tbla said:
The sound is fantastic.
Impressive dynamics, clean, smooth and very detailed midband and treble.
My GC is now at a center position between the speakers, with a 5 meter interconnect from my pre.
Not a problem with the BUF634.😉
The toroid is around 500ma.
I didn't buy it, I had it laying around.
It seams good enough for this application.
i suggest - just for fun - to use one or two bigger ones, you might be surprised in a positive way....! 
tbla said:i suggest - just for fun - to use one or two bigger ones, you might be surprised in a positive way....!
Then I would have to limit the current for the op-amps.
Nah...
This toroid has 2 independent secondaries (18V), and my PSU has 2 bridges made with Schottky diodes (BA159).
If I fiddle with anything at a later stage it will be batteries.
yes, thats what i was trying to say....if it was me, i would use dual mono 2 x 80 va trafoes with 2 independant secondaries....😎
tbla said:
I made an LM1875 GC with a 180VA toroid.
But that's a power op-amp.
You suggest me to use 2x80VA trafoes on my pre?
Maby it would be better, I don't say it's not, but I would better spend my money on batteries if I want to fiddle a little more.😎
BTW, the top of the range Naim pre has an optional external PSU with an 800VA toroid.😱 😱
there is just too much hazle with them.
they cost $$$
they need to be recharged
they have there own kind of noise
there impedance is too high
therefore you need to build a regulator..........
i just don't feel that there's anything to be gained over a standard well implemented trafo solution.
i also think that batteries is kind of a fashion thing too.....
they cost $$$
they need to be recharged
they have there own kind of noise
there impedance is too high
therefore you need to build a regulator..........
i just don't feel that there's anything to be gained over a standard well implemented trafo solution.
i also think that batteries is kind of a fashion thing too.....
Each thing has its advantages and defects.
Anyway, batteries are good for a pre.
One charge lasts so long that you even forget you're using batteries.
Noise for noise, it's better than mains supply.😉
And you don't need to regulate.
Some caps is all you need.
The batteries needed for this are not expensive.
Between 1 and 3 A will be enough.
The end result may be a question of taste after all.
But then you can even compare between mains and batteries.😉
The Jeff Rowland Coerence is made of two boxes: pre and PSU.
The PSU has a switch that allows you to operate on mains or (internal) batteries.
Batteries sound better.😉
Anyway, batteries are good for a pre.
One charge lasts so long that you even forget you're using batteries.
Noise for noise, it's better than mains supply.😉
And you don't need to regulate.
Some caps is all you need.
The batteries needed for this are not expensive.
Between 1 and 3 A will be enough.
The end result may be a question of taste after all.
But then you can even compare between mains and batteries.😉
The Jeff Rowland Coerence is made of two boxes: pre and PSU.
The PSU has a switch that allows you to operate on mains or (internal) batteries.
Batteries sound better.😉
....if drdg made a regulator as good as the alw/jung(didden,gallo)😉
i'm shure that the batteries will come in second......
i'm shure that the batteries will come in second......
nice
nice work on the wood. the tin foil on the inside im sure works good. the transformer does look a little small does it get hot?
under load ? 🙂
ahh batteries thay do sound good😉
nice work on the wood. the tin foil on the inside im sure works good. the transformer does look a little small does it get hot?
under load ? 🙂
ahh batteries thay do sound good😉
Re: nice
The toroid is around 500ma.
And it doesn't get hot at all.
Guys, this is an op-amp based pre!
Right now I opened the datasheets and summing the max. power requirements of all the chips I have a total of 114.8 ma.
Here it is:
Buf634: 20 ma (x4=80ma)
OPA2132: 4.8 ma (x1 = 4.8ma)
OPA627: 7.5 ma (x4=30ma)
😉
karma said:
The toroid is around 500ma.
And it doesn't get hot at all.
Guys, this is an op-amp based pre!
Right now I opened the datasheets and summing the max. power requirements of all the chips I have a total of 114.8 ma.
Here it is:
Buf634: 20 ma (x4=80ma)
OPA2132: 4.8 ma (x1 = 4.8ma)
OPA627: 7.5 ma (x4=30ma)
😉
Hi,
Remember this thread?
