Promitheus TVC passive preamp anyone?

ratso · « **Reply #1960 on:** 6 Jul 2007, 02:50 am »

i have asked a similar question in the bolder cable forum, so i hope i don't get accused of double posting. but something is very confusing to me. i have just ordered a new tvc (custom made box made out of ebony wood with knobs and cones, i could post a pix when it arrives if anyone interested). nowhere on the promi website, or in any forums i have read does it give minimum outputs or sensitivities for your equipment to be used with the promi. in other words, my squeezebox that i want to run through it has an output of 1.1V. is this hot enough? i have read things like "if you have sensitive speakers" or "if you have a sensitive enough power amp", what does that mean? can anyone give us noobs some actual numbers that would represent a ballpark figure for things like amp and speaker sensitivity, cdp output, etc? or is this impossible and dependent on individual systems. this help would be very appreciated, at least by me.

thanx, ratso.

Whitese · « **Reply #1961 on:** 6 Jul 2007, 12:31 pm »

You guys mucking around with caps...do ya'all have a desoldering iron, or just use the soldering iron? (which is what I do)...I want to replace the caps under the tubes and the space is very very tight. Maybe i should buy a thinner probe.

Gaara · « **Reply #1962 on:** 6 Jul 2007, 11:04 pm »

Ratso,

I will give your ? a whirl. First the way a TVC works you can't really give simple output impedance. Most pre-amps have a specified output but with a TVC the output impedance changes depending on the level of attenuation.

Gain with a passive pre-amp such as your TVC is maxed out with the gain of the source. With your SB3 the maximum output is 1.1v, if you were using an active pre-amp this number could be higher since active pres can increase the signal strength.

Now the issue that you could have is not enough gain to drive your amp. The input sensitivity of an amp is, to my knowledge, the minimum voltage to get to full output. So if say your amp had an input sensitivity of 2v but your SB3 only outputs 1.1v you will never get to full power.

This is where the "Sensitive speakers" or "sensitive power amp" come into play. I will cover the amp first. If you have a amp with input sensitivity of say .5v then max output could be attained at .5v. This means that with your 1.1v source you could get the max output of the amp with a TVC.

Now the "sensitive speakers" comment has to do with your listening preference. If you had speakers that had a sensitivity of 95db then they could attain 95db at 1 meter away with 1 watt of power. Now let us assume that you are using your 1.1v SB3 as a source with a TVC, and the amp has a input sensitivity of 2v and a output of 100watts. Since the max signal being sent to the amp is 1.1v we won't be able to get 100w from the amp, but it may not matter. It takes only 1 watt to get to 95db so if you listened at around 90db it would take less then 1 watt of power. This is somewhat simplified and we are ignoring distances and peaks but thats ok. The point is that even though you may not get full output on the amp since the TVC is passive you may never need it. Case in point I have a amp with 1.9v input impedance and a source that is around .7v, I have never had a issue using a TVC between.

If you want some basic ball parks a average digital source will have 2v output, amp will have between 1.5-2v input sensitivity, and your average speakers are around 89db sensitive.

In your situation the easiest way to see if there is a problem is to see how high you have the TVC volume set at. If you are a click or two away from max then there is a issue, if you are on the lower half of the scale then no problems.

If you have any other questions feel free to ask.

Jared

tanchiro58 · « **Reply #1963 on:** 6 Jul 2007, 11:25 pm »

Jared,

I have questions for you since I encountered this problem with my Promitheus DAC (it is still in break-in process).

I am using SB3 to Promi DAC (set at 2V output) to my active tube preamp (around 2V output) to my tube amp (I do not know how many volts input sensitivity) and my horn-based speakers (97dB+). In about first week the sound was like to be expected (warm rounded sound). But in a couple days later the sound suddenly changed to harsh and bright (I could not volume up even one step-my preamp has a dual mono 42 steps attenuators). It happened the same when I hook up to a TVC. Finally, I had to reduce the gain from 2V to 1V and the sound is coming back to normal like before. How do you explain this? Thanks in advance.

Tan

Gaara · « **Reply #1964 on:** 7 Jul 2007, 01:16 am »

Tan,

It sounds like you have the opposite of Ratso, and that is that you are overloading your amps input. It is my understanding that your average tube amp has a lower input sensitivity then a normal amp, closer to .5v instead of 2v like your average amp. I assume the reasoning for this is because older sources have lower outputs then current digital sources.

