DIAMOND DIFFERENTIAL INPUT POWER AMPLIFIER EBay kit

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OK, back from holidays.
I have removed all VAS transistors, checked them and they are all OK!!!. All the other components are OK. Bias transistor is OK (I have even repalced it with a new one), all the resistors in bias citcuit are fine. LTP is fine. Why do I get 1.3V across C15???
- while you get less voltage drop in the same circuit.
Even if the circuit oscillated that DC V drop across C15 should be within limits.

I can increase values of R17 and R20 from 47k to 120k or 240k as these together with the remainder of VAS circuit also affect voltage drop across C15.
Any suggestions???

cheers,
PS I'll be using 2sa1370/2sc3467 in VAS as I have enough of these and these are more linear and have even lower Cob. I also could replace Q9 and Q13 with jfets: 2sk170 and 2sj74. In simulation these give much lower phase shift but that would affect mainly sonics not voltage drop across C15 by 50%.
 
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Are you still working on amp?

OK, back from holidays.
I have removed all VAS transistors, checked them and they are all OK!!!. All the other components are OK. Bias transistor is OK (I have even repalced it with a new one), all the resistors in bias citcuit are fine. LTP is fine. Why do I get 1.3V across C15???
- while you get less voltage drop in the same circuit.
Even if the circuit oscillated that DC V drop across C15 should be within limits.

I can increase values of R17 and R20 from 47k to 120k or 240k as these together with the remainder of VAS circuit also affect voltage drop across C15.
Any suggestions???

cheers,
PS I'll be using 2sa1370/2sc3467 in VAS as I have enough of these and these are more linear and have even lower Cob. I also could replace Q9 and Q13 with jfets: 2sk170 and 2sj74. In simulation these give much lower phase shift but that would affect mainly sonics not voltage drop across C15 by 50%.
I am wondering if you have given up on your amplifier? I was going to give it a try.
 
Well, I might give it one more try. Actually, I have two different modification versions of it but haven't tried them yet. Apparently many people had problems with it. In simulation it easily turns into a current sink (that's what happened to my amp) or it oscillates - it's very sensitive to the quality of Iput and VAS PS.

cheers,
 
Fake Transistors

Well, I might give it one more try. Actually, I have two different modification versions of it but haven't tried them yet. Apparently many people had problems with it. In simulation it easily turns into a current sink (that's what happened to my amp) or it oscillates - it's very sensitive to the quality of Iput and VAS PS.

cheers,
I have been working on Jim's Audio KSA-100 MKII. Here is the thread:
http://www.diyaudio.com/forums/solid-state/183562-ksa-100-jims-audio-ebay-36.html
I am 'spurlte', and had problems with fake components with vintage components especially transistors. Many jumped up to help. It is totally amazing the kindness of others here at diyaudio.com. I read and will look to find where later to post here, that many components that fail lot testing are not just thrown away as they should, are illegally sold to those who pass these on as workable devices. I finally, with the help of others, got good parts to complete my boards. There are some crooks who are also taking old transistors and passing them on as newer updated devices. So, specifications could be all over the place. Someone said that you learn more when things are not working as they suppose to be working. Forcing you to investigate and I am learning alot. Check out page 25/quote #243 on Jim's Audio KSA 100. But in your case, could you have components out of spec?
 
Also, you will see how Kaplaars completed his Krell KSA-100 MKII Clone and is totally enjoying his effort. Kaplaars found a couple of major uncorrect art work, component markings and a faulty circuit passage. It is all details at different pages thoughout the thread. One example is what was found and explained by Kaplaars on page 15, quote #141. So attention while compairing schematics to PCB clone's circuitry passages is extremely important.
 
I did not have problems with components. I tested each one and transistors at different currents. I did not check everything but most of each board for consistency with schematics ane these seemed to be OK. Both of my boards seemed to display exactly the same fault: voltage drop across C15 was too high so up to 2-3mA bias current everything seemed to work well. Only exceeding that bias current made it rise quickly.

cheers,
 
I have done some experimentation on E305 amp & have similar experience as janusz ie; the amp running hot similar to Class A.

Circuit diagram & parts list of the amplifier I did:
An externally hosted image should be here but it was not working when we last tested it.


