mind you that the pre-in is kinda weird on the 508IA. it is not *just* bypassing the volume pot. Pre-in is actually substituting the volume pot with a attenuation stage (with a couple of resistor). It attenuates the input by around 10dB. I am guessing it is trying to mitigate active preamps that are too "hot" to drive the 508IA driver stage (6SL7/6SN7). Unfortunately, because of this, it might not work well with a passive pre-amp in front due to too much attenuation and impedance mismatch. Actually, I tried using a Audio Note Kit preamp and it doesn't have enough gain to make up for that -10dB attenuation.
But Chris has a good point, which is that one can definitely get better sound by replacing the cheapo (alps?) pot that comes with the 508IA. There are 2 issues. 1) some how bypass that 10dB attenuation stage, which is easy but require internal modification. 2) I don't want to lose the ability to do remote volume control. Too spoiled now.
This must be what I was experiencing with the passive Tortuga LDR. Sound was so lifeless with diminished dynamics.
Interesting. My VAC preamp has 10dB of gain. The tube rush doesn't increase through LM when I raise the volume on the VAC (while not playing music of course) but the tube rush does increase using the LM volume control (w/o music) when using the LM as an integrated. I had been wondering what was going on so this explains it with the attenuation.
If you want to try without that attenuation, instead what you can do is to connect your active preamp to the regular input 1/2/or 3, and then turn the 508IA volume knob all the way up. In theory that will have 0dB gain. In practice, it will still go through a little bit of the cheap volume pot but should be almost none. It would be more ideal if that pot isn't there at all.
related question - is it better to be using the el cheapo pots volume control in it's lower range or higher range? I have a gain switch on my Lampizator DAC and it's currently set to low gain (2V) and I tend to sit between 8 pm and 10/11 pm on the LM pot. High gain is double at 4V. Would I be better off with a bit more gain and using the pot at lower levels? I have read that potentiometers are best towards the top i.e. less attenuation. so I assume not. [edit - I think I have answered my own question.]
I believe this is correct regardless of the quality of the pot. The more you reduce the volume the more you're increasing the source impedance/resistance. Which Lampi do you have? I have an Atlantic TRP which I love.
Amber 3 with the new USB interface. I was shocked by the difference vs my old Schiit Gumby. Haven't touched the tubes yet but I am now looking for a Mullard 12AU7 Long Plate to replace the stock ECC82/12AU7.
I'm intrigued about your test with this valve. I'll wait for it. The following valves are sold here in Argentina at a reasonable price (about 45 USD the pair): Cisco-radio Valvulas 6f8 / Vt99 Jan Sylvania Nib Nos ~6sn7 - $7.187,00 If your experience is positive, I think I will give these a try with the adaptor.
Why? It's not the same thing at all! That isn't how to shop for tubes and why you continue to get subpar results. Get the right *specific* tubes and it'll sound great. If you get random tubes without doing your homework, be prepared to be repeatedly disappointed. Don't understand the
Very nice. I upgraded to the Atlantic TRP earlier this year from an Auralic Vega G1 - massive improvement. The G1 sounded cold, 2 dimensional, and analytical in comparison. My DAC uses a different tube set than yours so I can't reflect on the Amber 3. I'm using a Psvane 274B rectifier and a pair of NOS GEC KT66's. I really like Lampi's warranty and upgrade program. I'm already considering next year upgrading to the Golden Atlantic TRP with balanced outputs. I'm using the SE version right now. As I now have my LM805ia configured with the tubes I like I may go back to Lampi and see how my small arsenal of alternative tubes sound. I haven't changed them since replacing the 805 and 300B's. I suspect I'll end up retaining the same recti and input tubes but it's fun seeing if there is different synergy with an improvement. btw: I use the low gain setting as well on the DAC, which equates to ~10 o'clock on my preamp volume knob to get the VU meters starting to move a little on the LM.
