GregGC said:
Now that is something I would be very much interested in knowing about too! Perhaps a switch or even a pot would allow some tests in that area.
If you plan on using a NIGC that should be fine. For an IGC that might work if you are feeding a signal that's already buffered and with some output control, like on a Marantz CD player.
If not Joe Rasmussen's explanations on how different pots and different pot positions affect your response on an IGC are in order. A buffer should improve things, tube or solid-state.
Carlos
carlmart said:
Carlos,
I'm planing on NIGC (no buffers, because I believe that they have their own sound, good or bad). A high input impedance NIGC (47-100kOhm Zin) should eliminate the need for a buffer. I have even a PCB that can be used for High Z IGC, NIGC, Parallel or Bridge configuration. Really universal one, using single sided PCB and trough-hole components.
Will see when I'm gonna have time to try it.
/Greg
Attachments
PMA said:
Replace it with a descrete resistors attenuator, then. When I build my first GC I tried it with a pot and attenuator and I didn't find a difference. The first GC I build was 2 separate monoblocks. Now I think that that's an overkill (for me, others may think otherwise) and I'm considering using single PSU for both chanels and a stereo pot (from a Yamaha receiver) for the volume ctrl. My GC attenuators started making cracking noise (not very good switches I guess) after 3 mths of use and my Yamaha is 10 years old and the pot works verry well. So, I'm considering a good ($25CAN) stereo pot. seriously. At the end I think one of the original design GC's uses a sliding pot. also, so it can't be that bad. Mind you I subscribe to "Less is more" line of thinking.
/Greg
tbla said:TVC rules.......
...at a price.
This cheap thing is really attracting me:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=39258
Yes, for me a good active pre is better, but it still needs a pot or some way to control the volume, and it should be a good one.
If there's a cheap and good solution, I want it.
class A in PMA buffer
This week I tried biasing the OPA627's in my PMA-buffer preamp. As suggested by Carlos I used 2k resistors from the output to the negative rails of each opamp.
I really didn't expect much of a difference because, in this application, the OPA's are not really loaded and hence are in class A already.
The differences are small, but they're there. I notice a slight increase in resolution. Some instruments and particularly female voices seem to have more body.
You gotta love these kinds of tweaks. I don't know if anybody else has tried it, but one couldn't ask for more bang for buck!
ABo
This week I tried biasing the OPA627's in my PMA-buffer preamp. As suggested by Carlos I used 2k resistors from the output to the negative rails of each opamp.
I really didn't expect much of a difference because, in this application, the OPA's are not really loaded and hence are in class A already.
The differences are small, but they're there. I notice a slight increase in resolution. Some instruments and particularly female voices seem to have more body.
You gotta love these kinds of tweaks. I don't know if anybody else has tried it, but one couldn't ask for more bang for buck!
ABo
Re: class A in PMA buffer
I never felt there was a need to do this when using the buffers.
The OPA627+BUF634 board I took out from my pre is here looking at me.
Now you make me curious... gotta try it.
That is exactly my oppinion.
This op-amp can make you, when you know how to make it sing.
And it really sings.
Franz, you can call me Carlos, or Carlosfm, whatever you like.
FM in capitals separated from my name seams like Frequency Modulation.
No, I didn't have the chance yet, I've just finished an amp for a friend...
I need time, as I am now testing something new, I've been etching an hour ago.
I will then make the valve circuit and test it.
Stay tuned to 97.8 FM.
ABO said:
I never felt there was a need to do this when using the buffers.
The OPA627+BUF634 board I took out from my pre is here looking at me.
Now you make me curious... gotta try it.
ABO said:
That is exactly my oppinion.
This op-amp can make you
, when you know how to make it sing.And it really sings.
Franz G said:
Franz, you can call me Carlos, or Carlosfm, whatever you like.
FM in capitals separated from my name seams like Frequency Modulation.
No, I didn't have the chance yet, I've just finished an amp for a friend...
I need time, as I am now testing something new, I've been etching an hour ago.
I will then make the valve circuit and test it.
Stay tuned to 97.8 FM.
THS4061 and AD8610
Y'all should still consider trying either THS4061 or AD8610. Tried the former in a buffered (BUF634) preamp ala pavel macura and found it to be a more open, cleaner and engaging presentation. 627 is good, detailed, but quite dark.
627 plays good music, THS4061, unbiased I might add, makes it seem more live, especially on the highs, which have more air.
Another candidate is the AD8610. Currently trying this in a DAC IV stage (DAC is SAA 7350 of Theta DS Pro Pime) and again, seems more involving vs an unbiased 627. Also, bass and highs seem to have more extension vs 627. Only issue is that supply max is +-13V.
At some stage, will try Resistor and JFET biasing of both 4061 and 8610.
Y'all should still consider trying either THS4061 or AD8610. Tried the former in a buffered (BUF634) preamp ala pavel macura and found it to be a more open, cleaner and engaging presentation. 627 is good, detailed, but quite dark.
627 plays good music, THS4061, unbiased I might add, makes it seem more live, especially on the highs, which have more air.
