[Pricklely Peete]

Quote:

Originally Posted by realmassy /img/forum/go_quote.gif Roc owners, what do you think about using this amp to drive a pair of balanced AKG K340? These are pretty inefficient cans and people tend to use a speaker amp.

I would imagine the ROC might do very well but then again power hungry cans can be a surprise in this regard (may need more power may need less). Current delivery is also a consideration for such hybrid transducers but the ROC may have plenty of reserve current on tap or it may not, again my advice in this matter is not much help sorry to say. I do know the K1000's need a beefier amp than the Phoenix which has a bit more power on tap than the ROC.

Here are the power ratings for the ROC into various loads

25 ohm: 750MW
62 ohm: 1800MW
100 ohm: 2500MW
300 ohm: 1350MW
600 ohm: 700MW

Here is the link to the spec's page н¨ÍøÒ³ 1

Is there any way you can borrow a set of K340's to see if the ROC does the job to your liking ?

I would strongly suggest the K340's be re cabled for balanced drive ASAP since the difference in power and gain levels are considerable between SE'd and balanced operation, but I bet you already knew that by now

Peete.

 

[FauDrei]

As I see from old AKG K340 brochure, their impedance is 400Ω. Stock Roc should drive K340 with cca. 1130mW and cca. 53mA at their impedance. This will be loud enough, but can not claim it would be good enough.

My HE-5 (87dB, 25Ω) felt slightly weak at stock power Roc delivered to them (750mW, 175mA @25Ω). Things changed for the better once KingWa explained how to tweak Roc to give more current. Roc (and Phoenix also) by design has maximum current limit on lower impedances which prevents going into meltdown if something goes seriously wrong. But with simple addition of two resistors user can raise this limit and increase Roc's power. 1950mW and 280mA suited much better current hungry HE-5.

Given that K340 sensitivity is 94dB (more sensitive than HE-5), I'd say Roc would do them right even in the stock form. Especially if you balance them (4 pin XLR retermination).

K1000, on the other hand, are just 74dB (?!?) @120Ω... this really is speaker territory and I doubt even the maximum possible current out of Roc (Phoenix?) would drive the K1000 as they should be driven.

NOTE: Increasing current limit makes Roc run hotter. There is an absolute limit on how much current can Roc safely handle. If still interested, contact A-GD for further details on this tweak.

 

[Pricklely Peete]

Wow Fau Drei thanks for that excellent tidbit o technical news ! Is there anything Kingwa hasn't thought of ?, the man amazes me !

74 db even by speaker standards is exceedingly poor. My panels at 84db are pigs to drive (require 4 amps, 500W RMS and around 75 amps amps of current on tap) just to get a clean believable 95 db out of them, without it sounding like crap ( major current for the Maggies and major wattage for the LFT VIIIb's). It's no wonder the AKG K1000 manual suggests a min of 6W per channel for proper SPL levels. I would say 30- 75W tube watts per channel (true dual mono amp to boot) might be ideal for the K1000's.

I'll soon be bumping the ET and Maggies panels to double what I have now (1K W per channel not including the dual 504W subs) although the power company may complain about that (or some tree hugger)... Like the original Frankenstein movie from the 30's "It's Alive......IT"S ALIVE !!!"

Peete.

 

[arnesto]

I was reading through the Phoenix thread and owners were saying that the top of the power case gets about 105 degrees Fahrenheit.

How hot does the top of the case on a Roc get?

 

[realmassy]

Thanks FauDrei for your reply, very interesting.
I'll drop Kingwa an email asking what's the best way to drive those babies.

 

[realmassy]

Quote:

Originally Posted by arnesto /img/forum/go_quote.gif I was reading through the Phoenix thread and owners were saying that the top of the power case gets about 105 degrees Fahrenheit. How hot does the top of the case on a Roc get?

It gets warm, pleasantly warm.

 

[FauDrei]

Roc in stock form gets just warm, as Massy pointed out. Even lower plate, to which are regulators screwed. Around 30-35°C I'd say, had not monitored precisely because it was no concern at all.

With 100mA higher current limit, case goes to 40°C, up to 45°C on the lower plate around regulators. Caps inside are also in 40-45°C range, except the ones directly above transformer (not on main board) which can reach 50°C. To me - acceptable trade off.

