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His Master's Noise: A Thoroughly Modern Tube Phono Preamp
His Master's Noise: A Thoroughly Modern Tube Phono Preamp
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Old 15th May 2018, 09:08 PM   #501
craigtone is offline craigtone  United States
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Yes, the Equal Opportunity. I am making my own PCB and working with SY to get the latest updates. As for the unbalanced output, I am thinking of using a JT-10K61-1M and omitting the output buffers.
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Old 16th May 2018, 02:10 PM   #502
jackinnj is offline jackinnj  United States
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His Master's Noise: A Thoroughly Modern Tube Phono Preamp
Quote:
Originally Posted by craigtone View Post
Yes, the Equal Opportunity. I am making my own PCB and working with SY to get the latest updates. As for the unbalanced output, I am thinking of using a JT-10K61-1M and omitting the output buffers.
I didn't do PCB's for the EO -- if you want a balanced JFET front end, then build a balanced JFET front end. The grounded grid amplifier with JFET input is a solution in search of a problem.
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Old 21st May 2018, 11:04 PM   #503
jpjindex is offline jpjindex  Brazil
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Hello...
Are there PCB's of this project for sale? I'd like do buy a complete set - mainboard + PS.
Thanks
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Old 13th June 2018, 12:48 PM   #504
frankwilker is offline frankwilker  Germany
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Cause much people are interested in this project, i will post some hints for a faster building of the amp.
- the load resistor R1 is 6,8K. It had to be calculated carefully. The sound of my set up was awful. I changed to 56k and the sound changed to clear and marvelous.
- if using the D3a, use for R7 18,7k (1% tolerance) and 34nf (if possible 1% tolerance). Use for R8 2,61k. So you match the RiAA-line near perfect. You have a difference of 0,5dB at 20kHz.
- the current defining resistors with 120 and 300 Ohm are to large. I builded in the meanwhile 5 Boards for friends and me. I used for my DN2540 (in Europe bought) this solution:
Use for the first stage R5 between 68 and 82 Ohm. That gives me 20mA. In most times 82 Ohm matches 20mA.
For the second stage R14 and the cathode follower R18 use 150 to 180 Ohm.
- for a cheaper building you can use the T092 Version of DN2540 (G3) for Q1, Q3, Q5 and Q6.
- Sy used a red led for biasing the second stage. I found no red led with a correlating forward voltage. I used yellow leds. But a higher bias is no problem. The bias point is a little suspended.
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Old 13th June 2018, 12:53 PM   #505
frankwilker is offline frankwilker  Germany
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If somebody is interested, i have several board set (mainboard and ps).
PM, please.
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Old 13th June 2018, 12:56 PM   #506
frankwilker is offline frankwilker  Germany
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Old 13th June 2018, 01:08 PM   #507
frankwilker is offline frankwilker  Germany
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Old 13th June 2018, 04:49 PM   #508
mrdave45 is offline mrdave45  United Kingdom
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Ha, that looks so different to mine! I think Im probably going to replace my transformers with some torroidys, (i know it says not to use torroidal, but they seem to be the best transformers Ive used and they dont hum). Im really not happy with the one i got made. You found some r cores by the looks of things, Where did you get those?

Funny you should mention R1, I spent a couple of days trying out different value with the scope for this. I have the posh sowters (not the ones Sy had) and supposedly they should use just a 47k. I did try that on the bench but settled on something else with a zobel network. I think it did limit the bandwidth a bit but got rid of ringing and kept the gain whilst keeping pretty square square waves. I should try the 47k in situ just to see.

Cheers

D.
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Old 13th June 2018, 05:33 PM   #509
jpjindex is offline jpjindex  Brazil
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From the first time I read this topic, the value of R1 = 6k8 seemed strange to me.
Due to the gain of the Sowter 8055X (1:10), we have an impedance transformation of 100 (10 squared). With R1 = 6K8 the cartridge "sees" only 68 ohms. Typically, 10 times of cartridge impedance is the starting point - or 150 ohms in the case of the Denon 103R.
My cartridge is a Denon 301-mkII so 68 ohms is 2x its DC resistance ... very low and probably will sound somewhat dull
Anyway I'm planning to use a pair of Lundahl LL9226 instead of Sowter so I have to calculate / test R1. 6k8 would not work for me anyway

Last edited by jpjindex; 13th June 2018 at 05:39 PM.
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Old 14th June 2018, 08:48 PM   #510
frankwilker is offline frankwilker  Germany
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If somebody wants a R-Core-Transformer; absolutely no noise:

2016 LITE R-80 Type 100VA R-core Transformer --A variety of model is optional | eBay
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