I just finished a preamp based on the OPA627 and BUF634. It plays music but there are some problems to correct. It is in a integrated amp, with a NIGC in front.
PSU:
I am using a 15-0-15 500mA transformer for it. It is a bit too small I think, and it gets sligthly warm after some time, but does not rattle or anything like that. After I have schottys and then 1000u per rail. Then it has a 7818/7918, bypassed by 100n caps and finally a 470u per rail. Before the regulators I have around +/- 19VDC, but after them I have 18.4VDC and -17 VDC! I did mess with the regulators pins before I found the right ones. Does this means the regulators are not ok? Or is it the Tx?
Offset:
I am using caps between the pre and the NIGC, just in case. Nevertheless, the offset of the NIGC increased from 40mV to 210mV when I connected the preamp. Why is that?
The other funny thing is the position of the volume control. It is before the preamp, its ground goes to signal ground of the pre, which is connected to signal grouns of the NIGC. When the volume control is very low or very high, the pre shows an offset of about -300mV and 1VDC (!) and (even with the caps) the NIGC puts 22VDC on the speakers output!!!! No, I had no speakers connected. In the middle positions it is with the 210mV offset.
Can you tell what is wrong with my implementation?
Miguel
Remember this thread?
I just finished a preamp based on the OPA627 and BUF634. It plays music but there are some problems to correct. It is in a integrated amp, with a NIGC in front.
PSU:
I am using a 15-0-15 500mA transformer for it. It is a bit too small I think, and it gets sligthly warm after some time, but does not rattle or anything like that. After I have schottys and then 1000u per rail. Then it has a 7818/7918, bypassed by 100n caps and finally a 470u per rail. Before the regulators I have around +/- 19VDC, but after them I have 18.4VDC and -17 VDC! I did mess with the regulators pins before I found the right ones. Does this means the regulators are not ok? Or is it the Tx?
Offset:
I am using caps between the pre and the NIGC, just in case. Nevertheless, the offset of the NIGC increased from 40mV to 210mV when I connected the preamp. Why is that?
The other funny thing is the position of the volume control. It is before the preamp, its ground goes to signal ground of the pre, which is connected to signal grouns of the NIGC. When the volume control is very low or very high, the pre shows an offset of about -300mV and 1VDC (!) and (even with the caps) the NIGC puts 22VDC on the speakers output!!!! No, I had no speakers connected. In the middle positions it is with the 210mV offset.
Can you tell what is wrong with my implementation?
Miguel
Miguel,
With 19VDC before the regulators you should use 7815/7915.
I don't see the point of going the trouble of making a preamp like this for an integrated amp...
Anyway, I have no caps on the signal path of my pre.
My GC power amp has an input cap (2.7uf polyester).
No DC at all.
I have pots to adjust it, but even without, DC was very low.
There's a problem there, for sure.
Maby some close-up pictures would help.
BTW are you sure the problem is from the preamp?
Have you tried connecting a pot directly to the GC?
I see it's a NIGC...
Where did you put the cap?
Anyway, welcome to the OPA627+BUF634 club.😀
With 19VDC before the regulators you should use 7815/7915.
I don't see the point of going the trouble of making a preamp like this for an integrated amp...
Anyway, I have no caps on the signal path of my pre.
My GC power amp has an input cap (2.7uf polyester).
No DC at all.
I have pots to adjust it, but even without, DC was very low.
There's a problem there, for sure.
Maby some close-up pictures would help.
BTW are you sure the problem is from the preamp?
Have you tried connecting a pot directly to the GC?
I see it's a NIGC...
Where did you put the cap?
Anyway, welcome to the OPA627+BUF634 club.😀
miguel2 said:
Can you post the sch. please (at least on the NIGC and parts of the output of the sorce)? It'll make it so much easier and eliminate a lot of guessing and questions back and forth.
Thanks
Greg
I though that +/-18VDC was better...
Yes, the NIGC was working fine without the pre. And with that pot (100k log). The cap is at the pre output. I guess that it is not necessary, but I am still experimenting.
How do I ground the whole thing?!!
The NIGC is a LM3875 with 22k fb and 680 to groun, 22k from input to ground. 1000u per rail. 2.2u bypass rails. The pre schematic is on page 1 of this thread.
Miguel
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