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Old 6th May 2011, 01:12 PM   #1651
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Thank you for all thee inputs. Very helpful.

Quote:
Originally Posted by TheDealer View Post

12 V ??? I am really confuse now. Isnīt that too much for a pre out ?
Yes, it's a way hot... I never realized it until the curiosity about T amps arose...

Quote:
Originally Posted by alkasar View Post
12V is too much for any amp! Are you sure its not a typo ?
consumer electronics standard is 2Vrms output.
220ohms output impedance is excellent.
I've had another look at the techsheets. The preamp has a max gain of 16dB, wich would correspond to a 12V output with a 2V line source.
It's really a lot for a preamp.
The 220 Ohm on the output are indeed very impressing.

Yesterday I've found a thread of user Rabbitz. He had the same issue and found a sulution with a simple voltage divider before the power amp in. I think I'll go the same way:

NAD 106 pre gain changes

Quote:
Originally Posted by Jack Caldwell View Post
With the 15V/V gain that the hifimediy has, a 2.5V input would generate a 37.5V swing... which goes way beyond the power supply's capacity when set at 30V... the result will sound horrendous as it will be in full clipping and you will probably want to turn it down.
If you put in a 5V waveform, the result will sound like a square wave and drive you screaming to "turn that damned thing down!!"

The probability of damaging your amps before you damage your hearing is not very high!

The industry standard of 2V out is there to show what a line-stage or pre-amp will need to put out as a MINIMUM in order to drive the amp to full output.
A 5V maximum on the hifimediy is a fairly decent safety margin.

So don't worry about it. The amp will exhibit audible clipping at any levels exceeding about 2V. You'll hear that as clearly audible distortion.
Thank you Jack for the detailled explanation. As a drummer I'm used to high dB but the clarity and detail of t amps (the well designed ones) blew away all my assumptions on older architectures.

Maybe, before melting a hifimediy or helder amp iI'll try with a cheaper sure board.

Will keep you updated.
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Old 6th May 2011, 05:55 PM   #1652
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Quote:
Originally Posted by portomomo View Post
I've had another look at the techsheets. The preamp has a max gain of 16dB, wich would correspond to a 12V output with a 2V line source.
It's really a lot for a preamp.
The 220 Ohm on the output are indeed very impressing.

Yesterday I've found a thread of user Rabbitz. He had the same issue and found a solution with a simple voltage divider before the power amp in. I think I'll go the same way:
Maybe, before melting a hifimediy or helder amp I'll try with a cheaper sure board.

Will keep you updated.
The voltage divider won't cost much time or effort or materials, so if you're still worried about that go ahead and put one in.

But before you do anything read the following: both the hifimediy and Helder seem to benefit from a pre-amp with a little more gain, especially with tracks that are recorded way below the "0dB" level indicator on the recording system. The Sure at max gain setting has a little more gain than the hifimediy and Helder.

As an example, I have a CD called "Misa Flamenca" which must have been recorded at -20dB for the peaks and maybe -40dB average, or even less. It's very interesting music, and I like it a lot, but it can be very frustrating to listen to it: with a normal line level input into the T-amp, I can barely get this song to play at quiet conversation levels in the room!

The +16dB gain on your NAD would be a great addition for extreme situations like this. And, if you happen to use an extremely low output moving coil phono cartridge, you will definitely want more system gain. That's why the extra gain is there!

I guess the bottom line is that the volume control on your pre-amp is useful... turn it up or down according to the level on your recordings and you'll be fine. I highly doubt you'll be melting anything on your amps by using it just as it is, in stock form.

BTW, I was looking at the Burson pre-amp, that one will put out 25V !! Seems like overkill, but if you ever try one of those ultra-low moving coils phono cartridges, you'll quickly learn to appreciate it.

Last edited by Jack Caldwell; 6th May 2011 at 06:14 PM.
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Old 7th May 2011, 02:11 PM   #1653
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Default Warning about A123?

Quote:
Originally Posted by TheShaman View Post
The nice thing about batteryspace.com packs is that they come with a nice protection PCB. For the same price, give or take, EPBuddy offers genuine A123 ones (so better batteries) but no protection circuit. Not sure which would be the best buy.
On many of the Racing Car sites (RC) there is a whole lot of complaining about the a123 cells sold on ebay being fakes or worn out cells repackaged by unscrupulous vendors.

There are several statements to the effect that a123 systems have completely discontinued selling to retail outlets and vendors and are focusing only on large scale industrial sales.
...along the lines of this one:

"A123 just published in March a warning about pirated cells 26650 "B" (lower grade) cells that someone has been re-wrapping and passing off as "A" grade cells"

So, it's looking like a virtual CERTAINTY that what is being sold on ebay is NOT brand new functional A123 product, it is either fake or old worn out cells, or cells that did not pass QA and are being dumped on unsuspecting users.


Time to find some other alternatives. Back to the LiFePo4 batteries.

Maybe something like this 24V 10A unit from Ping Battery:
24V 10AH LiFePO4 Electric Scooter E Bike Ping Battery! | eBay

or for the 36V type suitable to drive the T3:
36V 10AH LiFePO4 Electric Scooter E Bike !Ping Battery! | eBay


We'd need to find out what kind of source impedance these units exhibit...
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Old 7th May 2011, 02:17 PM   #1654
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Default About source impedance...

Vinnie at RWA has mentioned that his 25.6V LFP-V packs have a source impedance of under 0.02 Ohms... that's under 20 miliOhms... that's a VERY low Zs.

As an example, the very highly regarded Burson low noise regulators have <15miliOhm for their 12 V reg.

