (From V1-a's Grid to V1-b's output) acts as NFB for the input stage? Also about the power supply - I assume about 1A for a single 610 stage would be sufficient?
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7th October 2013
Old 7th October 2013
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according to a UA catalog of 1967 the voltages are +300 volts DC at 10ma for B+ and 12.6 volts DC at 300ma for filament
#10
25th November 2013
Old 25th November 2013
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Just thought I'd drop in and mention that I finished building a pair of 610's based on John's schematic. They sound fantastic but I don't have a great frame of reference as it was the first piece of tube gear I've ever built. I'm so glad John was up for sharing it with everyone! Cheers!
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25th November 2013
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this one I was always curious why the high value grid resistors. Makes me wonder if the designer tried octal tubes like 6sl7's and settled on the 9 pin tubes.
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29th November 2013
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built it up, yea its ok. but the design is a "fix it with negative feedback" design. Will post a better version later.
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29th November 2013
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Quote:
Originally Posted by drtechno View Post
built it up, yea its ok. but the design is a "fix it with negative feedback" design. Will post a better version later.
I was thinking when I got the money together to make this I'd try and do a variable NFB design so you could run it in different shades of dirty.

Sometimes it's really just the low order distortion you want.
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29th November 2013
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the 1.2 M is too much bias for no reason. And they have to put all kinds of different NFB to keep that thing from oscolliating all over the place. As I see three NFB chains. and the tone circuit looks more like a presense controls than filters.


the gain control is blah. I don't like pots and don't like to rely on the wiper to keep the bias stable and in worse case senario, it would throw a lot of trash noise into the recording circuits if it failed or became dirty/scratchy. this part is one of the cheap in the design.

first change: R13 250k resistor 100% R9&R11 get turned into a rotary gain switch. H bridge attenuator on the output.

That a way, I can saturate the output transformer while controlling the output level. and more 2nd harmonics than 3rds should be produced.
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29th November 2013
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if the tone controls were ganged differenly it would be a Quad "tilt" tone control circuit.

maybe Puttman designed that for Quad who knows.
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30th January 2014
Old 30th January 2014
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Quote:
Originally Posted by drtechno View Post
the 1.2 M is too much bias for no reason. And they have to put all kinds of different NFB to keep that thing from oscolliating all over the place. As I see three NFB chains. and the tone circuit looks more like a presense controls than filters.
I can verify that one of the two channels I built was oscillating pretty badly until I shielded just about everything.

I'd love to know more about your thoughts on changing the volume out for a rotary switch for stepped gain and variable negative feedback. I started building another two channels. I built the first two following the schematic exactly but the tone controls are VERY subtle and I had to build in an input pad to make it work with most modern mics so I think I'd like this second build to be about exploring modifications to the design.
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6th February 2014
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Quote:
Originally Posted by diyguitarmods View Post
I can verify that one of the two channels I built was oscillating pretty badly until I shielded just about everything.

I'd love to know more about your thoughts on changing the volume out for a rotary switch for stepped gain and variable negative feedback. I started building another two channels. I built the first two following the schematic exactly but the tone controls are VERY subtle and I had to build in an input pad to make it work with most modern mics so I think I'd like this second build to be about exploring modifications to the design.
3K @ R9 , 3.9K @ R11 then put a 100K potentiometer (pins 1&3) between and remove hi/low gain switch and attach c14 to the wiper (pin 2)

c3 sould be .22uf ; c4 should be .47uf ; c14 should be .47uf no wima caps. polypropolenes are ok, but not ones in a square package.

R13: 270K with a 10K resistor to the grid.
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6th February 2014
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I was going to build this but reminding myself how many bugs that would have to be worked out (because of grounded cathodes), I'm saving my unused O-1's for a better design.
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27th February 2014
Old 27th February 2014
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Hello! This is my first post, so please be gentle

I just finished building a pair of 610's based on John Hinson's schematic (except that mine were setup with a 265v power supply) and I'm not super blown away. They sound kinda flat to me. I did a comparison against a new UA LA610 MK2 and mine didn't sound as complex and attractive.

I'm sure I probably messed up somewhere, tho. I built them from an old Roberts 997 reel-to-reel. Below is how I laid it out on the "turret" board...I hope it helps someone! I also have photos, audio samples and other build documentation if anyone needs it, too.

http://omargarciaportfolio.com/1-turretLayoutB-V3.gif

I was hoping someone could help me to understand the tone circuit on this mic pre and how it works through negative feedback. I've read lots of books and technical papers, but this pre doesn't make sense to me...I'm just not sure how the EQ works.

If anyone could help, I'd be super appreciative!

Thanks!
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27th February 2014
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part of it the "tone" comes from the parts used as well as technique.

show us a picture of the built unit, what parts were used (i.e. vishay resistors, mkp orange drops, etc). looks like cinemag transformers on your turret chart. Is there any info on them (datasheets)?
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28th February 2014
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Thanks for your response, drtechno

Here are some photos of the built unit:
www.omargarciaportfolio.com/610Photos.zip

The parts I used were:
Xicon 1W Carbon Film Resistors throughout
Panasonic EE series Electrolytic Caps for the power rail
Cornell Dubilier Orange Drop Film Caps everywhere except C7, C16, C12, C17 and LFC, for which I used Kemet Multilayer Ceramic MLCC Caps

The transformers I used were both Cinemags:
Input is a CMMI-7C (datasheet: http://cinemag.biz/mic_input/PDF/CMMI-7C.pdf)
Output is a CM-27101 (datasheet: http://cinemag.biz/output/PDF/CM-27101.pdf)

Do you think I should have used different kinds of caps instead of the ceramics?

Thanks so much!
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17th March 2014
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4 Weeks Ago
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yea I recommend mouser # 598-940C6P1K-F for c3,c4,c5,c6 & c7 also they need to be the same. I like full spectrum amplication. 0.047 chokes it too much.


r15,r27 mouser # 71-NS2B4.7K1% ; r10 mouser #71-NS1A-1K; r18 mouser # 71-NS2B5601%

r16, r26, and R28 mouser# 588-SM102031504JE
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you build is not too bad, but I like to give you my pointers on construction techniques.

when building high gain circuits with tubes, especially with using tag board:

keep unsheilded lengths from tag board to tube under 6". If your using it for your tube circuit.
and run heater line seperate and purpendicular from your signal, as a twisted pair if ac, strait pair if dc. I like to runthem along one side of the chassis. The plates B+ I like to run that along the opposite side of the chassis. the sig along the plane of the tube sockets, the gounds, beetween the heater runs and sockets.

In your build, I would do the power supply on one tagboard, the tone ctrls on another, the tube amplification circuit at the sockets, point to point. use shielded cable on signal interconnects between tagbord and point-to-point connections.
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2 Weeks Ago
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Thank you for your recommendations, dr. techno!

I am currently creating a PCB similar to the original and am going to use the parts you have suggested.

Thank you!
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