Just order the parts for my new intregrated dual mono block amp. I will use the Walter Jung preamp with four opa541 in the bridge parallel configuration. The opa541 will be set at unity and the preamp will have the total gain of 20x.
I want the use the opa541 because they are sample but will it be better to use four lm3886? All the components will be on a 6.5 x 5.5 inch veroboard,one for each channel or maybe I will put the power opamp on separate board and jump to preamp section.?
Any ideas?
I want the use the opa541 because they are sample but will it be better to use four lm3886? All the components will be on a 6.5 x 5.5 inch veroboard,one for each channel or maybe I will put the power opamp on separate board and jump to preamp section.?
Any ideas?
jaudio said:Just order the parts for my new intregrated dual mono block amp. I will use the Walter Jung preamp with four opa541 in the bridge parallel configuration. The opa541 will be set at unity and the preamp will have the total gain of 20x.
I want the use the opa541 because they are sample but will it be better to use four lm3886? All the components will be on a 6.5 x 5.5 inch veroboard,one for each channel or maybe I will put the power opamp on separate board and jump to preamp section.?
Any ideas?
just need to understand why you want to run anything in bridge or parallel mode. you only do that if you need power. rather up the gain of you poweramp. rather build Carlos's LM3886 or my version of Mauro Penasa's design - X-Calibre.
After I finish the amp,I will give it away and it is better to have more power in that case. I would like to hear the quality of the sound.rudi said:
Because of the OPA541 bandwidth,it best to run at unity at least that what I believe.
I will try Carlos's LM3886,when I build new speakers(the speakers I have now are power hungry).rudi said:
I been seeing the word"X-Calibre" but had no idea it was your's,other than the name I
know nothing about. I will do a search for more information.
jaudio said:
the reason i ask is that the anything in parallel or bridged, normally sounds worse. alot less musical
jaudio, what 'power hungry' speakers do you have now?
Btw 20x gain on the AD815 preamp is definitely not a great idea, you are exceeding it's limits, even if you use a +/-18V PSU.
Remember, you have to count that it would have to amplify a 'standard' 2V line signal (from a CDP) and multiply it by 20x.
Btw 20x gain on the AD815 preamp is definitely not a great idea, you are exceeding it's limits, even if you use a +/-18V PSU.
Remember, you have to count that it would have to amplify a 'standard' 2V line signal (from a CDP) and multiply it by 20x.
Im the only one I know that is really into audio,so when I give something away,it not really a problem. If it is loud they are Happy. I need the experiencerudi said:
Homemade,I will post picturescarlosfm said:
On Jung's schematics there is a gain of 5 for the ad831 and a gain of two for the AD815. I will incease the gain of the ad831(opa637) to 10,do you think that is a problem.carlosfm said:
I have to check the output voltage for Ipod.
I've built my first version of this amazing pre. I've used Rudi's servo and I'm using knackered old lead acids ( +10v, -12v) for power. The sound is clean, fast, dynamic; miles better than a passive pot into the Mauro rev C.
I have a problem though; when I turn the volume pot towards its lowest setting it breaks into a vicious buzzing oscillation. I've tried bypassing the +Vs and -Vs with a 100nf polyester right on the pins and this improved things slighlty, but its still not right.
Any pointers?
I did short the output to a power rail on first power up, and I was surprised it still worked at all; could I have damaged the chip in such a way as to cause this problem?
Panelhead's sending me more chips, so I'll build another soon, but any help much appreciated.
Carlos, Rudi, great project. Kudos guys.
I have a problem though; when I turn the volume pot towards its lowest setting it breaks into a vicious buzzing oscillation. I've tried bypassing the +Vs and -Vs with a 100nf polyester right on the pins and this improved things slighlty, but its still not right.
Any pointers?
I did short the output to a power rail on first power up, and I was surprised it still worked at all; could I have damaged the chip in such a way as to cause this problem?
Panelhead's sending me more chips, so I'll build another soon, but any help much appreciated.
Carlos, Rudi, great project. Kudos guys.
Input offset
Guessing, sounds like interaction with volume pot closed. Do you have a series resistor inbetween the pot and the chlp?
All mine have used the CFM nulling circuit, and not the servo.
Also if it plays, the chips is fine. I suspect they work until they die.
George
Guessing, sounds like interaction with volume pot closed. Do you have a series resistor inbetween the pot and the chlp?
All mine have used the CFM nulling circuit, and not the servo.
Also if it plays, the chips is fine. I suspect they work until they die.
George
Hi George, I've got 100kohm to ground after the pot and 1kohm in series, as per Carlos' schematic.
What would happen if I change the value of the series resistor?
As far as breaking the chip, the data sheet warns of 'changes' if overheated, and with my short it got very hot very fast...
What would happen if I change the value of the series resistor?
As far as breaking the chip, the data sheet warns of 'changes' if overheated, and with my short it got very hot very fast...
Hi Float.
just to confirm. I have build 5 of these pre amps now and the Servo circuit does not affect it or makes in unstable. but you have to use a FET opamp. such as a OPA134 of OPA2134 for dual or something similar.
