Emile Posted July 30, 2018 Share Posted July 30, 2018 15 minutes ago, wdecho said: either one should have more than enough power for 95db or higher speakers in most any room. Yeah ... that's what I thought Just "roughly" measured it with a sound meter ... will try my Umik microphone when I get a chance. Many thanks, Emile Quote Link to comment Share on other sites More sharing options...
Guest wdecho Posted July 30, 2018 Share Posted July 30, 2018 After getting satisfied with volume give us a review of sound quality. Quote Link to comment Share on other sites More sharing options...
rjp Posted July 31, 2018 Share Posted July 31, 2018 7 hours ago, Emile said: rjp, thanks! I have the (standard) Bob Latino ST-70, with the 21 step attenuator (and Russian 6550 tubes and caps). Understand the linear vs log attenuation now - thanks! But ... still a bit puzzled why the 35 Watt ST-70 gives me a lot less volume than my 35 Watt vintage Kenwood. Well, moot point now as my wife is returning from a trip ... meaning won't be checking max sound levels till she leaves again Cheers, Emile Ok, so the amp you have is a Bob Latino ST70. Most people call it a VTA70 (Vacuum Tube Audio) to distinguish it from the original Dynaco ST70. This is an amp I am very familiar with. The input level required for full power out is 1V rms. I bench tested mine and was able to get 38W rms per channel before I started to see clipping. This was with both channels driven into 8 Ohms at 1KHz. The input voltage required to achieve this was just slightly over 1V rms (i.e., 1.4V peak). Any modern input source can easily provide the required voltage swing to get the full 35W rms out of the VTA70 without an active preamp. It could be that the Kenwood is boosting the input signal more so that the overall output is louder but the peaks are clipped. SO it could appear louder but there might be distortion present. Just a guess. Are you saying that if you set the volume to full on both amps your VTA70 is still not as loud as your Kenwood? 1 Quote Link to comment Share on other sites More sharing options...
MEH Synergy Posted July 31, 2018 Share Posted July 31, 2018 Ah yes, Gain staging is magical (necessary) for bringing out the best in a system. 1 Quote Link to comment Share on other sites More sharing options...
Guest wdecho Posted July 31, 2018 Share Posted July 31, 2018 I 8 hours ago, Westcoastdrums said: Ah yes, Gain staging is magical (necessary) for bringing out the best in a system. Using gain pre does seem to give system more gonads. Quote Link to comment Share on other sites More sharing options...
Guest wdecho Posted July 31, 2018 Share Posted July 31, 2018 As far as kind, type of potentiometer being used, it doesn't really matter if quality one used. Simple answer, if pot is turned wide open on amp and still not enough volume with our speakers pre is needed. Been listening on my LaScala's with 2 watt SET 45 amp the last few weeks with plenty of power and volume in more than average room. That is if nothing wrong with amp. Quote Link to comment Share on other sites More sharing options...
Guest wdecho Posted July 31, 2018 Share Posted July 31, 2018 12 hours ago, rjp said: Ok, so the amp you have is a Bob Latino ST70. Most people call it a VTA70 (Vacuum Tube Audio) to distinguish it from the original Dynaco ST70. This is an amp I am very familiar with. The input level required for full power out is 1V rms. I bench tested mine and was able to get 38W rms per channel before I started to see clipping. This was with both channels driven into 8 Ohms at 1KHz. The input voltage required to achieve this was just slightly over 1V rms (i.e., 1.4V peak). Any modern input source can easily provide the required voltage swing to get the full 35W rms out of the VTA70 without an active preamp. It could be that the Kenwood is boosting the input signal more so that the overall output is louder but the peaks are clipped. SO it could appear louder but there might be distortion present. Just a guess. Are you saying that if you set the volume to full on both amps your VTA70 is still not as loud as your Kenwood? Nice to have another technical minded person on this forum with test equipment. Forgive and forget our past discussion on L-pads. If you only need 1V rms for full output there is no need for pre except maybe with phono. Most any source will drive to full output even computer. If nothing wrong with members amp I think if may just be he is not familiar with quality stepped pot. Most consumer amps pots reach almost max power at 10:30 whereas better equipment take full advantage of control over volume. I like to reach my listening level of sound around 2:00 PM on the potentiometer. Quote Link to comment Share on other sites More sharing options...
