Grampian feedback
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Grampian feedback
I've been searching the forum for info about Grampian feedback heads, and found that the feedback in them is actually not like traditional feedback, but more just to linearize the low-end on the heads. Does this mean that you could run a grampian feedback head without using feedback?
Re: Grampian feedback
Hi,
Yes. Many people do since the Gotham or Grampian RA7 amps designed to drive them are not easy to find. I did develop a summing amp with the proper loop compensation (simple dominant pole) in place to use the head with feedback. But you really can get away without it.
Mark
Yes. Many people do since the Gotham or Grampian RA7 amps designed to drive them are not easy to find. I did develop a summing amp with the proper loop compensation (simple dominant pole) in place to use the head with feedback. But you really can get away without it.
Mark
Re: Grampian feedback
Thanks Mark! Could you share your summing amp schematic if available?
Re: Grampian feedback
Hi,
I've attached a pdf's with the schematic. Also some construction notes, BOM and PCB layout. Hope that helps.
Mark
I've attached a pdf's with the schematic. Also some construction notes, BOM and PCB layout. Hope that helps.
Mark
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Re: Grampian feedback
Wow, thanks a lot! Very interesting info.
On the topic of feedback Grampians, would a 60W-ish LM3886 amp be sufficient for driving one of these heads?
On the topic of feedback Grampians, would a 60W-ish LM3886 amp be sufficient for driving one of these heads?
Re: Grampian feedback
Hmm, I doubt that 60w could be sufficient, better 120 or more for me...
Re: Grampian feedback
Hi Aaron,
Looking at the datasheet, the part is spec'ed at 38W into 8 ohms (about 17 Vrms, on +/-28 V supply rails). The Grampian is really a 16 ohm head. So given the same power supply, you would only be able to get about 19 Watts into 16 ohms. However, since the current is lower at 16 ohms, you should be able to bump the supply rails up closer to the datasheet limit of +/- 42 Volts (84 V total delta). Still, I think that is going to be a bit shy of what you need. If you could swing to the supply rails at +/- 42 Volts (which you can't), you would only be able to drive about 55 watts into 16 ohms. To really get the most out of the head, it would be good to have an amp that can supply 150 W into 16 ohms. That requires an output voltage of about 50 Vrms. You could use two devices in a bridge mode to get more drive, but you would have to make sure that the power dissipation and/or current limits were not exceeded.
A better choice might be a modern solid state amp rated at 300 watts into 8 ohms. That would yield 150 watts into 16 ohms.
Mark
Looking at the datasheet, the part is spec'ed at 38W into 8 ohms (about 17 Vrms, on +/-28 V supply rails). The Grampian is really a 16 ohm head. So given the same power supply, you would only be able to get about 19 Watts into 16 ohms. However, since the current is lower at 16 ohms, you should be able to bump the supply rails up closer to the datasheet limit of +/- 42 Volts (84 V total delta). Still, I think that is going to be a bit shy of what you need. If you could swing to the supply rails at +/- 42 Volts (which you can't), you would only be able to drive about 55 watts into 16 ohms. To really get the most out of the head, it would be good to have an amp that can supply 150 W into 16 ohms. That requires an output voltage of about 50 Vrms. You could use two devices in a bridge mode to get more drive, but you would have to make sure that the power dissipation and/or current limits were not exceeded.
A better choice might be a modern solid state amp rated at 300 watts into 8 ohms. That would yield 150 watts into 16 ohms.
Mark