I wanted to let you know that I've been listening to the Sansui 999 quite a lot since I picked it up and have enjoyed every minute of it! I will write a more detailed review for you and just wanted to give you feedback that I love how it sounds. Asita

I want you to know how much your professional restoration of our Sansui Stereo Receiver Seven is appreciated. We had forgotten what a terrific piece of equipment this 70's era amplifier/receiver is. My wife purchased it new in mid-70's and it had issues for a long time. The sound is now clean, spacial and accurate... like new... maybe better. Excellent work.

We also appreciate the condition of the component when we picked it up. You not only took the time to tell us ahead of time what was required, what it would cost, and made good suggestions (LED lamp replacement), but the unit was returned in clean-as-new condition. This is the most satisfying transaction/experience I had had with electronics repair, and I've had many over the years with stereo and sound reinforcement equipment.

Thank you for everything.

Ron Friesen

I purchased a used 1st generation Bryston 4B a couple of years ago, and was relatively happy with its performance. Then I read a testimonial about Mr. Kim's modification of Bryston's 4B input stage using a constant current source. This was intriguing to me, so I decided to have this modification performed. The cost was well worth it. Mr. Kim said the detail of the amp would be increased, and indeed, he is true to his word. The amount of detail and the now large open soundstage improvements are quite remarkable. With proper speaker placement, the speakers "disappear". Distortion is not an issue, and listening fatigue is gone. The clarity, separation and detail of the different instruments in a recording is now very good. I can pick out an instrument, and easily listen to that particular player whereas before, you knew it was there, but it was for a better word, slightly "hidden". Also, the cymbals have a noticeably better decay and ring to them. Overall, the sound is just better and more refined. I highly recommend this modification for anyone who owns a 4B model of various vintages. You won't be disappointed. You'll think you have bought a new amplifier. Don Kitchen
North Vancouver

I have owned my Bryston 4BST amplifier for 14 years and have generally been satisfied with it. The amplifier has been updated and improved three times since I bought it. I called Bryston, and they do not update this model. Due to the 20 year warranty and a solid design, you really don't see much online about modifying the Bryston. I ran across a forum that discussed a modification done by Minsoo Kim, Master Technician at Pure Sound In Vancouver, to the differential input amplifier stage Bryston uses. It replaces resistors used in this stage with constant current sources. This was quite different from the common cap, resistor, HEXFRED, and wire mods I commonly see. Mr. Kim was adamant about the significant improvement it made to the amplifier. If someone did not like the results, he would change it back to the original condition at minimal cost, not leaving a trace of the modification.

I'm not the kind of person who just takes someones word for it. I did quite a bit of research online and discovered that using constant current sources is the optimal way to run a differential amplifier. Minsoo Kim's claim was backed up by information on major university websites, as well as papers from major semiconductor companies.. It's solid engineering. An optimized differential amplifier reduces noise, second harmonic distortion and can improve dynamic range to a limited extent.

I called Minsoo Kim and asked him about the cost of the modification. It was very reasonable. Mr. Kim's customers seemed very pleased. Customers had high praise for his abilities. There were no posts about his modified amplifiers exploding or bursting into flames. I decide to ship my 4BST to Pure Sound and get the modification.

I have some words of warning to those who would consider this modification. I mentioned installing constant current sources to an engineer I spoke to. He said the person doing this has to really know what they are doing or very poor results may be obtained which can reduce the sound quality of the amplifier or worse. Mr. Kim is a Master technician. He can fix amplifiers without using a schematic. He has designed his own amplifier using constant current sources in the differential amplifier input stage. He has over 30 years experience with audio electronics. I will only endorse Minsoo Kim to do this modification. Hire someone else at your own risk.

