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

[abechap024]

I'd venture to guess that the SP3T switch needs to be on/on/on... I was looking for some yesterday for this project. I'm a bit confused on the input pad as far as what needs to be jumpered to what if I don't want an input pad? If anyone has a second, I would really appreciate a hand.... I'm assuming a couple of jumper shunts will do the trick, hopefully?

The switch needs to be on/off/on at least on how I've imagined it...there is always a small value cap in series with the sidechain, so with no switch enabled the sidechain defaults to "de-esser" Then you add a a capacitor with the switch, and when you flick the switch in the other setting you add a different capacitor. You can tune them to whatever frequency you choose.

I just found I liked the input pad, you don't have to have an input pad if you don't want, obviously, but the originals and the 176 retro both have one. and it seems to give a nice gain adjustment, but hey make it your own! Test it, mess with it Thats the most fun.
Where to put it is in the documentation on the first post.

 

[abechap024]

What is the purpose of the 1k Trim (R50 / R103) marked Output Sym?

I'm also a bit confused about the input set-up - options and jumpers, etc.  Would someone please clarify?

So the output trim is to adjust the symmetry and balance of the output stage.

The input has 2 options, the opamp input option, in which case you jumper the "in opt" jumpers just connect the 2 with wires.

The other option is to get a balanced 600 ohm attenuator and attach that directly to the input interstage TX using those "in_opt" jumpers.

The jumpers themselves are in between the opamp input stage and the interstage input transformer.

 

[abechap024]

Abe,

about SPTT: on schematic "pos1=de esser, pos2=200hz hpf, pos3=no hpf" and on wiring guide " on/off/on"... so to bypass hpfilter, sptt has to be on center or on pos3?
I'm designing my frontpanel, so which is correct? schematic or wiring guide?

about DOAs: considering I've got now five doas, which pair do I have ommit for a premium result: u5/u22 or u11/u28 or u12/u30?

thanks

Sorry I see how that is confusing, on the schematic it wasn't alluding to what position the switches were in, just what the different hpf modes were. Stick to the wiring manual.

In my experiments with the discrete opamps I have found the output position opamp has the greatest effect, probably because it does the most heavy lifting and I would put the other 2 in the opamp that drives the input interstage transformer (The first) So the first one and the last one, the middle one is just, buffering.

 

[e.oelberg]

Tip for the rev4 builders:

do set the trimmers of the PSU before powering up your unit. Otherwise you might blow some fuses or even the regulators.
Also 5k trimmer for the 1.5 V regulator is completely out of range. use 200 r instead.
set the trimmer for 18 V to 1.3K

 

[ilfungo]

Hi  e.oelberg
Thanks for the info...
Have you tested your 176?
Sound?

 

[e.oelberg]

Hi  e.oelberg
Thanks for the info...
Have you tested your 176?
Sound?

Still a way to go ..
Psu is working...
Now i check for voltages on the board...

 

[e.oelberg]

First smoke rings... The two 10r on the power rail on the board. Maybe on of my ne5532 is broken

 

[mrdarwin]

Tip for the rev4 builders:

do set the trimmers of the PSU before powering up your unit. Otherwise you might blow some fuses or even the regulators.
Also 5k trimmer for the 1.5 V regulator is completely out of range. use 200 r instead.
set the trimmer for 18 V to 1.3K

Tested my psu few minutes ago: everything is ok
My 100V rail is 116V and you?
1.5v is ok with 5k trimmer... for me!

Abe, do you confirm that heater voltage is 12.6V between A and C, and the tubes are powered in serial?

 

[e.oelberg]

tubes are powered in serial.

i have 105 v

 

[ilfungo]

For me with no load I've 150v on psu.... ???

 

[e.oelberg]

For me with no load I've 150v on psu.... ???

Seems you put a 1n4007 where you actually should have put a 100V zener

 

[ilfungo]

The diodes are all in right spot also the zener 100v 1W
I've a doubt:
My toroidal on secondary put out 158v instead of 120v ( on label)
can be this the problem?
Thanks

all the misure are without main pcb connected...

 

[e.oelberg]

The diodes are all in right spot also the zener 100v 1W
I've a doubt:
My toroidal on secondary put out 158v instead of 120v ( on label)
can be this the problem?
Thanks

all the misure are without main pcb connected...

look for ripple rejection or r-c filter psu calculator on the web, maybe you should bring down the voltage
ergo put higher value resistors in the r-c-chain

 

[abechap024]

The diodes are all in right spot also the zener 100v 1W
I've a doubt:
My toroidal on secondary put out 158v instead of 120v ( on label)
can be this the problem?
Thanks

all the misure are without main pcb connected...

You might want to increase your 1k resistors, But I would try it first, If the voltage is too high it would blow your zener. If the voltage is too high, measure (carefully) what it is before your first 1k resistor...I think it should be 160v - 180v

(1.414 x what input AC voltage will give you the approximate voltage after rectification)

so about 1.8k so find a resistor that is close to that, 5 watters.



Using the same calculations is how you 220v people can use just one transformer...just change all the resistors to 3k3 and you should be in business.

 

[ilfungo]

THANKS!!!
Tomorrow I will try...
I don't have the resistors


Just for curiosity
If I use some resistors on AC secondary for put down the voltage ,can work?

 

[e.oelberg]

you have to calculate the voltage drop of the capacitor resistor chain in your psu.
you need
power consumption of your two tubes in mA
capacitor value 100mF
to calculate your desired resistor


BE CAREFULL 150V IS No FUN

http://ampbooks.com/home/amplifier-calculators/RC-ripple-filter/

 

[abechap024]

Two questions:
What are the DOA added in rev4 relative older revision?
Can I use edcor xsm 10k:10k as xformer output 600:600? (I have spare xsm...) or Carnhill 600:600?

There is a DOA that buffers the input interstage transformer, a DOA that buffers the output of the output interstage transformer and a DOA for the make up gain stage...

The earlier revs didn't have the buffer for the output interstage transformer...


If you use edcor for the intserstages be careful of stray magnetic fields...you could use either TX's as an output TX

 

[mrdarwin]

The diodes are all in right spot also the zener 100v 1W
I've a doubt:
My toroidal on secondary put out 158v instead of 120v ( on label)
can be this the problem?
Thanks

all the misure are without main pcb connected...

You might want to increase your 1k resistors, But I would try it first, If the voltage is too high it would blow your zener. If the voltage is too high, measure (carefully) what it is before your first 1k resistor...I think it should be 160v - 180v

(1.414 x what input AC voltage will give you the approximate voltage after rectification)

so about 1.8k so find a resistor that is close to that, 5 watters.



Using the same calculations is how you 220v people can use just one transformer...just change all the resistors to 3k3 and you should be in business.

My voltage is 116-118v... is it too much?
How can I avoid stray magnetic field with edcor pcw10k:10k? mount offboard?

 

[e.oelberg]

hi abe

is it necessary to ground the sidechain at the bypass position of the switch ?

nicholas

 

[ding]

How can I avoid stray magnetic field with edcor pcw10k:10k? mount offboard?

That was a problem for Rev 1 boards because of where the PSU components were. Abe pull those components into a separate board in Rev 2 and that problem got fixed almost entirely. There were some, but for the most part everything was good. I imagine for Rev 4 now that the heater PSU components are separated out this should pose nearly no problems I would think. I am certainly not too worried about it. I will put the PSU board and toroid as far as possible from the main board and not think twice about it.