Transistors Low Noise

Does anyone know of a replacement transistor for 2SC2545? I am looking at 2N5961. Is there something better out there made for low noise audio. I prefer to pay less than $1.

Selecting an appropriate transistor depends on many things: The application, the source and load impedance, the desired current, amplifier gain level, input signal level, etc...

Can you offer some of the above details?

hoodun said:

Does anyone know of a replacement transistor for 2SC2545? I am looking at 2N5961. Is there something better out there made for low noise audio. I prefer to pay less than $1.

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Do you need specifically NPN? And yes, details on application would help.
I don't see the 2N5961 as particularly remarkable.
People have obtained excellent results with power transistors on low-Z applications because Rbb' is very low.

What is wrong with 2SC2545??

Over the range 30 Ohm to 100K Ohm you can find an operating point where the hiss is insignificantly higher than your source resistance.

And I see Futurlec sells them for 30 cents.

Futurlec is out of them. So they are pretty much absolete unsless you want to pay up to $15 a transistor on ebay.

I would be using them for mic pres. Langevin am-16 replacement and PM1000 replacements. MPSA-18 looks like it is the best I can do at the moment.

hoodun said:

Futurlec is out of them. So they are pretty much absolete unsless you want to pay up to $15 a transistor on ebay.

I would be using them for mic pres. Langevin am-16 replacement and PM1000 replacements. MPSA-18 looks like it is the best I can do at the moment.

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I don't understand. You ask for a transistor that's specifically designed for low noise at high collector current (>1mA) with low impedance sources, and these two products are transformer-based, thus providing a rather high source impedance (about 10k). This is typically the domain of more traditional LN transistors, designed to operate at about 50-100uA collector current, of which there are plenty e.g. BC560.

abbey road d enfer said:

hoodun said:

Futurlec is out of them. So they are pretty much absolete unsless you want to pay up to $15 a transistor on ebay.

I would be using them for mic pres. Langevin am-16 replacement and PM1000 replacements. MPSA-18 looks like it is the best I can do at the moment.

Click to expand...

I don't understand. You ask for a transistor that's specifically designed for low noise at high collector current (>1mA) with low impedance sources, and these two products are transformer-based, thus providing a rather high source impedance (about 10k). This is typically the domain of more traditional LN transistors, designed to operate at about 50-100uA collector current, of which there are plenty e.g. BC560.

Click to expand...

You seem to understand much better than I do. So in transformer based pre amps there is no benefit for low noise transistors? I've read the contrary though Im just going off of diy forums. What your saying makes more sense to me, since it explains why they used the transistors the chose in the first place.

> more traditional LN transistors... there are plenty e.g. BC560

Or 2N5089.

(Probably same die sold under different number-schemes.)

Either will be "perfect" in any plan which uses a transformer to come up from the 150 Ohms of a microphone.

hoodun said:

abbey road d enfer said:

hoodun said:

Futurlec is out of them. So they are pretty much absolete unsless you want to pay up to $15 a transistor on ebay.

I would be using them for mic pres. Langevin am-16 replacement and PM1000 replacements. MPSA-18 looks like it is the best I can do at the moment.

Click to expand...

I don't understand. You ask for a transistor that's specifically designed for low noise at high collector current (>1mA) with low impedance sources, and these two products are transformer-based, thus providing a rather high source impedance (about 10k). This is typically the domain of more traditional LN transistors, designed to operate at about 50-100uA collector current, of which there are plenty e.g. BC560.

Click to expand...

You seem to understand much better than I do. So in transformer based pre amps there is no benefit for low noise transistors?

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That's not what I wrote. There is a nuance. There are many LN transistors that are intended for low-Ic/medium source Z applications. That was what transistors were capable of at the beginning. After, when processes improved, there were some transistors that were optimized for lower Z at the cost of increasing the operating current. 2SC2545 is precisely of that type. There was time where manufacturers found interest in these applications and introduced remarkable designs such as 2SB737 (lowest Rbb' in the universe for a single transistor) or LM394 (2x50 paired transistors monolithic)

I've read the contrary though Im just going off of diy forums.

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Don't believe everything you read on forums!

Neither here nor there, but be a little cautious about Futurlec:  I purchased several different JFETs from them which proved to be counterfeit when measured.

hoodun said:

So in transformer based pre amps there is no benefit for low noise transistors?

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In general no. The transformer provides the initial low-noise amplification, after that it doesn't matter much.
But if you care, the BC337/327 is always my go-to transistor. It has Rbb around 30ohms which is remarkably quiet for a cheap, general purpose device.

merlin said:

hoodun said:

So in transformer based pre amps there is no benefit for low noise transistors?

Click to expand...

In general no. The transformer provides the initial low-noise amplification, after that it doesn't matter much.
But if you care, the BC337/327 is always my go-to transistor. It has Rbb around 30ohms which is remarkably quiet for a cheap, general purpose device.

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Indeed. They are surprisingly low-noise, considering they are not advertised for it. There are no noise specs for them. How did you get the info about Rbb'? Did you compute it out of measurements?

BC550/560 and BC337/327 are my "darlings" as well.

CHEAP&CHEERFUL

abbey road d enfer said:

merlin said:

hoodun said:

So in transformer based pre amps there is no benefit for low noise transistors?

Click to expand...

In general no. The transformer provides the initial low-noise amplification, after that it doesn't matter much.
But if you care, the BC337/327 is always my go-to transistor. It has Rbb around 30ohms which is remarkably quiet for a cheap, general purpose device.

Click to expand...

Indeed. They are surprisingly low-noise, considering they are not advertised for it. There are no noise specs for them. How did you get the info about Rbb'? Did you compute it out of measurements?

Click to expand...

Transistors designed for switching significant current will have low Rbb to manage internal resistive losses. Historically transistor processes were not very clean so low Rbb devices were not always free of other noise contamination. Back in the day some designers would secretly screen medium power transistors to use in low noise applications.  Since then the semiconductor processes have gotten a lot cleaner so I expect any number of medium power devices may be low noise. Another aspect of dedicated low noise devices is high beta so medium power devices may be good but still not optimal for low noise design.

JR