[mnats]

what is the point of the LDR? What does it do? If I were to leave it out what would eb the effect? How can I leave it out?

Please feel free to read the entire thread (it's only up to two pages so far).

Oh no, I've taken it to three...

[dustbro]

I used a Vactrol VTL5C9 but there are probably a lot of different ones you could use there. Each one will require playing around with the LED drive circuit to get the range you require.

would a simple circuit like this work?
http://www.retrospieler.de/e-flashbutton.html
There's no driver circuit onboard, right?

[mnats]

would a simple circuit like this work?
http://www.retrospieler.de/e-flashbutton.html
There's no driver circuit onboard, right?

As mentioned in post #18 the circuit doesn't even have to be as complicated as the one you've proposed, but go ahead and experiment...

[juanjovincenzo]

Hi guys!
Is possible change the Vactrol VTL5C9 for a NSL32 optocoupler or maybe use a NSL6910 photocell with a red led in a small enclosure?? The same thing I want to try in the Weak Joe Compressor circuit... is possible?
Regards
Juanjo..

[Hairball Audio]

Hi guys!
Is possible change the Vactrol VTL5C9 for a NSL32 optocoupler or maybe use a NSL6910 photocell with a red led in a small enclosure?? The same thing I want to try in the Weak Joe Compressor circuit... is possible?
Regards
Juanjo..

I think one of the goals of offering the layout was to encourage some experimentation with this circuit.  It's not a circuit a ton of people have used or experimented with.

I'd say you should just give it a try and let us know how it goes!

Mike

[Stagefright13]

Hmm but if i can't get one then how can I experiment with it. I hear Joe Satriani's engineer has a pair of these with xlr pigtails hanging off the back of the faceplate. And I know 2 other people who use them also in NY. In similar pigtail fashion. They were "handmedowns". The only one I have heard has a smoothed over high end.
The highs are clear but silky.

John

[livingnote]

This is really interesting, thanks

I just got into the whole LDR thing now that my opto for guitar actually sounds nice once
the input cap stuff is figured out...

[dustbro]

How hot should Q3 be getting? After about 30 seconds it's hot enough to burn my fingers.
does anyone have a chart of voltage references for the transistors? Trying to figure out if I've made a mistake

[bdubya]

So I've got my pair up and going in an uglycase without the input attenuators; haven't found time/money (mostly money) to order the vactrols.  When I do, I'm going to get 500-ohm pots and parallel them with a 750R to get the 300-ohms; the only 300-ohmers I found were unreasonably priced.

Haven't added the 8k2 parallel resistance that another gentleman referenced earlier (and is referenced in the urei documents), but I noticed something funny.  In one channel, I definitely get the oscillation(?) when flipping the gain switch down to the lower setting.  However, in the other channel, setup with the same passives, there's no oscillation.  Is this something that is influenced by the transistor's HFE, perhaps? I'll match a pair and experiment in due time, probably once I get the vactrols and pots ordered, but thought I'd ask any experts/passionate twiddlers out there for some insight in the meantime. 

I can only use them for very quiet things without the attenuators, of course, but what I have tried (mostly nylon string guitar and voice from about 3 feet away with a dynamic mic) sounds great. 

Oh, and I yanked out the zobel indicated on the silkscreen(which is for the cinemag mentioned in mnats first posts) and installed 150k resistor for the Jensen 115ke inputs I'm using. 

Just thought I'd add my experiences to the pile.  Definitely would be interested in building another two channels for a 4-pack at some point, if and when they become available.  Thanks for the opportunity to experiment on this, Mako!  You're a gem-encrusted Prince of a human being.





Ben

[dmp]

Finally found the time to finish these for my 51x rack.
I just used a 1meg pot on the front end and skipped R2 & the vactrol.
Has the Hi/Low gain switch on the front.

[dmp]

And the front...

[dmp]

Haven't added the 8k2 parallel resistance that another gentleman referenced earlier (and is referenced in the urei documents), but I noticed something funny.  In one channel, I definitely get the oscillation(?) when flipping the gain switch down to the lower setting.  However, in the other channel, setup with the same passives, there's no oscillation.  Is this something that is influenced by the transistor's HFE, perhaps?

Without the 8k2, the negative feedback is much less, which makes the gain higher. I'm not sure how dependent on Hfe the gain is for this circuit, but differences in layout or wire routing could cause one to oscillate when another does not.   

