Thank you solder tube. If i remove the LM317 resistors & put adjustable pots, do you think it would be ok ? I was also thinking to put a 7dj8 tube instead of a 6dj8 since with 13.5 bias, voltage on pin 4 goes to 7.8 volt .
Without heater mod you can use the 7DJ8=PCC88 as well.
Personally I would simply replace the LM317 resistor with a value closer to the desired one as a higher heater voltage also means you get to reach the crosstalk and non-linear distortion sooner. The resistors can be calculated to better fit a single tube. It is not accurate for all tubes by design as the heater is CURRENT fed instead of VOLTAGE fed (heater mod and all 'normal' tube amps)
It's not as universal for tube swapping as the sellers would like you to believe.
I ordered some Tesla 7dj8 tubes to see how this amp performs because I'm fed up with all these mods . So I'll adjust bias for 13.5v & since heater voltage will rise to 7.something volts , I'll just operate this amp without the heater mode. Will post my results here. Another question . Why do we have to use a high value 2200uf or 1000uf or 470uf output electrolytic capacitors ? What if we just use a good quality MKP instead ?
MKP in those big values don't exist. Values bigger than 220uF (at least not in the size you would be able to fit) will be hard to find. Because the output caps are DC blocking caps (coupling caps in series with load) there is always DC on it, making it pretty good coupling caps as electros are happy when there is enough DC voltage on it.
high values are needed to keep the low frequency cut-off point as low as possible.
For 32 Ohm HP's and 1Hz cut-off (-3dB) 2200uF is needed. For 300 Ohm HP's and 1Hz cut-off (-3dB) 470uF is needed, but will be even lower when 2200uF is used.
There are not much HP's around that can properly reproduce below 30Hz b.t.w. 3dB roll off in the lows CAN be detected though so to have no or almost no roll-off in the extremes 20Hz (< 0.5dB) it is 'important' to shift the -3dB frequency point as low as possible by at least a factor 2 or 3.
So if you would use 100uF MKP on a 32 Ohm HP you would end up with a low roll-off point at 25Hz (-3dB), which means -0.5dB around 60Hz. For a 300 Ohm HP it would already be 2.5Hz though.
The sonic improvements of MKP (or whatever other kind of non-polar or bi-polar cap) would give over polar electrolytics (of the same value) in this application is another discussion though.
The powersupply that comes with the PS-II is of higher quality. The PCB is of MUCH better quality (thicker and goldwash) The PCB has double sided and interconnected groundplanes which translates in a much lower common ground resistance backplane. Tube swapping is MUCH easier as you do not need a voltmeter to adjust and can use 2 LED's. All adjustments are accesable without having to lift the bottom or top perspex plate. It has 2 selectable output resistances (low and high Ohmic) on the sides of the amp, easy to change. You can select AC or DC coupled input (need to take the top off for that setting) No chance to blow up your sources when you accidentally touch the heatsinks as the PS-II doesn't have any voltage on the heatsinks and Indeed has (unless you mod them) Different quality parts are used. Output power is higher. Service/affter sales is completely different. The Horizon brings considerable more power to high-Ohmic headphones and has 3 output resistances selectable.
The price also is considerable higher... who can compete finacially with China anyway ? So it's a question of versatility, quality and ease of operation versus money.
Correct, IF you are using the same tube and if the headphone(s) used are not very sensitive to a difference in output resistance.
However, IF the headphones are sensitive to output resistance AND you own different headphones (ones that prefer lower and others that prefer highr Ohmic amps) in this case the PS-II / Horizon will be different and can easily be set to match that headphone by simply moving an easy accesable jumper, thereby improving the SQ.
If those sonic differences are worth the differences in price is a personal matter. A fully modded G2 afterall isn't as cheap as an unmodded one.
so planning in modding an Indeed G2, if i stick the same heatsink on top of the LM317 will it be cool enough? And do audio grade cap like Nichicon FG, KZ will sound better than the stock coupling caps and power supply cap?
When you do the heater mod (this is in the SR-II/Horizon) this will give the biggest leap in SQ. The LM317 cooling surface needs to become bigger than that of the current MOSFET's (the stacked heatsinks). Simply adding an equal sized LM317 heatsink (as the one it originally has) will be insufficient as the power dissipated by the LM317 is about 3x higher as 'standard' (more than double the voltage , same current) When the G2 in standard configuration is set to the proper bias voltage (15.5V) the LM317 already gets way hotter than recommended so the thermal resistance needs to be about 4x lower than that of the current LM317 heatsink.
Subjectively found differences are not my area of expertise. Using a 35V rated power cap is a 'life expectation' decision... 24V on a 25V rated cap is far from optimal.
The heatsinks are wider than the distance between the posts. Above those output caps you can still see a metal bar. It has screws going through them into the heatsinks. When those screws are tightened the whole heatsink gets clamped (like with pliers) to those posts. The screws are quite close to the posts so it can't slide forward or backward. It still can slide upwards a bit (when pushed upwards) but not downwards as it rests on the PCB. Near the front there are only screws that clamp to the front posts. The construction can be viewed better from above:
The front plate is only secured with the headphone socket and fits between the top and bottom perspex. At a later stage I also moved the on/off switch to the front plate, which seems a more logical location for it.
