Hello all,
After reading one of Poultrygeist's endorsements in another thread, I also got the Sainsmart version of the Guanzo pre-amp. I'd never had or heard tube sound, outside of guitar amps and this seemed like a good, affordable way to get some idea of what the fuzz was all about.
I'm quite happy with it, so I thought I'd post some impressions, and even some measurements and questions related to those.
Having never heard tube stuff before, I wasn't sure quite what to expect. In a way, I wasn't expecting much: I figured, if it just does the job it's supposed to do, it would be transparent, not audible in the signal chain, but the look of glowing tubes would be enough of a justification. I put it in the tape loop of my 90s Marantz integrated, adjusted the volume so it doesn't add gain and switched it in and out of the loop; and lo and behold: it does make a difference to my ears, a positive one. A warmer, slightly fuller bass and a more spacious sound, instruments seem a bit easier to place with the Sainsmart in the loop.
After reading some more here, I changed the four red caps to 1.5 uF 400V WIMAs, as that was what my local electronics shop had in stock. I'm not entirely sure what audible difference this made, I can't really A/B it of course. It still sounds good in any case. I did however take some before and after measurements, which show the same as bazz77's results, and some other things too.
The first image shows frequency response before and after changing the caps, and the response of the soundcard I measured it with. Strangely enough, it extends bass beyond what the soundcard is capable of. For these measurements, the volume knob was set so it provides about 8dB of gain as measured by the level meter of REQ Wizards, which is about 4 o'clock here. Then I took some more measurements at different gain settings, which I've included below.
As you can see, the setting of the volume knob changes bass response and extension, as well as adding some variation (and distortion?) to the treble. Please note the y-axis is only from +3 to -3, so the deviations are rather small really, and I certainly don't hear a problem (mind you, I use the volume knob of my Marantz to set the level, so the Sainsmart operates at a fixed gain over here). I was wondering however, what causes these differences. Is this what bazz77 meant when he said the volume pot is in the wrong place? Does the output impedance change with setting? Or is my soundcard acting strange? A combination perhaps?
Sorry for the long post, just thought I'd share my experience and I hope some people here might be interested in the measurements (or tell me what I've done wrong...).