Extrapolating from this, if we can get under 30miliOhm for a 24V batt-pack, or under 45 miliOhm for a 36V pack we're ahead of some of the very best regulators.

Last edited by Jack Caldwell; 7th May 2011 at 02:46 PM.
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Old 7th May 2011, 02:35 PM   #1655
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Quote:
Originally Posted by Jack Caldwell View Post
On many of the Racing Car sites (RC) there is a whole lot of complaining about the a123 cells sold on ebay being fakes or worn out cells repackaged by unscrupulous vendors.
But the same sites say that epbuddy for example is genuine, but a bit more expensive, and there are other sellers which are genuine, but a bit more expensive then the ebay ones.
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Old 7th May 2011, 03:42 PM   #1656
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Default Yeah but...

Quote:
Originally Posted by erozsolt View Post
But the same sites say that epbuddy for example is genuine, but a bit more expensive, and there are other sellers which are genuine, but a bit more expensive then the ebay ones.
The question for us as potential users is how can WE know for sure? If I'm going to spend $300 on batteries, I really do want to be know that I'm getting the real thing!!
A123 Systems has published warnings about fraud and piracy taking place, as well as re-labeling of B-stock as A-stock.

So I just called ep Buddy and found out they sell B-stock cells which they get directly from the manufacturing factory in China. These are not "authorized" A123 batteries.
They said that on these units the self-discharge rate did not meet QA, because the shelf-life would be shorter. Ep Buddy warranties the batteries for 1 year, but these come without any form of pcm for charging.

I don't get a real good feeling about buying units that did not pass QA. Draw your own conclusions, but for me it looks like it may be better to look elsewhere.

And that's a shame, as I really like those ultra-low source impedance figures on the A123 cells...

Last edited by Jack Caldwell; 7th May 2011 at 03:45 PM.
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Old 7th May 2011, 10:12 PM   #1657
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OK, then the best option is to buy DeWalt pack and take out the batteries. Those must be genuine. A quick search in endless-sphere forums turned out these:

10 for $90:
Endless-sphere.com &bull; View topic - DeWalt 36V Battery Pack (10 A123M1 cells)

20 for $175:
Endless-sphere.com &bull; View topic - DEWALT DC9360 Batteries + 1 HR Dewalt Charger

naked cells sourced from DeWalt packs with spot welding and pack building service:

http://www.nabatteries.com/ANR26650M1-A.php

A123 ANR 26650 M1A LiFePo4 3.3V 2.3Ah Battery Cell on eBay.ca (item 300534224788 end time 05-Jun-11 18:48:48 EDT)

But you need to invest in a good quality balanced charger which can charge the cells separately, as well as could tell you which cell is bad/overcharged/over-discharged in a pack.

Last edited by erozsolt; 7th May 2011 at 10:15 PM.
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Old 7th May 2011, 10:57 PM   #1658
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Batteryspace gives you the option to buy the protection PCBs separately. Check here.
Similar products from all-battery.com can be found here.

Last edited by TheShaman; 7th May 2011 at 11:21 PM.
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Old 8th May 2011, 04:25 AM   #1659
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Talking How good is battery management inside the Dewalt?

Quote:
Originally Posted by TheShaman View Post
Batteryspace gives you the option to buy the protection PCBs separately. Check here.
Similar products from all-battery.com can be found here.
I'm leaning more and more toward getting a Dewalt pack to power a quad of T3's for my powered bi-amped speakers.

Assumptions:
1) Since it's a batt-pack intended for very frequent and heavy use, I'm thinking (guessing? hoping?) that along with the A123 cells it would have some pretty decent battery charge protection modules already built-in.. yes?

2) Also, since power tools require huge currents for high torque at start up, I would think those modules are already designed with high instant current capabilities, much higher than need for the T3 amp boards. Overkill is good! Overkill is good! Overkill is good!

Has anyone here opened one up? Any opinions on the Dewalt batt mgt modules? Or do we have to rely on the RC crowd to find out... unlikely they would know, they strip 'em down to the bare cells and must recharge individually.

If assumptions 1 and 2 are any where near correct, then what's to keep us for using them in their standard un-opened case and thereby not void the 3 year warranty and possible re-sale value?
Betcha their connectors can handle it!

I think I'll pick one up new from Amazon and try it out on a pair of T3 + T3a soft-start boards... If it works well, I'll report back here.

Oh well, here goes another $300... one Dewalt 36V batt-pack & charger + 2x T3 amps...Battery powered T3, here we come!

Last edited by Jack Caldwell; 8th May 2011 at 04:28 AM.
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Old 13th May 2011, 06:00 AM   #1660
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Default Ping Battery

Even if it has decently low source impedance, the Dewalt 36V LiFePo4 pack delivers only 2.3AmpereHours... if the T3 burns an average of 20W/Hr as has been stated elsewhere in this thread, it means it's drawing about 0.55Amps per hour, so playtime between charges will only be around 4 hours.

So then we'd need to use TWO of these per channel to get 8 hours of playtime... that's gettin' expensive!

So, in looking around some more, it appears Ping Battery has a good reputation among the electric scooter crowd. Their base 3.2V cell has under 10mili-Ohm source resistance, Li Ping said it's more like 6 to 7 Mili-ohm typical, pretty comparable to the A123 cell, but with TWICE the stored energy at 5AH vs. 2.3

And Ping can outfit these with the special high current discharge Battery Management Modules.
For example, a pack that would be ideal for the TK2050 is this one: 24V 10AH V2.5 LiFePO4 Battery Pack
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