Premium Sweetie Amp: Technical Talk, Parts Options, Testing Results and Other Comments

[KT88]

On 8/31/2022 at 4:22 PM, henry4841 said:

For the 1/2 watt resistors I am going to use Vishay resistors. Both these name parts are respected in the electronic industry.

 

Henry, it sounds like a very fantastic project to me. I don't like to interfere, the components are your choice and your decision. But I would be very interested in your opinion and listening impression on your choice of 0.5 watt resistors (in the signal path or from signal to ground). I came up with this because a few weeks ago I had installed new resistors in a transistor preamp, Quad 34, at the output, the voltage divider. I wanted to increase the output voltage according to the manual, but for other reasons I went back to the original values. Unfortunately the brittle leads of the resistors broke and I needed a replacement. The pre amp is 35 years old and uses brown carbon film resistors. I had also bought Vishay metal film for the two lst Rs in the circuit, but I like the sound of carbon film better. For example, Mouser has these carbon film types from KOA, 0.25 or 0.5 watts.

 

https://www.mouser.de/ProductDetail/KOA-Speer/CF1-4CR50J?qs=JFoMzux4TxpPn4ppyPaeyg%3D%3D

 

I would be very interested to hear how your amp sounds with different types of resistors e.g. Vishay vs. KOA. But really don't bother if you are convinced of your choice. I didn't want to complain and just make a suggestion because you are in the building phase anyway.

 

[Curious_George]

5 hours ago, henry4841 said:

Some very good points. I have talked to Maynard about the subject of carbon film vs mf resistors years ago and he just said no difference in his opinion. I built one tube amp with carbon resistors just to see for myself. I could really not tell any significant difference. The only way to run a real test is to build two identical amps, one with carbon and the other with mf and then compare the sound with some significant time listening to both of them with the same source of music. Personally I think either way will sound just fine. The one advantage of mf is they do not drift from stated ohms over time like a carbon resistor does. But an amp such as this one is real tolerate of drifting value parts. Nor does carbon have some other properties not wanted as does mf, inductance, reactance etc. You can make a carbon resistor at home with just a lead pencil and a piece of paper. Scratch yourself a good thick line of lead pencil on a piece of paper and then measure with an ohmmeter to verify yourself. I have done it. 

The wrong type of resistor in the circuit can make a difference. It depends on where you put it. For example, for a plate load resistor, in a high gain microphone amp, you typically would not want to use a standard carbon composition if you are looking for a low noise circuit. Will the carbon composition resistor work? Yes. 

 

They use to recommend a "cracked carbon" resistor which was low noise back in the day, now you can use low noise carbon film or metal film. Typically, if a resistor sets any kind of gain or has high(er) current running through it, you want it to be low noise. 

 

 

[Curious_George]

For example, in the Cathodyne phase splitter, you could use carbon composition resistors with no noise penalty because this type of phase splitter has no gain. However, the LTP phase splitter has some gain and for the lowest noise you would not want to use a carbon composistion resistor. 

[tube fanatic]

5 hours ago, henry4841 said:

Some very good points. I have talked to Maynard about the subject of carbon film vs mf resistors years ago and he just said no difference in his opinion. I built one tube amp with carbon resistors just to see for myself. I could really not tell any significant difference. The only way to run a real test is to build two identical amps, one with carbon and the other with mf and then compare the sound with some significant time listening to both of them with the same source of music. Personally I think either way will sound just fine. The one advantage of mf is they do not drift from stated ohms over time like a carbon resistor does. But an amp such as this one is real tolerate of drifting value parts. Nor does carbon have some other properties not wanted as does mf, inductance, reactance etc. You can make a carbon resistor at home with just a lead pencil and a piece of paper. Scratch yourself a good thick line of lead pencil on a piece of paper and then measure with an ohmmeter to verify yourself. I have done it. 

I typically use metal film resistors in new builds for their usual 1% tolerance.  However, as Henry stated, it really is not necessary for values to be that close in an audio amplifier.  A change in value of even 10% should not be a problem.  Tube to tube tolerance differences are far more likely to cause an audible difference.  
 

Given how much enjoyment audiophiles derive from their vintage gear, which is generally loaded with carbon comp resistors, I don’t have any problem using them if needed.  Years ago I acquired a load of circa 1950 Allen-Bradleys from the son of a former Bell Labs engineer.  In spite of their being old (like me!), most are within 5% of their specified value and work just fine in anything in which they are installed.  In vintage audio gear which I restore, they allow the appearance to remain as it was originally which some prefer.  I don’t find them to be any more noisy than anything else.  Gassy tubes are much more likely to cause issues.

