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Yup. My point in providing the drawing is to help those people looking to jump into this hobby but are a little new or unsure how to construct devices such as this. I've seen a few people post on the site who expressed a desire to delve into the more technical aspects of the hobby but lacked the technical training or know-how when it comes to these sorts of things. Hopefully this will help one (or more than one) person along the trail and encourage them to "peel back the curtain" so to speak. We live in a physical world in which systems and devices work for very specific reasons; when we can get to the root of WHY and HOW they work, that's when the real fun begins.
 

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How would you propose using transformers to attenuate the signal? Do you mean signal-isolation transformers? If so, those are 1:1 devices and the voltage on the secondary side will be the same as on the input side. Which kind of transformer were you proposing?
 

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Related question (i think). I didn't really follow the process in the original posts, but i'm guessing its very similar to the approach I'm attempting.

I'm using a voltage divider to feed the line in on my laptop and then looking at the signal in Audacity (which displays sort of like a scope).

I'm pretty sure my voltage divider is ok (i have 10:1 and 33:1 with a switch). The output checks out when tested with a battery and voltmeter.

I get a trace on the pc ok, but seem to get clipping from my HU (i'm checking speaker outs not pre-puts) earlier than i'd expect. The trace is showing clipping at 18 out of 30 volume. I have turned down the levels on the input (in software) but still shows a clip.

I have not been able to check the signal voltage output from the voltage divider as my multimeter doesn't have a suitable range for measuring an alternating signal at this level.

Any ideas on how to improve?

Thanks
Stuart
 

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How would you propose using transformers to attenuate the signal? Do you mean signal-isolation transformers? If so, those are 1:1 devices and the voltage on the secondary side will be the same as on the input side. Which kind of transformer were you proposing?
That's like assuming a transformer in any application is 1:1... Just because it isolates does not mean it's 1:1.

There's transformers that will take speaker level down to mic level. They are called DI boxes. Yes, some are dividers to get it down to line level then the transformer takes it to mic level but some go straight into the transformer at speaker level and poop out mic level. Speaker level out of an Ameg SVT no less ;)

So speaker level out of a car headunit to line level, isolated is no big deal...

WELCOME TO JENSEN TRANSFORMERS, INC.

go crazy.
 

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Okay...just wanted to get clarifcation on which transformers you had in mind. Yes, a Line-to-mic level transformer will offer 20dB of attenuation on average, which should be equivalent to the "pad" circuit I drew above. And many of the line-level transformer primaries measure 20k ohms, there should be only a fractional amount of power flowing through the input side. I handn't considered using a matching transformer, but it seems it would work well.

I'm familiar with the Jensen transformer company. Thanks for the link.

Do you, by chance, know this company, who also make high-quality transformers--(all manner of them, in fact)?
 

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20B is a LOT of pad for car audio. Especially when a lot of amps can take the input levels many if not most stock head units put out.

Never used the company you linked, Usually go straight for Jensen, also used a bunch of Sescom. I'll do more looking at them. So a return thanks for the link :D
 

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20B is a LOT of pad for car audio. Especially when a lot of amps can take the input levels many if not most stock head units put out.
Remember, the 20dB pad is used only when setting the amplifier gains and is not wired into the system during normal use. We're merely dropping the speaker-level voltage coming off the amplifier to a level that doesn't overdrive the Mini Speaker's input stage, which is quite sensitive.
 

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No point in using an amplified speaker to "set gains" with, and for that matter an O-scope. What are you "setting gains to"? A random source volume setting using a worst case signal that won't ever be nowhere near your listening medium. You set your amp to clean output with that solid tone but then you play a track which only has 1 sample hitting 0dB. Great, now the rest of the track is not loud enough, and all the sub 0dB portions aren't "set to" anything.

I don't get it.

Find a range at the source that gives you a volume range that you are comfortable with, leave some gain on top of that for low level dynamic recordings, and turn the gain up by ear till just below you start to hear it strain. It's nothing more than a rough approximation since the primary device used to evaluate is an imprecise one.

Setting gains that precisely is like a tailor taking your measurements with a precision ruler.

Just look at a home setup which doesn't give you the option to be silly like that. Do we ever thinking about "oh is this volume setting where my preamp or amp starts to hit .123% THD?". No, you just set it to where it sounds clean for the material and accept the "rough approximation" used to get that outcome. Never heard of even the most elitist of audiophiles questioning even that. Magic crystals on RCA cables and Bob's barricades wire elevators get WAY more attention even.
 

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Remember, the 20dB pad is used only when setting the amplifier gains and is not wired into the system during normal use. We're merely dropping the speaker-level voltage coming off the amplifier to a level that doesn't overdrive the Mini Speaker's input stage, which is quite sensitive.
Ahhhh gotcha... brain was somewhere else.

There's also a trick with piezoelectric devices that works quite well.
 

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No point in using an amplified speaker to "set gains" with, and for that matter an O-scope. What are you "setting gains to"? A random source volume setting using a worst case signal that won't ever be nowhere near your listening medium. You set your amp to clean output with that solid tone but then you play a track which only has 1 sample hitting 0dB. Great, now the rest of the track is not loud enough, and all the sub 0dB portions aren't "set to" anything.

I don't get it.

Find a range at the source that gives you a volume range that you are comfortable with, leave some gain on top of that for low level dynamic recordings, and turn the gain up by ear till just below you start to hear it strain. It's nothing more than a rough approximation since the primary device used to evaluate is an imprecise one.

Setting gains that precisely is like a tailor taking your measurements with a precision ruler.

