IRF 230 or IRFP 140, what's better for AlephX ?

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I think it is not quite that simple

First of all, these are different form factor devices. The P model will be normally be better at transferring heat to sink except that you have the TO3 version which will be better still at about a square inch of contact area.

Secondly, it will depend on many factors -- one of my methods for sorting devices is to first look for devices which have relatively high on-resistance as this often goes hand in hand with low gate charge, not to mention gate charge which does not vary all that much with gate voltage.

'40 devices are usually more heavily optimized for swithing than '30 devices. Switching transistors are not optimized for linearity.

100 series devices are optimized for higher currents than 200 series devices. This is not necessarily an advantage.

What I have learned (from others) is that IRF units are typically not considered to be the best audio devices around -- where only a few manufacturers seem to make them sound good (with Pass being perhaps the most well known proponent). Japanese devices receive more positive "street credibility".

The question is thus one of taste, and I suspect both devices can be cajoled into sounding very good. There have been similar device discussions in the past where even NP has participated. The short answer is that it probably does not matter that much what you choose (an answer which I personally don't like).

Next time I purchase devices, I will try Japanese.

In your case, I would expect the 230's to sound smoother and based on other posts, the 140's to possibly have more robust bass.

So we are back to square one.;) I have enough of both devices and mounting is not a problem either. The amps would be used for mids and highs, so optimal sound would be preffered in that region. So you say that 230 would be smoother?....Maybe this is a better choice then.

As to Japanese devices, the price is still an issue, especially if you buying more for matching.
Re: Re: IRFP140

Coulomb said:
Peter why do you prefer the IRFP140 over the 240 and 244 again? Do you find there are sonic differences or is it due to the differences in the specs? If so over than voltage ratings, what do you find objectionable?


I quote Nelson Pass from Zen Variations Pt.1. There is more info on mosfet choosing in that article:

"I have specified the IRFP240 MOSFET transistor in Figure 5, but a wide range of similar N channel devices will work fine. The best performance is obtained with the IRFP040 or IRFP044, but unfortunately they seem very difficult to get. An in-between alternative is the IRFP140. When substituting other MOSFETs, the Gate to Source pin operating voltage becomes an important consideration. We will want a Drain voltage of about 12 to 15 volts, and if the Vgs of the MOSFET chosen is very different from about 4 volts, you will need to adjust the value of R1. Decreasing R1 will raise the Drain voltage, and of course increasing R1 will lower the Drain voltage. "
I admit that I'm a bit new to amp building, but it was the current Zen amp articles that got me interested in this. I have been tossing about the Idea of what makes the 'ideal' MOSFET for linear AF applications. I.E. what are the important characteristics to look for in this particular animal without having to try and find graphs for any possible MOSFET. I also admit that I have yet to play with the 140's and the 240's, however I have tried the NTE replacements because I found a local source that was fairly cheap. After breadboarding an amp set up similar to the Zen lite, I tried both of these (NTE2375 = IRFP140 and NTE2376 = IRFP240) as well as a Tosiba K2847 and a C3083 BiPolar slavaged out of a power supply. What I found was that there is a subjective difference in all of these transistors with the NTE2375 sounding more clear and crisp than the 2376. The K2847 (which I have not looked at the specs on) was fairly subdued and mellow in comparison. the BiPolar as I remeber was also fairly crisp, but I couldn't duplicate this the other day. Anyway, I would be interested in hear any other subjective opinion of any other transistors and peaoples subjective experience with them.

230 compared to 240 - sweeter mids and treble but not as good in the bass.

140 compared to 240 - less overall distortion ... but similar high frequency distortion.

It's not exactly a level playing field but i'd still probably opt for the 140 if it was for full range. If it's just for mids and treble, i'd probably go for the 230's.
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