I use either A1 or A2, although C1 AND C2 work as well if your transformer is <500 VA (roughly). The transformer could draw significant inrush current depending on its size and magnetization state on turn on. A1 or A2 are better positions. You could use both if the inrush is really problematic, but you'll have two CL drops.
Your D positions put the limit only on the amplifier draw, but avoids the sources of inrush current. Not sure what I think about the B spots.
Your D positions put the limit only on the amplifier draw, but avoids the sources of inrush current. Not sure what I think about the B spots.
A1 or A2 limit the inrush current for transformer start up.
B1 and B2 or C1 and C2 limit the charging current feeding the smoothing capacitance.
Use A2 as soft start.
Use the Bs or the Cs if you need a slow charge.
And of course you can use A2 and the Bs or A2 and the Cs for both soft start and slow charge,
B1 and B2 or C1 and C2 limit the charging current feeding the smoothing capacitance.
Use A2 as soft start.
Use the Bs or the Cs if you need a slow charge.
And of course you can use A2 and the Bs or A2 and the Cs for both soft start and slow charge,
While I'm not sure about the Class AB(I have a Class-A amp), I use the CL60 at point 'A' with good results.
Reviewing GE's data sheet for the thermistors :
Type Res@77degF Imax Res(Ohms)/%Imax
CL-30 2.5Ohms 8A 0.34/2A 0.14/4A 0.09/6A 0.06/8A
CL-60 10Ohms 5A 1.09/1.2A 0.44/2.5A 0.26/3.7A 0.18/5A
The CL30 requires over 2A of steady-state current to reduce the series resistance to 0.34Ohm and 4A for 0.14Ohm(I interpolate that 1A is needed for about 0.6Ohm and 3A for approx 0.2Ohm) . That's a lot of current at idle to minimize the series resistance and resultant voltage drop.
Can anyone here advise what a 10 device Leach(2 channel) amp's typical current draw might be at idle with specified bias current, 40-0-40 transformer and, say, 15- 20,000 ufd of capacitance per rail?
What are pros/cons of having a 0.2-0.5Ohm series resistance there in the power supply circuit?
Thanks for humoring a 'newbie' on a (slightly)off-topic query!
-Chas
Type Res@77degF Imax Res(Ohms)/%Imax
CL-30 2.5Ohms 8A 0.34/2A 0.14/4A 0.09/6A 0.06/8A
CL-60 10Ohms 5A 1.09/1.2A 0.44/2.5A 0.26/3.7A 0.18/5A
The CL30 requires over 2A of steady-state current to reduce the series resistance to 0.34Ohm and 4A for 0.14Ohm(I interpolate that 1A is needed for about 0.6Ohm and 3A for approx 0.2Ohm) . That's a lot of current at idle to minimize the series resistance and resultant voltage drop.
Can anyone here advise what a 10 device Leach(2 channel) amp's typical current draw might be at idle with specified bias current, 40-0-40 transformer and, say, 15- 20,000 ufd of capacitance per rail?
What are pros/cons of having a 0.2-0.5Ohm series resistance there in the power supply circuit?
Thanks for humoring a 'newbie' on a (slightly)off-topic query!
-Chas
fit a delayed relay bypass across the CLx0. The delay for position A1 or A2 is about 300mS.
But for slow charge in positions B1 & B2 or C1 & C2 you require a much longer delay, maybe 5S upto 10S if the smoothing is very large.
But for slow charge in positions B1 & B2 or C1 & C2 you require a much longer delay, maybe 5S upto 10S if the smoothing is very large.
You'll get some modulation of the PSU output with signal. Whether it is audible is an open topic. I don't think I hear mine, but I haven't tried a bypass like Andrew suggested. For the purist approach I'd say bypass it rather than leave it in.
Delay relay
Can anyone here specify a relay and simple circuit that will work with minimum parts/cost?
TIA
-Chas
Can anyone here specify a relay and simple circuit that will work with minimum parts/cost?
TIA
-Chas
Chas,
I found a nice enclosed ice cube type relay on ebay with a built in variable timer for about 5 bucks -- nice quality Allen Bradley stuff. You can vary the time delay with an externally mounted resistor across the blade terminals of the relay. It is rated at 10 amps and has worked for several years on my current Leach amp. Just wire it in parallel with the CL-xx and that is it. Or you can use the normally closed contacts which will take the thermistors out of the circuit when the relay closes. It also works good with a protection circuit, but you will have to do a few mods for your particular application.
Tad
I found a nice enclosed ice cube type relay on ebay with a built in variable timer for about 5 bucks -- nice quality Allen Bradley stuff. You can vary the time delay with an externally mounted resistor across the blade terminals of the relay. It is rated at 10 amps and has worked for several years on my current Leach amp. Just wire it in parallel with the CL-xx and that is it. Or you can use the normally closed contacts which will take the thermistors out of the circuit when the relay closes. It also works good with a protection circuit, but you will have to do a few mods for your particular application.
Tad
Still no response from you
Hi Tad, as we were discussing in private emails, I still have not received my 4 PCB's for this GB. We discussed splitting the loss which both of us seemed to think was fair at the time.
