RAAL-requisite CA-1a Circum-Aural Ribbon Headphone is here! @HeadAmp
Feb 9, 2024 at 10:25 AM Post #916 of 1,047
No, all amplifiers need the TI combo except the 2 direct drive amps the HSA-1 and VM1. In the early days of the SR1a you needed amplifiers with at least 100W output and the interface was a resistor box. This box was then replaced by the 1b version which is a transformer box instead and allows the use of higher output Headphone Amps.
Well then how would you connect the headphones to Benchmark AHB2?
 
Feb 9, 2024 at 11:05 AM Post #918 of 1,047
No, all amplifiers need the TI combo except the 2 direct drive amps the HSA-1 and VM1. In the early days of the SR1a you needed amplifiers with at least 100W output and the interface was a resistor box. This box was then replaced by the 1b version which is a transformer box instead and allows the use of higher output Headphone Amps.
Add Jotunheim R to the list of direct-drive amps.
 
Feb 9, 2024 at 1:32 PM Post #921 of 1,047
So with all that in mind, what's going to blow up first, TI-1b or CA-1a?
There's no question the listener's mind will be the first thing blown. 🤯 :laughing:

I'll see myself out.
 
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Feb 9, 2024 at 1:48 PM Post #922 of 1,047
So with all that in mind, what's going to blow up first, TI-1b or CA-1a?
So far, we've not had a single failure due to over powering. At the 32-ohm input, the AHB is running around 25-watts. Since the CA-1a only needs about 3-watts for full SPL, the potential for failure is there, however, with reasonable volume settings, there should not be a reliability problem. Crazy as it sounds, I've personally tested the TI-1b and CA-1a with a pair of 900-watt Bryston mono blocks without a failure. I've come to think of it as a 1000 horsepower car. With responsible application of power, they can be safely driven in a 25MPH school zone.
 
Feb 9, 2024 at 1:55 PM Post #923 of 1,047
with reasonable volume settings, there should not be a reliability problem
The only real danger is if the speaker amp doesn't have a muting relay, and makes loud Pops when you turn it or an upstream component on or off.
The volume control limits the power draw, and it's somewhat self limiting, in that you'll deafen yourself before you draw enough power to damage the headphones.
But if the amp pops, that can be a huge spike, and it will most likely take the driver out first.
Most modern amps have muting relays, and it's not an issue.
 
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Feb 9, 2024 at 3:20 PM Post #924 of 1,047
I'm using the AHB2 on its lowest gain and also sending it a lower level input. It's nowhere close to producing it's max power even if I crank it up. I'm using the A70 as the preamp in this scenario. I actually prefer the 16ohm input on the TI1b, and listen between -24db - -6db volume range on the A70 pre, which is also running on low gain. My entire chain is lower gain on everything to keep from any disasters from occurring with the CA1a.
 
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Feb 9, 2024 at 8:26 PM Post #925 of 1,047
That‘s correct, but firstly I forgot about it and secondly it’s been discontinued for some time……but mainly I forgot about it.

I mean technically you could buy the nearly identical Jotunheim A in close-out right up until last month.

....When I bought the last one. :D
 
Feb 10, 2024 at 5:53 AM Post #926 of 1,047
Fellows, help me understand whether it's Topping A70's failing, or my own misunderstanding. I'm discussing the issue with them but they are adamant it's "for my own protection".

The issue is that even though this amp can on paper output 12.6 watts per channel into 16 ohms and 17 watts into 32 ohms (much more than recommended by RAAL), I'm having issues playing at the top end of the loudness range. On 32 ohms when I put on a dynamic bassy track, like Parcels – Lightenup and go past about -10db on the amp screen, I start having audio dropouts that get worse when I start approaching -5db and the audio is completely gone by 0.0db (maximum level) on the amp. At the same time this amp starts to throw a cryptic "HP DC abnormal" message momentarily. On 16 ohms the problem starts to appear even earlier.

So Topping says "the A70 Pro is designed for different user scenarios, a protection mechanism has been set up to avoid that some users may damage the headphones unconsciously", but after reading @KaiSc post that mentioned a "problematic load at the low end" the transformer presents to the amp, I'm not sure that protection is necessary, meaning I'm highly unlikely to destroy the drivers regardless of what the A70 "feels".

If that is true, I need to argue that somehow to Topping in technical terms to make them agree to release a firmware update with an option that disables or appropriately adjusts their protection mechanism.

What's going on there? Who's right and who's wrong?
The problem origins from subsonic or even DC signals in the audio.