 

Maynard
 

 

[KT88]

As Henry writes, whether I like a sound is more of a long term effect for me. Then everything becomes more and more colourful and beautiful. I sometimes experience a dislike of the sound only after days of listening. Then it becomes somehow disturbing or there is e.g. a kind of resonance frequency in the treble range. To prevent misunderstandings in my post above, I deliberately meant carbon film resistors. Carbon composition resistors, according to my experience and of course assuming the right values, can sound fantastic in some respects but can also be very annoying in other respects to me. I would rather see CC in guitar amps where they can make a wonderful service to create „the“ sound. However, my experience is limited to the Riken brand. Unfortunately, I haven't had AB yet.
To put it briefly. MF can sound very clear and spacious but in a way "hifi like" if that makes sense. Some large orchestral sounds can convince me. But the impulse is somehow strange. As if there was a damping at the very beginning of a piano attack. With carbon film resistors, I don't hear any "deformation" of the impulse even with the softest and most delicate piano notes. So it's not about the overall picture of a sound event but about the perceived naturalness of the sound development and attack of individual instruments or voices.
Sorry, it's my impression, normally I'm more the sober type and I'm not interested in marketing slogans for magic remedies.

[KT88]

Somehow it is a mystery to deal with amplifiers and their components. When I make such descriptions of my sound impressions, I believe I am being sincere. One might think that there are only tiny nuances that one could neglect. But it has an effect, sometimes even hop or top. For example, I had the Quad 34 pre fitted with new electrolytic capacitors as a necessary renewal, 17 small pieces. The old electrolytic capacitors often leak in this model and can destroy the circuit board. I fell for the marketing gossip about Silmic 2 electrolytic capacitors. I was massively disappointed with the sound, at least in my pre amp. Most of these electrolytic capacitors correct op amp offset. It was boring, without dynamics and very flat two dimensional. Very quickly I swapped these Silmic 2's for just normal Panasonic FR types. All the good sound I wanted was back.

On the other hand, there are studies like the one by Richard Clark. I took the link from another current thread in this forum.

 

https://www.stevemeadedesigns.com/board/topic/193850-richard-clark-10000-amplifier-challenge/

 

What to say...Maybe it is like that if you don't listen long enough. Maybe what Clark found out is true and I am suffering from imagination, but I don't think so.

[henry4841]

9 hours ago, KT88 said:

As Henry writes, whether I like a sound is more of a long term effect for me. Then everything becomes more and more colourful and beautiful. I sometimes experience a dislike of the sound only after days of listening. Then it becomes somehow disturbing or there is e.g. a kind of resonance frequency in the treble range. To prevent misunderstandings in my post above, I deliberately meant carbon film resistors. Carbon composition resistors, according to my experience and of course assuming the right values, can sound fantastic in some respects but can also be very annoying in other respects to me. I would rather see CC in guitar amps where they can make a wonderful service to create „the“ sound. However, my experience is limited to the Riken brand. Unfortunately, I haven't had AB yet.
To put it briefly. MF can sound very clear and spacious but in a way "hifi like" if that makes sense. Some large orchestral sounds can convince me. But the impulse is somehow strange. As if there was a damping at the very beginning of a piano attack. With carbon film resistors, I don't hear any "deformation" of the impulse even with the softest and most delicate piano notes. So it's not about the overall picture of a sound event but about the perceived naturalness of the sound development and attack of individual instruments or voices.
Sorry, it's my impression, normally I'm more the sober type and I'm not interested in marketing slogans for magic remedies.

Interesting KT-88. 

[henry4841]

Nelson liked the old Simlac's but my understanding the newer ones have changed. Nichicon makes a cap series much like the old Simlacs. At least that is what I am hearing on the net. Hard to go wrong with the Nichicon brand of caps. When doing the kind of things Kt-88 has done just go by what you see and think and not what someone else on the nets says sounds good. Just please yourself. I like hearing what KT-88 has found. First hand experience with different parts. Good thing about a forum, hearing different and new views. 

[captainbeefheart]

https://elsmar.com/pdf_files/Military Standards/Mil-Std-2000.pdf

[Curious_George]

17 minutes ago, CWelsh said:

Thank you. This is good to know.

 

Part of my reason for asking is because of Henry's comment about the bass being stronger and quicker. This is a change I noted when I upgraded the capacitors in my Marantz 1060. My brother-in-law also has a 1060 that matches mine but is all original so we were able to A/B the two. If you weren't switching between the two, I'm not sure the changes would have been noticeable, but we were both able to clearly hear what I would also describe as stronger and quicker bass, so I wondered if the premium passive components might be contributing factors. The difference, though, is the new caps that went into my 1060 were also of different values than the originals, so that may be more significant than any quality differences.

Good modern quality caps will make a difference, but a value change will definitely change the sound. 

[Curious_George]

24 minutes ago, CWelsh said:

Thank you. This is good to know.

 

Part of my reason for asking is because of Henry's comment about the bass being stronger and quicker. This is a change I noted when I upgraded the capacitors in my Marantz 1060. My brother-in-law also has a 1060 that matches mine but is all original so we were able to A/B the two. If you weren't switching between the two, I'm not sure the changes would have been noticeable, but we were both able to clearly hear what I would also describe as stronger and quicker bass, so I wondered if the premium passive components might be contributing factors. The difference, though, is the new caps that went into my 1060 were also of different values than the originals, so that may be more significant than any quality differences.

Depending on where in the circuit said cap is, sometimes the original value is best. Some caps can be increased for better performance, some caps should not be increased (or decreased). 

