Promitheus TVC passive preamp anyone?

NewBuyer · « **Reply #40 on:** 25 Sep 2006, 01:29 am »

Quote from: GHM on 24 Sep 2006, 11:51 pm

Thanks for the links on the plugs guys. I'm still looking through the pages trying to find the $1.00 deals...

Here's a link that has the plastic-shelled Calrads for under a buck...

GHM · « **Reply #41 on:** 25 Sep 2006, 01:42 am »

Thanks a bunch New Buyer!!

.This makes it a whole lot easier. I'm ordering some tonight. You've been a great help!

PromitheusAudio · « **Reply #42 on:** 25 Sep 2006, 08:04 am »

Sorry for the late reply on this, greg just email me on this thread.

i would like to clear things up on the shipping.

Greg you did not draw the short straw. Gymane did .

We ship 7 units into the US only gymane unit arrive without any problems .

We have alerted DHL on this. I like the irony on the fragile sticker. Hopely some one from DHL sees the picture here and does something. There have not gotten back to us on what to do yet. But frankly their service is only a problem when shipped into the US only.

On the cables length from the TVC, our dealer here in Malaysia actually took the TVC back and compared with his Krell top of the line preamp driving 10meters(33 feet) of interconnect and said there was no signs of lost in dynamics.

Paul
I will be picking up your 6061 Aluminium Aircraft grade solid bars on Wednesday. Once we have that you will be the first person to have the aluminium casing.

Quick tip on the TVC users, can you guys get access to Weatherseal from your home depot? It is a black stuff(bitumen) to fix your roofs. Used some of this on the stainless steel plate and on the bottom and it will give a slightly better sound. Worthwhile considering the weatherseal is really cheap.
What it does is that it dampens the wood and stainless steel.

JLM · « **Reply #43 on:** 25 Sep 2006, 09:54 am »

GHM,

Seems to me the FTA-2000 already provides a quite "friendly" impedance loading to an amp with the TL bass and single driver. The Autotransformers only make a single across the board halfing or doubling of the impedance so I wouldn't expect any benefit with these speakers or using solid state amps.

Speaking of the FTA-2000, I was recently interested in tweaking the BSC component values to flatten in room response with boutique parts in a nice box. What fustrated me was the need for another set of connectors. While pondering how I'd do this realized that I'd need a mike, test tones, etc. and so I started thinking (in this case the obvious) about just using digital EQ (say between transport and DAC) to eliminate the BSC with superior compensation for both room and speaker. Then the speaker cable could be wired directly to the drivers and eliminate a veil between drivers and amp (I'm not willing to go so far as to wire the cable directly into the monoblocks). Note that I've been using only cryo'd pairs of single strand plenum rated CAT5 for speaker cables, even though I have nicer cable, just waiting to get all this in place.

I believe in having a good room to start with and doing the minimum amount of compensation, but for $350 the Behringer DEQ 2496 plus microphone should be well worth it. I've already got a dedicated room, insulated and correctly proportioned, and have six 2 ft x 4 ft high density fiberglass panels. I'll soon be adding 15 - 30 18 inch x 18 inch DIY diffusers in bands centered at driver height on the front wall and front end of the side walls:

http://pmerecords.com/Diffusor.cfm

I've replaced the Squeeze Box with a Ah! Njoe Tjoeb 4000 due to continued computer issues, so no longer have a way to break into the signal path while still digital, so I may do the TVC before EQ.

ashok · « **Reply #44 on:** 25 Sep 2006, 02:11 pm »

The transformer, as used in a TVC, consists of a primary winding, (the input) and the secondary winding (the output). Each winding consists of a coil with certain number of turns of wire. These coils are wound around a core made of iron or other high-grade alloy steel.

If we let Nin be the number of turns in the input coil, and Nout be the number of turns in the output coil, the voltage applied at the input Vin, and the voltage obtained at the output, Vout, have the following relationship:

Vin Nin
------ = ------
Vout Nout

Nin/Nout is also called the turns ratio of the transformer.

