Group Buy Interest?

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It was quite clear at psw if remember right, with pics & stuff - but not in one message.

Matti
 
crazydoc said:
I don't think switching to "soft recovery" will make any difference (though I admit to complete ignorance of soft recovery diodes - I believe they may be used in switching power supplies to reduce EMI.) If you're finding 20+ mv of ripple in the supply (if I'm reading it right), I'd think it's due to failure of the regulator, not the diodes or filter caps.
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But it did make a difference. I swapped out the regulator first (replaced the LM317 with a 7824 fixed regulator and rewired the circuit for it). That made no difference. I still had the ripple. I then bought an oscilloscope so I could confirm that the ripple was really a ripple. It was. I then swapped out the diodes and the ripple is basically nonexistent afterwards.

If you want to know what you have to do to swap out the regulator, basically you remove at least one end of every resistor in the circuit. Then, you cut the trace that goes from the capacitor to the farthest pin on the regulator and add a rework wire to the closest pin. Next, you add a rework wire jumper from the center pin to a nearby ground. Finally you add a rework wire jumper from the farthest pin to the + side of the cap nearest the output jack. It should take about ten minutes if you aren't sick. (It took me a couple of days because I was. :o) Be sure to trim the pins on the new regulator. If you don't, you'll get a nasty spark as it arcs across to the case. I say this from experience....


mshilarious said:
Check the voltage feeding the regulator on a stock unit--I wonder if somehow the drop is larger with the stock diodes, causing the LM317 to go out of regulation :confused:
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I think you're right. The specs for a 7824 would imply that you really need an RMS of 28-40V for consistent 24V output. With a 317, I'd expect it to need to be even higher. The transformer is only 26VAC. They probably should have built this with a 30V secondary or even slightly above that.
 
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dgatwood said:
But it did make a difference. I swapped out the regulator first (replaced the LM317 with a 7824 fixed regulator and rewired the circuit for it). That made no difference. I still had the ripple. I then bought an oscilloscope so I could confirm that the ripple was really a ripple. It was. I then swapped out the diodes and the ripple is basically nonexistent afterwards.
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Well, we we're working with two different units that probably have different problems. Mine has undetectable ripple at the output of both 24v supplies at the outputs of the PS board. With the connector unplugged from board 6, there is also no ripple at 24v on the cable. But when I plug in the connector giving power to the eq boards, a signal is present of about 2mv on the 24v supply on the boards. Removing the jumper from board 6 to board 5 minimizes this signal to well under 1mv. Leaving board 5 powered, and removing the next jumper to board 4 has a negligible effect - the signal is still present at about 2mv.

This same signal is present at the outputs of all the eq boards, at about 3 to 4mv. I can't seem to be able to separate this signal into discrete frequencies - it's basically a blur on the scope at any setting. There seems to be a component in the 60Hz range, and another much faster one. Here is the slower component:
 

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Here is the faster component at about 50kHz - probably beat frequencies. The upper trace is at the oupupt of board 5 (about 3+mv), the lower is the 24v supply on that same board (about 2mv). I really don't know what to make of this, except there seems to be an oscillation induced into the power supply traces on the boards by the eq circuits.

I haven't swapped the transistors, but they are only running at about 38 degrees C, measured by a thermocouple in contact with the case. I guess that will be the next attempt at a fix.
 

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awesome antichef! newark electronics has the transistor parts listed without the "6" at the end of the number. is this o.k.?
 
gemsbok said:
awesome antichef! newark electronics has the transistor parts listed without the "6" at the end of the number. is this o.k.?
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That's where I got mine, and they don't have the 6 at the end -- mine seem to work :D
 
I'm looking to sell all four of my group buy preamps:

Two -81s
Two -84s

I'm selling all four as a package for cost plus actual shipping (I paid $60 from CA to PA).

Simply, I haven't even had time to use them and have too many preamps as it is. I was thinking of doing the mods for the 81s - thanks to AntiChef for sharing his fix here: https://homerecording.com/bbs/newreply.php?do=newreply&noquote=1&p=3082785 - it's easy enough but I just don't have the inclination (I have too many preamps as it is - hey, anyone want to buy a GT Brick?!?!?).

Sorry for the post here, but it seems the best place for it.........
 
Madguitrst said:
thanks to AntiChef for sharing his fix here:
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I take all the props I can get :D, but I should say that it's zmix's fix, not mine...

oh, yeah, and if I didn't have to complete some hurricane repairs and pay property tax this month, I'd probably be all over this.
 
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Sooooooooo, now can I please have my replacement ribbons, I have been waiting to use my mics from the last group buy.
 
Under no circumstances should you play that stuff sped-up, it'll give ya cancer
 
ACM-310 example

Gilliland said:
I had the chance to use my new ACM-310s a few days ago. I've been mixing one of the shows that I recorded, and I thought I'd post a brief clip from one song. I should make clear up front that this clip isn't in any way a "pure" demo of the mic (unlike the bluegrass clip that I posted many months ago). The mic is used on the guitar, but it's mixed with several other sources - including a DI from the same instrument. The ACM-310 is mixed somewhat louder than the DI and is panned to the right (and the DI to the left), but you really won't easily be able to separate the two. So think of this as an example of the use of the 310 rather than a true demonstration of its character.
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For those who listened to the brief excerpt that I posted back in November, the entire concert is now online:

http://www.folkalley.com/music/livefrom/darrell-scott

The description quoted above is still accurate. The guitar that you hear is a mix of the ACM-310 and a DI, but the 310 predominates. Unfortunately, the data compression used in the stream detracts from the quality of the recording, but that's out of my hands. (Though I could post another excerpt at higher bitrate if there was any interest.)
 
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