[dcheming]

Quote:

Originally Posted by Miller-8 /img/forum/go_quote.gif Would a shock from them be enough to kill you? Do you know how big the current is? (amps)

I don't think these caps are nearly big enough to kill, but they're still pretty dangerous. I'm not sure what the current would be because that depends on the discharge speed, but capacitors like these can discharge their stored energy fairly quickly when shorted and all together there's up to about 17.5 Joules of energy in the four PS caps.

 

[troelsjorg]

Hi dcheming/all. I have been following this thread from Denmark, and doing some of the mods on my 708B. (I am guessing i have the only 708B in Denmark?)
I'd like to ask for some help on selecting caps.
I want to change the IC and the HP caps. I use Grado headphones exclusively, and having read all of this thread as well as the mod-thread, i learned that I should consider getting HP-out caps with a value of up to 470uF. I'd like to use Mundorf, but the closest ones i can find are the M-lytic HV 150+150uF 500V. the 200+200uF is too big for the 708B. They are also very expensive. Can you make any suggestions?
And for the IC caps, i read your text "I went with Auricaps for these, but I would recommend the Mundorf M-Cap ZN as a better choice for around the same price". I'd like to try those, but the only ones in 0.22 uF are 250V or 630V. The stock cap is 400V. Can i use a 630V cap and what would the difference be from using a 400V? Kind regards Troels

 

[dcheming]

Hey troelsjorg, welcome aboard.

I really can't make any other recommendations besides the Mundorf caps that you already suggested, but I'll look around some more to see if there might be a better solution that still fits and is relatively affordable. Even the 150+150uF are going to be a tight fit, as I'm sure you saw when Chops first put them in his amp. I know those M-Lytic HV are on the expensive side, but have you priced the same style in Black Gate?

Capacitor voltage ratings are simply the highest working voltage that they can safely be used up to. In film caps the various different plastics used have different electrical properties, but all things being equal the thicker the plastic film the higher the voltage rating. So going with the 630V ones will just give you a larger margin of protection in case something ever goes wrong in the circuit. I've also read that some people think the higher voltage version of the same cap sounds better, but I haven't tested that claim myself so I'm not sure.

Do you have any pics of the mods that you've already done that you'd care to post by chance?

 

[Chops]

Actually, the M-Lytic HV caps I'm using are the 100+100uF - 450V ones.

The 150+150uF caps you're talking about are the "snap-in" ones.

Eventually, I plan on moving the 708B's internals into a new all aluminum chassis. When I do this, I'll be getting two more of the 100+100uF - 450V M-Lytic HV caps along with a pair of the 47+47uF - 450V caps, which will give me a total of 494uF per channel. Heck, I might just go with another pair of the 100+100uF caps for a total of 600uF per channel.

As for the higher voltage caps, I have also heard that they have less distorsion of some kind as well, IIRC.

 

[Stephen_Ri]

Is there a way to decrease the gain on the 708B? I'm using it with an Entech 203.2 DAC which has a loud output (2.5V, I think) and Beyer DT-880s. If I turn the volume loud enough for it to "open up" properly both channels, it's louder than I prefer to listen. Lowering through software decreases bit depth, so that's not really an attractive option either. Any suggestions on the 708B gain or otherwise? I've heard of attenuators, but know nothing of implementation (and don't want to spend much money, if possible). Any response welcome, thanks.

 

[dcheming]

Quote:

Originally Posted by Stephen_Ri /img/forum/go_quote.gif Is there a way to decrease the gain on the 708B? I'm using it with an Entech 203.2 DAC which has a loud output (2.5V, I think) and Beyer DT-880s. If I turn the volume loud enough for it to "open up" properly both channels, it's louder than I prefer to listen. Lowering through software decreases bit depth, so that's not really an attractive option either. Any suggestions on the 708B gain or otherwise? I've heard of attenuators, but know nothing of implementation (and don't want to spend much money, if possible). Any response welcome, thanks.

Yeah the gain is pretty ridiculous, my normal listening volume is at only 8 o'clock. The easiest way to reduce the gain of the XS would be to build a simple potential divider at the input using some quality resistors, like I did with my T-Amp. The ideal way would be to find a tube that has similar electrical characteristics as the 6N3 but with lower gain. If such a tube were found I'm not sure if anything else in the circuit would need to be changed to accommodate it though.

 

[Agnostic]

I managed to get a 708B on Ebay for 120 US including shipping. Man, what a steal, it came in today and it makes my hd595 sing. Much better than the line out of my PC (which isn't bad) or the headphone out of my old Akai solid state. Even better than the portable Microshar uAmp107b that came in the same mail delivery (though I guess that needs some burn-in)
Much warmer sound and fuller, tighter bass. It also tames the sometimes slightly grainy mids of the HD595 very nicely. All this straight out of the box.

