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Old 4th July 2012, 08:18 PM   #6601
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Quote:
Originally Posted by Wavebourn View Post
What do you mean?

I don't remember any famous musicians that used hybrid cascodes. What kind of special effect would you expect from them?

A first guitarists found that overdriving amps made from datasheet examples they were getting sounds they liked. Then what they liked was shaped in specific guitar amp topologies. May be if datasheet examples contained cascodes they would go this way, I don't know. I played a lot with guitar effects, but all effect that guitarists liked were similar to what they already heard on records of famous musicians.
This reminds me of an event in the early 70ies. The folks at Yamaha had made up their mind to make a reference guitar amp. They did, it was announced and a selling date was established. The first day, there was literally a cue of people waiting to buy it; the second day, half of the first day, and by day four, sales had stopped altogether.

Obviously, this caused Condition Red at Yamaha. Two engineers from the project were quickly dispatched to L.A. to what was going on. It took them two weeks to get to the bottom of it, but they did.

The next model of the same amp actually included a pot marked "Distortion". It turned out that most rock guitar players didn't give a damn about low distortion and whatnot, they wanted "the sound", and the only way to get it was to enable them to distort the guitar as they saw fit.

Not to defend or attack anyone, but I must admit that you can get some really cool sound from a distorted guitar, especially the bass guitar. And in the late 60ies, London and L.A. were the places to be.
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Old 4th July 2012, 08:44 PM   #6602
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It is something new to me, about distorted bass guitar. Working with musicians I found that bass guitarists prefer as clean as possible amps. Lead guitar is a different story. It lacks of character, so increased with loudness distortions help to express emotions better.

Speaking of distortions, Roland made best pedals for this purpose. I did something similar, but my prototype had a real pedal to control overdrive by foot, from clean to very dirty sound. It was made of a filter that attenuated fundamentals and boosted harmonics combined with asymmetric logarithmic amp, then symmetric exponential amp and another EQ.
First I used matrixes made of Germanium diodes and resistors, then found that diodes without resistors sound Ok. Then found schematic of Roland pedal and surprised how similar it was.
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Last edited by Wavebourn; 4th July 2012 at 08:52 PM.
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Old 4th July 2012, 08:56 PM   #6603
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Wave, I distinctly remember reading about the whole case in the early 70ies, which was, after all, at least 37 years ago, I honestly don't remember where. It must have been a magazine, no Internet way back then.

Also, I am told that tastes change over time, and 37 years is quite some time.
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Old 4th July 2012, 09:23 PM   #6604
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Quote:
Originally Posted by dvv View Post
Wave, I distinctly remember reading about the whole case in the early 70ies, which was, after all, at least 37 years ago, I honestly don't remember where. It must have been a magazine, no Internet way back then.

Also, I am told that tastes change over time, and 37 years is quite some time.
You are right. Tastes change. Blues guitarists used slight distortions: their guitars were semi-acoustic and guitarists could express emotions without heavy distortions. Rock guitars were wooden, so needed more pronounced spectrum dependence on loudness added. Heavy metal is further "improvement", since all is compressed and no dynamics is needed from guitar.
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Old 5th July 2012, 07:21 AM   #6605
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I've been wondering for some time - has anyone here tried building a transistor output stage by using say one predriver, but instead of having one driver, using the same device for EACH of the output transistors, with a base resistor on the driver and a smallish value resistor from the emitter to base of the power device?

Effectively making a discrete Darlington transistor?

