vu meters on A VTA St-70 Kit

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vu meters on A VTA St-70 Kit

Postby islanddave » Mon Jan 14, 2013 3:14 pm

Hello All,

First post here.......seems like you people have a great board and I am happy to become part of it. I have a VTA ST-70 Kit that I built recently and have been enjoying it immensely. How would I go about wiring some VU meters to it. I would like to move the bias points up top to the slotted portions of the upper chassis in front of the tubes. This would leave me the locations where the former tube sockets were on the front of the chassis to mount the meters there. Where would the wires from the meters go to?

Thanks Dave
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Re: vu meters on A VTA St-70 Kit

Postby burnedfingers » Sun Jan 20, 2013 8:42 am

A Volume Unit (VU) meter or Standard Volume Indicator (SVI) is a device displaying a representation of the signal level in audio equipment. The ASA standardized it in 1942 ( C16-5 - 1942) for use in telephone installation and radio broadcast stations. Consumer audio equipment often features VU meters, either because they are useful (basically in sound recording equipment), or just for their looks.

The original VU meter is a passive electromechanical device, namely a 200µA DC d'Arsonval movement ammeter fed from a full wave copper-oxide rectifier mounted within the meter case. The mass of the needle causes a relatively slow response, which in effect integrates the signal, with a rise time of 300ms. 0VU is equal to +4 [dBm], or 1.228 volts RMS across a 600 ohm load. 0VU is often referred to as "0dB".[1] The meter was designed not to measure the signal, but to let users aim the signal level to a target level of 0 VU (sometimes labelled 100%), so it is not important that the device is non-linear and imprecise for low levels. In effect, the scale ranges from −20 VU to +3 VU, with −3 VU right in the middle. Purely electronic devices may emulate the response of the needle; they are VU-meters inasmuch as they respect the standard.

The VU-meter (intentionally) "slows" measurement, averaging out peaks and troughs of short duration, and reflects more the perceived loudness of the material than the more modern and initially more expensive PPM meters. For this reason many audio practitioners prefer it to its alternatives, though the meter indication does not reflect some of the key features of the signal, most notably its peak level, which in many case, must not pass a defined limit.


The description that I posted above describes the usage of a VU meter as well as some of the history behind it. I believe that the VU meter is more of an indicator for signal level for recording. Unless re-calibrated I believe it will peg easily with very little signal. You might want to consider something along the lines of a watt meter/led display to give a more accurate indication of actual sound level as opposed to the show effect of the VU meter. As mentioned above the +4 dbm= 1.228 volts. 0 db = .775volts across a 600 ohm load. Your peaks would exceed this.
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Re: vu meters on A VTA St-70 Kit

Postby Shannon Parks » Sun Jan 20, 2013 9:25 am

Dave, did you want a VU meter or a DC bias meter?

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Re: vu meters on A VTA St-70 Kit

Postby islanddave » Tue Jan 22, 2013 9:08 am

Actually I made a mistake by saying vu meters..........watt meters are what I would like to install. I know they are not necessary at all but i just think that they would look really nice.
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Re: vu meters on A VTA St-70 Kit

Postby burnedfingers » Wed Jan 23, 2013 5:55 am

Meters are really slow vers LED displays. I would suggest purchasing a Radio Shack Watt meter. Look for the older version that has meters and Led's. Check ebay.


Been there many years ago with SS amplifiers. I just had to have watt meters. I found out that I pushed the system harder to hit 100 watt peaks or higher and I eventually ended up trashing a midrange driver in a pair of Altec Model 9 speakers.

I would suggest that you put your money in tubes, or caps for your amp instead of meters.
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Re: vu meters on A VTA St-70 Kit

Postby islanddave » Thu Jan 24, 2013 7:43 am

I would agree that this is in no way an "upgrade" I have already upgraded the amp to what I have read is it's fullest potential. The only remaining would be a nice triplet of NOS 12BH7's for the driver board. I just think that the watt meters would look cool that's all. Still where would they be wired into the circuit?

Thanks Dave
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Re: vu meters on A VTA St-70 Kit

Postby burnedfingers » Thu Jan 24, 2013 5:27 pm

Watt meters parallel the output of the amplifier. It is important to have watt meters that are correct for the load. Some watt meters have a switch for 4 or 8 ohm speakers if they are aftermarket meters. It is possible to build a circuit and have several scales for different listening levels. Do a search for the Marantz M250 and look up the meter circuit and it will show you what is needed.