Anyways what it sounds like is happening is you have a low input sensitivity on the amp which is being overpowered by the source. When you say you could not volume up, I assume you mean you hit a wall with the volume where moving a step up made no change in volume. If the same things happened with a TVC which has no gain then it definitely sounds like the 2v output of the DAC is to high for the amp, as even attenuating the 2v signal there still is a issue.

The brightness and harshness sounds like the amp is clipping, which is generally a soft clipping with tube amps.

Jared

Jolojl · « **Reply #1965 on:** 9 Jul 2007, 08:27 pm »

Hi Gaara/Jared!

Just read your very informative answers to Ratso and tanchiro58. I have a minor question on the same theme, hope you can answer. I just placed an order for a standard TVC and am very happy to try it out. My DAC has output voltage of 2 V and my amp requires 2,3 V for full output. I don't really see this as a problem (hopefully), but I was just curious where I would put some gain (a gain stage?) if I wanted to, after the DAC and before the TVC, or after the TVC before my amp?

Thanks!
Johan

Gaara · « **Reply #1966 on:** 10 Jul 2007, 12:42 pm »

Johan,

I don't see any issues with the setup. If your DAC outputs 2v and the input sensitivity of the amp is 2.3v then you won't get full output, but you will come close. The easiest way to determine if there is a problem is to see how far up you are turning the volume control. With a source output lower then the amp's sensitivity you will be turning it up more then normal, in your situation of you find yourself turning it to the highest it will go then there could be a issue.

If you wanted to add some gain I personally would do it after the DAC and before the TVC. In my system the TVC system to eliminate any noise present, so if the gainstage added any noise to the signal it would be attenuated by the TVC.

Of course in your situation I see no need to add gain. I have been perfectly content using DACs with 1v output into 2v sensitive amps which is much more drastic then your situation. These were all 50wpc though, so your mileage may vary.

Jared

Jolojl · « **Reply #1967 on:** 10 Jul 2007, 01:46 pm »

Hi Jared!

No I hope there will be no issues, was just curious as to where to add gain if I wanted to. Interesting you use the TVC in some way to eliminate noise ... I can't wait til I have the TVC here for auditioning. Thanks for the answer!

Johan

rollo · « **Reply #1968 on:** 11 Jul 2007, 07:58 pm »

Quote from: tanchiro58 on 6 Jul 2007, 11:25 pm

Jared,

I have questions for you since I encountered this problem with my Promitheus DAC (it is still in break-in process).

I am using SB3 to Promi DAC (set at 2V output) to my active tube preamp (around 2V output) to my tube amp (I do not know how many volts input sensitivity) and my horn-based speakers (97dB+). In about first week the sound was like to be expected (warm rounded sound). But in a couple days later the sound suddenly changed to harsh and bright (I could not volume up even one step-my preamp has a dual mono 42 steps attenuators). It happened the same when I hook up to a TVC. Finally, I had to reduce the gain from 2V to 1V and the sound is coming back to normal like before. How do you explain this? Thanks in advance.

Tan

Its just breaking in. Thats all. It will take 400 Hrs for the DAC to fully break in.

rollo

1000a · « **Reply #1969 on:** 11 Jul 2007, 08:25 pm »

well I am finally on board, bought my used Ref2 TVC (maybe 2 months old)from magicjazz who is getting a C Core. Its IMS now-

Oh my God

, sorry I pulled my hair out deciding and waiting, I am running mine with an Integrated amp and even there the improvements are staggering. Thanks to Matt for giving me the heads up on the AC ad and the luck of the universe that I checked into AC that day. Its all true what all the raves say, at least IMS- more later

Nick this thing is utterly gorgeous in every way fantastic- a true gift to us not rolling in big money. totally floored me- glad I got on with it

if anyone has any photos of where they put the BHP on there TVCs trannies I would love to see them, maybe a link to a page I missed?

