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PostPosted: 19 Apr 2020, 16:11 
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Joined: 03 Feb 2018, 00:47
Posts: 61
Location: Brisbane, Australia
Has anybody tried these?
https://www.evatco.com.au/jj-e83cc-12ax ... crophonics


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PostPosted: 19 Apr 2020, 20:41 
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Joined: 04 Jun 2008, 20:59
Posts: 4325
Location: Arizona, USA
Hi, I have not. I have used a number of tubes but generally like the JJ ECC803S (standard pins) and the ECC802S (standard pins). The gold pin ones are OK, just IMO not any better. I have also used their ECC83S and it is fine as well. I personally think the long anode 803s is nicer to my ears. All are normally quite quiet and trouble free. I have had a large number of new production Mullards that are supposed to be quiet, but they were worse than the JJs and gain was not as consistent. EH ones are OK, but I don't care for them as much. Let us know if you get some and how they sound.

Good listening
Bruce

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PostPosted: 19 Apr 2020, 20:45 
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Location: Arizona, USA
Hi Everyone, an update on the flash. Depending on the voltage drop in your low voltage bridge rectifier you may not need the resistor either. I have a number of different ones and in two of the four preamps no resistor was needed. The heaters seem to be fine on anything from just over 5 volts to 6.4. The ones with the largest rectifier drop when the resistor was removed delivered about 5.7 to the heaters. The most efficient ones with a 1 ohm resistor were at 5.9. Both just fine and I am unable to detect any performance or sonic issues between them.

Good listening
Bruce

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PostPosted: 01 May 2020, 10:34 
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Joined: 14 Jul 2014, 13:18
Posts: 45
Location: Arizona
I am updating / rebuilding the Groovewatt that I started a couple of years ago. Revisiting this thread, I see the updated schematic posted a few weeks ago. I have a question regarding the updated power supply circuit.

The note on the schematic states "The low voltage power supply has 2 4700uF capacitors on the input side and one 4799uF on the output side each has a 1uF bypass". I am having difficulty identifying these components on the schematic. See attached extract with circles identifying the capacitors I think are being referred to.

Bruce, can you confirm where and what these capacitor pairs should be in the updated schematic?

Thanks,

Phil

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Revised%20Phono%20Preamp%204-2020.jpeg


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PostPosted: 10 May 2020, 13:29 
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Joined: 01 Feb 2015, 13:41
Posts: 182
Location: Athens-Greece
Hello to everyone. I have built this phono preamp successfully, using the MM stage. Now, I am going to upgrade my turntable and cartridge using MC cartidge. What should I check with MC selection and how can I adjust properly the resistors at MC input? For your info I am thinking to buy the Clear Audio Concerto V2 MC


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PostPosted: 11 May 2020, 10:20 
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Joined: 24 Oct 2010, 07:05
Posts: 314
metaldog99 wrote:
I am having difficulty identifying these components on the schematic.
Taking aside a typo in the text from Bruce's schematic (not 4799, but 4700) your assumptions are right. One of the circled bypass capacitor marked as 0.1u, but Bruce had mentioned that it is actually 1uF. "Input side" is on the left of LT1085, "output side" correspondingly - on the right.
dimitris1811 wrote:
What should I check with MC selection and how can I adjust properly the resistors at MC input?
The best way to connect MC to this phono preamp is to use MC transformers. The Clear Audio Concerto V2 MC has almost 10 times less output voltage than a common MM, so you'll have 10 times more noise if you try to raise gain.


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PostPosted: 11 May 2020, 11:11 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
Yes I will use LL1678 MC transformers, but still in Bruce’s schematics there are resistors and best combination if any has to be selected, but how to decide? Will this be only with real sound using my ear?


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PostPosted: 11 May 2020, 15:41 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, Yeah, I fumble fingers from time to time on diagrams. Using the LL1678s is fine, the resistors on the output side of the transformers are for adjusting the cartridge loading. LOMCs run anywhere from about 5 ohms to 400 ohms needed for proper loading and thus proper response. Many will work OK at a more or less standard 100 ohms. K&K Audio (on the Web) has kindly provided some values for the 8X and 16X transformer settings. I attached a screen shot of them. You first need to determine what the cartridge loading needs to be and what step up value you want. You will notice that the range of values for each gain setting is different. I have many SUTs and this one is rather nice ...especially at the price point. BTW it will be a standard option if we can ever get the built preamps to the market (no sales pitch, just and indication of how I feel about the transformers).

Good listening
Bruce
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PostPosted: 12 May 2020, 12:01 
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Joined: 01 Feb 2015, 13:41
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Location: Athens-Greece
Thanks Bruce. The cartridge I have in mind has required load resistance 300 Ohms, so that means I need to use 8x instead of 16x transformer set up? The r1-r4 according to schematics are 270k, 68k, 27k, 16k; which combination should be used? Should I change resistor values?


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PostPosted: 12 May 2020, 13:48 
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Location: Arizona, USA
Hi To get a 300 ohm load you will need to use the 8 to 1 ratio and a 38K resistor in parallel with the existing 47K in the preamp. If you never plan on changing cartridges you could just calculate the value of the 47K in parallel with 38K and use a single resistor from the grid to ground on the input tube.

Good listening
Bruce

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