Now I'm waiting for some tubes for tube rolling: 70's NOS 6n3p on the way as well as a pair of SYLVANIA JAN-6DJ8.

Anyone found any other nice tubes except the ones already mentioned earlier in this thread?

And which has more influence on the sound, replacing the 6n3, or the two 6DJ8?

 

[dcheming]

Nice find! I'm glad it works well with your 595's. Have any mods planned?

With my limited tube rolling experience in this amp I'd say the 6N3 tube has more overall influence on the sound.

 

[Shinobi]

Very nice I may have to see how this will pair up with some beyers.

 

[Agnostic]

No, not planning on any mods. I have no experience soldering whatsoever and I don't want to burn the house down or electrocute myself.

I'll stick with tube rolling for now. From what I read that's what makes the biggest difference in sound anyway, right?

I have another 6n3 equivalent on the way, GE JAN 5670W.

 

[Agnostic]

GE JAN 5670W sounds good, a little more airy and open and also has a bit less gain than the chinese original (maybe a one hour difference on the volume dial), it's also more quiet, my 6n3 has a slight buzz that's no longer there with the GE.
Going to compare those two a bit more extensively tomorrow. Only had a fast listen so far.

 

[dcheming]

Quote:

Originally Posted by Agnostic /img/forum/go_quote.gif GE JAN 5670W sounds good, a little more airy and open and also has a bit less gain than the chinese original (maybe a one hour difference on the volume dial), it's also more quiet, my 6n3 has a slight buzz that's no longer there with the GE. Going to compare those two a bit more extensively tomorrow. Only had a fast listen so far.

Nice. I need to get a replacement for my 6N3 too since it is starting to become slightly noisy. Any further impressions of the GE after a few days now?

 

[Agnostic]

I've done some more listening. Besides the points I mentioned the GE is less boomy than the 6N3, the lows are more controlled which allows more detail on the mids to come through. Highs are very nice, cymbals and hi-hat's sound great.
There's better decay on highs as well as on the mids. I was listening to Yasmin Levy, accompanied by classical guitar and you keep hearing the tones of the individual strings decaying clearly, even after a new chord has been played (admittedly it's very well recorded), but I noticed the same on cymbals and hi-hats: decay is sounding quite gorgeous.

Anyway I found the tubes very cheap, I paid 10 us dollars for two on ebay, including shipping from USA to europe, so I'd say go and try them.

Seller: http://myworld.ebay.nl/tubetoons/
He's not offering any now, but when I ordered he had more than 500 available so maybe you could just send him a message, he replied quite fast when I asked him for a shipping quote.

 

[Agnostic]

Found another interesting 6N3 replacement tube: Sylvania 5670. I got two and both had a bit of buzz when I got them (used) but cleaning the pins with some brasso took care of that on one, the other didn't stop buzzing after a cleanup; which is a pity because it sounded a bit better in the lower registers than the non-buzzing one.

This tube opens up the soundstage quite a bit and improves the definition; mids and highs sound clearer and more detailed. The only problem is that the one that is working without buzz is a just little bit light on lows with HD580, I'm guessing a NOS one should sound better than these used ones (hope I will manage to find one).

With the HD580 this tube sound very nice for most types of music but for rock they might be a bit to bright and airy for some people, though that depends on taste as well I guess. Listening to Julie London - "You'd Be So Nice To Come Home To" with this tube and the HD580 gave me shivers down my spine though.

With the HD595 this tube is definitely better than the GE JAN. Soundstage on HD595 isn't that big and this tube opens it up just enough to clear up the sound and add some air and space without taking away the intimate up front sound of the HD595. Lows seem to be much less affected than on the HD580, I think because HD580 needs a bit more juice and has a wider soundstage.

Now I'm just waiting for two NOS 6N3P-EV(EB) military stock to arrive from Russia. That will be the last one I try as a substitute for the 6N3 I think. If it's not better than the Sylvania 5670 I will try to find a NOS Sylvania.

I tried replacing the 6N11 with two Sylvania JAN 6DJ8 but one channel was much louder than the other. Anyway they didn't seem to have a very big effect on the sound signature, not nearly as big as the 6N3 changes anyway (maybe because the used Sylvanias I got were not good or just sound similar to 6N11, anyone have an opinion on that?). Not sure if I will try to find another pair of something or other to try in that position yet. The 6N11's seem to be doing ok there.

Wow, this became a much longer story than I intended.

 

[flu1d]

OK, I know nothing about amps but I need some help

I bought the 708b nearly a year ago and a few months later I started to get a low hum. I thought it was the tubes, so I replaced all of them and I still get the hum. The hum only comes in when the tubes are warmed up; however as soon as I cut the power off it goes away immediately. Also, it doesn't matter what the volume is set to, the hum is the same. Any ideas? Thanks.