What did you do for amp upgrades? Just the driver board? or other modifications?
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Re: vu meters on A VTA St-70 Kit

Postby islanddave » Sat Jan 26, 2013 7:12 pm

Thanks for the advice. It isn't a real st-70 it is one of Latinos kits..................couldn't love it any more. Went with the upgrade pio caps and put Gold Lion kt-66's for the power tubes and a NOS Mullard Gz 37 rectifier tube. The driver board has some old 12bh7 rca's in it that really make it sound sweet.

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Re: vu meters on A VTA St-70 Kit

Postby burnedfingers » Sun Jan 27, 2013 5:54 am

Well, you can gain quite a bit by changing to a add on power supply board. I realize that your board has increased capacitance but additional capacitance is needed in order to make the Dynaco perform even better. In the past I owned one of Bob's boards as a matter of fact it was the first Dynaco I put together. While its a good board to be honest there are better performers out there. I will point out that I have not tried Shannons boards but I have tried Geeks boards.
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Re: vu meters on A VTA St-70 Kit

Postby Bob01605 » Sun Jan 27, 2013 12:00 pm

Contrary to what burnedfingers has said, addition capacitance beyond a certain point does not make the VTA version of the ST-70 amp sound "better" or make more power. Increases in total amp capacitance over and above the the "anemic" 90 uF total on the ORIGINAL Dynaco ST-70 DO HELP the ORIGINAL ST-70 amp play better. The VTA ST-70 has 464 uF of total capacitance to run the amp. This has proven to be MORE than enough to handle current flow of the VTA ST-70 at any volume level. At one point I added in another 165 uF to a VTA ST-70 by using the VTA ST-120's Supplmentary Cap Module or SCM (total capacitance now with an SCM added = 629 uF). The VTA ST-70 amp with the added 165 uF of capacitance showed no more power, distortion rates were the same and the amp did not sound any different.

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Re: vu meters on A VTA St-70 Kit

Postby burnedfingers » Sun Jan 27, 2013 6:37 pm

burnedfingers wrote:Well, you can gain quite a bit by changing to a add on power supply board. I realize that your board has increased capacitance but additional capacitance is needed in order to make the Dynaco perform even better. In the past I owned one of Bob's boards as a matter of fact it was the first Dynaco I put together. While its a good board to be honest there are better performers out there. I will point out that I have not tried Shannons boards but I have tried Geeks boards.
,

Bob, I didn't say that any additional power would be made by the addition of the Triode power supply board. I didn't claim any difference in measurable distortion. I didn't claim any specific capacitance size either. The VTA as you politely pointed out with the upgrade has a total of 464 mfd. The Triode the way I put them together has 506mfd in the following order 41,195,135, and 135 and I will point out the capacitors are in series to increase the voltage rating so there are two 82's, two 390's, two 270's, and two 270's. This raises the first cap rating to 800 vdc and the rest to 500vdc. In addition I use only 105c rated caps. This point alone I push to people wanting to upgrade their 70 instead of replacing the weak link multi cap that you parallel several sections in. You seem to favor and push the russian coupling caps and I won't argue that point and by the same token I suggest what I feel is a superior cap upgrade. The Power supply board provides everything in one specific spot and yes I realize that you use your own bias circuit and that portion of the power supply board simply isn't needed when using your board.

Hey the guy seems to be happy with what he has and good for him. I simply suggested an upgrade. To me the upgrade is a way to eliminate the problematic multisection capacitor that has a proven faulty track record. While you seem to have done some work trying to provide a viable well performing product the addition of the power supply board is simply a better way to go. Yes, I also have several distortion analyzers and all the necessary equipment to make any and all performance tests necessary in order to achieve a maximal effect. Contrary to what you might believe I actually owned several of the dynaco 70's with your VTA driver board. One had the power supply board from Triode and the other was setup with your 464 mfd supply with the ganged multicap. Bob, I also have two sets of Klipsch Cornwall clones and two identical Aikido line stages in other words a nice little setup in which to do an A/B test. Out of 5 people that did my A/B test all favored the Triode supplied power supply board. Bob, I always buy two and or make two of everything and this rules out any possibility of an unfair test and I do this with every board I'm interested in.

I would be more than happy to discuss this further on my Dynaco2forum board and you don't have to worry because your not banned there unlike myself on your board.
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Re: vu meters on A VTA St-70 Kit

Postby burnedfingers » Tue Jan 29, 2013 6:04 am

out of respect for this board and its members I have invited Bob to drop in to my forum and continue this discussion. Hopefully he will do so. For any wanting to take a look see I will post this link

http://dynaco2forum.forumsmotion.com/t2 ... forum#1544
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