[BUILD] 1108 DIY project and PCB layout

[dmp]

How did you wire the input? Did you replace the vactrol with a pot & use a jumper in place of 82K?
If you ground the transformer side of C2, is it quiet?

 

[AdoreaRecordingStudio]

How did you wire the input? Did you replace the vactrol with a pot & use a jumper in place of 82K?
If you ground the transformer side of C2, is it quiet?

Right my fault, should have included that detail.  I decided to bypass using the vactrol at all in these 2 units.  I am using a 300ohm pot as output and am not using the LDR.  I have the pot wired in place of R2 and where the vactrol would sit. However, I checking right now if I jumpered 82k  -  I am learning as I go here so I do apologize, but which side of C2 is the transformer supposed to be grounded to? I can't tell you how much I appreciate the thoughts!! I am going to post pictures shortly!

Thanks again

Travis

- updated - I did not use the vactrol and from earlier posts which I perhaps misunderstood - I just left R2(82k) out of the circuit completely? I must have misunderstood the need to jumper it still? so I should try jumpering R2?

 

[dmp]

Well, take a look at the schematic. Link in the 1st post. I'm not sure exactly how you have it wired, but I made mine with R2 omitted, and a 1 meg pot in place of both R2 and the vactrol, with the wiper of the pot going to C2.
Having a mistake on connecting the input could cause a lot of hum.
I was only suggesting grounding the side of C2 to see if it stopped the hum. as a test.

 

[AdoreaRecordingStudio]

After taking a closer look at the schematic and my wiring I realized that I have the pot wired like you did on your unit dmp (in place of R2 and the vactrol / C2). An enormous amount of hum disappeared after grounding the pot with a heavier gauge grounding wire  and doing the same for my 0v tap. I'm gonna open the case  back up and see if I can give grounding C2 a shot and if it does anything.. Thanks for the thoughts - much appreciated

here are some pics of the build  - btw my wiring is total shite right now until I get it working 100%.  I'll clean up the guts, but for now I'm almost ashamed to post this mess of wires in here! I'll make sure to post finished pics/audio when I get this thing rock'n.

 

[dmp]

An enormous amount of hum disappeared after grounding the pot with a heavier gauge grounding wire  and doing the same for my 0v tap.

Sounds like you found the smoking gun. Reviewing and cleaning up the ground scheme will probably get you quiet performance.
- Dan

 

[waltzingbear]

That value is from the Waltzing Bear schematic linked earlier -  and it appears whoever re-drew that schematic was from the "bigger is better" school of device "mods".

nope, when I drew that up I couldn't find the schematic anywhere. That is a draw up from existing module in front of me, "as delivered". Have no idea if it was stock, been repaired or what.  Fortunately we have the original schematic available now.

Alan

 

[mnats]

That value is from the Waltzing Bear schematic linked earlier -  and it appears whoever re-drew that schematic was from the "bigger is better" school of device "mods".

nope, when I drew that up I couldn't find the schematic anywhere. That is a draw up from existing module in front of me, "as delivered". Have no idea if it was stock, been repaired or what.  Fortunately we have the original schematic available now.

Alan

Apologies for that comment - it wasn't meant to offend. I'm sure a lot of people appreciate your efforts on that and other schematics you posted long ago before anyone had access to them. Thanks for getting so much info out there!

Must have been interesting trying to figure out why your module was oscillating without a schematic!

 

[Stagefright13]

Here is some pics of the EQ if anyone is interested:

 

[Stagefright13]

 

[Stagefright13]

Adorea your power transformer is Awfully close to the board. This thing is sensitive to that especially when ya run pot wires from the board. But is A great sounding pre.

John

 

[Stagefright13]

If ya moved the power supply OUT of the case your pre should be virtually silent. Or used A nice quiet toroid with more power than ya need.  I did get some inside info on the original ones. Mines in A 1U rack so couldn't fit A Big overpowered Toroid to reduce flux or whatever. But is quiet now with Mnats new PS. And using A Toroid.

John

 

[Stagefright13]

Originally Posted by avedis
Quote:
Originally Posted by stagefright13
Hi my name is John. We are building some 1108's from scratch on the prodigy Pro forum. I quoted you from one of your posts here. Hope you don't mind. If so I will delete it.

The thread is here: http://www.prodigy-pro.com/diy/index.php?topic=37374.80

Not asking for any trade secrets or anything LOL. We just goof around and experiment. Maybe you can share some pointers with us on this old design? Mines almost done. I'm stagefright13 there also.

Thanks!
John
hey John,

I don't mind.. I forgot about this email but kinda glad it's archived so I can read it myself I have an original pair of them here but they haven't been racked up yet.. my prototype to Brent years ago was sold. A Japanese dealer wanted to buy all of them (about only 20 units) because it was from VH consoles and wanted a certificate from Donn, but that was going too far I told Brent.. so he sold them about half of them and the other half here in the US. I like them.

