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Post by clausdk on Jun 9, 2010 12:59:53 GMT
A pre pre amplifier
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Post by Deleted on Jun 9, 2010 13:21:12 GMT
You can connect the ground lead from the TT to the screen of the phono connectors. I agree with cjarchez and would connect it between the pre and power amp.
Why.. ? The phono cartridge has to be loaded with the right impedance (resistance + certain capacity) This is around 47k and a few 100pF for a MM cartridge. if you want it to be 'flat'. If you leave out the capacitor and change thi input resistance (to 11k instead of 47k) you change the 'flatness' of the cartridge. This MIGHT sound better but will defenitely sound different.
But if you like it... just use it. Not the correct load for MM/MC high-output cartridges though.
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Post by Deleted on Jun 9, 2010 13:40:25 GMT
Hi Claus and Chaz(cj?), Thanks for the comments. The signal path I tried was, to some extent, forced upon me by my inexperience (numptyness ). I had bought a Cyrus amp as the first stage to go pre + power rather than integrated. I then looked for a Cyrus pre to go with it and bought an aCA7. But numpty me wrongly assumed that all pre amps had phono inputs (from TT) so now I needed a phono amp and I wondered if the G2 would have enough gain(?) to do the job - the answer seems to be "Yes and no", with perhaps the emphasis on "No" . I might try earthing the TT directly to the pre (bypassing the G2) to see if that gets rid of the 'roaring' sound (if the L/S is ever returned by the guy that borrowed it for the duration of my holiday which ended 10 days ago . One thing I'm certainly going to do, unless you guys 'red flag' it, is to replace the G2 with a L/S Attenuator to see if the gain (?) on that is any better. The thought has just occurred that putting BOTH G2 and L/S between TT and pre might give me the gain needed - any thoughts? Bit 'unuser friendly' is my first reaction. Thanks for your interest, Dave.
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Post by Deleted on Jun 9, 2010 16:33:05 GMT
Hi Dave,
For playing with cartidges/TT you will need a phono input/pre-amp for only these inputs have a: enough gain b: (most important): RIAA correction. c: the proper load for a cartridge. G2 is not suited/equipped for this task. Without the RIAA you'll only hear the highs and not the lows.
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insomniac
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Post by insomniac on Jun 13, 2010 13:29:51 GMT
Nice work Chris. That's an unusual approach but it gives the amp a unique appearance.
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Post by Deleted on Jun 15, 2010 9:15:24 GMT
Hi Guys, Old numptie here seeking advice ;D I'm thinking about rolling the 6922 tube in my G2 and saw an advert for a cryogenic treated ECC82: www.voc-rock-guitars.com/Valves-Tubes/CRYO-JJECC82-valve.htmlCan anyone offer advice as to whether my little G2 could show any benefit to justify the x2 higher price? Any thoughts from more knowledgeable members than me would be appreciated. Thanks in advance, Dave.
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Post by Deleted on Jun 15, 2010 9:32:12 GMT
Have untreated JJ ECC83. Before that I bought ECC803S (long plate) but this one was crappy. One half didn't even work but could exchange it for ECC83. JJ ECC83 did have quite some difference between the 2 halves. More so then my old tubes. lower noise then all the stock (old and used) tubes I had (Siemens and Phillips) which was of most importance to me. Can't comment on SQ.
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Post by Deleted on Jun 15, 2010 9:49:30 GMT
Hi Frans, Thanks for your quick response. Sorry to continue the numptie theme but I don't quite understand your response . Do you have any opinion on the benefits of cryogenic treatment of ECC82 valves and whether the G2 is capable of taking advantage of any possible benefits, AND Are you recommending the use of the ECC83 because of the lower noise floor? Also, when discussing valves, is the 'getter' the arrangement of pins around the base? Any thoughts? Dave.
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Post by Deleted on Jun 15, 2010 10:16:09 GMT
My comment was about my experiences with JJ tubes. Don't know if the cryo treatment does anything or has advantages, be it technically or audibly) ECC82 is a different tube then ECC83. ECC83 has lower gain and lower current capabilities (needs other bias setting too, don't know if the G2 pot range is enough) Both are 12V types (selector to 12V) The getter is a metal ring or other shape but has to be a 'loop' too work. The shape and placement is irrelevant but is sometimes used to describe a certain tube. In the getter ring there is some kind of material. a tube isn't totally oxygen free/vacuum when it is sealed. By induction from the outside with a coil a large current is induced in this ring. (like a transformer works or the contactless rechargeable toothbrush) The substance in this ring is heated and reacts with the remaining air molecules in the tube and 'removes'them this way (better vacuum) This leaves the shiny stuff you see on the glass of the tube (which becomes white when the valve is leaking/broken) The Base says something about pin arrangement (noval 9 pin is used in G2) You'll have to download a datasheet to see the actual pin arrangement.
