I tested the AD797 on my El Cheapo phono pre (MM only).
I know this op-amp is better for low input impedaces like an MC input stage, but I just had to test it.
I removed the OPA637s and put these ones in.
The AD797 is a little noisier than the OPA637 on THIS circuit (MM), and, although a good sounding op-amp, I've put the OPA637, sounds better to me (on this application).
I haven't tried the AD797 more deeply, so I don't have a definitive oppinion.
It seams promising, but on the right application.
I know this op-amp is better for low input impedaces like an MC input stage, but I just had to test it.
I removed the OPA637s and put these ones in.
The AD797 is a little noisier than the OPA637 on THIS circuit (MM), and, although a good sounding op-amp, I've put the OPA637, sounds better to me (on this application).
I haven't tried the AD797 more deeply, so I don't have a definitive oppinion.
It seams promising, but on the right application.
guys,
I need some help here
After reading this thread right from the begining, I had built a similar preamp using Pavel Macura Schematic with some modification.
Modification as follows:
Used OPA2314PA and BUF634P (Stereo version)
R2 = 1 Mohm
R3 & R4 = 3.3 kohm
R12 = omitted
Voulme Pot = 100 kohm B x 2
(faked it with 18kohm between out and gnd)
The rest remain unchanged.
I had problem with the volume control. Less tahn 1/4 of a turn, I got full volume already. The volume was not log as I had faked it? What when wroung here?
Mind my noob question. Thanks for reading
I need some help here
After reading this thread right from the begining, I had built a similar preamp using Pavel Macura Schematic with some modification.
Modification as follows:
Used OPA2314PA and BUF634P (Stereo version)
R2 = 1 Mohm
R3 & R4 = 3.3 kohm
R12 = omitted
Voulme Pot = 100 kohm B x 2
(faked it with 18kohm between out and gnd)
The rest remain unchanged.
I had problem with the volume control. Less tahn 1/4 of a turn, I got full volume already. The volume was not log as I had faked it? What when wroung here?
Mind my noob question. Thanks for reading
juniorsg73 said:
I had problem with the volume control. Less tahn 1/4 of a turn, I got full volume already. The volume was not log as I had faked it? What when wroung here?
Is the pot you are using linear? If I am not wrong that faking can be applied only with linear pots, so they become "almost" log.
Have you tried the pot without the resistor?
Carlos
carlos,
firstly, thanks for the quick response.
yup. the pot that i used is linear.
initially, i configured the pot without the "fake" resistor.
i got full voulme in less than a 1/4 turn of the knob.
then tried with 18kom "fake" resistor, same problem with full volume in less than a quater turn
i was wondering could it be due to the input impedence (R2) that I choose to use at 1 Mohm (ot 100k as in the scehmatic) ? how about the values of R3 & R4 being 3.3 kohm (thus, gain = 2) with R12 = omitted. in short, could it be due to the modification that i had done to the original schematic by Pavel that lead to the problem that i am experiencing now?
will try to use an Alps Dual Log Pot to see if the problem persist..
please advice....... thanks in advance
firstly, thanks for the quick response.
yup. the pot that i used is linear.
initially, i configured the pot without the "fake" resistor.
i got full voulme in less than a 1/4 turn of the knob.
then tried with 18kom "fake" resistor, same problem with full volume in less than a quater turn
i was wondering could it be due to the input impedence (R2) that I choose to use at 1 Mohm (ot 100k as in the scehmatic) ? how about the values of R3 & R4 being 3.3 kohm (thus, gain = 2) with R12 = omitted. in short, could it be due to the modification that i had done to the original schematic by Pavel that lead to the problem that i am experiencing now?
will try to use an Alps Dual Log Pot to see if the problem persist..
please advice....... thanks in advance
guys,
had tried using an Alps 100k log dual pot.
with that, at about 30 degree clockwise, i got full volume.
can anyone here advice me as to how to make use of the full sweep such that i had smooth graduation in the volume.
do i need to change the gain or use 50k log pot instead of 100k log pot....
i'm not electrically trained thus requires help over here....
thanks guys
had tried using an Alps 100k log dual pot.
with that, at about 30 degree clockwise, i got full volume.
can anyone here advice me as to how to make use of the full sweep such that i had smooth graduation in the volume.
do i need to change the gain or use 50k log pot instead of 100k log pot....
i'm not electrically trained thus requires help over here....
thanks guys
Hi Guys
I have been listening to my build of the Pavel / Carlos pre (less enclosure) and it sounds wonderful feeding my inverted gc.
