(re)searching for a better preamp

Status
Not open for further replies.
Jump to Latest
#321
rudi said:
Hi Shehzad

you can omit the DC nulling but then you have to use the caps on the output (not bad sounding just use very good quality, a Wima MKP will work just fine.)

do not change anything else on the circuit, specially the powersupply, I did and the results weren't as i hoped so keep to Carlos's circuit
Click to expand...

Rudi, thanks a gem. You are always there to rescue me. I had sent you an e-mail, did you get a chance to read it?

In Carlos's schematics, I believe there is a provision for these caps on C5 (4.7uf) and C6 (0.1uf) right? If that is the case, the C10 and C14 from the LM317 and LM337 (PSU section?) would connect to which pins of the AD815 chip? The +Vs (Pin8) and -Vs (Pin 7)?
 
#323
rudi said:
Hi Shehzad

you can omit the DC nulling but then you have to use the caps on the output (not bad sounding just use very good quality, a Wima MKP will work just fine.)
Click to expand...

Without the DC nulling circuit you must use input and output caps. :dead:
This dc null circuit solved both problems, but as I said output DC is dependent of the volume pot position.
Much lower value, though.
The chip has some dc offset on the inputs. Without the dc null circuit and with some pots you will hear noise on the speakers as you rotate them.
Not good, an the pot will not last long.
With an input buffer most of the problems would be much easier to solve, but who needs a stinkin' buffer? 😀

It's not so easy to use a current feedback video op-amp for audio but hey, it sounds gorgeous. :bawling:
 
#325
carlosfm said:


Without the DC nulling circuit you must use input and output caps. :dead:
This dc null circuit solved both problems, but as I said output DC is dependent of the volume pot position.
Much lower value, though.
The chip has some dc offset on the inputs. Without the dc null circuit and with some pots you will hear noise on the speakers as you rotate them.
Not good, an the pot will not last long.
With an input buffer most of the problems would be much easier to solve, but who needs a stinkin' buffer? 😀

It's not so easy to use a current feedback video op-amp for audio but hey, it sounds gorgeous. :bawling:
Click to expand...

Carlos, I am going to proceed as per your schematics. Rudi came to my rescue by piecing together the "puzzle" for me and I can comprehend this much better. Sorry for all the naive questions but like I said, I have faith in your designs and the opinions of those who have built and listen to it, so onwards I will plod.
😉
 
#326
safetyman said:
Carlos, I am going to proceed as per your schematics. Rudi came to my rescue by piecing together the "puzzle" for me and I can comprehend this much better. Sorry for all the naive questions but like I said, I have faith in your designs and the opinions of those who have built and listen to it, so onwards I will plod.
😉
Click to expand...

Rudi is a really nice guy.
For you or others that may want to try something easier to build, try this:

http://myweb.tiscali.co.uk/nuukspot/decdun/gainclonepre2.html

Those who have tried it are reporting very good results.
Also, I think there's something really sexy about this one active discrete component per channel approach.
There's no excuse. Clear instructions, PCB layout...
What do you guys need more?

😎

PS: you don't even need to search for the thread and page where I posted the schematic. :clown:
 
#328
Back to the AD815

I am thinking of trying the power suppply for this as it is posted. But have a simple question.
The fixed value 3.3K resistor used on the common of the 317/337 regs. Is there a technical reason for this instead of a pot?
The pot is nice in my opinion, lets the rails be adjusted to exactly the same voltage.
When using the fixed resistor does this get it close to +/- 15 volts?
I am thinking of this because my supply is fairly high impedance, at least 3 ohms DCR. It is better suited for feeding a class A circuit.

George
 
#329
carlosfm said:


Rudi is a really nice guy.
For you or others that may want to try something easier to build, try this:

http://myweb.tiscali.co.uk/nuukspot/decdun/gainclonepre2.html

Those who have tried it are reporting very good results.
Also, I think there's something really sexy about this one active discrete component per channel approach.
There's no excuse. Clear instructions, PCB layout...
What do you guys need more?

😎

PS: you don't even need to search for the thread and page where I posted the schematic. :clown:
Click to expand...


Carlos, what can I say.........thanks. Hmm....not a bad idea, I should try both of them. 😀 Thanks again, mate.
 
#334
when i found this one i actually thought it was the one you tried. but I see the TPA is a headphone pre/amp and i also noticed that the spec is very simular to the THS. but i think we need to try it just to put our minds at rest. so far i am still VERY happy with the AD815

Rod Elliot did a circuit for this but once again i do not like the OPA2134 he used for the buffer . i think i will build it along the lines of the AD815 seeing that the resistor values that is recommended is exactly the same
 
#335
rudi said:
when i found this one i actually thought it was the one you tried. but I see the TPA is a headphone pre/amp and i also noticed that the spec is very simular to the THS. but i think we need to try it just to put our minds at rest. so far i am still VERY happy with the AD815

Rod Elliot did a circuit for this but once again i do not like the OPA2134 he used for the buffer . i think i will build it along the lines of the AD815 seeing that the resistor values that is recommended is exactly the same
Click to expand...

Try it, why not?
 
#336
Hi Rudi,

I finally got my AD815 today so i will have a go at building the cicuit you so kindly sent me. I will i think build the PSU as per your board as well since you seem to think that it make a noticeable differrence.

One think i dont understand though is that you are currently stating you dislike the OPA2134 even though it is in the design you sent me. Is there a straight towards replacement or would i need to change the layout. I have a pair of AD825 on adaptors could these be used? What would you recommend?

Any help much appriciated,

Phil Holder
 
#337
Hi Phil

The OPA2134 is a very good opamp in the manner that I used it for the DC servo but I do not find it to be a good sounding opamp if you use it directly in the signal path.
So in Rod Elliots design he used it before the THS6012 and that is not the way I would have done it.

So you need not worry. Use it as i advised. I tried several opamps in that position and they had no affect on the sound
 
#338
Cheers Rudi,

Thanks for that, put my mind at ease, one last thing, sorry to bother you but what make/model of caps did you use for the 3300uf 35v caps. I cannot find a source for any reasonable brands with a lowish esr in 16mm, no panasonic FC or FM and no nichicons or rubycon. What are you use there??

Also if anyone knows of a place in the u.k. where you can buy small variety packs of smt resistors and caps in a range please let me know

Kind Regards,

Phil
 
#339
for the 3300 i used on the one Hitano (nothing special there) and on my last one i used jamicon (also nothing special) they are not that important.

for the 33uf i used OSCON 20v (tightend the bass up) and for the 330 I used a Hitano low ESR

the resistors are 1206 (size) and just buy a 100 seeing that they are dirt cheap.
 
Status
Not open for further replies.
Top Bottom