Since then I have not received any more communications from you. Have you been getting my emails ? A simple response would be appreciated even if you did change your mind.
Thanks,
Marc.
Hi Tad, as we were discussing in private emails, I still have not received my 4 PCB's for this GB. We discussed splitting the loss which both of us seemed to think was fair at the time.
Since then I have not received any more communications from you. Have you been getting my emails ? A simple response would be appreciated even if you did change your mind.
Thanks,
Marc.
I searched ebay, to no avail.
Can you give a model number, or more specific description?
TIA
-Chas
Chas,
This is the exact relay,http://cgi.ebay.com/TYCO-ELECTRONIC...72:1205|66:2|65:12|39:1|240:1318|301:0|293:1, But the price was only 5.00 dollars when I bought them. If you keep looking you might find some cheaper or this seller might take a whole lot less.
Tad
This is the exact relay,http://cgi.ebay.com/TYCO-ELECTRONIC...72:1205|66:2|65:12|39:1|240:1318|301:0|293:1, But the price was only 5.00 dollars when I bought them. If you keep looking you might find some cheaper or this seller might take a whole lot less.
Tad
Chas, Here is another one much cheaper,http://www.electronicsurplus.com/co...-res-adj-----inter-set-cua-41-71016-7234.htm, Just keep looking.
Tad
Tad
Tad- It looks like a broken link.
Is there a similar relay listed here(?):
http://www.surplussales.com/Relays/RETimeD-2.html
TIA
-Chas
Chas,
The Surplus Sales site has quite a few good choices, but I do no know what price range you are willing to accept. First we need to know what voltages you have available to operate the relay. Then you can choose any of the relays with that coil rating and go from there. I liked the external resistor method of changing the time delay because it was simple and easy to incorporate into the chassis. Installing a simple pot works also and is more versatile. Be sure to choose the delay on/delay off which fits the application, they come in both forms.
Any setup you use to switch the mains power or DC off the thermistors after a predetermined time should work here.
Another option I like, proposed by Bob, is to build a complete separate power distribution unit with inrush surge protection and delay for all of the items in your arsenal. It could be something quite robust and have a mains power spike protector, like for computers and such, mounted in it. This also lets you turn everything on with one small low voltage switch. You can add earth ground hum isolators in there also. Real nice idea. This keeps you from going through this scenario on each build. Tad
The Surplus Sales site has quite a few good choices, but I do no know what price range you are willing to accept. First we need to know what voltages you have available to operate the relay. Then you can choose any of the relays with that coil rating and go from there. I liked the external resistor method of changing the time delay because it was simple and easy to incorporate into the chassis. Installing a simple pot works also and is more versatile. Be sure to choose the delay on/delay off which fits the application, they come in both forms.
Any setup you use to switch the mains power or DC off the thermistors after a predetermined time should work here.
Another option I like, proposed by Bob, is to build a complete separate power distribution unit with inrush surge protection and delay for all of the items in your arsenal. It could be something quite robust and have a mains power spike protector, like for computers and such, mounted in it. This also lets you turn everything on with one small low voltage switch. You can add earth ground hum isolators in there also. Real nice idea. This keeps you from going through this scenario on each build. Tad
Thanks
Thanks all for taking the time to help with the multitude of questions.
There isn't another current thread specific to assembling an amp from Jens' boards, and there are several of us (newbies) who need additional information to complete our amp projects.
-Chas
Thanks all for taking the time to help with the multitude of questions.
There isn't another current thread specific to assembling an amp from Jens' boards, and there are several of us (newbies) who need additional information to complete our amp projects.
-Chas
small signal transistor matching
I need six matched sets of 4, 24 in all. Out of a pool of 50ea of onsemi MPSA42's and 92's, I had nothing. Not even close to matched gain.
Bought an additional 100ea Fairchilds, hoping to get some different gains. Which I did. But out of a pool of three hundred transistors I have two matching sets, 8 transistors total.
Is it common to have so few matches???
I need six matched sets of 4, 24 in all. Out of a pool of 50ea of onsemi MPSA42's and 92's, I had nothing. Not even close to matched gain.
Bought an additional 100ea Fairchilds, hoping to get some different gains. Which I did. But out of a pool of three hundred transistors I have two matching sets, 8 transistors total.
Is it common to have so few matches???
Rob,
We (myself, along with Brutepuppy and WJH) found almost the same thing. The PNP's measured range was quite different from the NPN's in our similarly sized pool of devices, and we settled upon matched pairs of PNP's used together with matched pairs of NPN's("choice#3").
Please note, however, that in his construction notes Dr. Leach indicates DC offset may still not be a problem:
"Ideally, all four transistors should be matched. If this cannot be achieved, the second choice is for Q1 and Q3 to be matched and Q2 and Q4 to to be matched. The third choice is for Q1 and Q2 to be matched and Q3 and Q4 to be matched. The typical dc offset at the amplifier output is less than 50 mV. If you are concerned about how well the transistors are matched, I have seen amplifiers built without matching the input transistors, and they had no dc offset problems. "
Opinions?
-Chas
For what it is worth I did not match anything on my Leach and the total offset is less than 20mv. Matching is of course the best way to go, however sometimes you just want that thing to work.
Tad
Tad