Line Amp Capable of +35dbu

Try it in bridge mode first to see if the higher voltage will give you the results you are aiming for.
Bridging it means I only have one signal, so I sent it to the left channel. After that I duplicated the output when it got back into the interface, that way I can assess the final level.

Bridging it did allow me to go about 4 gain clicks higher before it distorted. That's better, but I think I need more. Although at some point I'm going to need to be able to tell when the distortion is from the amp vs the transformer. I don't know what max dbm I'm pushing into the 111c right now.

So this amp rated at 120watts @8 ohms bridged gets me closer to my goal. What amp wattage rating do you think I need? 200per channel? I either need a 2 channel amp or a 4 channel that I can bridge..
 
Can you hear or measure any third harmonic distortion when playing a 20 Hz sine wave at full volume? The transformer should distort to some extent now at low frequencies.
In order for me to really hear any change I have to drive the amp well past the redline, and at that point I'm pretty sure what im hearing is the amp. Hard to say.

There is always some harmonics in the signal whether I drive the amp at normal levels or smash it, it's just the level of those harmonics that change with more volume. I guess those would have to be from the transformer? I would have assumed the amp would be a cleaner signal. I don't know. I need to just run the amp signal without the transformer and see what happens.

Oh and also, something is now wrong with the left channel of the amp. It just buzzes and doesn't pass audio. That's strange because I did the bridge test this afternoon and it was fine.
 

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@MarcelvdG If I got an amp that was say 300w per channel at 8 ohms (max), would turning the input sensitivity down suffice to ensure that too much voltage wasnt sent to the transformer? Or does it not work like that?

I think the first things you are likely to damage are the ceramic composition resistor and the primary winding of the transformer. Both should be pretty good at handling temporary overload, so as long as you don't play continuous very-low-frequency sine waves at maximum volume, they may survive.

Why don't you go for a cheaper transformer, like jaddie suggested a long time ago? Blowing up a transformer is then also less of a waste.
 
If I was looking for heavy coloration I certainly would do that. At this point I'm just trying to complete the experiment, which is to get enough power into these transformers to hear what it sounds like when it's on the brink of distortion, which in this case would only be apparent below 40hz or so. This project is more about the process than the result. I have learned a ton so far and am having fun.
 
I might have to call it. I just got a used behringer amp that puts out 150w per channel at 8ohms and the signal craps out still before the SSL. In this case though I didn't do enough research on the amp and it has a DSP onboard, and the limiter defaults to 0db threshold. I don't think the DSP is letting the signal go past whatever it has set as 0dbfs. I can't imagine this amp isnt powerful enough to put the 111c into distortion, especially with Marcels schematic applied.

If I run a balanced signal into the 111c with it wired the way it is, will have any problems? I suppose it's just going to convert it from regular balanced to transformer balanced?
 
Nvm all good. Kept the transformer at same schematic but removed the resistors on all the wires.

Thanks everyone for all your time and knowledge to help me with this experiment. I don't think I was able to get the level I was after into the transformer, but I learned a lot and enjoyed the process. Time to get back to making music.
 

jaddie

Member
2011-04-01 12:06 am
Tell you what I'll do. If you send me your 111C transformers, I will send you a pair of transformers that you can get into the brink of distortion below 40Hz, or whatever frequency you like, as much as you like. I'll pay shipping both ways. You can keep all the gear and parts you got to do this, they'll all be useful. I can even show you a way to include a knob that progressively adds distortion when turned clockwise, takes it away when turned counter-clockwise.
 
Tell you what I'll do. If you send me your 111C transformers, I will send you a pair of transformers that you can get into the brink of distortion below 40Hz, or whatever frequency you like, as much as you like. I'll pay shipping both ways. You can keep all the gear and parts you got to do this, they'll all be useful. I can even show you a way to include a knob that progressively adds distortion when turned clockwise, takes it away when turned counter-clockwise.
Thanks for the offer but the whole point was to get the 111Cs there, not another transformer.