[BUILD] 1108 DIY project and PCB layout

[Stagefright13]

Well fixed the variable side easy enough... The 2200 UF was pretty large so I installed it then bent it over sideways. THEN soldered it. But somehow the land got cracked anyway. The other side I have 92 volts after d1 and d2 using a 30/30 transformer. Somehow I got a 63 volt 470uf cap there. Prolly cooked it.

Got a session in a couple hours. So gotta shelf this for today. I reinstalled the other power supply and am putting it into service! Will post back after I test it with the new power supply. Thanks for the help Mnats.

John

 

[ilfungo]

which can work in this project for 2 channels?

http://www.antekinc.com/gview.php?d[]=0

Thanks

 

[dtrax]

I ordered 2 preamp boards and a PS board and am in the process of putting a mouser order together. Looking at the schematic and reading through this thread, everything seems pretty straight forward. However, S3 (SPDT) on the schematic looks like it's switching between different windings on the input tranny primary. Is this for switchable input impedance?

I'm using the Jensen schematic AS016 for Phantom, Pad and Polarity circuits. This also has an input impedance switch, but seems redundant if I'm reading the 1108 schematic correctly. Here 'tis for reference: http://www.jensen-transformers.com/as/as016.pdf

Muchas gracias!

 

[dissonantstring]

hi dtrax,
your assumption is correct.  i would save yourself a few pennies and delete the input impedance (150 Ohm - low) switch in the jensen doc and just use a switch on the CMMI-7C primary winding pair (switch between the 200 and 50 Ohm windings).  both the jensen impedance part of the circuit and the cinemag transformer windings are just about the same impedance values anyway so redundant as you stated.
kind regards,
grant

 

[dtrax]

Grant,

Thank you for helping/confirming the imdepance circuit. I'm using a Cinemag 2511 for the input, which has two 150 ohm primaries (an oversight on my part; I ordered the 1108 tranny bundle from Hairball Audio w/o confirming first). It will work fine, but switching isn't as straight forward. I could make it switchable from series/parallel, 300/75 ohm respectively. I may skip this for now, as I'll need to work out a diagram first. It's on the backburner at the moment...

Moving on, I'm having a bit of trouble with the power supply. The main issue is that neither trimmers are effective. I found it odd that neither worked, so I double checked their orientation... I flipped them around, but still nothing.

I should note that the power supply PCB was difficult to solder (using the Mnats Variable + Phantom pcb). The pads are very small, and about a dozen of them were nearly completely covered with solder mask. I tried scrapping the mask away, but that ruined what little copper was left for each pad. I had to get crafty and connect the paths “manually”, ala breadboarding. It's a bit crude, but I've made all proper connections from what I can tell.

I've taken some readings, and I'm getting ~24VAC on the output of the “variable” circuit and ~9VAC on the output of the “phantom” circuit. In fact, I've tested all around the circuit and I'm getting the same readings as the output.

Each leg of the regulators is reading their respective voltage (24VAC or 9VAC). They aren't getting warm at all. Is it possible they're both DOA?!

I've checked for continuity and shorts... all seems well. Any of you gentlemen have some insight?

Not that it should matter, but I have a power led indicator wired in parallel off the PT secondaries along with the associated dropping resistor (100R, 5W). Obviously the preamp PCB's are not connected...

 

[mnats]

I should note that the power supply PCB was difficult to solder (using the Mnats Variable + Phantom pcb). The pads are very small, and about a dozen of them were nearly completely covered with solder mask. I tried scrapping the mask away, but that ruined what little copper was left for each pad. I had to get crafty and connect the paths “manually”, ala breadboarding. It's a bit crude, but I've made all proper connections from what I can tell.

I've had a look at several boards I have in stock and can't see any pads that are "nearly completely covered with solder mask":


click for larger image

If you received a board that was faulty, just let me know via my White Market board thread and I'd be happy to replace it.

I admit the pads are a little smaller than I would have liked (it was my first completed design using Eagle) but that's not to say I had any trouble soldering it:


click for larger image

How about posting a picture of your board so we can have a look?

 

[dissonantstring]

I've taken some readings, and I'm getting ~24VAC on the output of the “variable” circuit and ~9VAC on the output of the “phantom” circuit. In fact, I've tested all around the circuit and I'm getting the same readings as the output.

Each leg of the regulators is reading their respective voltage (24VAC or 9VAC). They aren't getting warm at all. Is it possible they're both DOA?!

I've checked for continuity and shorts... all seems well. Any of you gentlemen have some insight?

hi dtrax,
forgive me if i'm misunderstanding, but are you saying that you are measuring 24V AC on the VAR+ output pads?  this should be DC.  could there be a solder bridge since the AC and DC pads are side by side?  can you check continuity between the 24VAC in and the VAR+ output pads (as well as the 24VAC in to the phantom PS circuit and the PP output pads)? 

i can't see how AC would be present after the bridge rectifier.  are the bridge rectifier diodes beeping ok out of circuit?

