luvdunhill Posted June 26, 2009 Author Report Posted June 26, 2009 I mainly meant that I couldn't get the gate voltages down low enough to put the outputs into a somewhat decent bias, like you had originally targeted, somewhere in the 150mA range. Think I'll wait until you do some more testing and probing with a load on the output to comment further. My little proto was not quite as organized. yeah, I totally agree. At this point, I'm drawing the current I'd expect to be seeing with eight output devices. We need to decide on a reasonable adjustment range though, or at least a lower limit. DigiPete: Yeah, I have a build thread in mind and have been taking notes.
digger945 Posted June 26, 2009 Report Posted June 26, 2009 OH my bad. I thought you meant 1A per device. You mean 1A total right.
DigiPete Posted June 26, 2009 Report Posted June 26, 2009 cool. once all is settled, I'll put together the final BOM for the parts buy. we may consider extra parts for closer matching if that is what you decide after the prototyping effort is completed.
Icarium Posted June 26, 2009 Report Posted June 26, 2009 So be forewarned there are at least a couple people going with j4cbo's more smd oriented boards besides the people in the j4cbo group build.. so that may cut into the passive parts by a bit I apologize, but it kind of became necessary with our layout and the need to have a microcontroller on the board for the temperature/current sensing stuff.
luvdunhill Posted June 26, 2009 Author Report Posted June 26, 2009 (edited) At what point does the rising temperature of the board start to counteract the benefit from the tighter tolerances that the SMD devices have? I'm glad I raised all my devices off the board itself, but I'm wondering what happens in this case with SMD. It would be nice if there was feature parity between the two board layouts, IMHO. Edited June 26, 2009 by luvdunhill
DigiPete Posted June 26, 2009 Report Posted June 26, 2009 I will do a group buy only for the Luvdunhill group build board parts. Everyone who responds will get the same parts. Others who want a different parts set, should do their own parts buy (I think?)
Icarium Posted June 26, 2009 Report Posted June 26, 2009 At what point does the rising temperature of the board start to counteract the benefit from the tighter tolerances that the SMD devices have? I'm glad I raised all my devices off the board itself, but I'm wondering what happens in this case with SMD. It would be nice if there was feature parity between the two board layouts, IMHO. Yeah well I think the limiting reagent wasn't really lack of willingness but more timing (The micro-controller decision came about this week after the dynahi "compatible" boards were long ordered) + lack of real estate while keeping the boards dynahi board swappable.. this is re: feature parity.
Smeggy Posted June 26, 2009 Report Posted June 26, 2009 It's great to see this finally taking shape. You guys are great!
Pars Posted June 26, 2009 Report Posted June 26, 2009 DigiPete can step in here, but I would think you could go longer on the boards and still retain Dynahi compatibility? As long as the output transistors are on the same footprint so you could use identical mounting brackets, it should be OK. Not sure on mounting holes on the other end; whether those would need to be in the same place?
j4cbo Posted June 26, 2009 Report Posted June 26, 2009 I'm letting interested people get in on the purchase of my custom version of the board layout because there's no reason not to, but I am not designing it as a second group buy. The entire purpose of the custom work is to let me make whatever design decisions I need for my amps without worrying about compatibility; mounting bracket compatibility and identical features are explicit non-goals. If you just want to use surface mount parts in a Dynahi-compatible board, that's what the main design is for. At the moment it's looking like the custom board will be 3.7" x 3.4", with output devices right at the edge of the board for direct mounting to a heatsink, on 0.5" centers rather than 0.45". This will not be final until I send CAD files to HiFi2000 for custom chassis modification.
luvdunhill Posted June 26, 2009 Author Report Posted June 26, 2009 If you're doing that, I'd recommend spacing the transistors out as far as possible. Heck, make a single "dual channel" board and evenly space the transistors across the whole thing. This is the only way you'll be able to spread the heat effectively without using the mounting bracket as a heat spreader. I think you'll get very good results if you go this route... something like this: I think you have plenty of room on the original board for whatever you're doing with the controller board (and my gain relay suggestion ), and I assumed by Icarium's comment that this wouldn't be backported to the first revision. My comment was more or less, "why not?"
luvdunhill Posted June 27, 2009 Author Report Posted June 27, 2009 the specified MUR820 devices are rated at 8A Unfortunately, that assumes the devices are heatsinked. My rectifiers are running pretty warm at drawing 1A... It would be a huge PITA to have to use an off-board bridge.
j4cbo Posted June 27, 2009 Report Posted June 27, 2009 Here's what I'm thinking at the moment: I'll probably widen out the devices so they spread the full width of the board, and move the mounting brackets in a little bit, but it's using a fairly solid amount of width already.
digger945 Posted June 27, 2009 Report Posted June 27, 2009 Unfortunately, that assumes the devices are heatsinked. My rectifiers are running pretty warm at drawing 1A... It would be a huge PITA to have to use an off-board bridge. What about a dedicated unregulated PS just for the outputs, leaving the S22's to power everything else. I think you know where i'm going.
luvdunhill Posted June 27, 2009 Author Report Posted June 27, 2009 What about a dedicated unregulated PS just for the outputs, leaving the S22's to power everything else. I think you know where i'm going. yeah, we've both been staring at amb's beta24 for too long oh, and listening to music now Fostex T50 are driven quite nicely
Icarium Posted June 27, 2009 Report Posted June 27, 2009 Haha you bastard! Better than the dynahi? I'd love to hear your fostex t50 v1
luvdunhill Posted June 27, 2009 Author Report Posted June 27, 2009 Using the Squeezebox as source, as I don't have another source with volume control. I'll wire up an attenuator tomorrow. I'm happy with the volume at 50% on the SB. Offset is 0.00mV +- 0.05mV.. unbelievable.
naamanf Posted June 27, 2009 Report Posted June 27, 2009 oh, and listening to music now Fostex T50 are driven quite nicely I was worried it was going to play the music backwards. I guess my fear was unfounded.
luvdunhill Posted June 27, 2009 Author Report Posted June 27, 2009 (edited) I can take some measurements for you tomorrow if you'd like, let me know. Now that I've played with the bias, I'm going to recommend to put a series resistor inline with the bias pot. I can calculate the proper value, as there is in fact an upper limit on this value, assuming 4 devices minimum. I replaced the pot with a 50K and still cannot get as low as I'd like (well, as low as *you guys* would like ), so more experimentation is needed. Need to find some 10k resistors, then some desoldering.... then try again, repeat ad nasium. Edited June 27, 2009 by luvdunhill
luvdunhill Posted June 27, 2009 Author Report Posted June 27, 2009 I was worried it was going to play the music backwards. I guess my fear was unfounded. best damn 1kHz sine wave I've ever heard. Fixing to bump it up to 10kHz, be right back..... bliss...
Pars Posted June 27, 2009 Report Posted June 27, 2009 I was worried it was going to play the music backwards. I guess my fear was unfounded. Nope. Plays it inverted, however. Fear back on...
DigiPete Posted June 27, 2009 Report Posted June 27, 2009 Is Kevin building the prototype as well, or give any input on circuit tuning?
Icarium Posted June 27, 2009 Report Posted June 27, 2009 I think that's the plan, but he is really busy right now. I think the singlepower stuff is eating up all his free time.
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