I have over 150 hours of constant operation on my modified amplifier. There are no clicks, pops, buzzes, smells or anything abnormal I have observed in the Modified amplifier. It does look better as Mr. Kim cleaned it thoroughly

The modification has only resulted in positives related to sound quality and are as follows

1. Listening Fatigue has all but eliminated. This is huge. I own modified Yamaha NS-1000Ms with the famous or infamous Beryllium dome drivers. The speaker has great clarity, but with the wrong associated equipment and crossover caps this speaker will drive you out of the room. I can listen for hours with no fatigue. No brightness. Amazing.
2. Far less grain. Smoother sounding. The grainy haze that permeated the sound stage is gone. There is a more "airy" presentation which adds much to the realism of the sound.
3. Less Congested sounding with less smearing. I am hearing details I have not heard before because it keeps all the different sounds separate. Much better real sounding decay, especially on piano. Everything is there. One instrument of higher volume does not cover up the other sounds of lower volume.
4. The general character of the amp remains unchanged, but there are differences. Piano sounds more solid with more low frequency impact. Plucked strings have more real texture. More solid and deeper low frequency drum sound. synthesizer are much more clearly presented, like hearing them for the first time. Ambient information is clearer, especially on something like Cowboy Junkies: The Trinity Session. There is an increase in what Srajen Ybaen calls color saturation, making voices and instruments sound more real.
5. Generally more clarity, however the clarity does not jump out and grab your attention. It is evenly and naturally presented throughout the frequency range. It is not "HiFi" sounding.
6. More subjective ease to the presentation. The amplifier never sounds strained or rough.
7. Mod provides outstanding value for the money.
8. I now just listen to, and enjoy the music. It just sounds good.
9. Comparisons. I've been out of the market way too long to say. I think it sounds better than the Threshold Stasis Class A amps I sold during college. That's all I can say.

I think that Bryston is a great company. They have well deserved reputation for outstanding customer service, and equipment that is great sounding and extremely reliable. I have never regretted my purchase of the 4BST. My past interactions with James Tanner and Christopher Russell have been excellent. I asked Chris Russell one time about HEXFRED diodes in amplifier power supplies. He procured them, installed them in an amplifier, tested and listened to the amplifier, and then called me with a report. How many companies would do that for a customer? Zero, Nada, Nil, None. That's the kind of company Bryston is.

Minsoo Kim regards Bryston as an excellent amplifier design. He only disagrees on one thing, being the absence of constant current sources in the differential amplifier input stage. Mr. Kim has proved his point to me. The improvement is undeniable. With all due respect to James Tanner, Christopher Russell, Stuart Taylor, and rest of the great people at Bryston, I think that current sources in the differential input amplifier stage may deserve a second look.

Anonymous

Hi Minsoo, I had an opportunity to set up my amplifier last night & to listen to both CD's and records. I believe that I now own the nicest Sansui AU-999 on the planet. Regardless of the type of music I listened to, the detail of each recording was exceptional and far exceeds my expectations. WOW! I also find that my listening volume level does not need to be so high to enjoy the music I listen to, but when I turn it loud the sound gets even better. I have 2 other Sansui units, an AU-919 and a G-7700 receiver that will likely collect dust for a while. The modification that you completed on my AU-999.....is that something that will work on these items as well? THANK YOU! Brent Clifford

Hi Minsoo, I would like to leave some feedback on the work done on my Fender Deluxe 1953. I am extremely happy! The amp is so quiet and when I'm playing my tele through it, all you hear is pure beautiful sound; everybody knows a tele hums, no mater what. The work, the ethics and quality of workmanship: all exceptional... I hope you don't mind Minsoo , but you're my Number One go-to guy. I Would recommend you to all my friends. Keeping Tone Alive, Shakeypeet out... Shakey Peet
Vancouver, British Columbia, Canada

What a difference in the sound of the reference material I usually use to test with. The bass became tighter yet with more thump. Soundstage seem to extend past the edges of the speaker placement. It seems to take on a more airy quality on instrumental tracks, which is very appealing. Much more detail in the mid/high area than I have heard. The only complaint I have now is I will have to spend more money increasing my meager record collection!
Thanks for the wonderful sound I am now enjoying. Roy regarding a Denon DL-103 cartridge modified by Pure Sound

Minsoo is like the Ferrari technician of prized audio gear. In my case he not only effectively rebuilt a very complex amplifier; he transformed it into basically a new component that will easily provide another 20 years of enjoyment. If you are serious about your gear and it has value to you, Minsoo will ensure you are not disappointed. I can strongly endorse the services of Minsoo Kim at Pure Sound. Rudy Enzmann

I just wanted to let you know that I've had a few days to burn in the mod you did on my Bryston amp, and I'm very happy with the results so far. There is noticeably more detail, while the musicality of this amp is maintained. I'll be posting aome comments about this in the Canuck Audiomart forum. Thanks! Bill Pope