Hi Jaudio
I am. one will be able to build both versions on one board. but i am using OPA627's , i am etching the board tomorrow but will only build it over the weekend. hopefully without any glitches
I am. one will be able to build both versions on one board. but i am using OPA627's , i am etching the board tomorrow but will only build it over the weekend. hopefully without any glitches
has anyone looked at theAD815 DC ofset with a scope? i have tried it on both channels and it does the same thing. i am using a 25k pot. when the volume is at minimum it is around -20mv as you increase the volume the dc ofset increases to around +8mv at maximum level.
that is with 10k resistor across the output. with headphones it is much lower.
I have read you can decrease the dc ofset by lowering the input resistor. i will try 10k tomorrow with the same test. of course it depends what your source can drive properly. 10k may be a bit low for some sources.
100k input resistor seems to be pretty standard for audio circuit, while the input resistor is "supposed" to be 50 ohms on most of the AD815 data sheet examples.
that is with 10k resistor across the output. with headphones it is much lower.
I have read you can decrease the dc ofset by lowering the input resistor. i will try 10k tomorrow with the same test. of course it depends what your source can drive properly. 10k may be a bit low for some sources.
100k input resistor seems to be pretty standard for audio circuit, while the input resistor is "supposed" to be 50 ohms on most of the AD815 data sheet examples.
jaudio said:
Hi Jaudio
Well it didn't cross my mind (although I generally do it) I like to hear a circuit in its natural form before i tinker with it. It will be very easy with a 3k3 resistor.
I am almost finished with the new board. i just need 2x 100R resistors and then i can test it. (I could have sworn that it was on my shopping list)
here is the picture of the new pre. fingers crossed that i didn't mess it up in the design stage
Attachments
neutron7 said:
Right... I have explained several times how to adjust DC offset with my circuit...
neutron7 said:
Most sources don't have any problems driving a 10k ohm load. It it does, it's not for me.
But the circuit and components used were in a context that you have a 10k~20k volume pot.
And it's the volume pot that's the key component here: if you use a 10k resistor to ground after it, you are attenuating the volume too much, and also the driving problems are after the pot, your source if not guilty here.
After the pot you must use a resistor around 10x greater than the value of the pot, and this is a general rule, always.
Otherwise the pot will also not have a 'natural' log curve.
That's why I never agreed using a 22k to ground on a chipamp (the so-called 'gainclones') IF you are using a 'passive' (volume pot) pre. The circuit that's on the datasheets is for a power amp, not an integrated amp.
Yep, the choice of component values can make it or break it. Even one resistor can make all the difference. 😉
neutron7 said:
well it makes hardly any difference. it does pick up less noise from my sound card though. i dont think the EMU0404 breakout cable has very good sheilding.
I will end up doing it carlos way though. i just did not have the triimpots handy. off to ebay!
il will just use caps until then for headphones. the amps have a cap input so im not worried about them.
Nice,real nice
Rudi,
That is what I hope to build someday. A professional looking circuit.
I am slowly getting there, maybe five more years.🙂 🙂
George
Rudi,
That is what I hope to build someday. A professional looking circuit.
I am slowly getting there, maybe five more years.🙂 🙂
George
t. (and others in the UK)
If you want the non-surface mount version AD815AY, RS actually have it in stock.
Its on the web, but not in the manual -will cost you £15 mind.
I've just ordered one 🙂
If you want the non-surface mount version AD815AY, RS actually have it in stock.
Its on the web, but not in the manual -will cost you £15 mind.
I've just ordered one 🙂
jaudio said:
thanks,
it is the Walt Jung circuit. but you can use my normal DC servo aswell with limited changes. I left out L1. but that i will have on my next board. this board does have a few problems that i picked up once i gone through it again but it can easily be fixed. so hopefully i will have it working tomorrow
I thought the circuit would not need an additional servo
http://home.comcast.net/~walt-jung/..._Distortion.pdf
On page 79 second paragraph “…since driver U1b servos it to null condition”,wouldnt that be for dc offset as well?
http://home.comcast.net/~walt-jung/..._Distortion.pdf
On page 79 second paragraph “…since driver U1b servos it to null condition”,wouldnt that be for dc offset as well?
SIP AD815
If you need the leaded version, get together and I can order them and mail over. In quanties over 10 ten are about 2.00 USD each delivered to my house.
