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Post by Deleted on Jul 16, 2015 12:12:02 GMT
Hi Alex, These various schematics get a little confusing between the 15W poweramp and the preamp/HA. For example, the 15W has matched 200R for the LS352 compared to 150R in other preamp schematics. Just in kitting up, I've bought some 0.1% 150R. Are these now superseded by 200R in the preamp or OK to use the 150R? Also what's the latest diode type recommended for connection to the 3K3/BC547? SF12/ES1D? Just getting keen :-). I have the PS PCBs built using the suggested ES1Ds, Vishay 038RSU normal 63V/100uf used. Working on fitting the 18-0-18 transformers into their box now. cheers.. jeffc Hi Jeff Due to much colder temperatures in Europe, and way out of specification (forward voltage) SF12 diodes that some obtained,( Chris for example) it sometimes became difficult to get a complete front end balance adjustment without changing the 150 ohms to 200 ohms, and the 120 ohm VAS emitter resistor to 130 ohms instead of the original 120 ohms. As you have a DMM, why not get 2 packs of 200 ohm 1% resistors from Jaycar and select 2 closely matched pairs ? They don't need to be exactly 200 ohms. The same could be done for the LS313 100 ohms emitter resistors. You can use SF11 /SF12 for the adjust diode, or the ES1A to ES1D there too, but you would need to solder short leads to them first, or find a way to mount them under the PCB perhaps ?
Regards Alex
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Post by jeffc on Jul 16, 2015 20:49:11 GMT
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Post by jeffc on Jul 18, 2015 9:12:32 GMT
Hi Alex,
Are you using any 240V AC line conditioning positioned inside your external transformer box?
Space is at a premium in mine, so if any at all, I'm hoping parts are not too bulky......
cheers.. jeffc
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Post by Deleted on Jul 18, 2015 9:46:36 GMT
Hi Alex, Are you using any 240V AC line conditioning positioned inside your external transformer box? Space is at a premium in mine, so if any at all, I'm hoping parts are not too bulky...... cheers.. jeffc Hi Jeff No. Mine has the big Harbuch dual 21-0-21 winding transformer with an electrostatic shield for the 15W Class A, and 2 x 18-0-18 30VA toroidals for the Preamp, but no extras other than a couple of fuses .It's best to use a separate .5A fuse for each transformer if you are able to. However, the power for the AV room goes through a DIY dual heavy duty mains filter, with the TV by itself on the 2nd outlet. The 1st outlet goes to a Powerboard for Amp, Preamp, DAC and Oppo 103 I also have a smaller box ( 200 x 155 x 65mm) with just 2 x 18-0-18 30VA and 2 fuses for the HA at the PC, which is also used with the preamp at listening sessions, and seems fine without the mains filter used at home.
Regards Alex
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Post by jeffc on Jul 18, 2015 10:05:20 GMT
OK thanks Alex,
That's great then as I'm almost done :-). All I have is a fuse for each transformer as well, but 1A as I'm using those 50VA toroidals that Altronics had cheap recently. I'll have it plugged into my DIY RFI line filter box like you. I have some ~80% shielded LAPP CY mains cable that I was thinking to use both for 240V in and secondaries out to the amp box. Might be overkill but I have it and I'm guessing it won't hurt.
cheers.. jeffc
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Post by Deleted on Jul 19, 2015 6:02:24 GMT
A link should be soldered under the PCB, between the earth terminals as shown in GREEN. This is to correct a minor original PCB design error. An OPA134 will give slightly improved noise figure results over the original AD744 shown in the drawing. For Preamplifier use, 100 ohm 1% resistors are used instead of the 120 ohm resistors just above the Output terminal block. For Headphone Amplifier use, the 120 ohm resistor should be lowered when using low impedance headphones. Don't go below 10 ohms, and select a value that is tonally balanced for the headphones used. 68 ohms is a good starting point with many other headphones. 120 ohms suits AKG K701, AT W1000 and other headphones conforming with the old IEC 61938 specifications.
See p.1 for Amplifier and PSU schematics.
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Post by Deleted on Jul 21, 2015 5:37:34 GMT
In this application R1/RSet is typically 1 ohm to 1.5 ohms metal film. In the -V version, change Q2 and Q3 to BC560C. Change Q5 to BC640. change Q1 to 2SC5171, and change Q4 and Q6 to 2SA1930   |
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Post by Deleted on Jul 25, 2015 11:50:19 GMT
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Post by Deleted on Aug 4, 2015 6:03:14 GMT
Disappointing Result.
Today I tried replacing the OPA134s in the Offset Correctors with the very low noise LT1115. However, instead of a DC Out in both channels of under 1mV as previously, the change resulted in a much higher DC Out of around 22mV. Back in with the OPA134 ! 
Alex |
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jc
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Post by jc on Aug 4, 2015 10:43:14 GMT
Any thoughts on what it is about the LT115 architecture that may have caused the increase in DC out?
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Post by Deleted on Aug 4, 2015 11:13:08 GMT
Any thoughts on what it is about the LT115 architecture that may have caused the increase in DC out? Hi Chris I think that the LT1115 may be bipolar input, unlike the OPA134 etc. which are FET input. It should be great for microphone preamps and moving coil cartridge amplifiers though.
