Steve @ Apex.jr asked me a Looooonng time ago to make an amp and a "tutorial" on how it was assembled so other newbie’s can make one.
I have since made a few LM3875 and 3886 amps, but none worth documenting. First one was nice, rest were less so...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=40755
With this amp I hope to make a "reference" piece for a friend (Ole MacDonald) in Toronto.
I have a remote control Alps Volume and relay switcher set, and a fairly typical (but nice) case from Par-Metal.
I will be constructing the amp slowly and documenting all the steps from chassis drilling, power input, signal input to speaker outputs. I owe Steve something really nice and hope to fulfill that.
I may ask for suggestions to ensure my approach is the best for ALL people not just ones with drill presses and power tools.
I have since made a few LM3875 and 3886 amps, but none worth documenting. First one was nice, rest were less so...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=40755
With this amp I hope to make a "reference" piece for a friend (Ole MacDonald) in Toronto.
I have a remote control Alps Volume and relay switcher set, and a fairly typical (but nice) case from Par-Metal.
I will be constructing the amp slowly and documenting all the steps from chassis drilling, power input, signal input to speaker outputs. I owe Steve something really nice and hope to fulfill that.
I may ask for suggestions to ensure my approach is the best for ALL people not just ones with drill presses and power tools.
Beta Boards
The Beta rev C boards arrived in the mail today. Looks like a busy weekend.
By the way, I finally tried the Rev A in my main system. Cal Audio CL-10 to Marantz AV-9000 to MA-700 monoblocks driving Vandersteen 3A Signatures. So in effect, A/B comparison with the MA-700's.
Very close. Brighter in Rev A with a bit cleaner attack and release, but almost too bright. Imaging maybe a touch tighter, but hard to tell.
Good news is that Vandy's are recommended to require 200W and are typicall 6 ohms, needing stability to 2 ohms and the amp did not even get as hot as when I was feeding my homemade MTM's which are more like 4 ohms. And there was plenty of volume and even good clean bass on Ray Brown's Live at Starbucks.
If I find time, will try them with the Linn Tukans in the bedroom and report back, but for now, on to the Betas.
The Beta rev C boards arrived in the mail today. Looks like a busy weekend.
By the way, I finally tried the Rev A in my main system. Cal Audio CL-10 to Marantz AV-9000 to MA-700 monoblocks driving Vandersteen 3A Signatures. So in effect, A/B comparison with the MA-700's.
Very close. Brighter in Rev A with a bit cleaner attack and release, but almost too bright. Imaging maybe a touch tighter, but hard to tell.
Good news is that Vandy's are recommended to require 200W and are typicall 6 ohms, needing stability to 2 ohms and the amp did not even get as hot as when I was feeding my homemade MTM's which are more like 4 ohms. And there was plenty of volume and even good clean bass on Ray Brown's Live at Starbucks.
If I find time, will try them with the Linn Tukans in the bedroom and report back, but for now, on to the Betas.
Hey all,
I finally got my completed amp built into a enclosure w/ one of the tiny alpha pots (using Russ's board). Everything is good except for a strong hum across the middle portion of the pot... Zero hum at either end (fully on or fully off). Any ideas to why this might be happening?
thanks.
I finally got my completed amp built into a enclosure w/ one of the tiny alpha pots (using Russ's board). Everything is good except for a strong hum across the middle portion of the pot... Zero hum at either end (fully on or fully off). Any ideas to why this might be happening?
thanks.
I just finished a small external volume control using a dual 50k Alps pot and four jacks in a small plastic box. No hum.
Double check connections. Common ground on one end. Input on other end, wiper to amp. Also, make sure you have a proper taper pot and not a balance control pot.
Russ, a number 59 drill on the three NC pin holes and the 3886 slides right in.
Craig
Double check connections. Common ground on one end. Input on other end, wiper to amp. Also, make sure you have a proper taper pot and not a balance control pot.
Russ, a number 59 drill on the three NC pin holes and the 3886 slides right in.
Craig
Hi needlz, Its a gound loop for sure. I would have to say I am not sure where, but I have my suspicions. Make certain your pot i isolated from your case if your case is connected to mains ground, as it could be that power ground and mains ground are meeting at your pot, which would be bad. 
Make sure you don't connect power ground and mains gnd anywhere.
Cheers!
Russ
Make sure you don't connect power ground and mains gnd anywhere.
Cheers!
Russ
needlz said:
IN_GND and PGND are isolated in this circuit, so be sure that the only GND signal your pot sees is IN_GND if the two met at the pot that might be trouble. One way that could happen is if somehow you had PGND going to your case.