The maximum input voltage of 24V is a bit 'tight'. Also it puts out 5V which is too low.
very possible you can increase the output voltage on a similar way as with normal regulators by adding 2 diodes in series with the middle pin to ground. Because it is a switching regulator I don't know how it will behave and you probably have to use a capacitor in parallel with the 2 diodes to get it working properly.
The R-78B6.5-1.0 (Mouser part as above) is the correct one. This is the same one as used in the Sunrise.
220uF or 470uF with a 6V rating is already enough as a bypass cap. 1000uF/25 also should be O.K.
High extension is mainly from going to IRF or IRL510. The cathode bypass cap (in parallel to the bias pots) also helps in this aspect and makes it extend a little further. Because there is almost no voltage across this cap it may take a while to 'form'.
The IRF types simply have a 4V voltage difference between Gate and Source. It cannot be lowered. IRL types have 2V (these are intended for switching purposes at TTL voltage drive levels).
The 630 is the bandwidth limiter and causes phase shifting in the audible band. The distortion is caused by the heater being incorporated in the current source path.
bandwidth can only be increased by using 530, 520 or 510 type (bandwidth increases with lower type number) and by using cathode bypass caps. The distortion of IRF set to a bias voltage of 15.5V is exactly the same as that from IRL set to 13.5V. Only the maximum output power is 50% higher when using IRL types. Distortion can ONLY be lowered considerable by doing the heater mod (feeding the heater from it's own voltage source)
I have one of these MHHA amps (not Indeed), and have noticed while tube rolling that, in almost every case, a 6922 tube provides substantially greater bass response than a 6dj8. I've only tested a handful of tubes, but of the ones I listened to, I've noticed that 6922 very consistently beats out 6dj8 in amount of bass.
The 6922 tubes I've tested:
Mullard 6922 (NOS)
Chinese 6N11 (equivalent to 6922) (New)
Sovtek 6922 (Lightly used)
all have substantially better bass than the following 6dj8 tubes I tried:
Mullard 6dj8 (Used)
Amperex Bugle Boy (almost NOS)
Toshiba/Matsushita 6dj8 (Used)
Audio Research 6dj8 (Lightly used)
Is this difference in bass response just coincidence, just my imagination, or just due to the fact that the 6922 tubes I've tried generally had more life left in them? I know that 6922 and 6dj8 are pretty much identical except that 6922 has a lower heater current (300 mA versus 360 mA); could this technical difference have something to do with the bass? My knowledge and experience with tubes is very small.
Is this difference in bass response just coincidence, just my imagination,
When measuring these tubes in this kind of amps (and tube buffers e.t.c.) where there is no overall feedback there are measurable differences between tubes when measured with RMAA. Strange thing is when using a tone generator and specilaised equipment (AC voltmeters/oscilloscope) there asre also differences but smaller. It seems RMAA is not very reliable at very low frequencies.
Anyway... the measured differences are found on the extremes. I.e. at 20Hz for instance RMAA shows differences that amount to +/- 0.5dB in worst case. At 30Hz these differences are already below 0.1dB. One has to keep in mind that bass reproduction of really low notes is somewhere between 50 and 100Hz and at these frequencies the frequency range off ALL my tubes is the same.
Now there is another effect that doesn't show up in frequency graphs but falls under the 'hearable' category. Tubes (in this configuration) have rather high amounts of distortion. Pleasant distortion that is actually desired and determines the sound. This distortion is highest at the lower frequencies and can easily reach levels of -40dB (1%) The harmonics add to the harmonics of the instrument and thus make it more prominent. The amount of distortion is VERY tube dependent and can be -40dB to -70dB which makes it less audible.
Another factor is the amplification factor of the tubes can differe several dB (upto 6dB) meaning with the volume control in the same position the level may differ from tube to tube. When one looks at the Fletcher Munson curves one can clearly see the bass region shows a different sensitivity to perceived loudness as the mids/highs. So tubes that have more gain can appear to have relatively more bass simply because the whole signal is louder which is not that appearant when some time has passed between the 2 tubes heating up after being inserted and adjusted to the proper bias voltage.
So 3 technical aspects that can contribute and the last one is NOT to be underestimated.
Ofcourse expectation bias may also be a contributing factor, which can be eliminated by having someone else put in the tubes and adjust the amp and you start with 0 volume without seeing the tubes and noting the findings. This is my favorite passing of time when playing with amps and NOT simply enjoying music.
So perhaps the difference in bass I'm hearing could be due to mere coincidence and/or individual tube sound signature differences. Does the difference in heater current between 6922 and 6dj8 (300 mA versus 360 mA) have no technical bearing whatsoever on the sound of the tubes in this circuit?
In these tubes the heaters are not connected to the cathodes so have no influence on the audiopath of the electrons.
How much heat is needed for the cathode to start emitting enough electrons depends on the used material of the cathode, the distance between heater and cathode and the current the tube needs to reach (when working on higher voltages) and the type of heater. This and the 'standard' determines the (mA*V = heater power)
300mA was a 'standard' for tubes that could also be used with the heaters in series. Mostly the voltage was 7V or 14V (P types) where E types were made for the heaters to be connected in parallel 6.3V or 12.6V. For tubes with heaters in parallel the current was not of importance, the voltage is (6.3V or 12.6) For tubes with the heaters in series the current is of importance (300mA) the voltage not. So a tube with 300mA could be used in series and parallel circuits and work correctly in both modes.
The heaters, if fed by AC which was usually the case in older amplifiers, does have influence in the induced hum.