1176 in 51x/500 format, or 51X-F76 Build Support Thread

Very good. .. . that was actually what my friend first suggested.  "Why don't you just leave the zobel network out?"  But I was trying to build it close to how Igor's production units were set up.  Igor seems to have a funny way about doing things, but the results are fantastic.  The F76's are used heavily in the studio.

Great to hear that they're in heavy use!
The guy from whom I got the info about the zobel from is a live-engineer doing quite big shows,he's a forum member here.I'm about to using them in my next musical shows,live of course.The rehearsals will be a nice "platform" for checking things out,especially in the early rehearsal stage.
I think I'll build all of the doas and do some experiments,have done some APP992s as well.
Will keep you posted,promised!

Cheers,

Udo.

saxmonster said:

Anyone make a stereo pair of these yet?  Did you have to match resistors or any parts when you built them or is the matching of a stereo pair done in the calibrating?

-Scott

Click to expand...

i believe Igor will give you matched set of FET quads for a stereo pair for an extra charge? The +- of the suggested resistor values shouldn't matter, but what the hell do i know ;D

tonycamp said:

i believe Igor will give you matched set of FET quads for a stereo pair for an extra charge? The +- of the suggested resistor values shouldn't matter, but what the hell do i know ;D

Click to expand...

I got a quad of fets with my kits,seems Igor automatically does that when ordering them as a pair.
Have opened the aluminium foil some minutes ago,they're packed in two pairs.Each pair has a label on it with "Audio" and "GR" written on.So it seems that the both functions have to use matched fets,not Q1 matches Q10 in the build.Mine are 2N5457 although BF245 is written on the foils outside.
He didn't ask for extra money in my case.
Maybe Igor can tell us the specs?

Cheers,

Udo.

Hi igor, will there be another Batch for those DIYers have been late  8)  ??
greets
Axel

yes, igor I could use a pair, thanks.

anyone here replaced the in/out pots with stepped switches?  I know Jeff makes a little PCB/Switch kit that is perfect for this.  I'm wondering what the values are for the resistor settings and am unsure how to come up with them. 

I would like to order a pair of these. Any idea if they will be in stock again?

So I started final steps and did voltage checks,all very very well in specs (on one LM337 I even got -9,99 vdc,the other 9,89vdc).
That made me happy.
Happiness stopped immediately when I put in igor´s amps:I have the same issues than a lot of you guys,can´t get readings lower than around 5,2 vdc-on both builds,pots completely bottomed out!Have the transistors on sockets,swapped them,no change at all!
I even selected the BD´s prior to assembly as an "apocalyptic prevention2 from a bunch of 30,no luck at all.
This is getting on my nerves now.....will take a sleep first,then install the 560k´s (r11) tomorrow and try other configurations.
I´m pretty sure I will not spend any time on the cascode amps anymore because I must get them started very soon.
Have built all amps and do have some others ready for checking here,so I have a few choices still.

Will keep you posted (if interested),

Udo :-[

Hello,

audio part is o.k. now on both boards,I get nice gains of +37,1 dB,clipping is around +30 dB (1K sine) unloaded,very nice.
But then the next issue came up:
While I managed to get one build fully working is the second doesn´t work correct when ARR board is attached.
At the point of trimming the -10 for the meter in GR mode I figured out that I´m not able to get the difference of 10dB comparing off mode and ratio setting to 4.Even dialing both input and output level to max. gives me only a difference of roughly 6 dB.
So that´s wrong.
I can state that the fault is on the ARR board because it follows when swapping them out between both units.
Having them side by side I measured the values of the resistors more than 5 times,and I´m unable to track this issue down.
I thought it is around the ratio switch connections or so because there´s one strange thing happening when I switch ratio to higher rates,starting at 1:8 etc........the level measured on output starts to increase instead of constantly decrease on higher ratio positions!
I still haven´t found it.......

I decided that it might be the best to build a new ARR board,but they are part of the pcbs/kits.Have found they´re sold out on Igor´s homepage-Great....... :-[
Now how can I proceed,is it possible to get just this board from you Igor?
Or even betteroes anyone have a nice and elegant idea to track this issue down?

I´m completely lost now,this build is no fun anymore....my time is running and I have the feeling that this all won´t work out until rehearsals start.......seems I´m losing another chance to test them in a professional high class live situation.....

Udo.

Hi Udo,

if you get an error when connecting the ARR board, the error is not necessarily on the ARR board.
Check the detector area around the TL074

Wolfgang

wowi said:

Hi Udo,

if you get an error when connecting the ARR board, the error is not necessarily on the ARR board.
Check the detector area around the TL074

Wolfgang

Click to expand...

Thanks Wolfgang,

but the error moves with the arr board when attaching to the other unit.

Udo.

Hi Udo! In general, I have a feel like something is shorted somewhere at your att/rel board.
Or, maybe, wrong value resistor etc. You have to pass on every component with multimeter and check.
Or...maybe....what about stop pins for ratio switch?