The currents on the other hand have an inverse relationship with the turns ratio:

Iin Nout
------ = ------
Iout Nin

So, the following relationships can be derived:

Vin*Iin = Vout*Iout

and

Vin/Iin = (Nin/Nout)^2 * Vout/Iout

Zin = (Nin/Nout)^2 * Zout

So, in an ideal transformer:

1. If the output voltage reduces, there is a corresponding increase in the output current Iout.

2. An impedance connected at the output appears on the input side transformed by the square of the turns ratio of the transformer.

When used as a TVC, the transformer will have the source (CD player for example) connected at the input. The amplifier with an impedance of Zamp is connected at the output.

With no attenuation of the input signal, Nout = Nin. And so, the amplifier impedance Zamp is presented to the source.

As the input signal gets attenuated, Nout becomes smaller than Nin. Nin/Nout is greater than 1, and so is the square of Nin/Nout.

Therefore, the impedance presented to the source is greater than Zamp. It is Zamp multiplied by the square of the turns ratio of the transformer.

A rule of thumb in matching an output stage with an input stage is that the input impedance presented by the input stage be at least 10 times the output impedance of the output stage.

With the TVC, if at no attenuation, you know that Zamp > 10*Zsource, you are guaranteed that Zamp will be greater than 10*Zsource at other levels of attenuation also.

Further, at lower volumes (higher attenuation), there will be more current Iout to drive the amplifier.

It is important to note that the analysis above assumes an ideal transformer - no resistive losses of any sort, and winding inductances are zero. In real life, there will be losses in the core of the transformer and in the transformer coils. These can be made small with proper choice of material and construction techniques. There will also be a finite inductance in the transformer windings. The equivalent impedance presented by the winding inductance is directly proportional to the frequency of the input signal.

An autotransformer is a variation of the transformer. While the transformer has two terminals for the input and two for the output, the autotransformer is a three-terminal device. The electrical isolation between the input and output that is available in a transformer with separate windings is not present in an autotransformer. But an auto will give you a higher power handling capacity.

Gurus out there: please point out any errors in my discussion.

Ashok

Randy · « **Reply #45 on:** 25 Sep 2006, 03:10 pm »

Wow, some real techies posting here. I don't understand any of it. About a month ago I ordered a balanced version of the Promitheus preamp since I am unwilling to give up the balanced out of my CD player which is decidedly better than the RCA output. Nicholas has delayed the shipping because of his problems with the shipping company. I have had long time preamp issues here and have always gone back to running the CD directly into my power amps so am anxious to hear the Prometheus. I might have tried the new Bent, discussed it some with John Chapman, but it costs more than two grand above the little beauty from Malaysia. Maybe I can live without a remote.

Bwanagreg · « **Reply #46 on:** 25 Sep 2006, 04:30 pm »

Quote

We ship 7 units into the US only gymane unit arrive without any problems .

Wow Nick, I misunderstood this when you emailed me. That is a huge problem. Are there other shipping options for your locatation than DHL? If DHL needs any documentation from me let me know. I'd also like to publicly thank you for your help with these problems that are not of your own doing.

Shipping problems aside, this little preamp continues to amaze me. The consistency of the sound across all volume ranges is quite impressive, as is the bass response. I'm using first generation Omegas (the TS-1s, modified with Planet 10 plugs and Dammar) with a little AMC 2030 EL-34 amp, a combination that has always been light in that department. The TVC really fills out the mid bass (low bass is not surprisinlgy still MIA). The soundstaging can be breathtaking, and I haven't even started acoustically treating the room yet (this is a "new" second system).