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Post by Deleted on Jun 15, 2010 10:47:28 GMT
Thanks Frans, I understood most of that and am now a bit wiser. In the absence of further information from others regarding the benefits or otherwise of cryo treating I have no current plans to pay 2 x the going price. Seems a bit more complicated than just replacing one valve with another - I'll tread carefully Thanks again. Dave
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Post by clausdk on Jun 15, 2010 16:24:16 GMT
there is some info on cryogenics on Jenawires homepage.
I have an alo cryodock, but I have not meet anybody who could hear any difference, it has the bling factor and "my gear is expensiver than yours" factor that is for sure..
I guess it is a bit like cables that messures alike and some say they can hear a difference.
I have experince with crystals (from butter and ice) and you can make the intermolocular bindings different by using temperature treatments, that is how we keep the butter hard in the summer and soft in winther, despite them having different fattyacids, with different melting points..
Bu if it also works on the atomicarea (even smaller) I really can not say..
Does hardened metal have the same ohmic value as before the hardening ??
IMO it is almost like religions, some say it is true others do not..
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Post by Deleted on Jun 16, 2010 10:35:44 GMT
Schematics of the Indeed G2 headphone amplifier
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Post by Seamus on Jun 16, 2010 11:17:43 GMT
Great work again Frans, I think even I can understand that schematic so thanks for that. How would an autobiasing mod work, is it worth doing on the G2?
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Post by Deleted on Jun 16, 2010 11:35:51 GMT
I am working on similar mods as with the 'standard' Indeed amps for this amp. This involves taking the filaments out of the audiopath, removing the crosstalk and distortion at higher output levels. No auto bias though ... the pots work fine when the filament is fed from it's own power source. Mods will be published when ready. (pdf format) Before I had the G2 I thought they had pulled an ingenious way to deal with 300mA and 365mA tubes. Alas.. I got it wrong.. no ingenious way... just simple 2 resistors (68 Ohms) in parallel and the filaments are again shared for both channels. So 365mA tubes are always underpowered and 300mA tubes receive too much voltage/power.
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Post by Deleted on Jun 16, 2010 11:50:20 GMT
Frans, looking forward to your mods. If the G2 gets much better I see myself selling on one my other amps
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Post by roscoeiii on Jun 17, 2010 6:37:12 GMT
I am new to this amp and am trying to decide between a Genelex 6922 tube and a Genelex 12AX7 and am wondering what sonic differences I will hear from a 6922 vs a 12AX7. New to the tube world in general and not clear on pros and cons of 6XXX tubes vs 12XXX tubes. Any help would be much appreciated.
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Post by mrB on Jun 17, 2010 6:41:11 GMT
Schematics of the Indeed G2 headphone amplifier Regarding the 100nF filter on the PS rail, are we still thinking "outside the box", or should it be inside the box (shared between both channels) as in the G1 (who's schematic you have not yet updated [friendly reminder] ) I don't have a G2 so I can't check. regards,
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Post by Deleted on Jun 17, 2010 8:06:19 GMT
G2 has 2 100nF capacitors (you can see them in the G2 tweaks thread on the picture). older versions (G1) have the possibility of 2 capacitors. In some of these amps 1 is placed (shared) in other amps 2 are placed. Measured the frequency range with old ECC88 (thanks Mike) and 2 EH 6922 tubes. The frequency range of all these tubes are exactly the same (0.9Hz - 100kHz) -0.5 dB The gain varies with the tube (as would be expected for the tube's 'S' (mA/V around Ugk = 0.5V) is the gain determining part because there is NO feedback in this amp). Varying from 16x (24dB) to 21 times (26dB) with differences between tube halves (thus L and R) up to 1 dB. ECC88 = 6922. Other tube types will have different gain ! Will do tube comparison when there is time. Only electrical ... not soundwize. Be carefull when tube swapping. 365mA tubes will be receiving close to the appropriate voltage (6.2V) When a 300mA tube is used the voltage across is will be 7.3V No problem with PCC tubes but 12AX7 and ECC82/83 (12V setting) tubes will have about 1V (20%) overvoltage on the heaters. This will shorten their lifespan. Furthermore because of this higher heater voltage the crossover distortion when IRF are used will already be occuring at lower output levels. Increasing the bias voltage with 1 - 2V helps.
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Post by mrB on Jun 17, 2010 12:28:32 GMT
I'm curious why the G2 has a 100nF across each of the output caps. Can I expect any sonic improvement by adding them to my G1?
