BoyElroy
500+ Head-Fier
- Joined
- Apr 10, 2002
- Posts
- 502
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- 10
Well, I've had the balanced bridge Gilmore running as a head amp and preamp for almost a week now and wanted to share some notes with any Gilmore DIY'ers out there.
First, there is a noticeable difference between the BB Gilmore and standard Gilmore. Used as a headamp, I'm measuring (as KG states in his project description) twice the voltage swing at output. To my ears, at least, this translates to more midrange and bass. The upper freqs. don't seem that different to me, but the entire midrange to lower bass seems stronger, with greater bass extension on my 325's. I performed the necessary surgery on my Grados with a heat gun and soldering iron and found out that its actually a pretty simple, non-damaging procedure. I'm also going to put in a standard headphone jack so I can use regularly wired headphones as well.
I'm a bit confused on using the BB Gilmore as a preamp. I've put in both balanced and single ended output jacks on my BB Gilmore but because my McCormack amp only has single ended inputs, I'm using the two positive outputs and ground in a single ended configuration. As far as I can figure, this shouldn't result in any significant change from the standard Gilmore because I'm not using the full balanced circuit, but there seem to be some important audible differences between this amp and my prior standard Gilmore. I wonder if someone could explain to me what exactly is going on here...
As for the sound of the BB Gilmore, I'm hearing a more solid bass foundation (almost like my Apogee Stages have gone from a 40 Hz low end to 30 Hz) and things are shaking in my apartment that didn't shake before. The center image is also much more strongly defined and the soundstage seems wider and more firmly fixed. The biggest difference, though, is in the midrange and mid-bass. The sound is much fuller and where the standard Gilmore had a more airy presentation, the BB Gilmore sounds more balanced from top to bottom. The first thought that went through my head was that there was more resolution with the standard Gilmore but on continued listening, the BB Gilmore has the same high resolution imaging, just more bass and midrange along with it. The high freq. information on the BB Gilmore is still there, but it is offset (?) by a more full lower end so in that sense, I guess it sounds less "airy".
I'll stop there because I don't intend this to be a real review or anything like that. I suppose the main reason for posting this info. was really to point out that for someone planning to DIY a Gilmore, there doesn't seem to be any reason not to build the BB Gilmore instead of the standard Gilmore. The cost of adding the extra boards/transistors is actually quite small and there is no need to buy anything additional. You can still use a standard stereo pot/attenuator at the input and use only the positive outputs and ground to run the BB Gilmore as a single ended amp. If you decide to run it as a full balanced bridge amp in the future, all you have to do is add another headphone jack for the headphones and XLR outputs for the preamp side.
BTW, I didn't bother matching my transistors (again!) and my dc offset at output is .001 vdc on one channel and .006 vdc on the other. I'm not sure if handmatching the transistors (as long as they're from the same production lot) is necessarily required (as long as you intend to use the opamp in the circuit, that is).
One last construction note:
This being my first balanced project, I assumed that I had to connect only the positive and negative outputs to my two neutrik jacks. The sound quality was awful; all treble and little bass. When I turned up the volume, it caused all sorts of pain and aural agony. I took the whole amp apart, re-wired everything, still no luck. I finally picked up KG's insructions and realized that I had to ground the neutriks, even though the headphone jacks carry only + and - signals. Once I connected the neutriks to ground, everything sounded right as rain again. So for anyone having treble/bass problems, my tip would be to check all your ground connections...
First, there is a noticeable difference between the BB Gilmore and standard Gilmore. Used as a headamp, I'm measuring (as KG states in his project description) twice the voltage swing at output. To my ears, at least, this translates to more midrange and bass. The upper freqs. don't seem that different to me, but the entire midrange to lower bass seems stronger, with greater bass extension on my 325's. I performed the necessary surgery on my Grados with a heat gun and soldering iron and found out that its actually a pretty simple, non-damaging procedure. I'm also going to put in a standard headphone jack so I can use regularly wired headphones as well.
I'm a bit confused on using the BB Gilmore as a preamp. I've put in both balanced and single ended output jacks on my BB Gilmore but because my McCormack amp only has single ended inputs, I'm using the two positive outputs and ground in a single ended configuration. As far as I can figure, this shouldn't result in any significant change from the standard Gilmore because I'm not using the full balanced circuit, but there seem to be some important audible differences between this amp and my prior standard Gilmore. I wonder if someone could explain to me what exactly is going on here...
As for the sound of the BB Gilmore, I'm hearing a more solid bass foundation (almost like my Apogee Stages have gone from a 40 Hz low end to 30 Hz) and things are shaking in my apartment that didn't shake before. The center image is also much more strongly defined and the soundstage seems wider and more firmly fixed. The biggest difference, though, is in the midrange and mid-bass. The sound is much fuller and where the standard Gilmore had a more airy presentation, the BB Gilmore sounds more balanced from top to bottom. The first thought that went through my head was that there was more resolution with the standard Gilmore but on continued listening, the BB Gilmore has the same high resolution imaging, just more bass and midrange along with it. The high freq. information on the BB Gilmore is still there, but it is offset (?) by a more full lower end so in that sense, I guess it sounds less "airy".
I'll stop there because I don't intend this to be a real review or anything like that. I suppose the main reason for posting this info. was really to point out that for someone planning to DIY a Gilmore, there doesn't seem to be any reason not to build the BB Gilmore instead of the standard Gilmore. The cost of adding the extra boards/transistors is actually quite small and there is no need to buy anything additional. You can still use a standard stereo pot/attenuator at the input and use only the positive outputs and ground to run the BB Gilmore as a single ended amp. If you decide to run it as a full balanced bridge amp in the future, all you have to do is add another headphone jack for the headphones and XLR outputs for the preamp side.
BTW, I didn't bother matching my transistors (again!) and my dc offset at output is .001 vdc on one channel and .006 vdc on the other. I'm not sure if handmatching the transistors (as long as they're from the same production lot) is necessarily required (as long as you intend to use the opamp in the circuit, that is).
One last construction note:
This being my first balanced project, I assumed that I had to connect only the positive and negative outputs to my two neutrik jacks. The sound quality was awful; all treble and little bass. When I turned up the volume, it caused all sorts of pain and aural agony. I took the whole amp apart, re-wired everything, still no luck. I finally picked up KG's insructions and realized that I had to ground the neutriks, even though the headphone jacks carry only + and - signals. Once I connected the neutriks to ground, everything sounded right as rain again. So for anyone having treble/bass problems, my tip would be to check all your ground connections...