[CWelsh]

6 minutes ago, Curious_George said:

Depending on where in the circuit said cap is, sometimes the original value is best. Some caps can be increased for better performance, some caps should not be increased (or decreased). 

I bought a pre-packaged parts kit and assume the guy who put it together had that knowledge. I certainly don't...lol

[tube fanatic]

3 hours ago, CWelsh said:

Thank you. This is good to know.

 

Part of my reason for asking is because of Henry's comment about the bass being stronger and quicker. This is a change I noted when I upgraded the capacitors in my Marantz 1060. My brother-in-law also has a 1060 that matches mine but is all original so we were able to A/B the two. If you weren't switching between the two, I'm not sure the changes would have been noticeable, but we were both able to clearly hear what I would also describe as stronger and quicker bass, so I wondered if the premium passive components might be contributing factors. The difference, though, is the new caps that went into my 1060 were also of different values than the originals, so that may be more significant than any quality differences.

When doing comparisons, if the levels are not matched with extreme accuracy it is impossible to draw a valid conclusion.  Most listeners will pick the slightly louder of the two.

 

Maynard

[henry4841]

6 hours ago, Curious_George said:

In my experience, changing the output transformers will contribute the most difference when comparing two identical amps. Other components or toplogy changes (such as stereo vs mono) will have much less effect on the sound difference. 

I've heard as much on the net myself. I have use of the Edcor OPT'S already on the EL-34 amp to use but I sure want to install Hammond 125Dse's on my new build. I may just have to fork over the extra $150 or so for those Hammonds. To me they just sound better than Edcors, at least on this Sweetie. Just me probably. 

[henry4841]

2 hours ago, tube fanatic said:

When doing comparisons, if the levels are not matched with extreme accuracy it is impossible to draw a valid conclusion.  Most listeners will pick the slightly louder of the two.

 

Maynard

Very good point Maynard. I do a lot of listening when seriously comparing two amplifiers. Many, many hours. I have not done it in a long while but that is what it takes for me convince myself there is an improvement or not. Now at this time in my life those kind of things are not that important to me. My worse sounding tube amplifier sounds extremely good to me or I would not have kept it. It would have been torn down for the parts. I like all the tube amplifiers I have decided to keep. 

[John Warren]

If you're so inclined, try a "different" output transformer configuration.  For example, I have a customer that requested the 299C reproduction amplifier using the Lundahl C-core and based on my listening, sounded excellent.  They're a bit pricey.  The powder coated enclosure provides a nice aesthetic.   A 299C power supply transformer (Heyboer wound) is shown next to the C-core.

 

 

 

North Reading Engineering Forum - Index

[tube fanatic]

4 hours ago, henry4841 said:

The Sweetie has the same 2nd and 3rd harmonics but distortion numbers are not what one would call good. I tested my personal KT-88 along with this one I just finished with the intentions of selling somewhere and the Sweetie. The KT-88's were tested at 1Khz 1 watt. I would not test the Sweetie at 1 watt because that is all the power it makes at clipping. Would not be fair, but even at 250mw of power the distortion numbers were not what one would call good. All that being said the Sweetie is one amazing sounding amplifier. 

I am concerned that you found high distortion from the Sweetie.  At 250mw it should be very low.  Can you take measurements at the 6Y6 grid so we can see what the driver is doing?  If that measures high, try pulling its cathode bypass cap to get some current feedback and measure again.  It will drop the gain, but the 6SJ7 has so much it should not be an issue at all.  Also, if your signal generator can provide output of a solid few volts rms, you can try driving the 6Y6 grid directly and take that measurement as well.

 

Maynard

[henry4841]

4 minutes ago, tube fanatic said:

I am concerned that you found high distortion from the Sweetie.  At 250mw it should be very low.  

 

Maynard

Poor choice of words on my part Maynard. For a SET amplifier at 250mv the distortion is not anything to worry about. I was referring to a good SS  or say the SE KT-88 I just built amplifier distortion profile on Arta software. When I find time next week I will look at the Arta profile and see exactly what the number is. Arta does state in as distortion or distortion and noise. I can look at it each way. In fact I can take a picture of the screen and post it as well. I do remember when looking at the profile there was a lot more going on down low, something like 80 or 90db down from the fundamental. In other words nothing one should hear. 

[captainbeefheart]

I'm getting around 2.5% THD at 1 watt power

 

250mW of power 1% THD

[henry4841]

I decided to run Arta on the Sweetie today. Got my curiosity up. This is what I found, first picture left channel. When I first tried to take pictures I was measuring .59% left and .62% distortion and noise at .250mw. Respectable numbers in my book for a 1 watt amplifier. I certainly would not add any feedback to my Sweetie. 

 

One thing I notice in the profile is no or very little 3rd harmonics from this amplifier. One can see a lot going on from the 4th harmonic that my KT-88 build do not have. Nothing to be concerned about being the noise or whatever it is, is well below the fundamental. Another thing I like to see is there are no or almost minute spurs on the fundamental signal which my KT-88 amplifiers do have.