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A Very Compact Hybrid Amp - Page 112

post #1666 of 2213
I am pretty sure they are alright Judging by the meticulous way I put the board together. I think you may have missed my first post,the amp did initially work.It was after wards that I believe I caused a short that it stopped working
post #1667 of 2213
Thread Starter 
OK. Sorry about that. I guess we replace transistors until it works.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1668 of 2213
for the most part you can test transistors in circuit as if they were diodes. I think I have a post about that in this thread. Differences between NPN and PNP and pay attention to shorted paths using the circuit diagram and you can narrow down the exact transistor.

Transistor replacement on the CTH is a joy. When things short, the most likely culprit are the actual output transistors. They are on the edge of the board and easy to test.
post #1669 of 2213
GED, I think your kit shipped with extra buffer transistors - let me know if you need some more and I will send them your way...
post #1670 of 2213
Thaks wiatrob
you sent me some BC550,s and some BC569s which may be required
Igot some bc327 and bc337 as required for the repair here in the UK for £2 shipped just to save time
post #1671 of 2213
Quote:
Originally Posted by Ged View Post
I have just completed my cth and initially all the voltage readings were correct and the e12 functioning correctly. After checking for a second time and messing around I believe some thing must have shorted.
Ged - Later, after you have your CTH working again, you might find it a bit funny reading runeight's sig & the quote above

Note that I too broke one of my CTHs causing a short while taking measurements in the output buffer area. Searching for CTH trouble-shooting posts by holland, runeight, etc & the info here should narrow down the problem. IIRC in my case I replaced all the BC devices in OB & that fixed it.

Back in the proto days I'd a lot of practice pulling & replacing TO92s Using PCB vise, used a solder blob floated among 3 pins, pulled 'em then used solder vac to remove excess. Desoldering braid might sub/help too.

Good luck. You'll get a bit more DIY, learning & practice than you expected but the end result will be worth it.
post #1672 of 2213
I will bear in mind the solder blob idea if I have to replace the rest of the BCs on the right channel (the 2 I took out this morning were a right pain in the ar**)
post #1673 of 2213
Quote:
Originally Posted by Ged View Post
I will bear in mind the solder blob idea if I have to replace the rest of the BCs on the right channel (the 2 I took out this morning were a right pain in the ar**)
Another easy way is to cut the leads off under the transistor body and remove the leads one at a time. This assumes of course that you do not need to reuse it!
post #1674 of 2213
I ran across this transformer and was wondering if it would make a suitable power supply for the CTH. It looks like it is 26.2VAC but I am still waiting on a data sheet from the manufacturer. It is probably extreme overkill but I have it already and thought it might be fun to make a separate psu.

Does anyone have any tips on what I need to do to get it to work with a CTH.
post #1675 of 2213
Quote:
Originally Posted by blaken View Post
< snip > It looks like it is 26.2VAC but I am still waiting on a data sheet from the manufacturer. It is probably extreme overkill but I have it already and thought it might be fun to make a separate psu.
Does anyone have any tips on what I need to do to get it to work with a CTH.
Looking for 24VAC w/min. 0.7A or so input for CTH. 24VAC .8A+ adapters are around for like $12-$20.

But as you've that 26VAC around, if one of its windings meets the load req.s you would likely be able to use it directly. IIRC one of my 24VAC/1.25A adapters maintains 26VAC into CTH under load. But may need to check/improve heater & LV/24 reg heatsinking as they'll need cope w/higher input Vs.
post #1676 of 2213
Thread Starter 
Quote:
Originally Posted by Ged View Post
Thaks wiatrob
you sent me some BC550,s and some BC569s which may be required
Igot some bc327 and bc337 as required for the repair here in the UK for £2 shipped just to save time
Ged, please make sure that these are the "25" class hfe for these devices. If they are mixed class or a different class you still might have problems.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1677 of 2213
Thanks cfcubed, It looks like I can get a 24v AC wall wart for less then the cost of the case to put that transformer in. I will just hang onto it.

What are the exact dimensions of the board from spruce canyon? I might try to cram in a tangentsoft crossfeed into the 1602 case but I want to make sure it is going to fit first.

Also would there be a noticeable SQ improvement if I used the ALPS RK27 over the RK097 in the standard BOM?

Thanks guys.
post #1678 of 2213
I have just finished replacing all the transistors and still have problems
The V on R18R is still wrong currently 23.5V
I believe one of the parts was 40 class
The second phase of the repair were from bills I am sure they are alright
post #1679 of 2213
Quote:
Originally Posted by blaken View Post

Also would there be a noticeable SQ improvement if I used the ALPS RK27 over the RK097 in the standard BOM?

Thanks guys.
RK27 with a shunt mod sounds significantly better to me over the RK97 to me.
post #1680 of 2213
Thanks for the tip.

I found this article about shunt modding Shunt Pot Volume Control - World-Designs-Forum

Did you use a 47k metal film resistor?
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