GC passive pre-amp dissapointment - Page 18 - diyAudio
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Old 27th June 2005, 12:29 PM   #171
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Thanks a lot Nuuk,

Very helpful as always.

This is a seperate preamp and when it was passive it didnt have anything connected to the case. One thing i notice though now was that when i touch the pot spindle with my finger the amp hums, i guess this could suggest that there is an earthing issue since is wasnt present before.

Phil
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Old 27th June 2005, 12:43 PM   #172
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Quote:
One thing i notice though now was that when i touch the pot spindle with my finger the amp hums, i guess this could suggest that there is an earthing issue since is wasnt present before.
I've had similar experiences Fil. Fortunately, I use wooden knobs so it's not really an issue!
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Old 27th June 2005, 12:50 PM   #173
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Nuuk, sorry to interject this slightly off topic question but regarding the transistor buffer for the gainclone, do you know anyone who built it with the MPSA18?
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Old 27th June 2005, 12:54 PM   #174
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Hmm, that is a point i usually have a great big plastic one. Sorry school boy humor creeping in. Yeah it is usually insulated so maybe thats not an issue
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Old 27th June 2005, 12:55 PM   #175
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Nuuk, sorry to interject this slightly off topic question but regarding the transistor buffer for the gainclone, do you know anyone who built it with the MPSA18?
Not off-topic if it's to do with the buffer!

But the answer is no, I don't know what other people have used. It would be good if we could get feedback on different transistors though!

If the MPSA18 is a signal transistor then I would say try it if they are not too expensive.
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Old 27th June 2005, 02:59 PM   #176
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OK i have done a lot of thinking and worked out that what i must have done is by wiring the pot wrong, I have put a variable resistance in the curcuit but not sent any to ground. The resistance starts at 10 k and end at zero but because of the wiring the no gets set to ground, thus it does lower the volume but only a tiny amount. Face on looking at the pot I must have wired it G-O-I as opposed to I-G-O where G is ground I in Input and O is Output.

Feel pretty confided that I can fix it now.

Amazing what a quite day at work and a couple of hours thought can do.

edit:
Just to prove it, the resistance from Input to output and to ground the way I wired it would both be 10k each at miniumum volume, Thus as a voltage divider the ouput would be basicly be half volume, which is exactly what i got!!!

Phil
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Old 27th June 2005, 04:45 PM   #177
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Amazing what a quite day at work and a couple of hours thought can do.
Amen! But don't let the boss know that you are thinking about hi-fi!

Yes, that 'unwanted' signal has to be 'got rid of', ie it has to be shunted to ground.
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Old 17th November 2005, 02:04 AM   #178
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Reviving a long dead thread: I replaced the transistors in my buffer with all 2N5088's. I had been using the ones that Nuuk used. It sounds a little different than it did. I am not sure that it is better, probably not worse, but a tad different -- a bit more detail at the expense of some warmth. It is different enough that I think trying out different transistors is worth it.
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Old 17th November 2005, 05:47 AM   #179
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Another option:

MPS8098

These are less detailed than the 2N5088's, however, they seem to have warmer, fuller, smoother, punchier sounding bass. if you like revealing, sparkley, yet neutral sound, the 2N5088 is the better choice. For laid back sound, the MPS8098 seems to be a good option.
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Old 17th November 2005, 02:31 PM   #180
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Heeeey, here's a really simple fix and probably might just very well be the best.

Add a simple LM386 circuit post passive preamp. More than enough juice for what is needed and simple circuits to build. I've also noticed how dense, rich and tube like these little amplifier chips sound. I think their potential is still greatly untapped...

You've probably solved it by now but just a thought to throw out rather than read 5 pages of replys
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