By the way, I don't get random, I have the ACMEs 805, the Golden Lions 300B (the ones I can afford right now and not bad for the money), the Shuguang black treasures 6SN7 (wich many people claim to be very good compared to NOS tubes and Don Sachs recomends very much) and recently using a Sylvania VT-229 in the 6SL7 slot (wich was recomended here). Some tubes I bought, I did because they were extremely cheap here, just to try, for fun, but it's very expensive for me right now to spend 150 US plus shipping just to try.
Another recent observation I thought I'd share with this group. Since upgrading the stock 805's to RCA's and 300B's to EML I've noticed an even marked improvement in SQ when using the 16 ohm taps compared to the 8 ohm taps with my O/96's. I have to assume I've moved to lower distortion tubes with better output.
If someone says "The Ford Mustang 2021 is a great car", if you buy a Toyota Prius 2015 and assume you'll get the same experience, you'll be greatly disappointed. Won't be the same thing at all. The two have nothing in common because you're not buying the precise model that is good.
There's no need for the analogy, I'm not dumb. Sylvania also has good tubes as many of you mentioned, so I was just asking. Maybe not this one, I don't know. Here in Argentina there are tubes for sale a good price considering the exchange rate and not all of them must be crap. So, I'm on the search all the time for tubes here, because it's getting harder and harder for me buying them abroad as my national currency is devaluating all the time.
My speakers are 6 ohm nominal and 4 ohm minimum. I'm using the 8 ohm taps as I prefer them over the 4 ohm taps soundwise. Do you think there a risk using the 16 ohm taps with my speakers?
It wasn't meant as a slight; merely to indicate the very specific model needs to be bought if you want a great chance at replicating the great audio revelations we've enjoyed. If you buy a different model, you'll likely be disappointed again and I'd rather you not go through that again. The fix for that is to buy the very specific models that are being discussed. You can't go by "Sylvania makes some good tubes" because there are diamonds and dogs from every manufacturer. That's why the specific models matter greatly. If you shy away from buying tubes which cost $300/pair but buy a bunch of $50/pair tubes, you'll easily spend more than $300 and still not end up with the terrific sound the $300/pair tubes can offer. That's why I suggested changing the strategy.
Well, I find hard to believe that only spending more than $300/pair (on preamp tubes at least) we can have good sound. I don't have big broad experience on hearing high end systems, but I've heard three systems costing many times mine and they were not even close in sound quality, to my liking of course. In fact, I also have a well rewarded class D amp, wich was used on a stand that winned the best sounding award on the 2017 Melbourne Audio Fair and I prefer the LM-508 with my not too expensive tubes. I believe there must be alternatives not too expensive that should sound very close to top notch tubes, but we have to find them. In fact, the Tung Sol 6c8g tubes you are going to try cost about $120/pair. If they sound "close" to the best/pricey tubes, they will be a very good alternative. I also believe that 6SN7 tubes (as other preamp tubes like 12AX7) are getting popular so their price sometimes is not reasonable. Maybe compatible and less popular tubes like 6c8g can be more affordable with similar quality sound. We all will be waiting your impressions on these 6c8g tubes.
LM-508IA circuit does not have "pre amp" in it. It is a single amplifier with volume pot in front of it. Global feed back is from speaker output to first stage. Thus it is not possible to exclude anything to make it "power" amplifier only. Also keep in mind that input impedance from bypass input is much lower than from "preamp" input (1/4) of it. Thus passive volume control devices won't work. If you use external preamp, it has to have low output impedance.
The output impedance of my preamp is less than 150 ohms - and it's static (not dependent upon feedback). Perhaps that's one reason it works so well with the LM805
I don't think there's a risk - just start with volume all the way down. With this said I don't think you'll like the sound of a 6 ohm speaker on the 16 ohm taps - it will probably be too muddy and non-coherent. My speakers are 10 ohm nominal and never dip below 8 ohms.
On the other hand, I have discovered that my speakers, while listed as 8 ohm nominal, are much better on the 4 ohm tap than 8 ohm. They actually measure around 6.5 on average and have a large bass unit just over 4 ohms. Other folks with the same speakers also prefer them on 4 ohm taps. So point being that you won't know until you try. Seems like 'nominal' is more of a vague marketing value than anything else ...
