Upgrading Transistors for Low Power Amp

PTL60

Member
2002-02-01 6:30 pm
I have a low power amp that uses BD140 (PNP) transistors. I recently replaced them with NTE185's which is the NTE equivalent to the BD140's.

Does anyone know if there are some better transistors that I can use in place of the BD140's? The NTE185's are the same,so there wasn't any improvement.

It would be interesting to swap out different transistors to see if I can get better performance from the amp. The BD140 has a TO-126 case. Thanks for any help.
 
Geoff,

Sorry I took a while to get to your question but you could try a 2SA1261. It has a slightly larger case style but should work. If space is not a premium there are a bunch of TO-220 case style devices that could work.
In what part of the circuit is the device uesd in? Maybe a schematic would help.

Jam
 
Jam

This is very 'off topic' but what the hell. I'm sorry to say that the remaining translations are on hold at the moment. I have had very little interest shown in the Hiraga articles, much to my surprise, and at present my priorities must be to find some gainful employment and to answer the many emails I receive about other designs on my website. I do have some rough, machine generated, translations of the outstanding Hiraga articles and I have sent these out to the couple of people who have contacted me about them.

Geoff
 
Ptl60:
It's not as simple as dropping a new transistor in. There are many variables and plenty of math involved. Perhaps some research through many cross reference manuals. If you have a little patience these guys will get around to it. I have seen them engineer whole projects for people. Just realize it takes time, there is no instant gratification with diy audio.
 

PTL60

Member
2002-02-01 6:30 pm
To all DIYAUDIO Members,

I have to apologize for being rude and not having enough patience for someone to answer my question. I guess I'm used to other kinds of boards where people answer more quickly. I realize now that this is a more serious message board/forum and it can take longer to answer technical questions. Man,I must have been in a nasty mood the last couple of days; so again,I'm sorry for being a jerk.

Anyway; The circuit in question is actually inside the Creek OBH-11SE Headphone Amp. I'm always curious what's inside these amps,so I took a look,and they use 4 BD140 transistors for the ouput stage. So,since I had to take off one of the heatsinks to see the number on the transistor,I accidently broke 2 of the transistor legs. I just figured then that I would just replace all 4 and found the NTE185(PNP) which were equivalents to the BD140's.

Suprisingly to my ears these replacements actually sounded somewhat better,or maybe not much at all.

I have basic electronics knowledge and have built a few kits over the years,but I don't have the technical knowledge to design circuits. So,I figured you guys might be able to help,and you have so far. I don't have a schematic for this and I don't think one is available,since it is not a DIY kit.

I thought maybe there were other transistors that could be used in this amp that would possibly give me more output gain or overall sound quality.

Thanks again for any help.
 
PTL60

From the limited information I have been able glean on the OBH-11SE, it is a zero feedback Class-A design with capacitor coupling on both the input and the output. With zero feedback amps it is imperative to minimise distortion in all stages since there is no overall feedback to correct any errors. Without a schematic (and maybe even with one) it will not be possible to determine if a proposed substitute output transistor will be an improvement or not. Also, care must be taken to ensure that the stability of the amp is not jeopardized. A substitute transistor with a higher gain or higher ft could well make matters worse.

I think that this is one of those cases where you will need to accept (or hope) that the manufacturer got it right in the first place.

Geoff
 

PTL60

Member
2002-02-01 6:30 pm
Geoff,

Thanks a lot. I will definitely leave the amp as it is. The BD140 replacements(NTE185) worked out very well. I definitely did not want to replace them with something different unless I got some more information,such as what you told me. Actually,the amp is very good and I'm still happy with it's performance.

I now realize how just one component can change many things within a circuit. I was curious because I have heard of DIYers swapping out components for modifications. I'm glad I got my answer here before damaging my amp. Thanks again.

Pete