Preamp finished but it wont play..

XXLPeanut · 11th June 2006, 08:05 PM

Hello.
I just finished this preamp.
http://www.albertkreuzer.com/preamp.htm

And now for the big question.. It wont play.
The problem is not in the psu. That delivers +/- 15V as expected.
Should I take off all potmeters and switches and put them on one by one or how would you errortest it?
When I've had power on it and I turn it off, the threshold LED turns on for ½ sec as the caps are discharging I suppose.
When I put in a pair of headphones and turn up the gain I hear a click-like sound when the meter is about 2/3 turned up.. P1 and P7 are both in middle position. As well are all meters.
Any ideas or could the problem be anywhere?
Thanks

kubeek · 11th June 2006, 08:30 PM

First check the voltage on all + parts of the transistors, and the both supplies of the op-amp.
If it doesn´t help, then I would suggest making a signal-probe. As it is a bass preamp, you could take a tape player and connect it to the input. Then connect a jack-jack wire to some combo, make the shield grounded to your circuit, and start touching the signal part of the ciruit with the tip of the jack, and listen where the signal ends.

XXLPeanut · 11th June 2006, 08:38 PM

Quote:

Originally posted by kubeek
First check the voltage on all + parts of the transistors, and the both supplies of the op-amp.
If it doesn´t help, then I would suggest making a signal-probe. As it is a bass preamp, you could take a tape player and connect it to the input. Then connect a jack-jack wire to some combo, make the shield grounded to your circuit, and start touching the signal part of the ciruit with the tip of the jack, and listen where the signal ends.

What do u mean by +parts?
Do you mean measureing the gate on the fets? And in that case how should i measure? What should i look for.

I just tested the opamps.. they get +/- 15V on the correct legs.
Im a beginner so bare with me

Thank you

kubeek · 11th June 2006, 08:42 PM

by the +parts I meanrt the legs of the transistors which are connected to the +voltage, check the voltage by multimeter.

XXLPeanut · 11th June 2006, 08:55 PM

Quote:

Originally posted by kubeek
by the +parts I meanrt the legs of the transistors which are connected to the +voltage, check the voltage by multimeter.

ok the drainvoltages are

8,4V on T1
5,89v on T2
15,25V on T3
but i dont know if this is what its suppose to be..
Any ideas
Thanks

kubeek · 11th June 2006, 08:58 PM

seems OK. Now you should do the signal check, and you can also check the G-S voltages.

XXLPeanut · 11th June 2006, 09:11 PM

Ok first the G and S voltages..

T1:
8.4 D
1.21 S
0.02 G

T2:
5.89 D
5.10 S
5.10 G

T3:
15.25 D
4.52 S
1.99 G

Ill see if I can figure out how to do that signal check now.

XXLPeanut · 11th June 2006, 09:24 PM

about this signalcheck.. Could I plug in a mp3 player, and then use a pair of headphones, grounding the common and one of the speakers and using the tip on the headphonejack to probe on my pcb? That way just listen how "far" the signal gets in the path.
Or how would you do it?
Thanks

XXLPeanut · 12th June 2006, 12:15 AM

Quote:

Originally posted by XXLPeanut
about this signalcheck.. Could I plug in a mp3 player, and then use a pair of headphones, grounding the common and one of the speakers and using the tip on the headphonejack to probe on my pcb? That way just listen how "far" the signal gets in the path.
Or how would you do it?
Thanks

I did this and I could only get a signal until i hit the first resistor... after this I coudnt find any signal anywhere.
Any ideas?

anatech · 12th June 2006, 12:21 AM

Hi XXLPeanut,
Are you sure your jacks are wired with the resistor between them and the summing point? Are the resistors the correct value?

-Chris

11th June 2006, 08:05 PM	#1
XXLPeanut diyAudio Member Join Date: Feb 2006 Location: Aarhus	Preamp finished but it wont play.. Hello. I just finished this preamp. http://www.albertkreuzer.com/preamp.htm And now for the big question.. It wont play. The problem is not in the psu. That delivers +/- 15V as expected. Should I take off all potmeters and switches and put them on one by one or how would you errortest it? When I've had power on it and I turn it off, the threshold LED turns on for ½ sec as the caps are discharging I suppose. When I put in a pair of headphones and turn up the gain I hear a click-like sound when the meter is about 2/3 turned up.. P1 and P7 are both in middle position. As well are all meters. Any ideas or could the problem be anywhere? Thanks

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
finished my PCC88 preamp	Roemhild	Tubes / Valves	12	18th January 2012 08:04 AM
PGA2310 based preamp finished	bostjancek	Chip Amps	24	19th July 2010 08:59 PM
Will a tube preamp play nice with a F1?	G	Pass Labs	9	15th March 2009 11:46 PM
Giaime's Preamp Finished!!!	Giaime	Tubes / Valves	19	17th May 2006 07:36 PM
Just finished my first tubes-preamp	Ralph	Tubes / Valves	7	26th April 2002 09:26 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

11th June 2006, 08:30 PM	#2
kubeek diyAudio Member Join Date: Dec 2005 Location: Prague, Czech Rep	First check the voltage on all + parts of the transistors, and the both supplies of the op-amp. If it doesn´t help, then I would suggest making a signal-probe. As it is a bass preamp, you could take a tape player and connect it to the input. Then connect a jack-jack wire to some combo, make the shield grounded to your circuit, and start touching the signal part of the ciruit with the tip of the jack, and listen where the signal ends.

11th June 2006, 08:42 PM	#4
kubeek diyAudio Member Join Date: Dec 2005 Location: Prague, Czech Rep	by the +parts I meanrt the legs of the transistors which are connected to the +voltage, check the voltage by multimeter.

11th June 2006, 08:58 PM	#6
kubeek diyAudio Member Join Date: Dec 2005 Location: Prague, Czech Rep	seems OK. Now you should do the signal check, and you can also check the G-S voltages.

11th June 2006, 09:11 PM	#7
XXLPeanut diyAudio Member Join Date: Feb 2006 Location: Aarhus	Ok first the G and S voltages.. T1: 8.4 D 1.21 S 0.02 G T2: 5.89 D 5.10 S 5.10 G T3: 15.25 D 4.52 S 1.99 G Ill see if I can figure out how to do that signal check now.

11th June 2006, 09:24 PM	#8
XXLPeanut diyAudio Member Join Date: Feb 2006 Location: Aarhus	about this signalcheck.. Could I plug in a mp3 player, and then use a pair of headphones, grounding the common and one of the speakers and using the tip on the headphonejack to probe on my pcb? That way just listen how "far" the signal gets in the path. Or how would you do it? Thanks

12th June 2006, 12:21 AM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi XXLPeanut, Are you sure your jacks are wired with the resistor between them and the summing point? Are the resistors the correct value? -Chris

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