Dual ssl9k low gain???? 35-40dB on both ch.....

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bergis

Active member
Joined
May 12, 2006
Messages
34
Location
Stockholm
I´ve build a 2 channel ssl9k for a year ago and recently I start to feel that they have to low gain. they have had this low gain all the time but I´ve not cared before.

I searched lika a maniac to solve this..
I´ts only about 35-40dB of gain and it should be over 60??!!!!! (same in both channels..)

I´ve checked the oamps volt and it is 18v and 17.7v on the both channels. I´ve tried to swith my torroid to a bigger one but no succes.

the only part that i´ve switched is that I use 5534 instead of 5534A and a non reversed 2.2k dual log pot(even though the gain increase when turning it to the right??) instead of the reversed.


Wath could be wrong?
 
Normally you cannot substitute a rev log pot with a normal log pot.

Look here:
http://www.omeg.co.uk/e16data1.htm

They have the curve of a log pot and a reverse log pot (4th and 5th pic). As you can see they are quite different.

I have build 2 SSL9k mic preamps too and since i couldn't locate a pot which fits, i builded a rotary switch. Do a search here, PRR released some infos about which resistors to choose for this rotary switch.

Flo
 
sounds like a factor 10 (20dB) symptome, so you probably have a wrong resistor in circuit (i.e 390R instead of 39R...).
 
thank you for the quick answer! I suspected that it was something with the switch. i will try that.

Do you think the gain ewill differ betwen a 2.2k rev log and a switch? or is the only difference the minimum gain?
 
You ABSOLUTELY CAN use a log in place of a reverse log, just use it reversed, and it's a reverse log. there is NO performance tradeoff. In fact even a LINEAR can be used, with no actual performance tradeoff, just that setting gain becomes twitchy at one end of the control range.

I agree.. -the build has to be wrong to have 30dB low gain like that... Check the component values.

Keith
 
Using a non-reversed log instead of a reverse log just changes the "direction" of gain but should not affect maximum gain (neither would using a linear pot). A bigger power transformer doesn't help either (which honestly is not much of a surprise--or does anybody know of a micpreamp which changes the power transformer to switch gain? :grin: ).

The first thing is check is if the first gain stage or the second gain stage has too low gain. I suspect it is the second as otherwise the preamp would be pretty noisy (and I understand from your writing that the pre works fine, just got low gain). Inject a sine wave at the input and scope the input, the output of IC29 and IC30--the level should clearly increase at every stage, independent of gain.

The obvious candidates which might be wrong are R73, R109, Ra, R88, R115 and Rb.

Samuel
 
Ok, seems like i have something wrong. I always thought those pots aren't interchangable. At least i learned something new :green: Oh and maybe i should have clarified, i didn't think the low gain would come from using the other pot. I just thought the characteristics would be wrong.

Flo
 
Possible alternative:
When using a 'normal log pot' in the reversed direction you could consider using it 'upside down' for a less non-intuitive feel (a.k.a. more intuitive).

Explanation:
[A] normally you use a pot from say 7 o'clock thru 12 to 5.

Reversing it makes that from 5 o'clock thru 12 to 7. Might feel bad.

[C] So how about putting it upside down: rotate from 11 o'clock thru 6 to 1 o'clock. This is simply realized by mounting the knob on the pot-shaft 180' degrees rotated.
The from-left-to-right of [A] is preserved, at the expense of up/down-reversal. To me [C] feels better than the usual reversed direction ,
but that could differ of course for others.

Same trick can work for frequency-controls of EQs & hi/lo-filters that usually use rev-stuff as well.

Cheers,

Peter
 
Ok I ´m gonna check all resistors and the second gainstage before I spend my money on a new swith or something.

Thhank you all help so fa!r..
 
If you want to do a quick and dirty check, you could just put a correct value resister in the loop on each gain leg instead of the gain switch. just use some croc clips. This would rule out switch miswiring too.



[EDIT] just noticed that he's not using a gain switch.
 
The obvious candidates which might be wrong are R73, R109, Ra, R88, R115 and Rb.

I´ve checked theses ande they seems to be the right value..
I´m gonna check all the other to when I have time.
 
I´ve checked all components now and they seems to be fine. I dont have a scope so that can can be tricky.. Can I check this in another way like mA, V etc..?

i´m begin to feel desperate soon and just go with low gain even if I hate it! I sounds great otherwise..
 
Well if you have a volt meter you can use that as well to check gain.

Next step would be to replace the pot with shorts as this should give highest gain. Check the connections of Ra and Rb--if there is a bad solder joint the according gain stage might just sit at 0 dB.

Samuel
 
This is what I´ve done so far.. I´m quite a newbe at this so I dont now if I do something wrong when I measure..

1.Checked all components and they seems to be right.
2.Switcthed around the oamps.
3.Measure volt on all the ins and outs on the 5534 (from ground to pin?). With medium gain on the micpre.

IC24 seems to be ok, from about +-20mV in to 70mV out.
IC23 -26mV on both inputs and -24mV on output
IC30 -22mV on both inputs and -21mV on output
IC22,29 12V in on both and -2V out?

Could it be me MAT02 that is broke or will it not work without it? Is my way of measure correct or am I do wrong from ground to pin? Check the pictures and se if anything wrong...

Please help me!!!

Pictures:http://web.comhem.se/bergis/ssl9k/SSL9K.html
 
Disconnect the pots and connect the two wires going to each deck together, you should have full gain. If not, try the same thing without the pad, polarity and phantom circuit connected. If you still have low gain, yank the balancer board and try the output unbalanced. This should keep you busy for a while...
 
Now I`ve tried bypass the balancer and the phaseswith and nothing happen. But when I tried to switch from pin 3 to pin 1 on my gainpot something happened!

Whoola!! Now I have plenty of gain again(but the gain turn backwards)!!!!

Thank you for all the help!! I will probably buy me a gainswitch someday in the future...

/P.
 

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