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DIY: Transistor hFE


IvIark

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I was talking to a mate the other day and he mentioned a site that has info on various transistors used with effects including the hFE and recommendations for gain levels for transistors in a variety of effects.

 

Has anyone come across anything like this? It would be a great source of info

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As far as gain ranges for transistors I have never seen a website that has data like that combined but some more in depth articles about fuzzes will suggest an hfe range for transistors in that particular pedal. The problem with that sort of stuff is this - in the event that you have a build that suggests a certain gain range youre probably talking about a pedal using NOS parts or some sort of fancy component that isn't exactly a 2n5088 you can get from mouser. Generally you're talking germanium parts since silicon is more readily available and consistent. That all means youll need to find and audition anywhere between 10 and 100 transistors to get a pair or trio in the gain range you want. That is very very expensive. If you're building something that needs this type of part, I would suggest just getting a pair of parts that are already matched from small bear. It will be $15 or so but thats better than spending $100s just to get enough parts to match one or two perfect sets. Look at it this way - I doubt they were applying as much scrutiny to hfe values when the original pedals were made so I wouldn't obsess over it now.

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Thanks for the info guys. I'm not going to be looking for the holy grail of transistors or anything like that, it's really just for my interest. I like to measure them so that I can match a pair closely or so that I can select a lower and higher gain pair and use them in the right order, but someone mentioned this to me and I thought it would be interesting.

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I was talking to a mate the other day and he mentioned a site that has info on various transistors used with effects including the hFE and recommendations for gain levels for transistors in a variety of effects.


Has anyone come across anything like this? It would be a great source of info

 

If you find this site please let us know!!!!!!:love:

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It only matters when you are cloning something and only in some kinds of circuits like oscillators, filters and amplifiers otherwise you usually don't design a circuit for a specific hFE value. hFE varies per part sometimes it varies widely for the same model. Usually they use a code or a letter prefix that tells you what the range is.

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You may not design a circuit for a specific gain value but that doesn't mean a circuit won't sound better if you use a lower gain transistor instead of a higher gain transistor.

 

For instance I found using lower gain transistors in a fuzzface ended up sounding much better to me than with high gain.

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It only matters when you are cloning something and only in some kinds of circuits like oscillators, filters and amplifiers otherwise you usually don't design a circuit for a specific hFE value. hFE varies per part sometimes it varies widely for the same model. Usually they use a code or a letter prefix that tells you what the range is.

 

 

This is true. We recently tested a dozen brand new silicon NPN's and found the hFE varied between 164 and 241 across the lot. The transistors with the higher measured hFE didn't always have more gain in our circuit. The hFE value you measure is only valid at the collector/emitter voltage and base current levels used in the tester. Transistor manufacturers only publish hFE numbers as a guide, and they usually tell you the VCE they used to measure it. Some manufacturers publish a min/max and average for hFE, others only a min/max range, and others only a maximum.

 

For our transistors, the manufacturers data sheet only specified a maximum hFE of 300, so all of the transistors we measured were within that range.

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well from what I know if you depend of measuring hFE with your multimeter it is a useless measurement because it varies even with voltage so if you put that transistor in a high voltage circuit it may actually be very different than at the 100ma or whatever your multimeter measures at. From what I have been told you never design a circuit with a specific hFE it is bad circuit design.

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It doesn't matter if the value would be different when actually in use in the pedal or not. If an effect is tested with a variety of transistors and someone believes that the transistor that worked best for him had a hFE of 350, then that measurement was provided by a multimeter as well and not an actual measurement in circuit.

 

My interest in this is for ballpark information, not a "definitive best value" which is subjective anyway

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All I meant is that the hFE measurement needs to be made relative to the power source.

 

Obviously the higher the hFE the more it can amplify and if it is driving a clipping circuit the more it will change the signal. And if it is driving some other device and it pushes it out of the linear range it will behave non-linearly and change the harmonics of the sound.

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Look at it this way - I doubt they were applying as much scrutiny to hfe values when the original pedals were made so I wouldn't obsess over it now.

 

a good way to look at it.

 

:thu:

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well from what I know if you depend of measuring hFE with your multimeter it is a useless measurement because it varies even with voltage so if you put that transistor in a high voltage circuit it may actually be very different than at the 100ma or whatever your multimeter measures at. From what I have been told you never design a circuit with a specific hFE it is bad circuit design.

 

 

Yep.

 

hFE is defined as the ratio of the change in collector current for a corresponding change in base current, with the emitter/collector voltage held constant. Strictly speaking, it only applies to common emitter configurations. This will almost certainly vary with different emitter/collector voltages (VCE).

 

On the other hand, it usually varies by the same amount for a given transistor type. So, if you selected two transistors with the same part number, and both had the same (or very nearly the same) hFE on the tester, then they'd probably have very nearly the same hFE in your circuit, even if it wasn't exactly the same hFE measured on the tester.

 

In other words, the tester is still useful for matching transistors if you're trying to build a balanced push-pull or differential amp. It's also useful for verifying whether a transistor is completely hosed.

 

hFE is like transconductance in a tube. You design around a ballpark range of values, rather than a specific value.

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All I meant is that the hFE measurement needs to be made relative to the power source.

 

 

But it doesn't matter what the hFE measurement is in the circuit. Think about it. If you have a scheme that you're making and someone has made the exact same scheme and measured the value of the best sounding transistor to be 350. The gain was identified and measured with a multimeter, so whether it has more or less gain when you've actually put it on the board you don't even need to know.

 

Like I said, I'm not looking for exact science.

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I've been trying to tell you that you don't design a circuit with a specific hFE because it varies from transistor to transistor even in the same batch. The measurement might even be different from multimeter to multimeter. You might read 350 on yours and your friend might read 270. All that matters is if a higher gain transistor sounds better in your circuit, you pick the one with the highest gain and use it. You can't rely on the hFE value but if a higher gain transistor sounds better you can rely on that whatever your multimeter reads as the highest in your batch will be close enough.

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Who said anything about designing a circuit? This thread is about measuring gain and nothing more. You keep coming up with hypothetical stumbling blocks but really, I know but don't care that transistors and all components for that matter can vary in the same batch. I know that gain values measured with a DMM may not match the actual gain levels when in circuit, and I even accept that multimeters have a tolerance which have to be taken into consideration (although I think a difference of 25% may be unlikely assuming reasonable quality instruments).

 

But I can't say it any clearer, I'm not after definitive answer, just opinions on what worked for some people. If you can't see any value in measuring hFE then that's fine, more power to you for your methods. But I do see value in it, and after designing circuits for Siemens for 14 years I feel qualified enough to form my own opinion about that.

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If you designed circuits for 14 years you should have a general idea what to expect here so stop lying and being a big wank stain.

 

:lol:

 

I designed control circuits not audio circuits.

Big wank stain! Classic! :love:

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if you designed circuits you must've at least done some courses in analog electronics so you should have some clue, but obviously it depends on the circuit right so why not be more specific like 'hey gice, I am making a clone of this pedal, what do you think about changing the gain of this transistor what do you think, does it sound better?' instead of just asking dumb ass newb questions what do you think dumbass if you change {censored} it is going to effect something in the circuit depending on how it was designed right? You can't be that {censored}ing clueless mr. I designed circuits for 14 {censored}ing years.

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