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Old 11th November 2009, 07:48 AM   #21
rmgvs is offline rmgvs  Netherlands
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Default other ones

Yes, I think that's why they did the trouble around the LM318, to keep the speed but get rid of the noise.

I tried several Pass preamps but though they are good I never come around the sound of (what I think are) fets. Fairly soft and slightly warm and diffuse, I keep missing some things.

I've heard about the Holman but never seen it (on paper nor live). I would like to take a look at the schematics of the linestage (but googling for a short time did not bring me this).
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Old 11th November 2009, 08:15 AM   #22
jaycee is offline jaycee  United Kingdom
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Jez, is the diode connected BC550 there for thermal compensation?
I have a similar circuit that I am intending to use as a headphone amp
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Old 11th November 2009, 08:59 AM   #23
rmgvs is offline rmgvs  Netherlands
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Default diode

Good question. I have simulated the circuit without the diode. The circuit (driver + output) then is symmetrical. This works too (according to the simulation) though with a smaller idle current (around 4 mA) but this can be 'solved' by changing the emittor resistors of the bd's,

So, I don't know why this diode has been added to be honest.
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Old 11th November 2009, 09:28 AM   #24
jaycee is offline jaycee  United Kingdom
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The circuit I am playing with is here

As you can see very similar topology, but not running so hot.
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Old 11th November 2009, 05:56 PM   #25
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Quote:
Originally Posted by rmgvs View Post
Yes, I think that's why they did the trouble around the LM318, to keep the speed but get rid of the noise.

I tried several Pass preamps but though they are good I never come around the sound of (what I think are) fets. Fairly soft and slightly warm and diffuse, I keep missing some things.

I've heard about the Holman but never seen it (on paper nor live). I would like to take a look at the schematics of the linestage (but googling for a short time did not bring me this).
Hello

It's surprising that this LM318 circuit sound better than many others preamp, the LM318 are very good but an old op-amp and prone to oscillate, so most guy's said it was obsolete. Maby this circuit could be mod to do a good I/V amp for TDA1541.

Tomlinson Holman design the first version of the Advent 300 and the first version of the Nad 3020. The phono input was unique. They have both an excellent reputation.

Here is the circuits of a LM318 phono but I never try it, and of both Advent 300 preamp section and the Nad 3020 preamp.

Bye

Gaetan
Attached Images
File Type: gif LM318 phono.gif (58.2 KB, 359 views)
File Type: gif Advent 300 preamp section-old version by T Holman.gif (76.1 KB, 356 views)
File Type: gif nad3020pre.gif (87.9 KB, 353 views)

Last edited by gaetan8888; 11th November 2009 at 06:09 PM.
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Old 21st November 2009, 10:22 AM   #26
rmgvs is offline rmgvs  Netherlands
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Default problem answered

By combining the info on the LM318 and looking at the circuit of the preamp that is given in the thread on a phono-amp using the 5534 in a similar circuit, it is quite easy to fix the issue of using the 5534 in the Musical Fidelity MVT preamp line stage.

Here it is:
1. Take the 5534 and bend (up or out) away pins 1, 5 and 8.
2. Use an extra IC-socket and solder 2 small wires of short length to pins 1 and 5 of the IC-socket.
3. Put the 5534 in the extra socket.
4. Solder the wire that comes from socket/1 to 5534/8.
5. Solder the wire that comes from socket/5 to 5534/1
6. 5534/5 remains unused (can be cut away altogether)
7. Put the completed 5534+socket in the existing preamp-socket.

Ok, this can be done more neatly, but for testing it is not bad. For stereo off course this need be done twice.

I've tested this in the MVT and it works allright. Not that the sound is better, but changing/testing can begin now.
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Old 21st November 2009, 10:34 AM   #27
rmgvs is offline rmgvs  Netherlands
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Default noise floor

I expected to get a better noise floor by using the 5534. But this is not the case.

Compared to the original MVT my diy-version has a somewhat higher level of background hiss (that keeps annoying me).

Some 'facts':
- MVT uses LM318 and 2x BC550 at the first stage. No hiss to mention.
- Power supply uses 7815/7915.
- I tested 4 different power supplies with my diy-version. 317/337, 7815/7915, passive with RC's, and another one. In all versions my hiss level remains higher than in the original.
- I tapped off the powerlines of the original to feed my diy version: same level of hiss, higher.
- So I think conclusion must be that it is not the power supply.
- Then I took the LM318 (+22pf+.22mF soldered on the pins) and put it in my diy version: same higher hiss as before.
- So the brand or type of LM318 can not be the source.
- I made a second copy of my diy-version, some variations in the layout, changed the brand of BC's and BD's: same result as first diy version.
- The original is MVT MKII, I see some parts that are not in the circuit of my MKIII circuit. Notably I see a 47nF cap and a resistor of 120 Ohm extra.
- I tried all kind of arrangements in the oscillation-department: decoupling the IC with 100nF and some smaller electrolytics. No effect on general background hiss.

I'm puzzled, what can explain the difference in background hiss? It is not the active components, it is not the power supply. Layout? Maybe, but I think not. So what's left?

Somebody got me an idea?
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Old 21st November 2009, 12:09 PM   #28
rmgvs is offline rmgvs  Netherlands
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Default input filter maybe?

I'm wondering: I used at the input the filter 10k / 330pF instead of the original 1k / 100pF (because I hadn't a good quality 100pF in stock).

Could the higher R in series with the input be responsible for the higher noise floor (in the way you can hear the difference easily with your ears close to the speaker)?
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Old 21st November 2009, 05:20 PM   #29
rmgvs is offline rmgvs  Netherlands
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Default not the cause

Tried it, does not make any difference to the ear.

I seem to be in discussion with myself here ...

Any ideas out there?
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Old 21st November 2009, 06:16 PM   #30
rmgvs is offline rmgvs  Netherlands
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Default some pictures

I made a small piece of veroboard to put 2 IC sockets and the LTP with BC550 (including the 33k LTP resistor). From there it goes to one IC-socket dual-type (for instance NE5532).

Now I am able to test my LM318 + external LTP on sound and noise quality in any standard preamp like a NAD. On the picture you see the 'adapted' NE5534 with some pins put aside and the pieces of wire.

When put in my standard NAD preamp (using 5532 in the line-stage, some feedback around it including tone-controls): LM318 or adapted NE5534 in this setting are problemfree and without noise. The LM318 can be got to oscillation though by twiddling with its position and/or the wires. The NE5534 just seems to play never minds its position etc.

So again: the IC + LTP can not be the source of the higher noise-floor.
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File Type: jpg 21112009083 (Medium).jpg (67.3 KB, 253 views)
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