Official Forssell Limiter Build thread

[ChuckD]

I want to have both output drivers available. I stuffed both but need to what traces have to be cut and how to flip the output.

Can you help with this Tom?

Thanks

-ChuckD

 

[ChuckD]

OK nevermind I think I got it.

Let me know if this is correct ok:

1. Cut Trace coming from the common node on R8,R9,R10.

2. Connect TRansformer to output Ports 1(gnd) 2(hot). use 1:1 coloured transformer (Newark Inone OEP A262A2E ???)

3. switch DPDT between transformer output and {OUTPUT PORT 1(gnd) + Node R8,R9,R10 (hot) }

Transfomer (coloured) output = Vintage
Jfet992 out = Modern


Comments? Does that transformer sound like a good choice?

-ChuckD

 

[ChuckD]

More info on that transformer here:

A262A2E

http://www.oep.co.uk/audio_transformers_high_performance/audio_transformers_high_performance.html

Using the same on my 1176 rev G ording from Newark inone for 19.44 each.

 

[FredForssell]

Hey Tom (and everyone else)...

Just back from vacation, ahhhh!

Did you ever get that LF response problems fixed?

Let me know where your at with it and maybe I can help.

Cheers

 

[tommytones]

Chuck,i don't have the info in front of me right now so let me get back to you on that.

I haven't had time to check out the low freq thing yet but will do so in the next couple of days. It's kinda busy in the shop right now so I don't have access to the test set(s).

 

[Greg]

That roll off is concerning...

I wish I could help out some, but I haven't even started stuffing the two boards I have, and I've got API on the brain right now... thanks to Fabio and his killer boards.

 

[louder]

alo
something to note:
r34 in the schm.,it`s1meg,but in the parts list,it`s10k.
r35 in the schm.,35k,but in the parts list,it`s 1meg.
best regards
pedro

 

[tommytones]

Hey I didn't notice that ! That may be it. I wish I had my boards to check it out...maybe I'll take a ride out to the shop...hhhmmmm......

 

[ChuckD]

Man those thru hole resistors are hard to pull out and replace!
good catch though I fixed mine.

Tommy, still waiting on your response to my output switch idea. I don't want to cut until smeone confirms my thought on it. (see above)

Also can you go over how the stereo function is hooked up? I don't need both swicthes right? And what is the exact hookup? Just to be sure.


Just waiting on Newark to send me 4 optos and I can finsh my stereo unit!

-Chuck

 

[Infernal_Death]

I can't really contribute to this thread yet as i don't have any transformers. But i just finished the boards so far with all the parts i got (some parts are still missing) and here are two pics of one discrete board and one ic board ( will make a discrete stereo version and a ic stereo version).

The discrete board:

And the ic board:

Flo

 

[ChuckD]

Tommy, still waiting on your response to my output switch idea. I don't want to cut until smeone confirms my thought on it. (see above)

Also can you go over how the stereo function is hooked up? I don't need both swicthes right? And what is the exact hookup? Just to be sure.


Does anyone know what the GAin redution/Compression (-dbs) numbers are for each of the 10 LEDS?? Need to finish this frontpanel.

-ChuckD

 

[ChuckD]

...

 

[tommytones]

Okay Chuck ! Very simple....

The input to the 5534 circuit is at C35 (on the top). It continues to the discrete circuit (on the bottom) Lift this one side of C35 and place switch.

The output ties together at C39 (- leg / bottom). Lift this side of the cap and place switch. Bingo, you have the option between the 2 circuits.


I still haven't had access to the bench and the test set(s) but I'm confident that the flipped resistors might well be the problem. I should be able to get at it in the next couple of days. I'm anxious to get it done with so I can pass some audio through it and hear the thing work (or not hear :green: )

 

[ChuckD]

Thanks Tommy,

from looking at it I think I should also cut the trace just before the C35 Input lead. Thus preventing the signal from going to both circuits when using the 5534 output mode.


1. Switch between C35 hole (on the input side) and Input of the C35 (removed from hole).

2. Cut trace (top layer) between the C35 hole and input trace.

3. Remove - lead of C39 and switch between that and the output (pin 2)


-ChuckD

 

[tommytones]

There's no need to cut traces Chuck. If you lift the input leg of C35, then no signal will make it's way to the discrete side once the switch is thrown. Signal will either go to discrete or c35.

Yes, lift the output leg (-) of C39. You might need to cut that trace if you want to disconnect the unused circuit's output so that you fully isolate each circuit when not in use. Otherwise, the input will be bypassed but the outputs will still sum. Might be okay but might add noise.

 

[ChuckD]

Tommy,

I thought that the holes on the board were 'through-holes"? Then the Jfett 992 output stage would always be seeing the input signal even when switched to the "55xx" output stage.
That is why I thought I should cut that trace before hole C35.


More Important! Do you know the labeling for the reduction 10-LEDs ???? I want to send my Panel to FPE and need to have this info. THe one Frank did had -20 downto 0 dbs but wasn't linear or very clear. What should I do???

Also I am still confused on how the stereo switch gets hooked up.

Thanks. I hope you don't mind all the questions, I just want to finish this one up and report back some results.


-ChuckD

 

[tommytones]

Yes they are but if you switch between pin 2 (feeding the discrete) and the lifted leg of c35 (feeding the 5534) you'll be isolated. Your way will work as well but I just prefer not cutting traces unless really needed (you can't undo it down the road).

Without having tested the scale of the meter yet, I don't have an answer for you. I think that Frank's thing is pretty close though. It's really more of an approximation anyhow. I doubt the meter is very accurate.

Stereo switch...

Both channels get the ic placed (U9 I think...I don't have it in front of me right now) followed by the 1K resistor. All this feeds into the bypass switch. 1 of the channels gets the link switch installed. Behind this link switch are 2 pads which say "from wiper a & b". You run wires from the 2nd card link switch (it's just pads because there's no switch installed) wipers to these pads. Just be sure to connect a to a and b to b...don't flip them. With the card facing you (pots and switches towards you), A is the right side, B is the left.

 

[tommytones]

It lives once again! Flipped those 2 resistors and bingo. Now there is only slight roll off but nothing compared to what I was getting before. 4db down @32hz. This is transformerless though. I did notice a slight improvement with the iron in the chain. The best I could do for unity gain is 4db over. I'm sure if I played with it I could get it down but I can live with it as is. I ran it with +/-20.5V (the upper limit of 5534) and everything works well. I did notice that the 2604's in the sidechain get pretty warm. Nothing critical but as this is a new one for us, just thought I'd mention it in case this is abnormal behaviour (which it probably isn't).

I passed some music through it and I must say that my 1st impression is quite positive. And coming from me, Mr. transformer and anti-opto man (never been a big fan of optos other than la2/la3), that's a compliment. I don't miss the low freq roll-off at all. My setup shows an interesting bump in presence in the mid-range...seems a little more in your face. Not sure if this will happen for you but a big reason why my 1st impression is so positive. I like when a box does this :green:

I futzed around with the meter as well so I'll post a scale when I have a moment. It only seems usable for a 10db scale if you want it to be sensitive at low reduction (2-4db).

That's it for now.

 

[louder]

alo
now,what?
r34-?
r35-?
glad you solved the problem.
best regards
pedro

 

[tommytones]

Yes pedro, the parts list was the problem. It should fixed and posted by now.

Butta, thanks. I'll probably try it out although, right now I don't miss it.