Any experiences? Any thoughts? Any tangible gains, above the level of academic?
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Old 5th July 2012, 08:57 AM   #6606
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Hi Wavebourne . Interesting what you say . The example I was looking at was all ECC82 in Valve Wizard . The hybrid was my idea . I have some 12BH7A also which look great on scope . I did note the recommendation to respect maximum cathode voltages . I was having this same discussion about DI boxes ( Direct injection, for example bass guitar to mic input with ground lift ) . My friend wanted pentode sound . I suggested a cascode with singe triode option ( SRPP perhaps ) . Some guitarist use a Morph control with lets say an EF184 pentode . The 184 becomes an ECC81 approximately if going to full triode . The Morph circuit I suspect does find the Ultra-linear point of the pentode ? I am far more fussy about valves than op amps . Different valves are more obviously different than most sensible op amps , even valves with the same type numbers ( most ECC 82 measure about the same , none sound the same ) . Sure op amps sound different . Most never sound quite right to me regardless how how much I spend . OPA 604 and 2604 seem reference points , price is good .

A general question . Quad used 0.5 Vrms for full output . I have even used 0.25 V with superb results ( and passive preamp , 100 W output ) . My little valve amp is about 2.79 V . I am fitting a gain stage . However my instinct is to say that's the job of the pre amp . Most of the valve preamp's have the capacity to go to 3 V . Any observations gratefully received . I do suspect 0.5 V is ideal . My 100 W amp has very low distortion extending up to 100 kHz , setting the gain to 100 did not harm it . In fact the reverse . I feel the distortion was far too low to say I like distortion B rather than A ( lower gain ) . What I was hearing was genuinely better sound . My hypothesis is that long before the Nyquist instability point is reached the amplifier starts to show symptoms . Some say about up-scaling distortion harmonics as one possible reason ( 7 th and 9 th ) .

Many have been producing very low distortion amps as a challenge . I wouldn't mind betting that they are happy with them because there is no obvious problem . Our dear friend NE5534 is an example . Op amps are power amps , especially 5534 . I was asked to provide a MC preamp with a gain of 2000 at 1kHz ( clone of 5534 by a different number and lower current ) . This required the first op amp to have a gain of 125 at 1 kHz ( I was too lazy to do a redesign so just increased the first stage ) . I have to say it was magical . The MM version whilst nice enough was more enclosed sonically . The distortion was still 0.1 % if memory serves me correctly . Hiss was about > -66 dB weighted .

Last edited by nigel pearson; 5th July 2012 at 09:05 AM.
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Old 5th July 2012, 02:43 PM   #6607
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Originally Posted by simon7000 View Post
Have you ever measured the difference before and after you changed to wooden knobs? You just might be surprised by how large a difference that can make and why it does!

Now marbles for feet I don't know about, but rubber pads can make a difference on some gear under certain conditions.

Just remember absolute statements never are right, absolutely!
Well Wavey, you didn't bite, so I'll give you the answer.

One fellow who brought by an expensive preamp with metal knobs was not happy with it. Turns out the potentiometers were mounted to a PC card and went through plastic bushings on the front panel. When he walked across the carpet to change things he often heard a loud pop.

Changing to non conductive knobs not only solved that problem, but also reduced the EMI being conducted into the case.

So although there are silly claims often made, there can always be a case where the results actually happen and for a well understood reason.

Now after he spent all that money do you think he would have been happy with cheap plastic knobs?
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Old 5th July 2012, 02:52 PM   #6608
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DNM believe in as little metal as possible especially if magnetic . Stainless steel is less magnetic and can be bought as non magnetic grade . My phono stage housed in a wooden box did seem to sound better . The metal box never shielded it much anyway . Wooden knobs ? I would if you will forgive the pun . DNM pre amps were always a favourite of mine . The capacitors are excellent value .

Anyone every used Danbury's SE transformers ?

DNM Design Principles, Page 3 of 5 - Materials Technology

Last edited by nigel pearson; 5th July 2012 at 02:56 PM.
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Old 5th July 2012, 02:54 PM   #6609
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When he walked across the carpet to change things he often heard a loud pop.
Sounds more like an ESD problem, which should be addressed by clamping diodes and a low impedance path to GND and a power plane.

Hope for this guy there's no structural damage in one of the semiconductors..
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Old 5th July 2012, 06:16 PM   #6610
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I would prefer to ground shafts of potentiometers because discharge of static charge through wooden knob and base of transistor can be harmful.
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