Golden Gate DAC arrives.

[seatrope]

Hi Norm,

Thanks for the advice. What is the input sensitivity or your amp? Mark (Sablon) has a great point. I checked my Pass XA30.8 specs and the specs indicate max output at 770mV. Obviously since my speakers are 99dB sensitive I won't be close to max most of the time, but the XA30.8 is also rated at 30W output.

My main concern is reducing the background noise level relative to the music signal.

As a side note, with regards to murphys33 report of tube shielding, I have built a faraday cage out of soldered copper mesh for my big 7 tubes, with a grounding wire to the chassis. I find the tube cages still leave the top of the tubes unshielded. This works very well to eliminate RF pickup. Images attached, not beautiful first attempt but functional.

Just adjust it to 550mv and you should be Golden.

My new speakers are 94db and so with the GG and 242 tubes, I get max SPL already at roughly 45% volume. On my older 90db speakers, I needed 70% volume to have the same SPL. Its a combination of several factors.

 

[wisnon]

Integrated amp:

Preamp input:
Input impedance (R and C)
100k?+ 320pF
Maximum input signal
8V rms (ref. 0.1 THD)
Output impedance

Pre-out
75?
===========
Main in/Speaker out:
Input impedance
10k? + 200pF
Input sensitivity
1.2V (ref. rated power)
Voltage gain
29dB

 

[seatrope]

Here are some quantitative measurement with an inexpensive DMM which might be useful to those interested in the differences with the 242 tube and 45 mesh. This was primarily done to evaluate the low volume on my new GG.

Measured at RCA Out with rigged RCA cable to digital multimeter in AC voltage mode:

Squeezebox touch:
1 kHz tone, 0 dBFS = 2.050V

Old Big 7, EML 45 mesh and Jan CD-R recti, TAIV volume fully open, PCM thru toslink:
1 kHz tone, 0 dBFS = 2.373V
Mahler Solti 8 first mvt = 0.918V

Old Big 7, 242 and 5U4G recti, TAIV volume fully open, PCM thru toslink:
1 kHz tone, 0 dBFS = 8.11V
Mahler Solti 8 first mvt = 3.005V

GG, EML 45 mesh and 5U4G recti, R2R PCM thru toslink:
1 kHz tone, 0 dBFS = 1.144V
Mahler Solti 8 first mvt = 0.410V

GG, 242 and 5U4G recti, R2R PCM thru toslink:
1 kHz tone, 0 dBFS = 2.960V
Mahler Solti 8 first mvt = 1.062V

I am uncertain what the accuracy of my inexpensive multimeter is, so the absolute levels may not be accurate at all. But it is useful as a relative measure of differences in output from my old Big 7 and the new GG.

Yeang

 

[seatrope]

repost, sorry

 

[Sablon Audio]

Great work Seatrope and your Squeezebox measurement is pretty much identical to Stereophile's -

www.stereophile.com/content/logitech-squeezebox-touch-network-music-player-measurements

 

[bonzo75]

Thanks, what do you guys interpret from the results

 

[Sablon Audio]

Pretty much confirms what was already known - that 242 runs 'hotter' than the valve types normally specified and needs quite a bit of padding down via resistors, the quality of which will have a significant impact on sound quality. This can be done either by special request or via a switchable option to give greater flexibility.

Seatrope's measurements inidicate a large difference in the outputs of his older Big 7 and latest GG, so perhaps Lukasz has made some changes to the circuit design?!?

 

[bonzo75]

So, if AR ref 6 can take in 9v, why did my 242 distort on it

 

[Sablon Audio]

could be an impedance mismatch

 

[bonzo75]

With 45 on it and PX25 (on ref 10) it sang

 

[Sablon Audio]

Typical Audiophile behaviour - doesn't know when he's got it good

 

[seatrope]

Hi guys, thanks for the feedback. No idea how if at all these measurements relate to the "absolute maximum output" that Lampi provides on their spec sheet. My GG states 285mV which is clearly not reflected in the numbers obtained, although it might be measurement error due to my cheap dmm.

Mark thanks for pointing out that the squeezebox touch control measurements are very close to reference though.

Ked, I wonder if your GG was significantly hotter than mine hence problems with your ref 9. Did you tell me what your "absolute max output" spec was?

Yeang

 

[bonzo75]

It's just 560 mv. But I don't think that's the only factor, not sure what else is

 

[seatrope]

Hi Mark,

Thanks for info. Do you know if all the 242 optimized systems are just padded down with resistors near output? L is having me remove a resistor near each RCA jack (which I have yet to do) to fix my issues with low volume. Remains to be seen if the noise level will increase proportionally.

Do you know if there is flexibility with tube gain and such?

Note that part of the difference btw my new GG and old Big 7 is that the big 7 has the integrated volume control. I was measuring it at max volume.

Pretty much confirms what was already known - that 242 runs 'hotter' than the valve types normally specified and needs quite a bit of padding down via resistors, the quality of which will have a significant impact on sound quality. This can be done either by special request or via a switchable option to give greater flexibility.