Bare PCB:
An externally hosted image should be here but it was not working when we last tested it.


Assembled & testing with 28v-0-28v 2A transformer & Peerless 12" 400w 4Ω subwoofer.
An externally hosted image should be here but it was not working when we last tested it.


Amplifier is rated 250w 4Ω which is lower than than the connected load.
Output stage replacement transistors are NJW0302 & NJW0281. Rest all transistors are the same as per the the parts list. Driver transistors are 2SC5171 & 2SA1930. FET transistors 2SJ103 & 2SK246 were not available locally hence had to import them.

At 28v -0- 28v AC =~ +39v -0- -39v DC (after rectification) 2A even with lowest forward biasing set with the variable resistor, the heatsink is running hot. I guess the size of the heat sink is inadequate. Increase the biasing of the driver transistors the heatsink will become quite hot. This characteristic would fit this amp's description in a conjugate Class AB-A model.

The 400w speaker excursion is quite good due to the input stage at the above mentioned VA. However, the current draw for this design is so much that the transformer core also becomes too hot within few minutes.
 
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Initially I connected a 20w 8Ω speaker with 20Ω 2W resistor in series. The amp runs fine with this low load & very less heat. Remove & connect the subwoofer, the equation changes.

With the subwoofer connected & fingertip on the input for 60 seconds the transformer is as 'fresh from the grill' barbeque chicken.
 
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In-between finishing this amp I had a chance to test another Class AB amplifier board from a local commercial audio component supplier which uses the same Toshiba 3x 2SA1943 PNP & 2SC5200 NPN pairs.

It's design similar to the Leach amp / JBL circuit inspired using Sziklai pair complementary or ' Compound complementary ' in contrast to the Darlington complementary output stage of the Diamond differential amp.

It uses half the parts count other than the output transistors - (would require more input gain) but runs much cooler - even better than an ebay Class-D IRS2092 IRFB4227 mosfet amplifier I tested few months back ! I am impressed with that topology rather than pursuing this amplifier.

Andrew, thank you for your replies wrt troubleshooting. Initial observation of the Leach amp makes me forget the Differential amp. Anyway will see where I end up.
 
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Diamond Diff Amp finished

With help of this forum, I finished my amp. It took two years of on and off effort. The only problems I had with tubehunters version:
1. No instructions - when asked instructions provided were not adequate. I am talking about the adjustments for bringing the amp up first time. I used those from forum.
2. Some parts were missing or the wrong part provided (resistors and caps). These were mostly mistakes I believe. No problems with the major components.

Currently installing in a very nice old Puchini integrated case.

Then I am moving on to a tube amp!!
 
With help of this forum, I finished my amp. It took two years of on and off effort. The only problems I had with tubehunters version:
1. No instructions - when asked instructions provided were not adequate. I am talking about the adjustments for bringing the amp up first time. I used those from forum.
2. Some parts were missing or the wrong part provided (resistors and caps). These were mostly mistakes I believe. No problems with the major components.

Currently installing in a very nice old Puchini integrated case.

Then I am moving on to a tube amp!!

What's your operational bias?

I think I know what went wrong with my Diamond but I have to bring back original resistor and cap values first. Unfortunately both bords are a bit worn because of my de-soldering - soldering of parts.

When I got a similar problem with HB I discovered that it was a fault in components used in Soft Start unit. 10W resistor caught fire, relay burned. I bought four soft start units and the first worked very well in another amp but possibly parts for these two were faulty. I bought new parts, tested them and HB is working fine so I guess Diamond might work fine as well when fixed but probably only on moderate bias values.

cheers,
 
With help of this forum, I finished my amp. It took two years of on and off effort. The only problems I had with tubehunters version:
1. No instructions - when asked instructions provided were not adequate. I am talking about the adjustments for bringing the amp up first time. I used those from forum.
2. Some parts were missing or the wrong part provided (resistors and caps). These were mostly mistakes I believe. No problems with the major components.

Currently installing in a very nice old Puchini integrated case.

Then I am moving on to a tube amp!!

Can you be more specific and precise on what were the changes you made? I have one that I did not assembled yet, so you info would be very valuable.

Thanks!
 
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This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.