Tuesday, April 13, 2010
Murphy's Law strikes at Preamp Shootout
First, a big thank you to Francis for being an accommodating host for us at the shootout. He recently had his Shanling CDP modded by a local guru to have the opamps working in class A. It was wired to use this stage with XLR connections and single ended connections via RCA will rely on the CDP's in-built tube buffer stage.
When it was my turn, with the same track played, there was this nasal vocal that emerged from the speakers... something was not right. I knew that there was nothing I could do if the preamp was at fault... I did not bring any tools and was definitely not in the mood to troubleshoot even if I brought tools... I told Francis that we should move on and bring in another preamp. By the time I was finished unhooking my preamp, I was perspiring as the air conditioning by then, was not as cold... There were more than 10 people in the room.
Later, Nick and William suggested that either I have some loose part due to transporting it to the location or it could be clipping. I told them that my bias for the 5687 was at -2.1V. Nick was guessing that it could be that the CDP's tube buffer had gain in it, which is not uncommon of the chinese designs that he came across. I thought it was a possible hypothesis. I was just disappointed that the audience did not get to hear the preamp. I was most interested to know if it lacked "speed", as that was the general comment about the tube preamps... unmatched for vocals, but lacked speed. The mercury rectifier and the shunt regulated supply should satisfy any "Need For Speed" fans. A quick A/B was done at some point in time to check if the 24/96 upsampling vs the normal red book had any effect on the sound as the Shanling CDP had a remote controllable feature for this. One guy was asked of his opinion and he did not have any reply at first, when the feature was explained, he said something like the 24/96 was better or something... I phased out and did not pay much attention at this point... I disagreed quietly as I could not discern any noticeable difference... not strikingly huge anyways... and not in the few seconds of A/B switching.
I tend not to be too judgemental when it comes to music. There are always generalisation that certain stuff cause certain sound. I think the DIY guy especially, should be open when approaching different topologies and implementation. In the same vein, most commercial gear people seem to have this unspoken discrimination of folks who build their gear. It is almost always in the same breath as low cost. I wonder how many of them would know that Tamura is used by Air Tight, Sun Audio, etc. Tango is used by Wavac, etc. Lundahl is used by Manley, VAC, etc. Some parts used by the DIY guys will rival those used by the commercial companies. In fact, it may in some instances, trend into the esoteric and exotic range.
When the solid state preamp brethren were playing, I gave them lots of leeway in their sound presentation. However, I felt most of them just seemed too bright and shrill sounding in the treble regions for extended listening. I immediately want to leave the room or find refuge from the assailing soundwaves... Nick echoed similar sentiments. Saying that the tube folks will not adjust to this type of sound well. I was also surprised that the Densen preamp (which the owner said had a SGD3k price tag when new) exhibited almost the same shrillness. I used to own the Densen Beat 100 integrated and found that it was quite a nice piece of gear. But it really required warming up to sound the best though. I'm not sure if that preamp was already warming up prior to being played in the system or my ears (or age have caught up) have slowly grown used to something not as exciting in the higher frequencies.
Unfortunately, I had to leave early as I had to bring Lucas for his lessons. So I promptly packed my stuff, thanked Francis and said my good byes to people I knew. On my way back, I was thinking that my system could be too tuned to my chain of equipment. DAC was a passive I/V unit, which had lower than the normal 2v RMS output. Maybe that was the reason why it did not clip the preamp... but 2.1V bias point would mean an input swing of 4.2V, and should be sufficient for any decently built gear...
Later in the day, when I was heading to Novena with my family, I got a call from Nick, informing me that my preamp should be fine as the problem of the nasal voices is back to haunt every gear they tried! I then recalled Francis saying that the CDP was modded and was running hot into class A. I guessed it could be due to that. It exhibited thermal runaway. That was just a conjecture. Not sure what really happened... cos the opamps were biased into class A and that should only affect the XLR connection. Why would RCA connected preamps be affected as well? No idea... but the guys were playing LP instead and seemed to be having fun.
I concluded that either I should raise my bias point, or don't lug such tailored stuff over for shootouts when the possibility for mismatch would be great. Oh, and I just listened to my system... it's working... no nasal voices.
Some pics here... from my iPhone.