Seatrope's measurements inidicate a large difference in the outputs of his older Big 7 and latest GG, so perhaps Lukasz has made some changes to the circuit design?!?

 

[seatrope]

Well interesting that my GG rated at 285 mV produces a 242 peak output of 2.96V. By logical extension yours may produce a peak of about 6V...

It's just 560 mv. But I don't think that's the only factor, not sure what else is

 

[microstrip]

Here are some quantitative measurement with an inexpensive DMM which might be useful to those interested in the differences with the 242 tube and 45 mesh. This was primarily done to evaluate the low volume on my new GG.

Measured at RCA Out with rigged RCA cable to digital multimeter in AC voltage mode:

Squeezebox touch:
1 kHz tone, 0 dBFS = 2.050V

Old Big 7, EML 45 mesh and Jan CD-R recti, TAIV volume fully open, PCM thru toslink:
1 kHz tone, 0 dBFS = 2.373V
Mahler Solti 8 first mvt = 0.918V

Old Big 7, 242 and 5U4G recti, TAIV volume fully open, PCM thru toslink:
1 kHz tone, 0 dBFS = 8.11V
Mahler Solti 8 first mvt = 3.005V

GG, EML 45 mesh and 5U4G recti, R2R PCM thru toslink:
1 kHz tone, 0 dBFS = 1.144V
Mahler Solti 8 first mvt = 0.410V

GG, 242 and 5U4G recti, R2R PCM thru toslink:
1 kHz tone, 0 dBFS = 2.960V
Mahler Solti 8 first mvt = 1.062V

I am uncertain what the accuracy of my inexpensive multimeter is, so the absolute levels may not be accurate at all. But it is useful as a relative measure of differences in output from my old Big 7 and the new GG.

Yeang

The value you get with the Squeezebox touch is very accurate - Stereophile measured 2.06V, so I would consider it as calibrated and that your values are correct. They explain a lot about the sound differences using different tubes - no miracles in this aspect.

8.11 VRMS means 11.3V peak - some preamplifier attenuators will distort heavily with such input.

 

[seatrope]

Hi microstrip,

I *think* the values are Vmax that I measured not VRMS although I'm a newb at multimeter use. It did say max value on the display.

Plus I double checked stereophile reference and it did say 2.06v was the max output level.

So I think 8V was truly maximum with the big 7.

Yeang

The value you get with the Squeezebox touch is very accurate - Stereophile measured 2.06V, so I would consider it as calibrated and that your values are correct. They explain a lot about the sound differences using different tubes - no miracles in this aspect.

8.11 VRMS means 11.3V peak - some preamplifier attenuators will distort heavily with such input.

 

[microstrip]

Hi microstrip,

I *think* the values are Vmax that I measured not VRMS although I'm a newb at multimeter use. It did say max value on the display.

Plus I double checked stereophile reference and it did say 2.06v was the max output level.

So I think 8V was truly maximum with the big 7.

Yeang

Cheap meters will give you RMS values - you can check it just measuring the mains voltage. Manufacturers usually specify power, output level and sensitivity in RMS vunits. The standard CD output level is 2V RMS, as you measured in the Logitech. The 0dB 8V should be the maximum RMS voltage (0dB is the maximum DAC output) . VRMS is the magnitude of the DC voltage that dissipates the same power value as a signal having Vpeak voltage.

Remember Vpeak = 1.404 x VRMS and Vpeak to peak =2 x 1.404 x VRMS.

 

[Audiophile Bill]

Hi Mark,

Thanks for info. Do you know if all the 242 optimized systems are just padded down with resistors near output? L is having me remove a resistor near each RCA jack (which I have yet to do) to fix my issues with low volume. Remains to be seen if the noise level will increase proportionally.

Do you know if there is flexibility with tube gain and such?

Note that part of the difference btw my new GG and old Big 7 is that the big 7 has the integrated volume control. I was measuring it at max volume.

Hi,

That was my conclusion also - they are just padded down with a resistor on the output.

 

[Sablon Audio]

Hi Mark,

Thanks for info. Do you know if all the 242 optimized systems are just padded down with resistors near output? L is having me remove a resistor near each RCA jack (which I have yet to do) to fix my issues with low volume. Remains to be seen if the noise level will increase proportionally.

Do you know if there is flexibility with tube gain and such?

Note that part of the difference btw my new GG and old Big 7 is that the big 7 has the integrated volume control. I was measuring it at max volume.

Sorry for delay in replying Yeang however I only just saw your post. Is good that Lukasz is happy for you to adjust the resistor values to tailor your output level. I'm not sure how many resistors you have in series with the output or what values they are however you would be well advised to take some impedance measurements with your meter en-route. Once you know your optimal final value, then you can look into buying an exotic replacement like AN Silver Tantalum.

I'm not sure if your tube noise will increase along with the output - suspect it may well do - however some resistor types are quieter than others.

Wrt your comment on the B7 having a volume control, it is actually a resistor based attenuator between the valves and the rcas and does not add any gain of its own. Lukasz is best placed to answer your question about the inate gain of his circuit and whether that can be adjusted endogenously.

Good luck and keep us posted on your progress!