I saw your board and it looks like a nice job. Sometimes toroidal transformers can actually be very noisy if the core is too small so if you keep having problems and you know it changes from moving it around... just try another quality brand that's the same rating but a little bit bigger. Toroids only work well if it's within it's rating, which is not always accurate with it's publications; outside of that and it just throws off a large field that's hard to contain. And the input to the first transistor is very high impedance so this node could be susceptible to any strong field.

Enjoy your homemade 1108s! Record some music! I know it's a good feeling

-Avedis
My 1108 is working great now. I swapped out the power supply board and had grounding issues. Actually been used for A while now. It's on at least 3 CD's I did. Thanks for the help! Antique input transformers and all. Great on guitars and such.

Thanks Again,
John

 

[duantro]

Damn these don't look too involved!
has anyone tried building them?

edit: I just noticed that you posted 2 different eq's. Are they 508's and 509's?

 

[rhythminmind]

Just completed a pair, looking forward to putting them to use. I'm getting 43dB of gain out of these two feeding them 26v from the PSU. Only thing I'd like to improve is the 1meg pot response. Any tips?


DSC_0013 by rhythminmind, on Flickr


DSC_0009 by rhythminmind, on Flickr


DSC_0006 by rhythminmind, on Flickr


DSC_0005 by rhythminmind, on Flickr


DSC_0004 by rhythminmind, on Flickr


DSC_0002 by rhythminmind, on Flickr


1108 fr by rhythminmind, on Flickr


1108 thd by rhythminmind, on Flickr


IMG_20120918_193217 by rhythminmind, on Flickr

 

[dmp]

Damn these don't look too involved!
has anyone tried building them?

The hard part is figuring out the inductors and making them.

Just completed a pair, looking forward to putting them to use. I'm getting 43dB of gain out of these two feeding them 26v from the PSU. Only thing I'd like to improve is the 1meg pot response. Any tips?

Very cool. Nice idea to use Dan's cases for some portable preamps.
How are you connecting the power from the psu to the pre? It looks like the preamps have IECs on the back?
You could replace the pot with a stepped switch. ClassicAPI has grayhills with a little pcb that makes it really easy. Just figure out log scaled resistors that add up to 1meg.

 

[3nity]

WOW that seems dangerous.

 

[duantro]

Damn these don't look too involved!
has anyone tried building them?

The hard part is figuring out the inductors and making them.

Let me know if I'm hijacking this thread.....
Has anyone used the 508 eq's? I know they are pretty limited, but do they sound good? Any clue on how to find a compatable inductor? I've just bought a 508, and am in the process of racking up 2 original 1108's, and 2 original 1008's. I can't decide what to do about my lack of eq for the other 3 UA channels.

 

[Indecline]

Let me know if I'm hijacking this thread.....
Has anyone used the 508 eq's? I know they are pretty limited, but do they sound good? Any clue on how to find a compatable inductor? I've just bought a 508, and am in the process of racking up 2 original 1108's, and 2 original 1008's. I can't decide what to do about my lack of eq for the other 3 UA channels.

I haven't ever tried them, but I would love to build a pair of (because I'm the eq type of junkie!). Just a guess, but they're probably more of a sweetening eq than a problem solver, and could sound really nice on the mix bus. It'd probably be pretty cheap to build and it's always nice to have a different flavor at your disposel. As far as measuring inductance, you'd have to remove it from the circuit to measure it. Then trace out a schematic and values. And considering all the excitment a few pages back, I'd be willing to bet the communtiy would help make it happen.

But yes, I think this deserves a new thread if you want to make it a reality

 

[tomas1808]

Need some help! :'(

I finished building my 1108 a few days ago, but I am going crazy with the high amount of hiss. With gain maxed out I get a noise floor of around -65dbFS when terminating the input with 150ohm  metal film resistor.

There is most probably something wrong with the grounding.

I did everything as said in this thread: Pin 1 of XLRs to chassis, PSU Ground to chassis, checked the chassis for continuity, transformer's faraday cage to circuit ground and Can to chassis. Input XLR connected to transformer via Quad Canare, the secondary goes to the PCB unshielded (but twisted and short).

BTW, using a CMMI-7C and EA-5002, Vactrol (LED disconnected for testing --> max gain), toroidal onboard.

Any idea what to do? I am really lost here. Did everything in my power (knowledge) but no results.

Many thanks!

EDIT: Uploaded noise just in case -->  http://soundcloud.com/tomas1808/1108-hiss

 

[dustbro]

Need some help! :'(

I finished building my 1108 a few days ago, but I am going crazy with the high amount of hiss. With gain maxed out I get a noise floor of around -65dbFS when terminating the input with 150ohm  metal film resistor.

Hiss is usually associated with a component issue, not grounding. Swap out the J309 and see if your noise goes away.