Just look at a home setup which doesn't give you the option to be silly like that. Do we ever thinking about "oh is this volume setting where my preamp or amp starts to hit .123% THD?". No, you just set it to where it sounds clean for the material and accept the "rough approximation" used to get that outcome. Never heard of even the most elitist of audiophiles questioning even that. Magic crystals on RCA cables and Bob's barricades wire elevators get WAY more attention even.

In theory I'll agree with you. As you know in home audio we have two pre-amplifier/amplifier system architectures. We either have an integrated system, with the home theater receiver being the most well-known example, where the pre-amplifier and the amplifier(s) are in a common chassis. Or, we have separate components with a stand-alone pre-amplifier and a separate amplifier.

In the case of the integrated system, the signal level between the pre-amplifier stage and the amplifier stage is handled by the design engineer and none of the signal levels between the stages can be adjusted by the user. They’re fixed. In the case of the separate pre-amplifier and amplifier, the situation is different, where the signal level on the pre-amplifier’s outputs varies based on the volume control’s level setting. Most all separate amplifiers have a set input sensitivity, and that level is almost always set to a 2.0 V RMS level on the unbalanced inputs, meaning the amplifier will go to full power just below clipping when it receives a signal of that level. There are exceptions to this input sensitivity number, but not a great deal. Many pre-amplifers have a signal output level of between 5.0 and 9.0 V RMS on their unbalanced pre-amplifier outputs. Thus, we have a “gain overlap” potential of 3:1 on average, and this works well where the user is completely capable of getting the amplifier to go to full power, while providing them the ability to find a comfortable listening level.

In a car audio system, as you know, we have a different situation with the amplifier because they have a variable input sensitivity adjustment. Why? Because unlike home audio, where the pre-amplifiers have a fairly standard output voltage that’s more than capable of bringing the amplifier to full power, the power amplifiers are designed with the knowledge that pre-amplifier components have a wider range of output voltage levels, and the amplifier needs to be designed to be adaptable to these levels. If that weren’t true, the amplifiers would be designed with a fixed input sensitivity. There was a time when car audio looked very much like home audio “separates” systems. For those of you who were into car audio back in the 80s, you may remember when Alpine and Kenwood made their amplifiers with proprietary DIN signal jacks designed to work exclusively with their tape decks. Those amplifiers had fixed input sensitivity settings because the manufacturers knew the signal levels coming from their pre-amplifiers.

That said, I fully believe in the approach of needing to match the amplifier’s input sensitivity to the upstream pre-amplifier components. In simple systems with just a CD player and an amplifier, yes, I agree that setting the amp’s gain setting can be quite simple and can be done by ear with reasonable accuracy. The only downside is the system’s signal-to-noise level isn’t optimized. But when the system includes one (or more) pre-amplifier components in the signal chain, optimizing the system’s signal-to-noise performance gets exponentially more complex and therefore requires a more technical and science-based approach.
 

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I know this is old, but I drew this for those that want to make the voltage divider for the radioshack amp. This if for checking the speaker outputs on your amp with the radioshack amp.




I have mine in a small project box. The car amp input side has tinned speaker lead coming out, and the other side has an rca pigtail. You can then purchase a female rca to 1/8 mono phono plug to plug into the radioshack amp.
 

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Discussion Starter #34
Thanks jbholsters! I still use mine!
 

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This is a great write-up...but....what the hell is a mini-amp. Seems to just start talking about this mystical mini-amp without any explanation of what it is. What is this device?
 

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You know...first thanks for the help...and second....you don't have to be such an elitist prick about it. I know how to google. I come to forums to have an interactive discussion...not to Google. If you don't have the strength, energy, or the ability to intelligently answer a question yourself. Then simply don't answer it. It's a better choice instead of being an elite troll. I am sure everything that everyone here is talking about is somewhere on the internet...and I could 'cop' these forums all day slagging down folks talking about stuff that has been asked somewhere in history. But you know...that is the magic of a forum...a discussion. Or is the forum about...DIY and don't ask stupid questions?
 

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You know...first thanks for the help...and second....you don't have to be such an elitist prick about it. I know how to google. I come to forums to have an interactive discussion...not to Google. If you don't have the strength, energy, or the ability to intelligently answer a question yourself. Then simply don't answer it. It's a better choice instead of being an elite troll. I am sure everything that everyone here is talking about is somewhere on the internet...and I could 'cop' these forums all day slagging down folks talking about stuff that has been asked somewhere in history. But you know...that is the magic of a forum...a discussion.
if I'm elitist for doing what you were too lazy to do, so be it. Asking what a mystical miniamp is when it was brought up, what, 7 months ago, is hardly a discussion item.

part of the reason so many people leave this forum is so many new people are afraid to search for an answer first. the same questions keep popping up over and over and over again. If you can't find an answer, then ask. That would a new discussion and thus worth having.

So if you don't have the strength, energy, or the ability to intelligently search for an answer to your question first, why waste bandwidth and other's time?
 

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if I'm elitist for doing what you were too lazy to do, so be it. Asking what a mystical miniamp is when it was brought up, what, 7 months ago, is hardly a discussion item.

part of the reason so many people leave this forum is so many new people are afraid to search for an answer first. the same questions keep popping up over and over and over again. If you can't find an answer, then ask. That would a new discussion and thus worth having.

So if you don't have the strength, energy, or the ability to intelligently search for an answer to your question first, why waste bandwidth and other's time?
You see....you just don't listen. Your response is a testament to the fact that you are only here to cause trouble. Congrats...I hope it was worth making a point. Hopefully most aren't like you. Just PLEASE refrain from commenting on any questions I ask. I REALLY do not want your help because it comes with your trolling!! Block me, put me on your do not contact list...and avoid my questions.

Don't worry, I will try not to mess up your little home here at DIYMA with all my really lame questions. Sheesh...what an a-hole.
 
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