Studer 169 EQ in API 500 format

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karloff70

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Hi Gents......starting a pair of these and looking to go 5534 input with the transformer and put a DOA for the output. As the output is boosted and the input is pulled I am thinking that might make a good cost balance to tone benefit.

That means use the 'transformer input' parts layout and just leave the output DIP-8 socket and two caps out and have the DOA sockets/amp there instead, right? Or do I have to put any extra connects anywhere?
 

timtom

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Did you guys mounted an LED to the switch button. I haven't finished mine and i'm not an expert here, but with a friend of mine that is quite knowledge I was told that if I wanna add an LED I need to put a 4U switch and not a 3U as the PCB was designed. If the noise come from else where, let's see if I have the same once I'm done :D
I didn't mount LED's.
 

OneRoomStudios

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Hi Gents......starting a pair of these and looking to go 5534 input with the transformer and put a DOA for the output. As the output is boosted and the input is pulled I am thinking that might make a good cost balance to tone benefit.

That means use the 'transformer input' parts layout and just leave the output DIP-8 socket and two caps out and have the DOA sockets/amp there instead, right? Or do I have to put any extra connects anywhere?

The DOAs aren't on the input/output. They replace U2 and U3 - U2/DOA1 is for the hi/lo shelves and U3/DOA2 is for the the mid band. The input and outputs are U1 and U4. When using a transformer on the input, U1 is reconfigured from an electronically balanced input to an unbalanced buffer. U4 just inverts one leg of the balanced output. There's no real reason to replace U1 or U4 with a DOA since they're not doing any gain, but if you really wanted to, you could put something like a Sparkos SS3601 in place of U1. U4 is best left as an IC since it only affects one leg of the output.
 

karloff70

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The DOAs aren't on the input/output. They replace U2 and U3 - U2/DOA1 is for the hi/lo shelves and U3/DOA2 is for the the mid band. The input and outputs are U1 and U4. When using a transformer on the input, U1 is reconfigured from an electronically balanced input to an unbalanced buffer. U4 just inverts one leg of the balanced output. There's no real reason to replace U1 or U4 with a DOA since they're not doing any gain, but if you really wanted to, you could put something like a Sparkos SS3601 in place of U1. U4 is best left as an IC since it only affects one leg of the output.
Oh wow, so I completely misunderstood what audiox said earlier in the thread about in and out amps then. Looks like then I will be instead considering whether I need a DOA in the mids, where I likely am pulling stuff out, not boosting, mostly. The shelves are getting a DOA for sure.

Thank you for putting me right and explaining it!!
 

karloff70

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Numpty question: What type of submini switch do I use to make 3 frequency choices for the bass and hi shelves?
 

Ricardus

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Numpty question: What type of submini switch do I use to make 3 frequency choices for the bass and hi shelves?
One DPDT, and one SPDT, OR you can use 2 DPDT. They have to be ON-OFF-ON.

Somewhere earlier in the thread around page 12 or 13 there's a wiring diagram.

I use two DPDT just because I think it makes the job a little cleaner. I use these:

 

karloff70

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Ok, so I have them both running, without switched shelves for now. Sounds beautiful! Only, unfortunately one of them seems to have an issue I can't diagnose. It works, but when engaged it loses about 7 and a bit dB in level. In bypass no loss of signal. All eq functions work. Looks like the perfect one, as far as I can tell. Any ideas what dumbness I am dumbing here?
 

OneRoomStudios

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Ok, so I have them both running, without switched shelves for now. Sounds beautiful! Only, unfortunately one of them seems to have an issue I can't diagnose. It works, but when engaged it loses about 7 and a bit dB in level. In bypass no loss of signal. All eq functions work. Looks like the perfect one, as far as I can tell. Any ideas what dumbness I am dumbing here?
Double-check your resistor values. There's probably a wrong value in there leading to an opamp not operating at unity. The quickest way to do it would be to measure the level after each stage (i.e. at C3, C9, R16, and both balanced out legs). If the level is good at C3, you know everything around U1 is operating properly...if it's good at C9, but low right before R16, you'd know there's something wrong around U3/DOA2.
 

karloff70

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Double-check your resistor values. There's probably a wrong value in there leading to an opamp not operating at unity. The quickest way to do it would be to measure the level after each stage (i.e. at C3, C9, R16, and both balanced out legs). If the level is good at C3, you know everything around U1 is operating properly...if it's good at C9, but low right before R16, you'd know there's something wrong around U3/DOA2.
Nope, just double checked, and they are identical resistor wise. Even OCD'd out when building and oriented the respective resistors the same way on both modules. No differences.
 

