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 NEW  Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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It is currently 23 Aug 2014, 08:23

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 Post subject: Re: 6dj8/6n1p phonostage
PostPosted: 21 Aug 2008, 10:20 
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Joined: 04 Jun 2008, 21:02
Posts: 84
Location: Philippines
I don't have a picture of the underside.

I have compared the 6922 and the 6n1p, I liked the 6n1p better.

Today, I got bored and recomputed the RIAA for ECC81/12at7 (the 6n1p have a very lowish gain). So I re-wired the phonostage using ECC81/12at7 based on this schematic:

Image

I am listening to it now, and it has better and tighter bass, the highs has more dynamic and it seems the vocals are a bit more clean/defined.

Will continue to listen to it and see if I can tweak it some more. Unfortunately, I cannot do a side by side comparison with my 6n1p phonostage (I am using the same chassis and PSU).


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 Post subject: Re: 6dj8/6n1p phonostage
PostPosted: 21 Aug 2008, 23:17 
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Joined: 31 Jul 2008, 23:21
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Hi Alexg,

I found these comments about those tubes on the DecWare site.

"The input tube is a single 6N1P, 6922 or 6DJ8 - your choice. 6N1P's have the warmest tone, 6922's have the best dynamics, 6DJ8's have the most air and micro-detail with a touch less bass."

I like the 6DJ8 over the 6922, but have never tried the 6N1P.

Was the previous RIAA equalization not accurate?

Thanks for sharing.


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 Post subject: Re: 6dj8/6n1p phonostage
PostPosted: 22 Aug 2008, 08:26 
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Location: Philippines
billp wrote:
I found these comments about those tubes on the DecWare site.

"The input tube is a single 6N1P, 6922 or 6DJ8 - your choice. 6N1P's have the warmest tone, 6922's have the best dynamics, 6DJ8's have the most air and micro-detail with a touch less bass."

I like the 6DJ8 over the 6922, but have never tried the 6N1P.

Was the previous RIAA equalization not accurate?

I just like the sound of 6n1p better than the 6922 and the 6DJ8, on circuits that I have tried.

The previous RIAA equalization is accurate, but since I used ECC81/12at7, the plate resistance and the plate load resistor is different, so the values for the passive RIAA capacitors and resistors needs to be recomputed.

Thanks.


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PostPosted: 26 May 2014, 18:16 
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Joined: 11 Oct 2011, 19:39
Posts: 180
I just finished the 6n1p version of this phono preamp. I really like the results. I used dc for the heaters (lm338) and the HT+ is regulated with lr8 regulators and pass transistors (one per channel).

I used Soviet PIO caps where possible and all wiring is point to point, as in socket to socket, to keep the lengths as short as possible. I think that I may have used maybe two short lengths of wire, other than those which I used to connect to the rca and power jacks.

http://i1189.photobucket.com/albums/z436/lexx221/IMG_0075_zpscb06fd56.jpg

http://i1189.photobucket.com/albums/z436/lexx221/IMG_0083_zps3b77f99b.jpg

http://i1189.photobucket.com/albums/z436/lexx221/IMG_0084_zps089e4b2c.jpg

http://i1189.photobucket.com/albums/z436/lexx221/IMG_0085_zps40f68381.jpg


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PostPosted: 04 Jun 2014, 04:58 
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Joined: 09 Jul 2012, 14:49
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Nice work.
Can you use LR8 regulated HT (like the fore watt supply) with the RJM phono. Or can you post the schematic of your supply.
Thanks


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PostPosted: 08 Jun 2014, 17:38 
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Joined: 11 Oct 2011, 19:39
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I used two separate lr8 HT supplies. The schematic for them is the standard one that you will find in the datasheet. The pass transistors are horizontal output transistors. They don't even get warm. I did have some T092 heat sinks that I used for the lr8 regulators though. Just thought better safe than sorry.

The output voltage is completely and absolutely quiet. No ripple at all that I have been able to detect. The phono preamp sounds great. Completly neutral and no microphonics from the 6n1p-ev tubes that I used. I even thumped them to see but nada...

I need to use a larger heat sink with the heater supply though. The heatsink gets quite hot and the voltage starts dropping. I will deal with that this week. Interstingly though the audio doesn't degrade as the heater voltage drops. It only does when it hits about 3 volts or so. After that I just switch off. That was something that I had been wondering about (but not to use on any sort of permanent basis of course).


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 Post subject: Re: 6dj8/6n1p phonostage
PostPosted: 08 Jun 2014, 21:38 
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Joined: 06 Jun 2008, 18:23
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alexg wrote:
It is illegal to cut those Dao trees in the Phlippines. I was able to salvage the wood from a tree uprooted by a typhoon in my property a few years ago.

The timber is very nice.

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PostPosted: 09 Jun 2014, 07:40 
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Joined: 09 Jul 2012, 14:49
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Attachment:
lr8n3_reg.jpg
Thanks for the info.
Do you mean like this or similar for the ht regulators? I was concerned that the LR8 on its own has too little current for the ECC88


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PostPosted: 10 Jun 2014, 08:45 
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Joined: 11 Oct 2011, 19:39
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The lr8 on it's own can handle maybe 10ma and that is it. That's why I used a pass transistor. My regulator circuit looks very similar to what you have with the following exception:

For R7, I have a 75K resistor in series with a 500K pot. You can use just a 500k pot if you want, but if you bring that resistance down to zero, you will smoke both the transistor and the lr8 (I made that mistake). The 75k just keeps it far enough above ground to prevent that. Other than that, what you have shown above would work fine.

To note here though with lr8 regulators.... do NOT short across the caps to discharge stored voltage. The lr8 doesn't handle that well and it will eat the regulator. Let the load on the circuit drain the caps.


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PostPosted: 10 Jun 2014, 13:20 
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Joined: 09 Jul 2012, 14:49
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Many thanks for the response. Do you know how much current this version will handle and how much the ECC88 uses?
John


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