[raindance]

I recently purchased one of these amps with the standard tube package, as I was interested to hear for myself why the 300B SET has such a large following.

Firstly, the amp is very well made. It is solidly built, much heavier than I anticipated.

Secondly, the internal build quality is stellar. Point to point wiring, well thought out and tidy, good soldering.

Now the bad: You are likely to receive one of these amps with paint chips. The tube cage vibrates in transport and chips the transformer cover. Not a huge deal, but something to be aware of. Also, the mains transformer hums quite a bit. It is OK in a normal setup, but if you are using it nearfield in a small, quiet room, it will annoy you.

Listening impressions: At first, I was disappointed with the amp. It sounded OK, but there was no magic present. It has limited low bass and seemed to have limited dynamics compared to my other 300B amp that I am also trying (the Dared 300b monoblocks).

Opening up and examining the amp, the obvious difference compared to the Dared is that the Shuguang uses global negative feedback. I emailed Rachel and enquired whether this could be removed. She did not know but suggested it might damage the amp.

Being the cautious person I am, I removed the negative feedback 

I would say that this transforms the amp. There is no instability. The gain increases a little, but the jump factor that was missing is now there and the amp sounds intimate and natural. The really low bass is missing in action, but this might be a good thing as 300b's are not known for bass control and a subwoofer could help here.

There was a professional review on the amp that was lukewarm. Perhaps it would have been more favorable without the feedback which has obviously been added to make the amp measure well.

I'm still comparing the Shuguang with the Dared but my initial impressions are that the Shuguang is sweeter sounding (the Dared is dynamic, but a bit coarse). The Dared has better low frequency extension.

Now I am wondering if the Shuguang would be able to be made world class by upgrading output transformers... It is really not a bad buy at the current price at all.

PS: I am using Athena AS-F2 speakers. They work wonderfully with a low power amp in a largish room.

[Ericus Rex]

This one?

http://shop.grantfidelity.com/FACTORY-CLEARANCE-Shuguang-S300I-Integrated-Tube-Amplifier.html

[Freo-1]

Good write up, raindance.  Got any idea how much feedback is being applied?
 
That feedback loop is likely there to keep the amp stable in case the speaker presents a difficult load.  Seems like your speakers are not, but would be leery with certain speaker types until we know more about the circuit.

[raindance]

Seems to me judging by the small increase in gain that there is not a lot of feedback being used. I'd guess at 3 or 4 dB. I'm going to add a switch so I can compare it with & without feedback. I'll put it on the scope when I have a free weekend and see if there is any ringing or other nasties, but my ears are liking the result.

I'm going to dig into the circuit a bit more and see if there are any frequency response limiting components being used.

[raindance]

This one?

http://shop.grantfidelity.com/FACTORY-CLEARANCE-Shuguang-S300I-Integrated-Tube-Amplifier.html

Yes, that is the unit.

[SET Man]

Hey!

   Hmmm.... why would anyone want to build a 300B with feedback anyway. Would love to see those oversized transformers.

Take care,
Buddy

[Ericus Rex]

Price and no return/refund policy should yield a highly modifiable amp!

[raindance]

Today I connected the feedback back in place. The amp still needs some run-in time. As I listen to it it improves. I'll probably add a switch later to enable/disable feedback.

Compared to the Dared, the Dared has more bass. I am not sure if that is necessarily better, it is just more. The Shuguang is leaner balanced. The other thing that has jumped out at me is that the Shuguang is MUCH more extended on the high end of the spectrum and it portrays harmonics very well. The Dared is a tad glassy sounding and piano sounds "blunted" in comparison.

I'd say that the coolest thing about the Shuguang is that it has me listening to recordings that are not that great, but I am finding new things to like about them. Cymbals especially just sound amazing. The bass is well controlled and stops quickly, no overhang. Vocals are sweet, no sibilance.

So far, this is the better amp by quite a long way.

[raindance]

Update: I found a schematic for the S300i and S300MK, so I opened up the amp to make the following changes:

• Add feedback on/off switch.
• Remove input capacitors at the volume control (not needed)
• See if I could fix the transformer mechanical hum.

Taking off the transformer cover yielded a surprise. The transformers look pretty decent, however look at the voltage on the power transformer:







From the GF website, it says:

Limited quantity in stock - only 115V for North America.

The S300I was initially made mostly for Chinese market and European market without remote control. Factory has changed the main transformers on those now offered for North America to suite 115-120V/60Hz.

I am going to check some voltages against the schematic and see how the operating points look.

[raindance]

It appears that the mechanical hum is exaggerated by the transformer cover which appears to be made of mild steel. It is MUCH quieter with the cover removed.

 Bypassing the input caps makes a large difference. Everything seems clearer and a fog has been lifted. The caps look like Orange Drops, but I could not be sure, as I cannot see writing on them.

The effect of the feedback switch: Feedback off gives a laid back vintage 300B sound with rolled off frequency extremes and great mids. Feedback on gives a much wider bandwidth with sparkling high frequencies. There is a volume difference, the pot has to be moved from 10 o' clock to about 11 o'clock to compensate when feedback is restored.

The hum balance pots work well.

[Quiet Earth]

Glad you are enjoying your amp raindance. It looks like you found a good one to tinker with. Maybe the power transformer can be swapped out for the correct voltage type? Ask Rachael if they have a spare one that they could sell you. You never know.

I'd say that the coolest thing about the Shuguang is that it has me listening to recordings that are not that great, but I am finding new things to like about them.

Very well said! This is the main reason why I prefer zero feedback, single ended triode amplifiers over all other types. They just serve the recording better and allow me to enjoy the album for what it is.

Low Wattage Systems are where it's at! 

[raindance]

According to Rachel at Grant Fidelity the transformer is rated for 115V but the silk screening was not updated.

I have fixed the hum mostly by rubber mounting the transformer housing.

The amp is respectably quiet now.

[Speedskater]

For US units, I hope that it's rated for much more than 115V.  The new normal is approaching 125V.