JLM 60Watt Power AMP Kit

Support for JLM Audio Kits

Moderator: Joe Malone

Post Reply
greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: JLM 60Watt Power AMP Kit Now Available

Post by greenmanhumming »

wow those curves look pretty close, what component did you put where to achieve that?

my vol control is a 4 gang stepped attenuator, so matching shouldn't be too much of an issue.

the hum thing though i suspect will be a problem, and if the passive is incompatible with the crossover system you've worked out then all the more reason to ditch it.

i guess i should try what you worked out for the crossover and if it sounds good then go for the dINgO to buffer it. I'm a bit wary of adding ever more circuitry to the system, but OTOH a full active crossover would be another bunch of opamps...

thanks!

BTW I just got a good deal on some end of line 1200uF 63v panasonic FC low ESR caps so i put 4 on each rail of each monoblock, 16 caps total, and I think it opened up the clarity of the amp quite a bit, but it was sort of subtle and not at the same time, hard to know if i'm imagining it!

User avatar
Joe Malone
Site Admin
Posts: 2070
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: JLM 60Watt Power AMP Kit Now Available

Post by Joe Malone »

Tweeter Amp overlay below
http://www.jlmaudio.com/Tweeter%20Amp.pdf
Remove two 10k marked NF
1k changes to 3k3 in series with 33nF
Two 10uF caps change to 33nF each
Two 10k under 1k change to 1k each
Fit 100mH generic tyco type inductor with about 100ohm internal resistance across +vol-

Woofer Amp overlay below
http://www.jlmaudio.com/Woofer%20Amp.pdf
Remove two 10k marked NF
Fit 8n2 cap across +vol-
Fit 82n cap across +in-
Add two 1k resistors in series to +in-
Add two 10k in series with 150nF across 10k resistors above 1k resistor for 6dB bass boost extension.

Needs to be driven by low impedance so filters do not move
Joe :-)
JLM Audio
Capturing Audio without Injury

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: JLM 60Watt Power AMP Kit Now Available

Post by greenmanhumming »

brilliant thanks! looks easy enough.

does the woofer amp stuff need to be done to both woofer amps? or does some of it interact? the stuff on the input would be paralleled with 2 amps and both fitted like this.

how low impedance does it need to be driven by?

I'm thinking of making a balanced input buffer of a single opa2604 setup as 2 separate unity gain opamps one for +ve one for -ve, would that work?

might still get the dingo pups if that would work better, but i could build the 2604 buffer right away...

nothing needs to be rated above 50v right?

i'll start ordering parts...

User avatar
Joe Malone
Site Admin
Posts: 2070
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: JLM 60Watt Power AMP Kit Now Available

Post by Joe Malone »

greenmanhumming wrote:brilliant thanks! looks easy enough.

does the woofer amp stuff need to be done to both woofer amps? or does some of it interact? the stuff on the input would be paralleled with 2 amps and both fitted like this.
The 2 x 1k and 82nF could be shared by both amps with only a small change to its load by the 2 amps but it may change the woofer level a bit as well.
how low impedance does it need to be driven by?
Any good 600ohm opamp like NE5532A and OPA2604A
I'm thinking of making a balanced input buffer of a single opa2604 setup as 2 separate unity gain opamps one for +ve one for -ve, would that work?
Yes that will work fine but for testing just use a any device that is electronic or transformer balanced out will work fine.
might still get the dingo pups if that would work better, but i could build the 2604 buffer right away...
They will be good for making a active volume control but not needed for this stage of testing.
nothing needs to be rated above 50v right?
Yes that is correct.
Joe :-)
JLM Audio
Capturing Audio without Injury

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: JLM 60Watt Power AMP Kit Now Available

Post by greenmanhumming »

Joe Malone wrote: The 2 x 1k and 82nF could be shared by both amps with only a small change to its load by the 2 amps but it may change the woofer level a bit as well.
but putting it on both won't change the freq response? do the 1k resistors separate the 82nF enough that fitting to both is OK, ie not like putting 160nF across both?

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

I built a opa2604 buffer, works great, and fixed my low level hum problem with the passive volume before it too.

not many places here sell 82nF caps or 82 anything really. everything jumps from 68 to 100. i guess a 68 and a 15 in parallel would be ok?

looking for decent mkp caps. any recommendations? wima FKP2 look good but hard to find some values.

these ok for the inductors? http://uk.farnell.com/jsp/search/produc ... ku=1193630

User avatar
Joe Malone
Site Admin
Posts: 2070
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

greenmanhumming wrote:I built a opa2604 buffer, works great, and fixed my low level hum problem with the passive volume before it too.
Cool
not many places here sell 82nF caps or 82 anything really. everything jumps from 68 to 100. i guess a 68 and a 15 in parallel would be ok?
Yep that is fine
looking for decent mkp caps. any recommendations? wima FKP2 look good but hard to find some values.
Normal MKT 50v types will be fine in this roll as there is no super load on them. Don't go putting jumbo polys in there. Use small polys if you can get them.
yes perfect.

The 3k3 in series with 33nF may change if the tweeter level needs to go up or down when the triamp is finished.
Also the tweeter will need to be ear height when finished due to the now symmetrical mid/woofer setup.
Joe :-)
JLM Audio
Capturing Audio without Injury

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

thanks! its great to have all this help!

what are the consequences of getting out of line with the tweeter when using symmetrical drivers? phase cancellation between mid drivers i guess? comb filter effect?

aside from the simplicity, whats the advantage of going 2 way rather than the original 2 1/2 way setup?

i meant to ask earlier - does the bass boost have phase consequences?

there is very limited room to move the speakers, and they are a bit low at the moment. (my mackie monitors are sitting on top in fact) good for the sofa at the back of the room, not so good for at the computer.

