Leach amp treble problem

fabix · 18th February 2009, 06:13 PM

Hi,

I'm new to this forum but I think I'm at the right place asking about problems with the Leach Amp V4.5.
At the moment I build my own Leach Amp. One channel is already finished but the trebles are quite muffled. The rest works fine.
First I had no bass response but then I recognized that I forgot the jumper over C6B.

After solving this problem I saw that D16, a zener-diode, is in the wrong way. I changed that but the problem didn't got better.

My speculation is that maybe one transistor in the Input-stage is blown. Could this be possible?
What other reasons could cause this problem?

Thank you,
fabi

AndrewT · 18th February 2009, 06:26 PM

measure the voltage across each of the LTP emitter resistors.
measure the voltage across the Zin resistor.
measure the output offset.

pooge · 18th February 2009, 06:35 PM

There is no way to answer your question without more information. Perhaps you are not used to the subjective impression of a treble that isn't glaring. We don't know that. Also, we do not know what you've checked yet, other than what you posted.

Have you measured frequency response or any of the other tests Leach recommends?

Have you made sure all the parts used are correct, such as the cap in the input? Diagnosis cannot be performed from afar without solid info.

jaycee · 18th February 2009, 08:42 PM

You might want to check the capacitors C8 and C9 - if they aren't correct it might roll off high frequencies in the feedback loop.

Also check C1 is correct, this forms a low pass filter with R2, if it is incorrect it may be rolling off trebles.

You also need to check Q3, Q4 and Q6 are not damaged by the incorrect installation of the zener.

fabix · 18th February 2009, 10:04 PM

I think the sound hast to be a lot better because there isn't even a bit of brilliance. It's just muffled.
The parts are all correct, I think. Every transistor is right(NPN, PNP) and all the diodes are in the correct position.
With a sine wave on the input it looks fine on all frequencies. There is also a lot of power in the amp. There is no distortion or anything, just muffled.

Is there a typical mistake which can cause such a sound?

fabix · 19th February 2009, 01:40 PM

So, I just solved the problem.

I changed Q3,Q4 and Q6 but nothing got better. Than I soldered out C1, so that there is no lowpass but even then nothing got better.

Finally I changed the loudspeaker and the cable and everything works fine. Such a great sound and so powerful. I like the amp already.
Now, I just have to finish the other channel, anodize the case and search a preamp for full power.

Thanks to all who tried to help me with my quite embarassing problem.

18th February 2009, 06:13 PM	#1
fabix diyAudio Member Join Date: Feb 2009	Leach amp treble problem Hi, I'm new to this forum but I think I'm at the right place asking about problems with the Leach Amp V4.5. At the moment I build my own Leach Amp. One channel is already finished but the trebles are quite muffled. The rest works fine. First I had no bass response but then I recognized that I forgot the jumper over C6B. After solving this problem I saw that D16, a zener-diode, is in the wrong way. I changed that but the problem didn't got better. My speculation is that maybe one transistor in the Input-stage is blown. Could this be possible? What other reasons could cause this problem? Thank you, fabi

18th February 2009, 06:26 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	measure the voltage across each of the LTP emitter resistors. measure the voltage across the Zin resistor. measure the output offset. __________________ regards Andrew T.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Leach amp problem	Curioprop	Solid State	95	1st September 2008 09:58 AM
Problem with treble on NAD 3020B	Gareth B	Solid State	1	15th January 2007 12:06 AM
Problem with leach amp	AudioG	Solid State	1	8th June 2005 02:40 PM
problem with leach amp	xxsmiffxx	Solid State	5	25th February 2005 07:50 PM
Leach amp problem	Ed LaFontaine	Solid State	3	19th July 2004 12:04 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

18th February 2009, 06:35 PM	#3
pooge diyAudio Member Join Date: May 2003 Location: Northern Va.	There is no way to answer your question without more information. Perhaps you are not used to the subjective impression of a treble that isn't glaring. We don't know that. Also, we do not know what you've checked yet, other than what you posted. Have you measured frequency response or any of the other tests Leach recommends? Have you made sure all the parts used are correct, such as the cap in the input? Diagnosis cannot be performed from afar without solid info.

18th February 2009, 08:42 PM	#4
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	You might want to check the capacitors C8 and C9 - if they aren't correct it might roll off high frequencies in the feedback loop. Also check C1 is correct, this forms a low pass filter with R2, if it is incorrect it may be rolling off trebles. You also need to check Q3, Q4 and Q6 are not damaged by the incorrect installation of the zener.

18th February 2009, 10:04 PM	#5
fabix diyAudio Member Join Date: Feb 2009	I think the sound hast to be a lot better because there isn't even a bit of brilliance. It's just muffled. The parts are all correct, I think. Every transistor is right(NPN, PNP) and all the diodes are in the correct position. With a sine wave on the input it looks fine on all frequencies. There is also a lot of power in the amp. There is no distortion or anything, just muffled. Is there a typical mistake which can cause such a sound?

19th February 2009, 01:40 PM	#6
fabix diyAudio Member Join Date: Feb 2009	So, I just solved the problem. I changed Q3,Q4 and Q6 but nothing got better. Than I soldered out C1, so that there is no lowpass but even then nothing got better. Finally I changed the loudspeaker and the cable and everything works fine. Such a great sound and so powerful. I like the amp already. Now, I just have to finish the other channel, anodize the case and search a preamp for full power. Thanks to all who tried to help me with my quite embarassing problem.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)