I have the same problem as juniorsg73. I first tried a 10k log bourns pot I had around and the resolution was very small. I then tried a noble 25k pot I borrowed from a Soundcraftsmen Pre. Same result. I then changed the 3.3k resistor to 4.7 k to lower the gain a touch which seemed to help. I think most of my problem stems from the fact that my speakers are quite efficient (Klipsch Lascala) and don't require a lot of drive for normal listening. (I know LISTEN LOUDER) (Am in appartment)
The gain issue is not a problem with the phono pre(VSPS opa637) as it has less o/p than my cdp.
Options as I see them are:
1. Pad the input for the cdp. (More resistors in chain)
2. Lower the gain of the o/p stage on the cdp(rotel rcd 965bx). (Haven't checked yet to see if this is feasable but I can't see why not)
3. Lower the gain of the line amp again. (works good as is with phono)
4. Lower the gain of the gc amp.(Still have large difference between phono and cdp)
If anyone wants to comment I would be very interested.
Thanks
Hugh
I have been listening to my build of the Pavel / Carlos pre (less enclosure) and it sounds wonderful feeding my inverted gc.
I have the same problem as juniorsg73. I first tried a 10k log bourns pot I had around and the resolution was very small. I then tried a noble 25k pot I borrowed from a Soundcraftsmen Pre. Same result. I then changed the 3.3k resistor to 4.7 k to lower the gain a touch which seemed to help. I think most of my problem stems from the fact that my speakers are quite efficient (Klipsch Lascala) and don't require a lot of drive for normal listening. (I know LISTEN LOUDER) (Am in appartment)
The gain issue is not a problem with the phono pre(VSPS opa637) as it has less o/p than my cdp.
Options as I see them are:
1. Pad the input for the cdp. (More resistors in chain)
2. Lower the gain of the o/p stage on the cdp(rotel rcd 965bx). (Haven't checked yet to see if this is feasable but I can't see why not)
3. Lower the gain of the line amp again. (works good as is with phono)
4. Lower the gain of the gc amp.(Still have large difference between phono and cdp)
If anyone wants to comment I would be very interested.
Thanks
Hugh
preamp schematics
Hi carlosfm,
still followed this thread in order to build the preamp...
unfartunately i didn't found the schematics of the headphone-amp and the line-loops.javascript:smilie('
')
xeye Did you made the standard applications from the datasheets?
In germany the opa627 costs about 20 Euro per chip. yesterday i found a seller via ebay for about 30 Euros per 10! Is it possible (with low tech ) do determin if these chips are genuine (or not)?
What kind of source-switch did you use in the pre? Do i really need a hyper dyper gold-platin-diamond switch?
Hi carlosfm,
still followed this thread in order to build the preamp...
unfartunately i didn't found the schematics of the headphone-amp and the line-loops.javascript:smilie('
')xeye Did you made the standard applications from the datasheets?
In germany the opa627 costs about 20 Euro per chip. yesterday i found a seller via ebay for about 30 Euros per 10! Is it possible (with low tech ) do determin if these chips are genuine (or not)?
What kind of source-switch did you use in the pre? Do i really need a hyper dyper gold-platin-diamond switch?
Re: preamp schematics
Yes, the circuit is basically the same, but with more gain.
I used 10x, if I remember.
On the headphone amp I used the (double) OPA2132+BUF634.
Are there false OPA627s around?
You should preferably use a reliable switch.
Something better than those cheap plastic-body rotary switches.
slackman said:Hi carlosfm,
still followed this thread in order to build the preamp...
unfartunately i didn't found the schematics of the headphone-amp and the line-loops.javascript:smilie('
xeye Did you made the standard applications from the datasheets?
Yes, the circuit is basically the same, but with more gain.
I used 10x, if I remember.
On the headphone amp I used the (double) OPA2132+BUF634.
slackman said:
Are there false OPA627s around?
slackman said:
You should preferably use a reliable switch.
Something better than those cheap plastic-body rotary switches.
because of high costs of quality-semiconductors labelling lowcost items to highcost is practice. this often occurs with expensive audio- transistors (japan types) and of course in the microprocessor market.
At the price i've payed for the 'ebay-chips' i was a little afraid (1/8th of normal price).
At the price i've payed for the 'ebay-chips' i was a little afraid (1/8th of normal price).
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