Thanks (man am I glad I checked out this thread)

tanchiro58 · « **Reply #1970 on:** 11 Jul 2007, 08:46 pm »

Quote

f anyone has any photos of where they put the BHP on there TVCs trannies I would love to see them

1000a,

It is easy to install the BHP to your TVC trannies. Cut them out the sizes of the covered metal (appear in gold) parts of the laminated cores then stick with super glue or double taped them. But if you have a good handyman skills you just place the cutting BHP underneath the trannies (where? between the bottom of trannies and a bottom aluminum plate then make a holes to screw them up. Is that easy to understand?

gooberdude · « **Reply #1971 on:** 11 Jul 2007, 10:14 pm »

I finally added BHP underneath each tranny...it is real easy. For the transformer shields, cut 1" wide strips that are the length of each side of the cover. Simply unpeel the paper and use the BHP adhesive to adhere to the cover.

For under the trannies, gotta remove the screws holding 'em to the chassis bottom, and kind of tug the beast to one side...the factory adhesive will come loose easily when under stress. carefully tilt each trans to a side & un-peel the stock goo. the goo is held together by a sheet of paper. After the goo is gone, cut a piece of BHP larger than the tranny footprint & install. I left mine right like that, no screws going back into the chassis. each tranny is very heavy and some of the stock goo is still tacky. they aren't going anywhere.

no need to cover the entire cover with BHP though, 1" is wide enough to bring out the bass.

1000a · « **Reply #1972 on:** 12 Jul 2007, 01:56 am »

Thanks Matt and Tan

That is very clear instruction, I have a good handle on it now

.
My God I have definitly been missing out, this is some kinda wonderful device if there ever was one.

thanks again

Gaara · « **Reply #1973 on:** 16 Jul 2007, 01:32 pm »

Thread is back...yay!

I see that all the posts about the Promi US deal seem to be gone...sad.

Still waiting on my BHP, ordered 6/19/07 and to my knowledge they still haven't even shipped. I hope this wont be like the time I ordered a Test Disc from Music Direct and received it 11 months later.

rollo · « **Reply #1974 on:** 16 Jul 2007, 02:19 pm »

To all my friends on this thread, I am sorry if I caused any problems for you . I am back to audiophile status thanks to John R's understanding.

rollo

guest1632 · « **Reply #1975 on:** 16 Jul 2007, 03:03 pm »

Quote from: 1000a on 11 Jul 2007, 08:25 pm

well I am finally on board, bought my used Ref2 TVC (maybe 2 months old)from magicjazz who is getting a C Core. Its IMS now-

Oh my God , sorry I pulled my hair out deciding and waiting, I am running mine with an Integrated amp and even there the improvements are staggering. Thanks to Matt for giving me the heads up on the AC ad and the luck of the universe that I checked into AC that day. Its all true what all the raves say, at least IMS- more later

Nick this thing is utterly gorgeous in every way fantastic- a true gift to us not rolling in big money. totally floored me- glad I got on with it

if anyone has any photos of where they put the BHP on there TVCs trannies I would love to see them, maybe a link to a page I missed?

Thanks (man am I glad I checked out this thread)

Hi, Sorry no pics, but go read my review in the Critic Circle. That will tell you exactly where to put the BHT If you have any question, you can PM me or just ask me here.

Ray Bronk

1000a · « **Reply #1976 on:** 16 Jul 2007, 09:14 pm »

Hi Ray

Thanks very much- I have not been to that circle in a while, I look forward to your comments on the piece. wonderful

also I am thrilled this thread is active again

GHM · « **Reply #1977 on:** 16 Jul 2007, 09:29 pm »

I'm glad to see the Promitheus Novel back up and running.

There's a lot of great info here buried in these pages for the curious. It's too long to be called a thread any more.

rayd · « **Reply #1978 on:** 16 Jul 2007, 10:25 pm »

Quote from: GHM on 16 Jul 2007, 09:29 pm

I'm glad to see the Promitheus Novel back up and running. There's a lot of great info here buried in these pages for the curious. It's too long to be called a thread any more.

How about "Gone With The Wind*"

(*transformer wind... ...sorry)

Say · « **Reply #1979 on:** 17 Jul 2007, 01:29 pm »

Yup! Glad to see this "Novel" is being read again. New chapters being added everyday.

rollo, no harm done. I am familiar with various forum fules and codes of conduct. Each forum has there own policies. Figuring out where not to cross the line is sometimes a tricky situation. Anyway, hope for all the best.

Promitheus TVC passive preamp anyone?

guest1632