If someone speaks up, 50.00 USD should get 25 to Europe. The supplier is slow, usually 2-3 weeks to my home. The mail is next day, must take them a couple weeks to fill an order.
George
If you need the leaded version, get together and I can order them and mail over. In quanties over 10 ten are about 2.00 USD each delivered to my house.
If someone speaks up, 50.00 USD should get 25 to Europe. The supplier is slow, usually 2-3 weeks to my home. The mail is next day, must take them a couple weeks to fill an order.
George
jaudio said:
What i meant,... you can do one or the other.
Carlos's preamp circuit with my DC servo or just the WJ circuit. you can do this just by replacing the daughter board and removing or adding 2 resistors
I will try both versions; I still have the servo board that I couldn’t use on pre/headphone amp.
Matter of fact I have two boards with dual servos each.
I was thinking of using one board on the phono amp and remove the output capacitor but that is a whole other can of worm.
Matter of fact I have two boards with dual servos each.
I was thinking of using one board on the phono amp and remove the output capacitor but that is a whole other can of worm.
Walt Jung Composite line stage circuit
Well I have the pre running and obviously we will have to give it some time to settle.
First the basic configuration.
18-0-18 transformer.
Dual regulation. Voltages being 25v – 21v - 15v
First stage – OPA627 x2
Well the sound is very much down to opamp selection. With the OPA627 one get the impression that you are listening to a 6h30 valve line stage, meaning that it is very sweet in the midrange and tops but in this instance you have AWESOME bass. Obviously you also have the current drive of the valve.
I think it might be the power supply but the preamp is quieter than before and the definition shows a lot of promise (I say this because it really needs lots of burning in) but that said. What I heard is very good.
I will have to build another with the dc servo to do a direct comparison. But I think the AD815 on its own might be a more “edgy” meaning that it has sharper definition/ one thing is for sure. You need a amp with a cap on its input. I am measuring 1mv with nothing connected but I will check it again when all is connected
Well I have the pre running and obviously we will have to give it some time to settle.
First the basic configuration.
18-0-18 transformer.
Dual regulation. Voltages being 25v – 21v - 15v
First stage – OPA627 x2
Well the sound is very much down to opamp selection. With the OPA627 one get the impression that you are listening to a 6h30 valve line stage, meaning that it is very sweet in the midrange and tops but in this instance you have AWESOME bass. Obviously you also have the current drive of the valve.
I think it might be the power supply but the preamp is quieter than before and the definition shows a lot of promise (I say this because it really needs lots of burning in) but that said. What I heard is very good.
I will have to build another with the dc servo to do a direct comparison. But I think the AD815 on its own might be a more “edgy” meaning that it has sharper definition/ one thing is for sure. You need a amp with a cap on its input. I am measuring 1mv with nothing connected but I will check it again when all is connected
Re: Re: Walt Jung Composite line stage circuit
Hi Jaudio
I was speaking generally. it would vary from valve to valve. a opamp does not really have the ability to drive capacitave loads as well as a valve. but the AD815 does have that ability (better, worse...??? i am not to say). it was in that light that i made this statement.
jaudio said:
Hi Jaudio
I was speaking generally. it would vary from valve to valve. a opamp does not really have the ability to drive capacitave loads as well as a valve. but the AD815 does have that ability (better, worse...??? i am not to say). it was in that light that i made this statement.
Hello Rudi
Sorry I misunderstood. I thought you meant the composite had the drive capability of a tube which a thought was strange that is why I asked the question. I really should pay more attention.
Youre getting a stable 1mv no matter which position the pot is in?
Sorry I misunderstood. I thought you meant the composite had the drive capability of a tube which a thought was strange that is why I asked the question. I really should pay more attention.
Youre getting a stable 1mv no matter which position the pot is in?
jaudio said:
well it does have a simular drive capability and that being of the "able nature" the AD815 and a Valve have a very good ability to drive a heavy load.
I am using a PGA2311 digital volume control so setting does not matter in my case. i haven't check it with all the equipment hooked up. but it could also have been a earthing issue i had yesterday. so my refference was playing havoc.
you also have to remember that i am using a Walt Jung design and this does not need DC correction circuits (well theoretically) and on my other pre's i use a DC servo and for them pot position also does not matter
the preamp have about 12 hours on it now and it is improving by the hour. it is really sounding awesome. but i would like to have another 30 on it before i make my final judgement
- Status
- Not open for further replies.