[grantlack]

That... is... AWESOME. Well done. Added to my to-do list, which is starting to look more like a bucket list at this point .

Finally found the time to finish these for my 51x rack.
I just used a 1meg pot on the front end and skipped R2 & the vactrol.
Has the Hi/Low gain switch on the front.

[dmp]

Does anyone have a internal picture or schematic of the UA 508 EQ?
It is a passive EQ that can be connected across the feedback loop of the 1108 (instead of the 8.2k resistor)

"Envelopmental equalization is achieved by electronically enclosing an external equalizer within an active feedback loop of the amplifier. Used with the UA 508 eq the 1108 provides flexible eq with 0 gain loss. High frequency equalization (switch selectable at 5 or 10 kHz) can be set at 0, +3dB, +6dB, or +9dB boost or -3dB or -6dB rolloff. Low frequency equalization can be set at 0dB, +3dB, +6dB, +9dB boost or -3dB, -6dB rolloff at 50 Hz. "
 

[dmp]

That... is... AWESOME. Well done.

Thanks!

[mnats]

Respect. Nice 51X build dmp.

Does anyone have a internal picture or schematic of the UA 508 EQ?

Search is your friend: http://www.groupdiy.com/index.php?topic=32729.msg401828#msg401828

I also have a picture that I found on my hard drive - not sure who to credit for it...

[bdubya]

Haven't added the 8k2 parallel resistance that another gentleman referenced earlier (and is referenced in the urei documents), but I noticed something funny.  In one channel, I definitely get the oscillation(?) when flipping the gain switch down to the lower setting.  However, in the other channel, setup with the same passives, there's no oscillation.  Is this something that is influenced by the transistor's HFE, perhaps?

Without the 8k2, the negative feedback is much less, which makes the gain higher. I'm not sure how dependent on Hfe the gain is for this circuit, but differences in layout or wire routing could cause one to oscillate when another does not.   

Dayum, nice job!  And thanks for the answer on the 8k2 thing.

ben

[Praqtice]

this is great... so inspiring.

i've been thinking these are perfect for send/receive amps in a homebrew cooper time cube. would need 4 of them. then maybe another 2 just for mics/line.

pre and post emphasis 509 eq's in time cube 1109 amps seem to work on the same feedback loop idea as in 1108/508, am i right?

would this be quite easy to implement instead of the 8.2k resistor like dmp mentioned? would you need to change any values on 509 eq circuit to match it? and any ideas to where the eq's common attach also? eq's in there look easy enough to perfboard and im a total novice.

the eq circuit is on pages 20 and 21 of the time cube manual...

http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/UREI-920-16.PDF

i think that 509 eq design in manual could be easily moded to make a simple 3 band with both the pre and post emphasis circuits combined...? just a thought. im guessing the variable resistors are to 'factory set' the eq for time cube too..

also any in/out transformer and impedance suggestions/advice for using the 1108 to drive a line level signal into a SM57 cartridge acting as a speaker very much welcome? (600ohm?, 150ohm?)

as soon as i can afford it i'll put an order in and get going with this.

thank you so much Mnats!

sam

[mjk]

Does anyone have a internal picture or schematic of the UA 508 EQ?
It is a passive EQ that can be connected across the feedback loop of the 1108 (instead of the 8.2k resistor)

"Envelopmental equalization is achieved by electronically enclosing an external equalizer within an active feedback loop of the amplifier. Used with the UA 508 eq the 1108 provides flexible eq with 0 gain loss. High frequency equalization (switch selectable at 5 or 10 kHz) can be set at 0, +3dB, +6dB, or +9dB boost or -3dB or -6dB rolloff. Low frequency equalization can be set at 0dB, +3dB, +6dB, +9dB boost or -3dB, -6dB rolloff at 50 Hz. "
 

I do have a 508 I could take some pictures of...

Also UA Bulletin SE-08 which has installation notes, schematics, board layouts, and detailed specs for both 1108 and 508.

The LDR was also called "Inputrim" and SE-08 has a thorough description of it's use.

If there's interest I can look to see if I have pdfs or could possibly make a scan.

Michael

[Stagefright13]

That would be great if you could post that UA bulletin Michael. I have been interested in the 1108 for quite some time.

And great job DMP!!

John

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