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Batting ? Bating isn't a word in that context . And what about you being in a 'fray'? This isn't fight club .
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Topping Pre90 Review (preamplifier)
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MaxwellsEq
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I've done that, but I didn't find it very informative.
Background: when I started as an EE there were still some line-level 600 Ohm audio installations. These operated with 600 Ohm output impedance feeding 600 Ohm input impedance. They worked fine.
The 1:10 ratio is a rule of thumb, known as impedance bridging: it's not a cast iron rule that must never be broken.
The 600:600 Ohm line-level impedance matching approach I mentioned above, maximises power transmission, vs maximising voltage transmission with impedance bridging. The result of impedance matching is up to a 6dB signal reduction compared to bridging, it's also less efficient, but it can reduce noise. As we both agreed, this signal reduction in a sighted comparison made without controls is probably what the listener noticed.
Low input impedances means the source does need to source and sink more current. But (considering the current through the load) at 2V, into a 10k load impedance (single ended) that's 0.2mA; at 4V into 2K (balanced) it's 2mA. The source should easily be able to supply that.
Is one of the optimal input impedance values for general audio devices about 100kohm? (Is Balance about 200kohm?)
At this link, we measured 1.9kohm load and 46.6kohm load, but no problems were found.
www.audiosciencereview.com
www.audiosciencereview.com
The balanced output of a hifi device should not cause any problems with a 2kohm load.
The balanced output of a vintage device should also not cause any problems. At that time, there were more devices with an input impedance of 600ohm than there are today.
I don't know about vacuum tube devices or boutique audio devices.
By my standards, a balanced output device that has problems with a 600ohm load is defective.
For unbalanced output, is a 10kohm load the lower limit? If it's a modern DAC, a 1kohm load may be fine.
That's all for the numbers, but anyway, enjoy it with your favorite device or system. Ignore other people's complaints.
However, if you are going to discuss superiority or inferiority in a scientific setting, you need scientific evidence. For audio, this is either proper measurement or blind, controlled listening test results.
At this link, we measured 1.9kohm load and 46.6kohm load, but no problems were found.
Schiit KARA Preamp and Headphone Amp Review
... However, Topping adopts that off standard very low impedance for balanced inputs that is a try and error situation. ... Yeah, that seems to be an example of chasing specs at the cost of practical utility. The non-standard low input impedance makes it less flexible/practical/useful...
www.audiosciencereview.com
Topping Pre90 Review (preamplifier)
Hi, I have the same setup: Denafrips Ares II, VTV Purifi with the EVAL1 input buffer and the Topping Pre90 and I would like to know the best way to connect them. If I use the RCA outs on the DAC instead of the XLR does it fix the impedance issue? If not, what should I do? Thanks!!!
www.audiosciencereview.com
The balanced output of a hifi device should not cause any problems with a 2kohm load.
The balanced output of a vintage device should also not cause any problems. At that time, there were more devices with an input impedance of 600ohm than there are today.
I don't know about vacuum tube devices or boutique audio devices.
By my standards, a balanced output device that has problems with a 600ohm load is defective.
For unbalanced output, is a 10kohm load the lower limit? If it's a modern DAC, a 1kohm load may be fine.
That's all for the numbers, but anyway, enjoy it with your favorite device or system. Ignore other people's complaints.
However, if you are going to discuss superiority or inferiority in a scientific setting, you need scientific evidence. For audio, this is either proper measurement or blind, controlled listening test results.
I looked and could not find any balance control. Correct me if I am wrong. Thanks
I've always found the Pre90 interesting. I ended up with an A70 Pro because it was able to be a preamp + headphone amplifier for me. I do have two LA90Ds - having all 90s would have looked so nice. If I didn't buy silver amps and black everything else it would have looked nice too - oh well.
I like how the Pre90 has three full stages for the preamp. The TPA6102A2 (current amplifier) is used in both the Pre90 and A70 Pro (plus almost all their other HPA), but the way things [PCB traces] look (also+ the way I've observed operation), the A70 Pro's 6102A2s only go to the headphone outs while the Pre90s [obviously] go to the XLR/RCA outs- meaning the A70 Pro's XLR and RCA outs are driven by probably the output of OPA1612 through multiple surrounding 50 ohm resistors (given RCA output impedance spec is 50 ohm, XLR 100 - it tracks!)
I wonder if I could make the output from my A70 Pro more like the Pre90, turn its balanced headphone out to XLR somehow..
The below graphic is from the 1612s datasheet, it's got me wondering if it's generally bad to drive op amps from extremely low impedance (like 0.003 ohms). Most things are 50 to 600 -I've even seen as high as 2,000. I don't know what's listening first inside the LA90 Discrete (it's permanently hidden in epoxy or something), but it could be this 1612, or some other extremely low distortion opamp
I like how the Pre90 has three full stages for the preamp. The TPA6102A2 (current amplifier) is used in both the Pre90 and A70 Pro (plus almost all their other HPA), but the way things [PCB traces] look (also+ the way I've observed operation), the A70 Pro's 6102A2s only go to the headphone outs while the Pre90s [obviously] go to the XLR/RCA outs- meaning the A70 Pro's XLR and RCA outs are driven by probably the output of OPA1612 through multiple surrounding 50 ohm resistors (given RCA output impedance spec is 50 ohm, XLR 100 - it tracks!)
I wonder if I could make the output from my A70 Pro more like the Pre90, turn its balanced headphone out to XLR somehow..
The below graphic is from the 1612s datasheet, it's got me wondering if it's generally bad to drive op amps from extremely low impedance (like 0.003 ohms). Most things are 50 to 600 -I've even seen as high as 2,000. I don't know what's listening first inside the LA90 Discrete (it's permanently hidden in epoxy or something), but it could be this 1612, or some other extremely low distortion opamp
Roland68
Major Contributor
Are you sure that the A70 Pro uses TPA6102A2 and not transistors?
Yes, 100%.
OPA1656 (probably input)
OPA1612 (probably TPA6102A2 and outputs)
TPA6102A2 (headphone outs, there are 4 of them I think channels are separated to one under each
Each one of those 4 surface mount resistors you see to the immediate right of the heatsink, I believe, are 2.2 ohm for the outputs. Top 2 are one channel, bottom 2 are the other.
6120 #1 L+R = L +
6120 #2 L+R = L - (opposite)
6120 #3 L+R = R+
6120 #4 L+R - R- (opposite)
For single ended just + are used with ground (L- above isn't ground, it's going to -2V when L+ is at +2V
Roland68
Major Contributor
I was never sure about the A70 Pro, as I only saw the board with the heatsink and Topping didn't mention the TPA6120A2 anywhere.
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If you look on the product page on the manufacturer's website under general (first tab, default), in the bunch of pictures that detail noteworthy aspects not covered in specs, there is one that shows a portion of the heatsink with the heatsink turned nearly translucent- there, you can see the chip, fortunately with enough detail to make out 6120A2.
Other than "Discrete" models and the 10x OPA1656 model (I forget which one that is), I believe all their headphone amplifiers use it except one, one which uses a similar chip - same amplifier type, but not specifically audio designated / possibly slightly lower power if memory serves (it's in a single ended, it might be good to +/- 18 instead of 15. Designation was for DSL lines, I think it'd drive the phone cable to the node. Starts THS
dcolak
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pfff... any good alternative? My Nad M3 died and I've been using its awesome preamp. I need at least left-right balance, two outputs... Nad M3 also had built in crossover, I will miss it.
Roland68
Major Contributor
Last edited:
dcolak
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One of the speaker outs (right channel) stopped outputting sound. The initial "click" when I turn it on comes too soon. :-(
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