 

[XLR1]

Quote:

Originally Posted by Zombie_X /img/forum/go_quote.gif The ROC will surely be a huge upgrade IMO. It will have a on of power for those phones. Hell it easily drives the 600Ohm DT880 like no ones business. Also the ROC excels with lower impedance headphones as well. It gives them oodles of current so amping is not an issue. Also the ROC will power the K701/2 no problem as well. It has enough output power and voltage swing to melt those drivers!

I would like to move up to a balanced amp for my balanced Senn HD-800, 300ohm. (Bought used with 4-pin balance.) Sounds like the Roc would be great with them. However, I plan to keep my Beyer T1 600 ohm with SE connection. When you say no problem driving the 600 ohm DT880, are they balanced? Do you think the Roc could also easily drive the DT880 600 ohm in SE configuration? I find my Corda Opera can barely power the T1 600 ohm in SE and I want a strong amp for my next amp.
Thanks

 

[Pricklely Peete]

IIRC the ROC driving 600 ohm cans SE'd will be half the power rating of 700mW, so 350mW or thereabouts since you are only using 2 of the four channels. Do you know what the Corda can produce into the same load by any chance ?

Peete.

 

[XLR1]

Meirer Audio's manuals and web site are a little short on such details. One positive reference point for the Roc, the Roc claims to have a positive gain of 14db in SE mode but the Opera is held to a positive gain of 8db (although the headroom is higher).

 

[Poleepkwa]

I have read a bit and while the balanced amp seems like a worthwhile investment if you want to run balanced headphones, how does this affect the preamp outputs?
Would there be a difference between the ROC balanced pre-outs and the C-2 line-outs?
Wondering which one would work better with my active Genelecs...

 

[FauDrei]

Quote:

Originally Posted by Poleepkwa /img/forum/go_quote.gif Would there be a difference between the ROC balanced pre-outs and the C-2 line-outs?

Well, beside, as you said, Roc having balanced outs with 4 active channels, and C2 having "just" single ended outs with 2 active channels, I'd say the difference is in voltage input stage: Roc has discrete voltage input stages which "clone" single ended RCA signal to make it balanced, or "correct" the balanced XLR input to be completely symmetrical. At the end of Roc's input stage, voltage signal is converted to balanced current signal before entering the fancy black boxes that read "BPM-7110 V2.0" (ACSS/CAST gain stage). C2 has opamp based input stages which convert voltage signal to single ended current signal before entering ACSS gain stage. The opamps in C2 are swappable, so the voltage signal can be somewhat "tailored" with different opamp flavors.

That said, if you feed Roc and C2 through their ACSS inputs, there are no topological differences per single channel between the two. It is just that Roc has 4 of them and C2 has "only" 2 channels. The sound of headphone/preamp out should also be very similar.

 

[Pricklely Peete]

Poleepkwa.......

If the Genelecs have balanced inputs I would imagine running them that way will improve a number of parameters vs SE'd. IIRC Genelecs are Pro monitors of the highest quality and as such they most likely are designed to be driven by a balanced source (if they are powered monitors) and as such that difference vs SE'd would likely utilize the internal amp's circuitry at it's native line level (+4db vs SE'd -10db) to it's fullest advantage. I could be wrong about that however....

That being said the SQ difference between balanced (fully differential balanced) and SE'd won't be huge but should be noticeable in terms of clarity,SNR, control etc.

IMO at least

Peete.

 

[Poleepkwa]

FauDrei and Peete, thank you for clearing that up. The Genelecs users guide says:"The audio input is via a 10kOhm balanced XLR connector, but unbalanced leads maybe used as long as pin3 is grounded to pin1 og the XLR." So not sure if that confirms that the the are indeed fully balanced or not...

None the less, the reason I am asking is because I am considering either the DAC - 19 and C-2 or the ROC and its balanced DAC(both combinations with ACSS). I have bought some Senns HD650 and they could be run balanced from the ROC ( have not tried myself to run balanced headphones) and if the balanced amp also benefits the speakers it might be easier to "ignore" the large price difference of close too 700 USD

 

[russell-w]

The new DAC is available, they are referring to it as the Reference 5.
н¨ÍøÒ³ 1