Tarheel Posted July 31, 2018 Share Posted July 31, 2018 Haven't read all 4 pages and may have missed it. Have you contacted Bob Latino for help? 1 Quote Link to comment Share on other sites More sharing options...
rjp Posted July 31, 2018 Share Posted July 31, 2018 1 hour ago, wdecho said: If you only need 1V rms for full output there is no need for pre except maybe with phono. Most any source will drive to full output even computer. If nothing wrong with members amp I think if may just be he is not familiar with quality stepped pot. Most consumer amps pots reach almost max power at 10:30 whereas better equipment take full advantage of control over volume. I like to reach my listening level of sound around 2:00 PM on the potentiometer. Technically speaking 100% correct. Zero NEED for a preamp. But preamps (good ones, I'm told) add a host of magical musical qualities and gonads (a.k.a., dynamics). I have recently been involved in extensive research and technical discussions on this matter, and though I could uncover no good technical reason for the preamp, I just bought two of them so I can find out for myself if they really make the VTA70 sound better (compared to the 21-step attenuator direct approach). I purchased a Dynaco PAS 3X from ebay and a VTA SP12 kit from tubes4hifi. I am really looking forward to building the SP12 kit! If I realized I could get the basic board for under 200 bucks I would have skipped the PAS option. Well, it will be fun to try both. I'll keep the one I like and sell the other. They will both be in super amazing condition when I'm done owning them. So...I intend to be in serious preamp mode shortly You know what's the dumbest thing? Calling a simple potentiometer or stepped attenuator a "Passive Preamp". Well, actually, that's just a misnomer. The dumbest thing is paying 800 dollars for "really good ones" 1 Quote Link to comment Share on other sites More sharing options...
avguytx Posted July 31, 2018 Share Posted July 31, 2018 My VTA ST-70 with the 6550's would run the snot out of my CF-3's, Norman Lab Model 9's (less efficient) and definitely had no problem running my Belle clones with authority. Great sounding amplifier for the money. 1 Quote Link to comment Share on other sites More sharing options...
Emile Posted July 31, 2018 Share Posted July 31, 2018 1 hour ago, Tarheel said: Have you contacted Bob Latino for help? Yeah ... all I got was turn TVA-70 to max; use pre-amp for volume. Yes; works very good ... just "limited" max volume (say 85-88dB's on Forte's). Quote Link to comment Share on other sites More sharing options...
avguytx Posted July 31, 2018 Share Posted July 31, 2018 I use an Onkyo P-3000R preamp with my amps now and also a fully modified Carver C-1 with what's called the "BillD mods". They are both great sounding preamps. 1 Quote Link to comment Share on other sites More sharing options...
NOSValves Posted July 31, 2018 Share Posted July 31, 2018 On 7/30/2018 at 12:22 PM, rjp said: Emile, Are you running an original ST70 or a modified version? Where is the attenuator you mention installed? BOTH a stepped attenuator and ANY volume pot of ANY taper will be effectively out of the circuit at full clockwise rotation (well, unless it's wired up wrong). What is you input source? Actually no they are never 100% out of the circuit they always add a resistive path to ground... 1 Quote Link to comment Share on other sites More sharing options...