Kind Regards Alex
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jc
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Post by jc on Aug 4, 2015 14:01:40 GMT
I lifted the following off the data sheet that may also explain the negative effect; page 7 & 8 LT1115 data |
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Post by Deleted on Aug 4, 2015 22:05:42 GMT
I lifted the following off the data sheet that may also explain the negative effect; page 7 & 8 LT1115 dataHi Chris I didn't get to check it to see if there was any change in noise performance due to the measured high DC offset. The data sheets I had saved are only a couple of pages long. It would appear that I needed a low input resistance to achieve a low DC offset with this bipolar input opamp.
Regards Alex |
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Post by Deleted on Aug 4, 2015 23:51:48 GMT
Bill
Please check your email Inbox as it may be full.
Regards
Alex
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Post by Deleted on Aug 6, 2015 0:25:35 GMT
I lifted the following off the data sheet that may also explain the negative effect; page 7 & 8 LT1115 dataHi Chris I didn't get to check it to see if there was any change in noise performance due to the measured high DC offset. The data sheets I had saved are only a couple of pages long. It would appear that I needed a low input resistance to achieve a low DC offset with this bipolar input opamp.
Regards Alex Chris Further to this, this morning I tried using the low noise OPA27GP instead in the Offset Corrector of one channel of the HA. It isn't a FET Input I.C. and I ended up with 1.5V DC out ! When I put the original OPA134 back in ,I still had 1.5V DC out,(!!!) so I thought I had damaged something. Luckily, I then remembered that I had seen this type of behaviour before. Apparently, the 1uF and 3.3uF capacitors at the input of the corrector retain a charge, and the high impedance input of the FET opamp causes it to take a while to settle down again. A couple of on/off cycles saw it back to normal again.
Kind Regards Alex
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jc
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Post by jc on Aug 10, 2015 12:27:20 GMT
We have incoming!  Not sure when I'll be starting though  |
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Post by PinkFloyd on Aug 10, 2015 20:43:52 GMT
I have incoming too Chris BUT...................
I don't have the time or the need to build one of these (I must admit I rushed in a tad) so my boards and transistors are up for grabs if anybody wants them.
Mike.
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jc
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Post by jc on Aug 10, 2015 22:23:23 GMT
Au contraire Monsieur Rose,
You may not have the time to build one, I don't think I do for some time either BUT you do neeeeeed one, honestly!
It has beaten off all comers that I own or have heard, convincingly.
You owe it to yourself to build one to the full "Alex" spec. and be blown away.
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Post by Deleted on Aug 30, 2015 9:11:56 GMT
REFERENCE.- Differences between Preamp/HA and 15W Class A.  |
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Post by Deleted on Aug 31, 2015 4:37:27 GMT
Progress Report. As expected, it's all going together nicely at the moment, but slowly.  |
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jc
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Post by jc on Aug 31, 2015 12:35:03 GMT
Compared to me you're blazing a trail Alex! I haven't even checked the BOM for needed parts yet  |
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pingu
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Reallising what has been taken on with the GB
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Post by pingu on Sept 3, 2015 13:37:34 GMT
Compared to me you're :Da trail Alex! I haven't even checked the BOM for needed parts yet Hhhmmmm well Chris the PSU boards arrived today so now I have the HA and the PSU boards to populate. time, time, time, none left BUT on the up side the JLH REs are done  so onwards and upwards The sun is on its way too Oh well it will all get done some time Martin |
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Post by videoguy on Sept 14, 2015 15:52:28 GMT
Last week I was able to populate both boards w resistors & capacitors, with the exception of 1 resistor & 3 capacitors.
The only thing left are to select the transistors by beta, install them. Will be etching the combo. regulator/JLH boards & building them. Hopefully doing the machining on the chassis next week.
Bill W.
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pingu
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Reallising what has been taken on with the GB
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Post by pingu on Sept 14, 2015 23:25:28 GMT
Last week I was able to populate both boards w resistors & capacitors, with the exception of 1 resistor & 3 capacitors. The only thing left are to select the transistors by beta, install them. Will be etching the combo. regulator/JLH boards & building them. Hopefully doing the machining on the chassis next week. Bill W. You are way ahead of me Bill. I have not had time to even look at getting a BOM together yet. It is going to have to be an autumn project I'm thinking Martin |
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Post by Deleted on Sept 14, 2015 23:51:40 GMT
Last week I was able to populate both boards w resistors & capacitors, with the exception of 1 resistor & 3 capacitors. The only thing left are to select the transistors by beta, install them. Will be etching the combo. regulator/JLH boards & building them. Hopefully doing the machining on the chassis next week. Bill W. You are way ahead of me Bill. I have not had time to even look at getting a BOM together yet. It is going to have to be an autumn project I'm thinking Martin All I have left to install are the 3.3V Zeners, which I will pick and match from a batch when they arrive from the U.K., and a 79L15 for one PCB where I am still waiting on a few more 78L15 and 79L15 to arrive. |
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so onwards and upwards