For cascode input amps - do you run the unit at +/-24V?
No need for 560k input resistor with cascode amp
Feels like a same mistake on both pcbs. Maybe, wrong resistor, reversed polarity of diode/zener/etc. Maybe zener replaced by diode.
We built about 30 of F-76 for now using same pcbs from same batch; if everything soldered correct, it simply works.
So... let's try by way of hi-res pictures, maybe, I will find something.

Matched fet's: quad fet sets were coming with stereo kit. Better matched for audio, "less better matched" but within same specs, for GR.
Written BF245, 2n5457 inside, dats right. On PCB it is written BF245, too. 5457 should face back to silkscreen (reversed) vs 245.
Just check the BOM and docs, I already wrote about 5457 here.

For kits requests: if there are more than 10 kits, can do small run; won't be fast - if pre-order and 3-4 month delivery is ok with you, possible.

Replaced pots with stepped switches - search this forum for excel stepped attenuator calculator in excel or switch to pot excel calculator.
The rest is your time. I did pair of UN-76 units (same but in 2RU, with Neve output stage and our output trafo's) with ELMA switches for input/output.
Takes exactly 2 min to get all values and it is your homework.
Input/output pots values (in case of our input stage and balanced line receiver) are 10k log.
I used to add 100R from ccw to gnd to get 40db range on these pots (more precision scale).
Steps of 3db for input and 2db for output should work.

O.K.,thanks for posting Igor.
Will go over it at the weekend,again.....
Maybe I made more mistakes while swapping things/boards between the units than I wanted due to my disappointment.
I have the feeling too that it must be on the arr board,and as said there's one thing that is pretty strange:while I'm on adjusting ratio to 4:1 and toggling between this and compressor off position I can not get a difference of more than 6 to 7 dB,even with output level fully up.
Also after the 4:1 ratio,so 8:1 etc. the output level starts to increase again instead of decreasing with higher ratios!That can't be right I think.........

Anyways I must have this up and running in general before I can go back to repairing doas.As said motherboard readings on audio are pretty fine at the moment,troubles start when attaching arr board.

Thanks for watching,

Udo.

Hi Igor (and those who are interested)!

Some huge progress today."Faulty" ARR board is now working correctly.Patience was the key.
A couple of days ago I went into some kind of disappointment,I have been stressed heavily by my real work as an audio engineer,time is running and I had caught a heavy cold.No good combination at all ;D
In one of my trials and errors while I was swapping boards and re-adjusting stuff again and again i certainly missed the point to pull the fets again and then putting them in prior to setting the "-1dB-point".So I trimmed the bias on that ARR board to somewhere in nirvana or so.
Readjusted the whole thing from start again today (I have 2 days off-horray!) and yes-it works,at least my measurements tell me that,both units behave the same now,pooooooooohhhhhhh........The board was never faulty!My apologies for causing trouble here!

O.K.,next step is my issues on the cascode amps,I posted before that I´m not able to bring them down to less than 5,6vdc both.

Igor said:

For cascode input amps - do you run the unit at +/-24V?
No need for 560k input resistor with cascode amp
Feels like a same mistake on both pcbs. Maybe, wrong resistor, reversed polarity of diode/zener/etc. Maybe zener replaced by diode.
We built about 30 of F-76 for now using same pcbs from same batch; if everything soldered correct, it simply works.
So... let's try by way of hi-res pictures, maybe, I will find something.

Click to expand...

So yes,I´m running them on +/-24V,I didn´t have the 560k soldered in.
Maybe someone can see an error in the picture?

Thanks again,

Udo.

P.S.:The transistors are mounted on sockets.

Oh, I forgot to post a pic-here´s (are) the blue(s),nice look,no?

...and another one (to proof that I´m not only showing frontpanels and knobs ;D)

Woohoo!!  For anyone interested, i used Jeff's VP gainswitch PCB and grayhill switch, with resistor values taken from the Switch/Pot spreadsheet floating around the forum.    Also of note, the pots that these switch assemblies were replacing had a lot of variance in their values.  the 4 pots were: 7.5K, 9.2K, 10.3K and 9.59K, and they're supposed to be 10K.    each switch assembly is 9.93K, so my units should match much closer.  This might also explain why my voltage values were never identical to the test procedure values. 

Hi
Sorry for hijacking this thread; I didn't exactly know where to put this.
I'm looking for someone who bought the original PCB set to confirm the price of the PCB set only (not PCB + hardware kit/parts kit, just the PCB set):
Was it $90 ???

Thanks

ramshackles said:

Hi
Sorry for hijacking this thread; I didn't exactly know where to put this.
I'm looking for someone who bought the original PCB set to confirm the price of the PCB set only (not PCB + hardware kit/parts kit, just the PCB set):
Was it $90 ???

Thanks

Click to expand...

Hello,

yes,in that area at least.Prices changed from time to time.Must do a search on my old bills.

Best,

Udo.