PRR-176 REV 4 Build Thread ***Manual up!***1/16/14 - (chk 1st post)

[abechap024]

Are you guys testing both channels? Only the left channel needs the links, as shown in the drawing...at least one of the channels with past signal fine without the links installed...

I'm sure its something simple, I didn't experience this when I built mine, so I'm scratching my head....

 

[abechap024]

today I've powered up my 176 and nothing is exploded!
I've seen 2 strange things:
My tension instead 100v is 125v
Can create some problemS??

possibly. Did you try the resistors to knock down your transformer?

The first tube is more bright than the second,
between point A/B is 6.7V
Between point B/C is 5.8V
???

that should be fine...though I've never experience that..shouldn't be a large difference. Make sure your voltage is set to 12.6V

I only hear low sound and no bass
I tried to follow the signal and to the primary of T1 there is full signal,
on the secondary signal goes down as described above ...

The level drops on the secondary of the input interstage by a fairly large amount. Are you using a scope? What tubes are you guys using?

is there any other link necessary?
Thanks

No only the ones shown in the manual.

 

[prh]

It appears that the Lundahls are connect with pin 1 and 3 as input.  It seems to me, from the Lunhdahl data sheet, that pins 2 and 4 need to be jumpered for that to work?

On the PCB, there is not continuity between pins 2 and 4 for the Lundahl footprint...

 

[abechap024]

It appears that the Lundahls are connect with pin 1 and 3 as input.  It seems to me, from the Lunhdahl data sheet, that pins 2 and 4 need to be jumpered for that to work?

On the PCB, there is not continuity between pins 2 and 4 for the Lundahl footprint...

That is correct. Had it on the other revisions...overlooked it on this one. The output pins are correct just the input pins need to be jumped...I'll add that to the manual. Good looking out..

 

[prh]

It appears that the Lundahls are connect with pin 1 and 3 as input.  It seems to me, from the Lunhdahl data sheet, that pins 2 and 4 need to be jumpered for that to work?

On the PCB, there is not continuity between pins 2 and 4 for the Lundahl footprint...

That is correct. Had it on the other revisions...overlooked it on this one. The output pins are correct just the input pins need to be jumped...I'll add that to the manual. Good looking out..

You're welcome  8) 

 

[ilfungo]

Hi
Now with the help of prh  (transformers link), I have sound but
completely misses the HF
The VU meter move very little and can not control the compression, I just feel the difference with the Bypass.
With the trimmers can not bring them to 0...
Some suggestions
Thanks


"Did you try the resistors to knock down your transformer?"

Yes Abe I've changed the resistor first to 1.8K and after to 2.2k but I get 125-130v on psu and 115v on tube pin....

 

[mrdarwin]

Fired up my unit...
voltages are ok everywhere: +18-18 for opamps, 1.5V, 12.6 for heater
changed 1k 2w with: 3k3 5w, 1k+1k 2w, 1k+1k 2w: psu gives me 104V now.
6bz8 are both glowing
I use only ne5532/ne5534 for test, no DOA for the moment...
I can calibrate my vu: "0Vu" is ok
I use Edcor PCW10k:10k transformers, no transformer output.

...and I have a big hum and a smaaaall sound past through unit
It sounds like bad wiring but I double checked... missing jumper for edcor like lundahl?
what is trimmer for "THUMP"?

 

[ilfungo]

Finally my unit is working and passes audio!!!
Now I will make some test and will try to resolve 100v problem
Can I use a biggest resistors values ( now 3 x 2k2)?
In SC bypass mode the level droop down of about 20 db...

 

[e.oelberg]

Hi
Now with the help of prh  (transformers link), I have sound but
completely misses the HF
The VU meter move very little and can not control the compression, I just feel the difference with the Bypass.
With the trimmers can not bring them to 0...

We seem to have very similar problems

 

[ilfungo]

Hi e.oelber
have you make a link on both primary of lundhal ?
Pin 2-4
For me the problem was this...
See the pdf for pin number

 

[prh]

Hi e.oelber
have you make a link on both primary of lundhal ?
Pin 2-4
For me the problem was this...
See the pdf for pin number

Yes, if you are using a Lundahl in any of the four transformer locations, you need to jumper pins 2 and 4.