Tomorrow I should be getting a Grado PH-1 to use with my JA Michell Synchro and Grado MCZ (longhorned!). I'll post comments on the analogue sound with the TVC.

skite30 · « **Reply #47 on:** 25 Sep 2006, 06:43 pm »

I received one of these units a couple of months ago shipped to the usa by dhl and it arrived in good shape. No problems at all. Just thought I'd add my two cents worth on the shipping problems. I don't work for dhl, i've worked for ups for 33 years.

riverdog · « **Reply #48 on:** 25 Sep 2006, 08:30 pm »

I am in the UK and received mine in perfect condition. I was actually prepared for the worst but a nice surprise. The TVC has probably 50hrs under its belt. It has replaced the rather cheaper Luminous Audio Axiom passive and a rather more expensive AVI active pre. I was never entirely happy with either. Sure the passive was great with sparse musical arrangements on singer-song-writer type albums, Norah Jones and the like but with more aggresive material, System of a Down, Tool, Clutch etc it lacked dynamics. It was not that the bass went awol, merely that the higher harmonic elements bled into the rest of the spectrum. The AVI active which is renowned on this side of the pond as an accurate and dynamic performer suffered the same affliction. With rock music the active had apparent drive but in presence of the TVC is is faily obvious that the active pre was merely accentuating the bass but without removing the higher harmonic grunge. Listening to either could only be done in short spells.

So far the TVC has been a god-send. There is good clarity higher up and the impact down low. In the same passage of music the cymbals shimmer and the drums thud convincingly without each getting in the other's way. I was really worried about having to do without the remote. In absolute honesty I have not missed it at all. Previously I constantly found myself reaching for the remote to increase the volume to better hear some lyrics or a rip-roaring guitar solo. I would then settle on this new higher volume. Then inevitably I would have the itch to increase the volume again for the same reason. Listening sessions became painfully loud or illegally so as far as the neighbours were concerned. With the TVC in place I feel able to sit back and just listen, whatever the volume, low or loud, without the itch to turn it up. One other effect of the TVC I have noticed so far is that the music seems to actually flow into the room and is more enjoyable when seated off-axis whereas previously the system used to create a flat wall of sound which simply got bigger, though still just as flat, with an increase in volume.

I could spot all this within the first few minutes but I am afraid I have not noticed the sound change over the 50 hours or so. Burning-in may well be an urban myth in my books!

For 350 dollars (or US peso as we like to call it here!) there is not much to quible about. I found two so far of which the most important is that even at the highest attenuation it is a little too loud for late night listening. I would guess I have an average sensitivity system with CD palyer output being 2V and the speakers 86db/w/m.

So far it has been a pleasant surprise considering that I only came across it whilst searching for a case and switches to build my own TVC based on the S&B transformers which have been sitting in my drawer for the last five months. Rather ironic! I would be rather interested to read what 6moons makes of the Promitheus and the Bent/MF pre.

GHM · « **Reply #49 on:** 25 Sep 2006, 11:05 pm »

Quote from: riverdog on 25 Sep 2006, 08:30 pm

One other effect of the TVC I have noticed so far is that the music seems to actually flow into the room and is more enjoyable when seat off-axis whereas previously the system used to create a flat wall of sound which simply got bigger, though still just as flat, with an increase in volume.

Thanks Riverdog for the nice review. I noticed the same thing..I failed to mention this. When you can sit in the next room and still hear the depth of the voices and the acoustics of the recording venue..things are sounding pretty good.

Good listening

Quote from: PromitheusAudio on 25 Sep 2006, 08:04 am

We ship 7 units into the US only gymane unit arrive without any problems .

I guess I need to start playing the lottery more often !!

PromitheusAudio · « **Reply #50 on:** 26 Sep 2006, 02:02 am »

Randy
Yours is going out today. With all prayers, let us hope yours arrive safe and sound. From our dealer in Malaysia, the balanced was able to be compared with his Krell Top of the line preamp. I am looking forward to hear what you think about it.

I was told by DHL it could be cause by the custom department in the US. THey could be responsible for the rough handling.

I reall like TVCs because of the reasons that it allows music to follow into the room.
coming back to room tuning
Have you guys tried out room lenz?