OneRoomStudios

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Nope, just double checked, and they are identical resistor wise. Even OCD'd out when building and oriented the respective resistors the same way on both modules. No differences.
Did you do what I suggested and measure the output after each stage to determine where the issue is? That should be step #1.
 

karloff70

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Did you do what I suggested and measure the output after each stage to determine where the issue is? That should be step #1.
I haven't got a setup where I can have the module powered whilst having access to it, nor would I really know how to, so no, sorry.
 

OneRoomStudios

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I haven't got a setup where I can have the module powered whilst having access to it, nor would I really know how to, so no, sorry.
Your best bet might be bringing it to a tech then.

If you want to try it yourself (and arm yourself to do more in the future), I'd recommend picking up something like this extender. Once you had that, all you'd need is a cheap oscilloscope or a meter that can measure AC Volts RMS.

If you decide to go that route, I can walk you through the steps to debug the circuit.
 

Ike Zimbel

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I'm very late to the party here, haven't looked at the schematic either, BUT, I have seen this in an Eq that was inadvertently fitted with audio taper pots (detented ones at that) instead of linear ones. With the pot in the centre détente position (which looked like the Eq was flat) there was actually 6-7dB of cut going on. Check your pots, they should have "B" after the value, like "10kB".
 

karloff70

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I'm very late to the party here, haven't looked at the schematic either, BUT, I have seen this in an Eq that was inadvertently fitted with audio taper pots (detented ones at that) instead of linear ones. With the pot in the centre détente position (which looked like the Eq was flat) there was actually 6-7dB of cut going on. Check your pots, they should have "B" after the value, like "10kB".
Hi Ike, thanks for your suggestion. But these are LIN A and the same on both modules, and one is perfect, so can't see how. Also, it sounds flat when engaged and the eq actually works, just everything down level only when engaged.
 

Ike Zimbel

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Hi Ike, thanks for your suggestion. But these are LIN A and the same on both modules, and one is perfect, so can't see how. Also, it sounds flat when engaged and the eq actually works, just everything down level only when engaged.
No problem. It occurs to me that another thing that I've run across is resistors that are "x" times higher value than the correct one, so for example 470K in place of a 4K7 or 470R. I had a Neze 1084 through the shop a few years ago that passed signal as expected except that it had really, really low output when the Eq was engaged. From my notes: "Fault found! R-110, 24v to Eq amp section was 120k instead of 120 ohms." That error was enough to kill the signal through the Eq section, but I have seen more subtle versions that have caused 6-10dB level drops.
 

karloff70

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No problem. It occurs to me that another thing that I've run across is resistors that are "x" times higher value than the correct one, so for example 470K in place of a 4K7 or 470R. I had a Neze 1084 through the shop a few years ago that passed signal as expected except that it had really, really low output when the Eq was engaged. From my notes: "Fault found! R-110, 24v to Eq amp section was 120k instead of 120 ohms." That error was enough to kill the signal through the Eq section, but I have seen more subtle versions that have caused 6-10dB level drops.
Could have been, but I checked very carefully (by eye, comparing stripes) and all is like the good one. Have given up now and given it to the tech. lol
 

karloff70

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Weird, so tech says I blew the transistors on the DOA because R1 wasn't in and it overheated. But on the transformer pdf it says no R1should be in, plus the other unit works perfectly, or so it seemed? Confusing. Think I'll revert to 100% 5534's on both for now. Does it need R1?
 

Ricardus

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Weird, so tech says I blew the transistors on the DOA because R1 wasn't in and it overheated. But on the transformer pdf it says no R1should be in, plus the other unit works perfectly, or so it seemed? Confusing. Think I'll revert to 100% 5534's on both for now. Does it need R1?
I've built 6 of them according to the "With Transformer" PDF, and they all work fine without R1. I've tried them all with DOAs and 5534s, so the tech is wrong. There is something else going on.

No R1 means nothing though. No jumper, no nothing. Is that what you did?
 

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