And don't forget that the jumper in the second inter-stage transformer needs correction, like the diagram posted by ilfungo here:  http://groupdiy.com/index.php?topic=54563.msg704963#msg704963

Because differing transformer combinations require jumpers, it will be helpful if everyone states which transformers and in which position they are using.

 

[shot]

Wow guys, that is a lot of problems...
I haven't started working on my board yet, but I'm hesitating to start till those problems are at least documented so I can try to avoid them.

Hey Abe could you do us a favor? Could you start and populate from the scratch one unit so if you stumble upon a problem you can report it and find solution for it? Seems a lot of board problems are present here... we need help from the designer! And you said somewhere you will finish the board butler for the main board. Still waiting for that... maybe even BOM for the DOA (even though it's easily written out from the DOA butler, I know)
:-\

 

[e.oelberg]

Don't firget shot this is stil diy. So lets figure it out together

(typing on mobile phones is a pain)

 

[prh]

I have attempted to illustrate how I believe the on-board transformers need to be jumpered.

First, Left Channel...

 

[prh]

... and Right Channel.  (Abe and others, can you please comfirm?)

 

[abechap024]

Thanks for helping document these. Sorry for the confusion. I am making a full fledge PDF that should help organize them all and help us and those after us through the build process.

Yes build butler is almost done for the 176, I think it will help get everything more organized. Do you find build butler very helpful? Any ideas on how to make it better? We are getting a search and complete BOM list incorporated too...

So some things to keep in mind that I found when doing my first build (this will be covered in the pdf but probably good to go over it now)...

Thump is adjusted by sending a short signal like a hi-hatt with all the lows cut out. Do it with the fastest attack and fastest release and adjust till you don't hear any thump. If you cant adjust the thump out all the way either switch tubes or rematch (or slightly unmatch) the 2 6k8 resistors on the input of the vari-mu stage.

Adjust the threshold to "max" or lowest threshold...at least to me this sounded best. you could just jumper the trimmer but then you couldn't experiment.

If you are using the opamp input stage, it doesn't distort very pleasantly, at all. So if your already sending a fairly hot signal into the unit, and apply 20db of gain it clips fairly easily (not because of lack of headroom, just because it has a lot of gain!). Hence the 470R pad on the input...Seems silly to cut just to boost again, but in practice it works great, the pad attenuates the noise floor also on all the originals they had a pad on the input.

The output pot should be rev log or linear, the gain stage circuit is loosely based on the api line amp.

I think that is a good idea about building from start to finish, I am planning to do it very soon as I have some more I want to build. I will take pictures and step by step instructions. Again thanks everyone for helping to make this hopefully a great project.. I should post some clips of the final finished unit...

 

[abechap024]

Fired up my unit...
voltages are ok everywhere: +18-18 for opamps, 1.5V, 12.6 for heater
changed 1k 2w with: 3k3 5w, 1k+1k 2w, 1k+1k 2w: psu gives me 104V now.
6bz8 are both glowing
I use only ne5532/ne5534 for test, no DOA for the moment...
I can calibrate my vu: "0Vu" is ok
I use Edcor PCW10k:10k transformers, no transformer output.

...and I have a big hum and a smaaaall sound past through unit
It sounds like bad wiring but I double checked... missing jumper for edcor like lundahl?
what is trimmer for "THUMP"?

Edcor PCWs work. Thats what I initially used for testing before switching to cinemag.

What votlages are you starting out with that you need to change the 1k resistors? Are you using the primary trick the 120V people are doing and stepping up the resistance?

 

[ilfungo]

Thanks Abe
just for my HT problem:
After the diodes 1n4007 I've 220v and with 3 x 2k2 resistor I've at least 125v on PSU out and
113v on tube input pin...
It's yet too hight?

second problem:
Second channel work perfectly
The first channel is sounding good but there is something strange on compression:
little compression and very slow (attack and release times do not seem to work)
Any idea?
Thanks

 

[mrdarwin]

Ok, I forgot jumpers near input... that was not clear, I was thinking these pads were for optionnal transfo input.
So!
Channel 1 seems to work, sound goes very low when bypass(?), I still don't put 470r resistors pads...
Channel 2, problem with sidechain, bypass and hf selectofr don't work, have to check jumper 3
sound is passing trough unit (2channels)!

I'll be back...

 

[ilfungo]

Hi mrdarwin
same problem here
in bypass mode the signal go down