This is a simple upgrade:
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Change U11 7805 regulator to ST L4941BV. The different is the sonic of the sound – more dynamic and clean.
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LM7805 is a more mellow sound with less clarity but it is still very good.
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Enjoy!
February 20, 2011
January 4, 2011
Subminiature Tubes (6111, 6021) on 9-Pin socket (6DJ8, ECC88, 6922 etc)
Since I have solder the subminiture tube on the SE mu-stage preamp, it do not allow easy swapping of tubes and thus lack lots of fun. Thus I have found some 9-pin extention sockets and find a way to put a submini tube onto it. I solder the leads of submini tube onto a pin head with 1mm diameter size. The pin head can be inserted into the 9-pin socket. Thus now I can swap tubes easily again!
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In picture, the tube is 6021 to replace the 6DJ8 tube on my SE mu-stage preamp. I put the two triodes in parallel and thus there will be only 5 connections from submini tube onto socket.
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December 31, 2010
Hybrid Balance Mu-Stage preamp with subminiature tube
This is a new made preamp – Hybrid Balance Mu-Stage. Dual triode medium gain subminiature tube like 6N16B-V, 6N18B-V, 6N28B-V, 6111, & 6021 etc… can be used. The choice of submini tube is due to its low noise and good microphonic effect.
Features:
- Hybrid (Mosfet + Tube) mu-stage design with full balance at input and output
- Supply voltages: +128V, +59V, -69V and two 6.3V DC – all regulated supply
- Tube biased at about 1.5mA at about 60V plate voltage
- Mosfet IRF710 as Source Follower biased at about 7.5mA
- Gain about mu of the tube, about 20 to 40 times
- Non feedback design and thus tube may need to match for gain.
- Tube can be replacable using IC sockets, the submini tube is first soldered on 8-pins leads and then inserted into IC socket.
FFT measurment:
Update new photo on Jan 3rd, 2011 …..
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December 23, 2010
FDA-1 PCM1794A DAC with Headphone Buffer (K170/J74 x 6 pairs)
The is a V1 FDA-1 PCM1794A DAC board. I have implemented a headphone buffer on to it and the result is super! Details is on the photos.
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Features of the buffer:
- K170/J74 x 6 pairs is used for each channel. Idss of matched pairs is at about 6.5mA.
- DC supply at +/-20V DC and thus ok to drive high impedance headphones.
- Bias of each channel is about 40mA after warm up.
- Gain of buffer is x1. The loudness is high enough for most headphones.
- A 100k(A) volume is used for gain reduction at the buffer input.
- Only SE DAC is used but the sound is transparent and full of details.
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December 20, 2010
Mu-Stage with subminiature tubes – 6111, 6021 etc…
For 9 pin tubes, I think Amperex 6DJ8 is very good performer in mu-stage pre-amp. Thus many other triodes are evaluated in Tube post. Now here is some photos of the mu-stage with subminiature tubes. The way is to solder the small tube on the bottom of the tube socket and the two triodes in one tube is put in parallel. Insulation shrink tubes is used to prevent short circuit of leads.
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I have purchased one pair Sylvania 6021 and 4 pcs Raytheon 6111 tubes (non marking type). The pair of 6021 give very good matching for the gain but only 2 out of 6111 tube are with good gain match. The worst 6111 tube is about 1 db lower gain than the other 3 pcs.
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Note that the mu-stage is also upgraded with KBG and Telfon capacitors!
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