The Ti1a/b presents an almost dead short to the amp at those frequencies, and obviously Topping A70 can‘t handle that, even sends a ”HP DC abnormal” message, which means exactly that.


Use a low cut filter EQ to remove frequencies below ca. 15-20 Hz from the music.

Maybe you have a parametric EQ handy somewhere in your chain, e.g. the player soft, which would be the easiest way.

Another position for a filter would be a series capacitor between Topping output and Ti1a/b‘s input.
The cap should be one bipolar 500 uF / 35 V for each left and right channel.
This construction raises Ti1a/b’s low frequency impedance to ca. 16 Ohm, which Topping can handle.

Maybe you or a friend could built such a filter adapter.
All you need is: 4 pin XLR male and XLR female, two caps, a piece of wire and some shrink wrap hose.
 
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Feb 11, 2024 at 2:23 AM Post #927 of 1,047
So far, we've not had a single failure due to over powering. At the 32-ohm input, the AHB is running around 25-watts. Since the CA-1a only needs about 3-watts for full SPL, the potential for failure is there, however, with reasonable volume settings, there should not be a reliability problem. Crazy as it sounds, I've personally tested the TI-1b and CA-1a with a pair of 900-watt Bryston mono blocks without a failure. I've come to think of it as a 1000 horsepower car. With responsible application of power, they can be safely driven in a 25MPH school zone.
Not quite 900W, but I run my CA-1a on my 225W Van Alstine monoblocks all the time without issue.
 
Feb 12, 2024 at 4:40 PM Post #928 of 1,047
The problem origins from subsonic or even DC signals in the audio.

The Ti1a/b presents an almost dead short to the amp at those frequencies, and obviously Topping A70 can‘t handle that, even sends a ”HP DC abnormal” message, which means exactly that.


Use a low cut filter EQ to remove frequencies below ca. 15-20 Hz from the music.

Maybe you have a parametric EQ handy somewhere in your chain, e.g. the player soft, which would be the easiest way.

Another position for a filter would be a series capacitor between Topping output and Ti1a/b‘s input.
The cap should be one bipolar 500 uF / 35 V for each left and right channel.
This construction raises Ti1a/b’s low frequency impedance to ca. 16 Ohm, which Topping can handle.

Maybe you or a friend could built such a filter adapter.
All you need is: 4 pin XLR male and XLR female, two caps, a piece of wire and some shrink wrap hose.
Well, I got really excited about this theory as it seemed entirely plausible and ran to test it out! Unfortunately, that seems not to be the case. I had to set the EQ to cut everything sharply below 750 Hz before dropouts started to diminish in frequency, but they were not gone entirely. In fact, the limit of -11db where dropouts never occur on the A70 remained there even regardless of that brickwall EQ - i. e. with or without that EQ going past -11db is guaranteed to give me dropouts on a certain song.

It looks like the "HP DC abnormal" that only appears very rarely may be related to those subsonic frequencies, but overall the issue lies elsewhere.
 
Feb 12, 2024 at 4:52 PM Post #929 of 1,047
Well, I got really excited about this theory as it seemed entirely plausible and ran to test it out! Unfortunately, that seems not to be the case. I had to set the EQ to cut everything sharply below 750 Hz before dropouts started to diminish in frequency, but they were not gone entirely. In fact, the limit of -11db where dropouts never occur on the A70 remained there even regardless of that brickwall EQ - i. e. with or without that EQ going past -11db is guaranteed to give me dropouts on a certain song.

It looks like the "HP DC abnormal" that only appears very rarely may be related to those subsonic frequencies, but overall the issue lies elsewhere.
I believe there's a known early run of the A70s that experience this HP DC abnormal message error with difficult loads. You may want to get it exchanged for a more recent build. I have a very early build, but have been lucky to never run into that.
 
Feb 12, 2024 at 4:58 PM Post #930 of 1,047
I believe there's a known early run of the A70s that experience this HP DC abnormal message error with difficult loads. You may want to get it exchanged for a more recent build. I have a very early build, but have been lucky to never run into that.
I bought it second hand, but what's worse Topping doesn't seem to acknowledge a problem (and they never even asked for a serial number to check if my unit was an early run) and keep insisting that it's "for my protection". We've exchanged numerous emails about the issue and they stopped replying when I presented them with a question to state the power rating for sustained load. It's of course somewhat expected from a manufacturer in China, seems to be how they operate in general in my experience.
 

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