It is actually very simple to do, take 3 pvc pipes and tuning them to by stuffing dacron/polyester filling into different locations into the pipes. Really helps to cut down on reflective waves.

Ashok
Your formula looks right. Check out our faq http://www.promitheusaudio.com/tvcfaq.htm
Should be the same.
Also for other guys to understand perhaps you should change this formula
Zin = (Nin/Nout)^2 * Zout to
Zout = Zin/(Nin/Nout)^2
This just a better way to understand what is the output impedance of the TVC

If you read this part guys you would understand at low volumes you gain alot of current drive
Further, at lower volumes (higher attenuation), there will be more current Iout to drive the amplifier.
Because of this in lay man terms, low volume allows you to hear alot of details is because you have alot of drive due to this same principle mention above

JLM · « **Reply #51 on:** 26 Sep 2006, 09:50 am »

Everybody blames the other guy, especially if its the government. I don't like the sound of that excuse from DHL. Every shipper has to go through customs, I doubt if they take the time to brutalize 6 of 7 packages. They were in DHL's hands for 10,000 miles versus customs for 100 feet, what are those odds?

Are there other shipping options? Cheaper isn't better if you have to go through this much hassle (my 2 cents).

NewBuyer · « **Reply #52 on:** 27 Sep 2006, 09:39 pm »

Nick earlier said in this thread that the DHL shipping damage issue is a problem only for units shipped to the U.S. That narrows it down a bit, so it does appear that customs could be responsible.

I'm curious about the aluminum case Paul is receiving, versus the Malaysian Nyatuh wood case with steel top. They will clearly look different, but should this difference in case material have any effect at all to the resulting sound?

GHM · « **Reply #53 on:** 27 Sep 2006, 11:35 pm »

Quote from: NewBuyer on 27 Sep 2006, 09:39 pm

I'm curious about the aluminum case Paul is receiving, versus the Malaysian Nyatuh wood case with steel top. They will clearly look different, but should this difference in case material have any effect at all to the resulting sound?

I was thinking the same thing.

I hope it retains the "SOUND". Hey Nick..what do you think? If this is the first one..I guess you wouldn't know till it's complete.

Randy · « **Reply #54 on:** 28 Sep 2006, 03:27 am »

Nicholas - Just saw your message tonight (Wednesday.) Looking forward to receiving the preamp esp. one with a balanced input that won't clip like a model I owned previously. Will let you know if it arrives in one piece. Can you e-mail me a tracking number?

GHM · « **Reply #55 on:** 28 Sep 2006, 04:55 am »

Hey Randy if it shipped out on Wednesday 2:30 a.m (MST) which is Wednesday 4:30 p.m. in Malaysia. It will most likely be at your location by 10:30 a.m.(MST) on Friday morning. Unless you live a good distance from a major city. It may arrive just before 10:30 am Saturday of this week if that's the case.

skite30 · « **Reply #56 on:** 28 Sep 2006, 08:58 am »

Nick, one of the earlier posts mentions that you need 100 hours on each volume position to break this tvc in. Is that true?

GHM · « **Reply #57 on:** 28 Sep 2006, 12:51 pm »

Shite30, Zero Gain is where I read about the burn in on the TVCs. From the comments here you can burn the unit in by using the full volume with the amplfier turned off or with resistors on the outputs.

skite30 · « **Reply #58 on:** 28 Sep 2006, 06:33 pm »

GHM, thanks I had run mine for quite awhile with the amp turned off but not at the full volume setting.

PromitheusAudio · « **Reply #59 on:** 29 Sep 2006, 01:56 am »

actually most of the customer find that the preamp sounds good when used out of the box.

but the improvement gets better and better once you run it in. I remember if you hit 100 hours the sound will change quite abit more and last jump in performance is at 300 hours

Anyway good news, i have retired from my day job. I find doing this preamp is more rewarding. When you are helping people reach better sound and their gratitude back makes this all worth while.

Hence our current turn-around time is 1-2weeks.

Cheers
Nicholas