Correct me if I am wrong but I don't think you are supposed to deviate from stock supplied tube types (for instance substituting a 12 ax7 for a 12 au7, as they have different gains. Different brands of 12 au7s will give different sonic signatures. 12au7's have the lowest gain and lowest intrinsic distortion (compared to 12ax7s and 12at7s. To my ears, the Mullards are soft,warm, and lush sounding. Telefunkens are very neutral sounding, and detailed. The RCA's, and their premium variants, 5814s, and 6189's are kind of "in-between". The regular version Amperex tubes seem to me to have more "air" and top end detail than the others, and the premium Amperex 7316 versions are highly sought after (I have not heard them). My preference (IMHO) is for the Telefunkens, but your ears will tell you what you prefer,as, in your application, results may vary.
Tube Comparisons on VTL 7.5
I just did a bunch of comparisons on my VTL 7.5 preamp. A long process. These are all based on my listening opinions in my system. Some of you will benefit from this as it is an apples to oranges comparison. I know some of you are waiting for this.
First Straight to the results of my peference;
1) Telefunken 12AU7s - great mids.
2) Svetlana (from VTL) 12AX7s - live sound, very good mids
3) Siemens 12AU7s - Not my cup of tea, but good overall
4) EH 12 AU7s - Not very good at all
I did the comparisons for a few reasons. First the gain on the 12AX7 is very high under some circumstances (depends on the recording). Second, my preamp originally came (second hand) with the EH 12AU7s, so I purchased new 12AX7s. Then I felt the gain was slightly too much on some recordings. I then purchased the Telefunkens & Siemens to find out & learn more.
I matched volumes w. a test tone & SPL meter on all tubes first & kept the volume control at set volumes for listening so everything was mostly equal. There was no talking or sounds between demos to keep my auditory memory as intact as possible. I used an SACD sampler of Rock, jazz, & classical. I also switched back & forth multiple times on each track for each tube until I was more or less sure beyond a question.
The Telefunken just has amazing midrange. It is missing the last bit of treble energy & the very lowest bit of the bottom octave. It is very smooth sounding & you can listen all day. You really don't know you are missing anything until you listen to the Svetlana 12AX7s.
Now the 12AX7 has great midrange as well but it isn't as smooth or musical as the Telefunkens. It does have great dynamics and gives the VTL 7.5 a different personality. You don't get the sence of space or ambience as you do w. the telefunken. You do get definitely more solid bass which you feel in your stomach. The treble is alive & the mids are musical as well.
The Siemens has more treble energy than the Telefunken, but the midrange did't have that musical flow of the Telefunken. The Siemens also didn't have the dynamic flow of the 12AX7s.
Lastly the EH 12AU7. It just makes the VTL 7.5 sound lifeless or soft. It does have decent extension at the top end. The bass isn't up to the 12AX7. But most of all, it sounded lost in trying to make the music flow.
My final conclusion is that I need to figure out if a Telefunken 12AX7 will do it all. But honestly doing this comparison is a pain in the....
Anyone have any ideas of what is next I am open for input.
First Straight to the results of my peference;
1) Telefunken 12AU7s - great mids.
2) Svetlana (from VTL) 12AX7s - live sound, very good mids
3) Siemens 12AU7s - Not my cup of tea, but good overall
4) EH 12 AU7s - Not very good at all
I did the comparisons for a few reasons. First the gain on the 12AX7 is very high under some circumstances (depends on the recording). Second, my preamp originally came (second hand) with the EH 12AU7s, so I purchased new 12AX7s. Then I felt the gain was slightly too much on some recordings. I then purchased the Telefunkens & Siemens to find out & learn more.
I matched volumes w. a test tone & SPL meter on all tubes first & kept the volume control at set volumes for listening so everything was mostly equal. There was no talking or sounds between demos to keep my auditory memory as intact as possible. I used an SACD sampler of Rock, jazz, & classical. I also switched back & forth multiple times on each track for each tube until I was more or less sure beyond a question.
The Telefunken just has amazing midrange. It is missing the last bit of treble energy & the very lowest bit of the bottom octave. It is very smooth sounding & you can listen all day. You really don't know you are missing anything until you listen to the Svetlana 12AX7s.
Now the 12AX7 has great midrange as well but it isn't as smooth or musical as the Telefunkens. It does have great dynamics and gives the VTL 7.5 a different personality. You don't get the sence of space or ambience as you do w. the telefunken. You do get definitely more solid bass which you feel in your stomach. The treble is alive & the mids are musical as well.
The Siemens has more treble energy than the Telefunken, but the midrange did't have that musical flow of the Telefunken. The Siemens also didn't have the dynamic flow of the 12AX7s.
Lastly the EH 12AU7. It just makes the VTL 7.5 sound lifeless or soft. It does have decent extension at the top end. The bass isn't up to the 12AX7. But most of all, it sounded lost in trying to make the music flow.
My final conclusion is that I need to figure out if a Telefunken 12AX7 will do it all. But honestly doing this comparison is a pain in the....
Anyone have any ideas of what is next I am open for input.
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