Panasonic SMF Stacked Metal Film or wima FKP2 or vishay MKP1837 any preferences?

i've used the vishay as an extra bypass cap in passive crossovers with surprisingly good results, but this is a different situation, and probably much less critical.

any values I can't find i'll use MKT - i sort of assume the tweeter 33n ones are most critical? i have several good choices for that.

if i wanted to shift the bass boost up in frequency a tiny bit what would I change? the 150n caps?

User avatar
Joe Malone
Site Admin
Posts: 2070
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

greenmanhumming wrote:thanks! its great to have all this help!

what are the consequences of getting out of line with the tweeter when using symmetrical drivers? phase cancellation between mid drivers i guess? comb filter effect?
Just distance timing issues of each woofer to your ear can cause comb filtering and high freq extension in soft dome tweeters is poor and very directional.
aside from the simplicity, whats the advantage of going 2 way rather than the original 2 1/2 way setup?
The 2 way listening area lobe is directly forward from the speakers and larger so stays more balanced over a larger range of listening positions. The old 2 1/2 setup would lobe up or down at about 15 degrees or so depending on which driver was the mid/woofer originally.
i meant to ask earlier - does the bass boost have phase consequences?
Not so much in the new mid/woofer setup but in the old setup would have had some strange response where the extra woofer roll off at a couple of hundred hertz.
there is very limited room to move the speakers, and they are a bit low at the moment. (my mackie monitors are sitting on top in fact) good for the sofa at the back of the room, not so good for at the computer.
That is fine. Just something to be aware of.
Panasonic SMF Stacked Metal Film or wima FKP2 or vishay MKP1837 any preferences?
No preference from me. There are much greater problems than cap types when trying to convert audio back to air for ones ears.
i've used the vishay as an extra bypass cap in passive crossovers with surprisingly good results, but this is a different situation, and probably much less critical.
Yes low impedances in passive speaker xovers certainly shows up different cap types big time but again the below rule applies as well.
any values I can't find i'll use MKT - i sort of assume the tweeter 33n ones are most critical? i have several good choices for that.
More important in the caps is if you can match the left and right caps to 1% would be better than spending money on fancy cap types.
if i wanted to shift the bass boost up in frequency a tiny bit what would I change? the 150n caps?
If you want to shift the bass boost higher freq goto larger cap value.
Joe :-)
JLM Audio
Capturing Audio without Injury

syn
Posts: 6
Joined: Tue Mar 27, 2007 6:02 pm
Location: Belgrade-Serbia

Re: JLM 60Watt Power AMP Kit

Post by syn »

HI
I'm about to build this amp. I want to add some more filtering caps. Is this a proper way to do it and also is star grounding as drawn OK? I'm keeping the caps that are on the amp PCB, too. Sorry for the rough sketch.
Thank you very much.
You do not have the required permissions to view the files attached to this post.

User avatar
Joe Malone
Site Admin
Posts: 2070
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

syn wrote:HI
I'm about to build this amp. I want to add some more filtering caps. Is this a proper way to do it and also is star grounding as drawn OK? I'm keeping the caps that are on the amp PCB, too. Sorry for the rough sketch.
Thank you very much.
Yes that work fine but yes you do need the local AMP 1000uF caps for best results.

If using a star ground and running the speaker to a single amp it is best to take the speaker 0v from the star ground as well.

We have a similar Cap PCB that holds 4 x 10000uF 50v caps with a bridge rectifier and use it the same way.
Joe :-)
JLM Audio
Capturing Audio without Injury

syn
Posts: 6
Joined: Tue Mar 27, 2007 6:02 pm
Location: Belgrade-Serbia

Re: JLM 60Watt Power AMP Kit

Post by syn »

Joe
thank you. So you add 20000uF pear a rail on your PCB? On my sketch I showed one channel only, but I plan to use it
to power my monitors (a pair of KRK7000B), but I was thinking two "mono" blocks. If I change to one "stereo" amp, is
taking the speaker 0 from the star ground still the best solution?

User avatar
Joe Malone
Site Admin
Posts: 2070
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

syn wrote:Joe
thank you. So you add 20000uF pear a rail on your PCB? On my sketch I showed one channel only, but I plan to use it
to power my monitors (a pair of KRK7000B), but I was thinking two "mono" blocks. If I change to one "stereo" amp, is
taking the speaker 0 from the star ground still the best solution?
Best 0v for speaker is always the star ground. But when bridging two amps to get more power the speaker doesn't use 0v as it is between the two amp outputs.
Joe :-)
JLM Audio
Capturing Audio without Injury

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

great to see someone else building these, keep us posted on how it goes!

my caps for the crossovers arrived today so Joe - a few more questions:

* should i leave a passive zobel on the tweeter or is that not now needed with the active setup?

* any thoughts on tweeter protection with active? I thought i'd test with the passive xover still in place the first time....

* what is the point of diminishing returns with adding extra power supply caps to the powerrails? I have an additional 4800uF on each rail plus whats on the 3 amp boards in each monoblock. Is there any point in adding more?

* any suggestions about reducing transformer vibration? I have encapsulated toroidal power transformers and I can still hear the damn things vibrating away softly at 50hz plus harmonics - is there anything I can do other than buy better ones?

greenmanhumming
Posts: 117
Joined: Tue Apr 10, 2007 1:19 am

Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

well I've changed one channel to active

it works, it sounds good, but i'm not yet sure if it actually sounds better than the passive version.

certainly it is different. very hard to describe the difference, other than the tweeter level. theres actually maybe subjectively a little less deep bass. but the mids are significantly different in a way i can't describe.

the tweeter is too loud, i put a 2 ohm resistor in series with the tweeter to see, and that brings it about to where it should be. what increase in the 3.3k resistor would that translate into?

Post Reply