It very hard to troubleshoot these things from a distance.
Cheers!
Russ
On the hum problem, is it there with and without source connected? Agree with Russ, hard to figure from a distance. The one I put together is in a plastic case to keep everything clean. Maybe a short on the ground side of one of the connectors to the box with the pot?
Russ,
A couple of notes. I think you already caught it, but the 30mm diameter Elnas for C3 and C8 are very tight. Might want to slide C3 over a bit so we really can use that diameter cap, even if it is not what will be in the group buy.
The upright Xicon 7 watt resistors I got (Mouser 280-PRM7-0.47) have offset leads. Really only a silkscreen issue as they still fit fine.
Notice you changed the spacing on C4 and C5 so that the MKT's that were the right size for Mauro's rev A board won't fit. I assume again the group buy ones will fit. Had to scrounge some that will fit as the MKT leads are not long enough to bend in.
Will start soldering tomorrow.
Russ,
A couple of notes. I think you already caught it, but the 30mm diameter Elnas for C3 and C8 are very tight. Might want to slide C3 over a bit so we really can use that diameter cap, even if it is not what will be in the group buy.
The upright Xicon 7 watt resistors I got (Mouser 280-PRM7-0.47) have offset leads. Really only a silkscreen issue as they still fit fine.
Notice you changed the spacing on C4 and C5 so that the MKT's that were the right size for Mauro's rev A board won't fit. I assume again the group buy ones will fit. Had to scrounge some that will fit as the MKT leads are not long enough to bend in.
Will start soldering tomorrow.
The hum when source is connected has now magically gone (for peace of mind I will pretend the problem never happened ) but all 3 sets of inputs hum badly without an input. Is there a trick for killing this hum while the inputs are disconnected? Sorry for the newbiesque questions. I am very close to replacing my gainclone with this amp (the nervous looking little amp in the background of the other photo)... the Rev A sounds amazing. I'll have to wait for another paycheck to fund a Rev C but if it indeed sounds better, I'll have to check it out.
) but all 3 sets of inputs hum badly without an input. Is there a trick for killing this hum while the inputs are disconnected? Sorry for the newbiesque questions. I am very close to replacing my gainclone with this amp (the nervous looking little amp in the background of the other photo)... the Rev A sounds amazing. I'll have to wait for another paycheck to fund a Rev C but if it indeed sounds better, I'll have to check it out.
hayenc said:
Hi Craig,
Good notes.
Here are some explainations.
The 30mm caps are intended to sit exactly adjacent to eachother. I have tested Panasonic,Nichicon, and Rubycon and they all fit. But I don't mind moving them a milimeter or two apart if yours were tight.
On the film caps I tried to standardize on 5mm for most of them, but the 100V I did 7.5mm (if I remember right). The parts list(BOM) and the kits Brian puts together will have all the correct parts and sizes. Sorry if this caused you some confusion as there are some differences between my monobloc PCB and the REV A PCB which likely never got mentioned.
I really appreciate your input. I am taking notes.
Thanks.Cheers!
Russ
needlz said:The hum when source is connected has now magically gone (for peace of mind I will pretend the problem never happened
Sometimes a beer or two makes stuff like that go away.
Seriosly even commercial gear can have issues when nothing is connected to the source. There is a lot that can explain that, usually it is wiring and cable dressing. Glad it sounds good. Please enjoy it.
Keep the old GC around for reference.
Beta Kits
The beta kits are packed up. I will try to ship the two US kits tomorrow. I am actually waiting on the post office to drop my some Global Express envelops for the three international kits. Maybe tomorrow, maybe, early next week.
Also, just did a quick test fitting of the Panasonic C3 and C8s. They fit with about .5mm space in between.
The beta kits are packed up. I will try to ship the two US kits tomorrow. I am actually waiting on the post office to drop my some Global Express envelops for the three international kits. Maybe tomorrow, maybe, early next week.
Also, just did a quick test fitting of the Panasonic C3 and C8s. They fit with about .5mm space in between.
Ten million dollars. Boo ha ha ha.
Russ and I are putting together a kit price which we intend to sell though our web site. We haven't worked out the final costs yet, as it depends heavily on how many unit we purchase. Probably in the $100 range for a stereo kit with boards. The kit is everytihg you need to stuff the boards.
Does that sound reasonable?
Russ and I are putting together a kit price which we intend to sell though our web site. We haven't worked out the final costs yet, as it depends heavily on how many unit we purchase. Probably in the $100 range for a stereo kit with boards. The kit is everytihg you need to stuff the boards.
Does that sound reasonable?