Guest wdecho Posted July 31, 2018 Share Posted July 31, 2018 1 hour ago, rjp said: 1 hour ago, rjp said: Technically speaking 100% correct. Zero NEED for a preamp. But preamps (good ones, I'm told) add a host of magical musical qualities and gonads (a.k.a., dynamics). I have recently been involved in extensive research and technical discussions on this matter, and though I could uncover no good technical reason for the preamp, I just bought two of them so I can find out for myself if they really make the VTA70 sound better (compared to the 21-step attenuator direct approach). I use a linestage or buffer for all my amps to be able to use a sub. I do think a good pre adds some omph to the presentation. Quote Link to comment Share on other sites More sharing options...
rjp Posted July 31, 2018 Share Posted July 31, 2018 1 hour ago, NOSValves said: Actually no they are never 100% out of the circuit they always add a resistive path to ground... Fair enough. I meant they were 100% out of the signal path. I wonder, can the additional path to ground make any difference in the sound? The attenuator Bob supplies is 100K. The VTA board itself has an input impedance of about 270K I believe. So the (full volume) input impedance at the RCA jacks with the stepped attenuator in place must be down to about 75K. The output impedance of an iPhone 6S is 3.2 Ohms, so even 75K seems huge in comparison. A higher resistance attenuator could be used to keep the input impedance up, but that would potentially introduce another more significant problem. Loss of high frequency content due to Miller effect. I assume this played into the 100K choice. 1 Quote Link to comment Share on other sites More sharing options...
richieb Posted August 1, 2018 Share Posted August 1, 2018 --- I do believe one gets a true "look" into the sound of an amp when using a purely passive (volume pot) for the amp to speaker interface. Bsically nothing but the facts - nothing added to or subtracted from what the amplifier really sounds like. Much like tone controls an active preamp can and will "tailor" what you hear, skewing what the amp was engineered to sound like. Some skew to the good, some to the bad but few achieve the holy grail "gain with wire" sound. And those that do become rather $$$$ -- 1 Quote Link to comment Share on other sites More sharing options...
Guest wdecho Posted August 1, 2018 Share Posted August 1, 2018 1 hour ago, richieb said: --- I do believe one gets a true "look" into the sound of an amp when using a purely passive (volume pot) for the amp to speaker interface. Bsically nothing but the facts - nothing added to or subtracted from what the amplifier really sounds like. Much like tone controls an active preamp can and will "tailor" what you hear, skewing what the amp was engineered to sound like. Some skew to the good, some to the bad but few achieve the holy grail "gain with wire" sound. And those that do become rather $$$$ -- I like that approach as well but with my phono I need some gain. When I just want to hear amp and be able to use sub I use my B1 buffer for volume control. The Firstwatt B1 is about as neutral as it gets some say even better than passive pots. At least Nelson Pass believes so. http://www.firstwatt.com/b1.html Quote Link to comment Share on other sites More sharing options...
Emile Posted August 1, 2018 Share Posted August 1, 2018 Thinking about selling my VTA ST70 ...and maybe build a pair of VTA M125 mono-blocks. Have over $1100 in it ... 7 months old ... probably used less than 20 hours (9550 tubes not even fully burned in). Just looking for some response before I put in in the garage sale No clue what a reasonable price is Cheers, Emile Quote Link to comment Share on other sites More sharing options...
rjp Posted August 1, 2018 Share Posted August 1, 2018 5 hours ago, richieb said: --- I do believe one gets a true "look" into the sound of an amp when using a purely passive (volume pot) for the amp to speaker interface. Bsically nothing but the facts - nothing added to or subtracted from what the amplifier really sounds like. Much like tone controls an active preamp can and will "tailor" what you hear, skewing what the amp was engineered to sound like. Some skew to the good, some to the bad but few achieve the holy grail "gain with wire" sound. And those that do become rather $$$$ -- I tend to agree. Every amplifier has a characteristic sound. It seems that the question comes down to do you which sound you like better, the preamp, or the power amp? From what I'm reading it appears most of the big money is invested in preamps to get a super great sounding but very fragile signal, and then the power amp is just about making this louder and strong enough to drive speakers. So using a path into the power amp that is as transparent as possible only has value if indeed the power amp is what you want to hear. 1 Quote Link to comment Share on other sites More sharing options...
Emile Posted August 2, 2018 Share Posted August 2, 2018 OK; put my VTA ST70 in the garage sale section to see if anyone is interested. Just made someone an offer for a Pioneer SX-1250 ... big beast (and big $$$) Just easier when playing with multiple speakers and multiple components Quote Link to comment Share on other sites More sharing options...
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