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Post by Deleted on Jun 17, 2010 13:28:23 GMT
Most audiophiles will say defenitely: Yes ! Technically 100nF are put parallel to big capacitors (actually only decoupling caps in power supply lines) because the inductance of the capacitor (it's made of rolled up foil) increases the ESR above say... 1 MHz. This is important for the proper operation of fast IC's and switching things (SMPS, clock, digital IC's) proper decoupling of power lines can MAKE or BREAK the audioquality of these devices. The amp has it's -3 dB point at 200kHz (fully modded, otherwise 30kHz) so ... Since the Indeed/Bravo/Miridiy/Muse amps all sound much alike and the G2 sounds different (all in stock form) my technical explanation for this is MOSTLY caused by the difference in output resistance 30 Ohms instead of 47 Ohms (has more or less influence depending on the used phones). Of less importance are the increased class-A current and the 100nF over the output caps IMHO. Simple arithmetic says: impedance of 100nF @ 20kHz = 80 Ohms impedance of 1000uF @ 20kHz = 0.008 Ohms (10,000x times smaller, well ...actually slightly higher... namely the ESR value of that specific capacitor to be exact) These 'resistances' are in parallel, guess where the majority of the (audio)current flows. So to put it in perspective: 99.999% of the audiosignal (current) passes through the 1000uF capacitor and 0.001% through the 100nF. in dB's we are talking about 80dB difference ! Even when a 1uF capacitor is placed in parallel it still has 8 Ohms (1,000x times higher) resistance. This same ratio is there throughout the entire audio range. At 20Hz a 1000uF cap = 8 Ohms... 100nF = 80 kOhms. These ratios become smaller above 100kHz and will be in favor of the 100nF above say... 10 MHz (depending of capacitor) Your choice: look at the technical data or trust your ears. One thing is for sure .... It will NOT make the amp sound worse if you do.
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Post by Deleted on Jun 17, 2010 22:17:46 GMT
Frans The chemical formulation of electrolytics has improved immensely since the days you felt the need to put 100uF flash capacitors across mama honker 10,000uF supply electros.Back then, the ESR increased dramatically well before 1MHZ. Incidentally, it was recently claimed elsewhere that much of the sound of valve amplifiers is really attributable to the typically large output coupling capacitors usually used in many designs.
Alex
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Post by Deleted on Jun 18, 2010 5:35:16 GMT
Alex, Yes capacitors have improved very much. Look at the specs of low ESR types to prove it. 20-30 years ago they could not even dream of this quality caps. I think the difference in sound between SS and tubes can be mostly attributed to: a: limited bandwidths (if applicable, look at the Novo) b: output resistances being different. c: spread of harmonics and the amplitude of this 'distortion' when little feedback is used. As long as it sounds good.... use it ! Who cares where the perceived differences come from. Glowing bottles ad 'something' (nostalgic ?) to the whole experience. The 'magic' of it all. The fact that musicians love their tube amps is because they are driven into 'clipping' (or at least the input stages are) and have limited bandwidths also. This clipping is 'rounded off'.. softer.. then SS would and the spread and amplitude of harmonics is vastly different. This gives these amps a specific sound (in conjunction with the speakers themselves that play a BIG role, sound settings, volume) which they really like. That's why they love tube swapping so much because the overdrive characteristics of tubes tend to differ from tube to tube. In the High-end world these 'overdriven' amps would sound awful. Hifi amps will not (never ?) be driven into distortion. Just use 2 of these amps as 'hifi' amps and you'll immediatly see .. actually... hear my point.
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Post by Deleted on Jun 18, 2010 6:04:57 GMT
Frans Go wash your mouth out with hot soapy water !!! Regarding my comments about the "mama honker"capacitors, it is quite incredible how much smaller, and better, modern electros are in the larger capacitances especially. I well remember the huge screw terminal electros used in the earlier Telephone Exchange -52V 2,000A rectifier cubicles .Even those used in the much smaller +52V 20A rectifiers were quite large back then. Regards Alex
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Post by Deleted on Jun 18, 2010 7:29:04 GMT
I think the difference in sound between SS and tubes can be mostly attributed to:
a: limited bandwidths (if applicable, look at the Novo) b: output resistances being different. c: spread of harmonics and the amplitude of this 'distortion' when little feedback is used.
As long as it sounds good.... use it !
Absolutely!
The nostalgia thing is a strong one for many people. For me, I think it may be more the sound that I have become used to since everything was valves when I was young.
Reading your post made me also think about how we all 'hear' harmonics. Maybe the reason why we pereive headphones/amps etc differently is due to ear canals being different but also perhaps some of us are more sensitive to certain harmonic frequencies and others are more sensitive in other harmonic frequencies?
When we compare things 'relatively' most of us kind of agree in the differences of sound, but listening to items individually is totally different and you have to try to trust your own judgement.
For instance, with headphones, I use the HD600 as a reference. However, if I don't, I may well focus on another aspect of the sound moreso than just tonal and totally ignore the tonal aspect. (Unless it's way off)
I have always wondered whether Sennheiser produced the HD650 in an attempt to emulate a 'tube' sound. (In terms of tone) Especiallo now the Novo is trying to. I must hear one of these things!!!!
Ian
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rowuk
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Post by rowuk on Jun 18, 2010 17:00:44 GMT
Tube amplifiers when properly warmed up, or when never turned off, warm up the air molecules in a certain way which changes their transmission characteristics. Speakers/HP behave differently when the air is warm.......................
I think that the differences with headphones could be tweaked just by making the ear pads "adjustable". 1mm closer to the ear can change the frequency response dramatically making designs like the DT770 boomy or giving K701s reference low end, even with modest amplifiers.
Bob Carver just inserted a series resistor in the output of his t series transistor amps to give them the transfer function and sound of an Audio research tube amp.
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