 

[dtrax]

Good news! I found a few shorts, and got them all fixed up. Chalk it up to inexperience or whatever. I printed out the schemo and systematically went through and checked off each component until I got everything working. A good night's sleep and fresh perspective can do wonders.

Mnats, thanks for the offer on replacing the board, but that's not necessary. I think the issue was probably a bit of oxidation, and while the pads are on the smaller side, it's my own fault for not cleaning them up first. I'm burning in the PS board at the moment to see if any faults arise, but so far so good. I've ordered quite a few PCBs from you and they've all been great! I hope my above post didn't come off as a knock on your work.

Cheers everyone, and thanks for the guidance. Now I'm off to finish wiring up the rest of the circuit...

 

[dtrax]

Yea, the outputs were reading AC... I found a few small shorts so the voltage wasn't being rectified. But I got the traces fixed up and all seems to be well!

I've taken some readings, and I'm getting ~24VAC on the output of the “variable” circuit and ~9VAC on the output of the “phantom” circuit. In fact, I've tested all around the circuit and I'm getting the same readings as the output.

Each leg of the regulators is reading their respective voltage (24VAC or 9VAC). They aren't getting warm at all. Is it possible they're both DOA?!

I've checked for continuity and shorts... all seems well. Any of you gentlemen have some insight?

hi dtrax,
forgive me if i'm misunderstanding, but are you saying that you are measuring 24V AC on the VAR+ output pads?  this should be DC.  could there be a solder bridge since the AC and DC pads are side by side?  can you check continuity between the 24VAC in and the VAR+ output pads (as well as the 24VAC in to the phantom PS circuit and the PP output pads)? 

i can't see how AC would be present after the bridge rectifier.  are the bridge rectifier diodes beeping ok out of circuit?

 

[tomas1808]

Hi.

I am building a 1108 pre using the vactrol for the input level control. It's a VTL5C9.

I was wondering what should the circuit for the LED part of the vactrol be. I'm sure it needs at least a resistor and the level pot, but which values? Can I power it using the 24VDC line?

Thanks!

 

[tomas1808]

Hello? Hello? [sub]Hello?[/sub]   

 

[dustbro]

I was wondering what should the circuit for the LED part of the vactrol be. I'm sure it needs at least a resistor and the level pot, but which values? Can I power it using the 24VDC line?

I messed around with this for a while.. basically you can take any lm317 circuit and trim it down to 3V (aprox)... send that to a pot that feeds the LDR.
At the end of the day, it's a lot more trouble than it is worth. The use of the LDR was to be able to remote control the mic pre at a great distance without adding additional noise into the circuit. If you are building this into the usual 1U or 2U unit, you dont need the LDR. Just replace R2 + the LDR with a voltage divider (pot)  Works great!

 

[tomas1808]

Thanks dustbro.

I am quite new to this, but why wouldn't you take the  "limiting resistor + pot" route?

Seems a lot simpler. Any drawbacks?

 

[ilfungo]

Hi guys
I have problems with New Mnats PSU
I think the problem is  to pads
Has anyone had the same problem?

 

[mnats]

Hi guys
I have problems with New Mnats PSU
I think the problem is  to pads
Has anyone had the same problem?

Did you see reply #126 and #127 above? It appears that there may have been some oxidation on that person's board but I have not experienced this myself.

Can you post a picture?

 

[ilfungo]

thanks for the answer Mnats
The first PCB is not working,
the second works ....
I put the photos as soon as possible
how to connect Cinemag CM-2511?
thanks

 

[juanjovincenzo]

Hi guys!
Somebody knows if the Self-Etch copper layer version Preamp 1108 V1.2 is OK  and works the circuit?, and  what is the board dimensions to fit to real size and then print it?
Regards
Juanjo

 

[Stagefright13]

Trust me the circuit works and sounds great. I just have been sick for a long while so didn't get the new power supply up yet. I am missing the right caps. And the ps is too tall for 1u. so ya gotta bend them over. That's how I messed up the land on the board.
  But am very excited about mine. Trying to get better and finish!

If ya don't want to goof around just use an external ps. I think the new ps will solve everything. But haven't been able to try yet. Sorry.

John

 

[Stagefright13]

Oh and the impedance switch is not very useful unless you have ribbons. And the low setting is not very useful either. Wich I suspected and put it on a jumper on the board. But set on high and the 500 ohm winding sounds best.

Damn good sound tho! Not dark at all. Nice and bright. With a good bottom end. VERY COOL!

John

 

[juanjovincenzo]

Hi John thanks !!! Did You etch  the 1108 rev 1.1 or the 1108 Rev 1.2 board? and remember the dimensions of the board? because I think that in the Mako´s  PDF file 1108_V1.2_DOC the copper layer is not fit to real size. Maybe the layer is little small.