Another candidate is the AD8610. Currently trying this in a DAC IV stage (DAC is SAA 7350 of Theta DS Pro Pime) and again, seems more involving vs an unbiased 627. Also, bass and highs seem to have more extension vs 627. Only issue is that supply max is +-13V.
At some stage, will try Resistor and JFET biasing of both 4061 and 8610.
Ryan, the THS4061 is too noisy for my taste, and it also has high input offset voltage.
Much more appealing, and I suggest that you give it a try, is the THS4031/2.
IMHO.
The THS4031/2 has:
- Much lower input offset voltage.
- Much lower noise (1.6nv/sqHz compared to 14nv/sqHz of the 61/2).
- Much lower distortion.
In my oppinion, the parameters where the 31/2 have inferior specs are not so important.
The only thing is that the 31/2 is stable at gains of 2 or -1, but for a line or headphone preamp this is no problem.
Much more appealing, and I suggest that you give it a try, is the THS4031/2.
IMHO.
The THS4031/2 has:
- Much lower input offset voltage.
- Much lower noise (1.6nv/sqHz compared to 14nv/sqHz
of the 61/2).- Much lower distortion.
In my oppinion, the parameters where the 31/2 have inferior specs are not so important.
The only thing is that the 31/2 is stable at gains of 2 or -1, but for a line or headphone preamp this is no problem.
Re: THS4061 and AD8610
I was using AD8610 for some time in my preamp. It is indeed more open and more involving than OPA627, but for some reason it never sounded completely natural. The highs seem a bit artificial (sort of proccessed). I was running it at +/- 15V rails (as ML preamp provides only that) so maybe that was influencing the sound somehow. But during constant operation at higher voltage for at least a month, I didn't get any problems.
I'm back to OPA627 and I think it can be made to sound fine. At the moment I'm using 4.7 BG N additional bypasses directly on the pins. It seems to be slightly better than previous 0.01u film caps, but nothing really major.
Dr.H said:
I was using AD8610 for some time in my preamp. It is indeed more open and more involving than OPA627, but for some reason it never sounded completely natural. The highs seem a bit artificial (sort of proccessed). I was running it at +/- 15V rails (as ML preamp provides only that) so maybe that was influencing the sound somehow. But during constant operation at higher voltage for at least a month, I didn't get any problems.
I'm back to OPA627 and I think it can be made to sound fine. At the moment I'm using 4.7 BG N additional bypasses directly on the pins. It seems to be slightly better than previous 0.01u film caps, but nothing really major.
This is a little off-topic here, but anyway the thread is mine and I think this may be of interest.
I spent some good moments this night playing with my small battery-powered preamp, one that I made some years ago for tests.
One input, one output, an input pot, very minimalist.
+/- 16V with 4x7.2V nicad 300ma batteries.
The voltage at the op-amps is around +/-13V.
The circuit is very small, the pot is on the circuit and the board has around 4x4cm.
Talk about small signal path...
It uses a double op-amp.
I use it with my favourite double op-amp: the LM6172.
Tonight I opened this thing and started testing op-amps, again.
Here's what I tested:
- LM6172
- OPA2132
- NE5532 (from Signetics)
- THS4062
- AD826
- AD8620
And the winner is: LM6172.
It beats the OPA2132 by a very small margin, it's almost on par, you have to be an experient listener to pick the differences.
The THS4062 made my speakers move with the movement of the pot.
As I predicted, it has input DC-offset. Not bad sounding, but there's better and I think this is not indicated for audio use, it has some peculiarities for a voltage-feedback op-amp.
The Signetics NE5532 is not bad at all, but... nah. A little synthetic sounding.
The AD826 has a common characteristic usually found on AD op-amps: a recessed midband. Not neutral, veiled midband, not for me.
The AD8620 confirmed my first test some time ago: a "thin" treble, it lacks "body" and harmonics, it's a girl treble.
Now it's late, bed it is.
The pre is here, charging the batteries.
and I think this may be of interest.I spent some good moments this night playing with my small battery-powered preamp, one that I made some years ago for tests.
One input, one output, an input pot, very minimalist.
+/- 16V with 4x7.2V nicad 300ma batteries.
The voltage at the op-amps is around +/-13V.
The circuit is very small, the pot is on the circuit and the board has around 4x4cm.
Talk about small signal path...
It uses a double op-amp.
I use it with my favourite double op-amp: the LM6172.
Tonight I opened this thing and started testing op-amps, again.
Here's what I tested:
- LM6172
- OPA2132
- NE5532
(from Signetics) - THS4062
- AD826
- AD8620
And the winner is: LM6172.
It beats the OPA2132 by a very small margin, it's almost on par, you have to be an experient listener to pick the differences.
The THS4062 made my speakers move with the movement of the pot.
As I predicted, it has input DC-offset. Not bad sounding, but there's better and I think this is not indicated for audio use, it has some peculiarities for a voltage-feedback op-amp.The Signetics NE5532 is not bad at all, but... nah. A little synthetic sounding.
The AD826 has a common characteristic usually found on AD op-amps: a recessed midband. Not neutral, veiled midband, not for me.
The AD8620 confirmed my first test some time ago: a "thin" treble, it lacks "body" and harmonics, it's a girl treble.
Now it's late, bed it is.
The pre is here, charging the batteries.
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