I would suggest to try another pot. it is very difficult to damage this chip. but i suppose possible 😉
just to confirm. I have build 5 of these pre amps now and the Servo circuit does not affect it or makes in unstable. but you have to use a FET opamp. such as a OPA134 of OPA2134 for dual or something similar.
I would suggest to try another pot. it is very difficult to damage this chip. but i suppose possible 😉
Hi Rudi, I'm using the opa2134 and it seems to do the job perfectly. It drags the dc down to 0.1mv on the meter.
My source does output some DC, around 30mv; I did wonder if this could cause problems, but the servo seems to cope with this.
How close does the servo need to be to the circuit? I have it on a daughterboard with about an inch between the servos resistors and the main circuit.
My source does output some DC, around 30mv; I did wonder if this could cause problems, but the servo seems to cope with this.
How close does the servo need to be to the circuit? I have it on a daughterboard with about an inch between the servos resistors and the main circuit.
float said:
I do not know if this could mess things up. Maybe Carlos or somebody else can help out here but 30mv is not very promising. just for a test i would put a cap before the preamp, but expect that it would mess up the sound a bit
float said:
the servo goes between the input (after the 1K) and the output (before the 33R) the distance is not that critical but keep it as short as possible just to sure
Hi Rudi, it does seem to be the source dc thats the problem.
I plugged a dvd player in with only 4mv offset and all is well (apart from cack sound😀 )
Measuring the ad815 output dc with my usual source (30mv offset) shows fluctuating dc up to about 250mv when the vol pot is in a low position.
I really dont want to add coupling caps anywhere apart from the poweramp input; is there anything you could suggest to fix this?
Is it possible that the Carlos nulling circuit would better cope with the source offset?
One things for sure; this pre is worth the effort🙂
I plugged a dvd player in with only 4mv offset and all is well (apart from cack sound😀 )
Measuring the ad815 output dc with my usual source (30mv offset) shows fluctuating dc up to about 250mv when the vol pot is in a low position.
I really dont want to add coupling caps anywhere apart from the poweramp input; is there anything you could suggest to fix this?
Is it possible that the Carlos nulling circuit would better cope with the source offset?
One things for sure; this pre is worth the effort🙂
Hi Float
both nulling circuit designs will have this problem. what is the source that is giving you such high outputs. a CD player?? or a DAC.
You have serious problems. decoupling caps might just be your only option unless you can find a way to use the DC servo to null the output of the source.
I have another problem to contend with. I have some serious hum on my new design. i seperated the ground planes of the power supply and what a nightmare. Well i will have it fixed soon
both nulling circuit designs will have this problem. what is the source that is giving you such high outputs. a CD player?? or a DAC.
You have serious problems. decoupling caps might just be your only option unless you can find a way to use the DC servo to null the output of the source.
I have another problem to contend with. I have some serious hum on my new design. i seperated the ground planes of the power supply and what a nightmare. Well i will have it fixed soon
My problem source is a Marantz cd63 KI(modded) with no output caps. I may be able to fiddle with resistors after the dAC to lower dc.
Do you star ground everything in this pre?
I did separate signal L/R star grounds (including the servo opamp input) and linked these to the power ground star.
Good luck with your probs
Do you star ground everything in this pre?
I did separate signal L/R star grounds (including the servo opamp input) and linked these to the power ground star.
Good luck with your probs
yes i try and star everything and this time i might have painted myself into a corner. but i am sure i will soert it out soon.
my first guess is a solder bridge somewhere but i will have to go through everything again.
" my pre amp hums because it doesn't know the lyrics "
my first guess is a solder bridge somewhere but i will have to go through everything again.
" my pre amp hums because it doesn't know the lyrics "
Signal and power supply grounds
Rudi,
Try inserting a 1 - 20 ohm resistor inbetween the signal ground and your power grounds. I used to ground everything together and always was banishing hum by cleaning contacts.
Now I get 0.0 mv of hum on all my components. Guess I would break down and get a 4 1/2 digit meter it could be measured.
George
Rudi,
Try inserting a 1 - 20 ohm resistor inbetween the signal ground and your power grounds. I used to ground everything together and always was banishing hum by cleaning contacts.
Now I get 0.0 mv of hum on all my components. Guess I would break down and get a 4 1/2 digit meter it could be measured.
George
Thanks George
I actually got it working a while ago. bad connection on one secondary 😡
I will certainly try your method
I actually got it working a while ago. bad connection on one secondary 😡
I will certainly try your method
Hi guys,
I've not had chance to try it with my amp yet although I did take it to work and measured it on the scope🙂 I even had chance to run a high powered PA amp at work with it
I can't say I heard any hum at work but I'll no more when I get chance to try it with my amps at home, I really hope its ok
Anyway, thanks to Rudi,Carlos,George,Shehzad etc😀
I've not had chance to try it with my amp yet although I did take it to work and measured it on the scope🙂 I even had chance to run a high powered PA amp at work with it
I can't say I heard any hum at work but I'll no more when I get chance to try it with my amps at home, I really hope its ok
Anyway, thanks to Rudi,Carlos,George,Shehzad etc😀
Attachments
- Status
- Not open for further replies.