It was all to do with the transformer wires.
The sound is impressive and was worth doing, I'm not good with describing how an amp sounds but it keeps up with my weston acoustics kt120 driving ns1000m's.
The ns1000m's are notorious for sounding harsh and unlistenable when played with mediocre equipment and I think it has passed the test.
So much so I am considering selling the kt120 and building a pair of obl-11's.
Oh and I still waiting on the tortuga ldr so it could be even better
Well done Feckie 
Care to share your impressions on the differences between the FEs and that tube amp? It's a perennial subject of discussion/comparison on many threads.
EDIT - OOPS! ... almost a simultaneous post. Would still like to hear more on your comparisons after some time passes. 😉 The FEs can continue to mellow over a long period of time - particularly if something like the Isotek break-in disk has not been used.
Care to share your impressions on the differences between the FEs and that tube amp? It's a perennial subject of discussion/comparison on many threads.
EDIT - OOPS! ... almost a simultaneous post. Would still like to hear more on your comparisons after some time passes. 😉 The FEs can continue to mellow over a long period of time - particularly if something like the Isotek break-in disk has not been used.
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Seems quite an achievement... 🙂
Now that you have working boards populated with really good quality parts you should consider replacing caps in C9 with some Blackgate PK 220uF/4V, FK 220uF or even better NX 220uF/6.3V, you'll have a really nice improvement.
You can find PKs from Parts Connexion or eBay for less than 5 US$, audiotuning on ebay has NX for 16.90€, a really honest price nowadays, NX are the best caps you can use for C9.
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Trying to start an argument - eh?
Just picking fun at you 😉
"Did you managed to try yours?"
No, but you did put me in semi-panic mode - can't find them - tonight's project 😱 I also have some Elna RJH 220uF/50 for C1/C2 that you sent me. Still holding off on the Final till I get the wandering FE back.
I've 'mostly' put the soldering iron down for a few weeks as I'm listening to speaker XO and C-13 swaps. I did do a quick stereo board build of the original TP V1.2s just so I knew they still work. They sound fine and will join the clearance sale planned for next month. From the other thread - dual mono V1.3 are working again and I'm doing new auditions of Siva's opamp modules.
No info on the Supremes other than I really like them. Will know more when I have the TCs.
Attachments
Hi Dario,
I was out of town when you posted this. When I got home, I was curious enough to check out NX on ebay. I found that audiotuning didn't have anymore for sale. It is clear that the NX are becoming very hard to find and expensive.
That reminded me the Bob had suggested the possibility of the Mundorf AC series as being available and a possibility for good sound in the C9 position. Like the NX, they are bi-polar and have very low tan delta. PCX has them available for $3.49, but the problem is their size and that they are axial caps. At 16 mm diameter and 39 mm length, they would be difficult to fit to the current board. Maybe soldier style would work.
Looking at the board, I can imagine a future revision of the board that could fit them. I wondered if you have considered them, even auditioned them? If not, maybe I'll give them a try the next time I place an order with PCX.
Jac
As they say in DIY audio - We may have some wires crossed 😉 I have made several references to Mundorf AG as a good piece for C101/201, but If I called out 'AC' it would have been a typo. I did list some Mundorf M-Cap ZNs (which I now learn are rated AC) for C-13 that I got from Tom a few years ago - and did mention I would include them in the direct coupling comparisons when I get the Coppers back. However, the caps I have present no space challenge even for the V1.2 and V1.3. Not sure if you are describing something different. Sorry if there was some confusion.
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Bob,
It's probably my poor memory. Sorry. However I got to the idea, incorrect memory of something you said or just a fantasy in my own mind, somehow I started thinking about Mundorf electrolytic as being close to Blackgate, at least the possibility.
At any rate, since the Mundorf AG work well in power supplies, perhaps the fat Mundorf AC would be worth a try in C9 for the same reasons. Here is a quote from Mundorf on their technology suggesting some similarity to the Blackgate which used graphite.
"MUNDORF electrolytic capacitors with black cathodes feature a real cothode foil! This enables extremely fast and almost lossless ion movements, reducting the ESR, distortions and noises it produces itself to an absolute minimum. The positive effects are comparable to when modified electrolytes are used, which are produced for example with the addition of graphite, although the effects of the former are more pronounced. The result is a holographic music playback with a wide and deep on-stage representation and a completely stable focus."
Jac
It's probably my poor memory. Sorry. However I got to the idea, incorrect memory of something you said or just a fantasy in my own mind, somehow I started thinking about Mundorf electrolytic as being close to Blackgate, at least the possibility.
At any rate, since the Mundorf AG work well in power supplies, perhaps the fat Mundorf AC would be worth a try in C9 for the same reasons. Here is a quote from Mundorf on their technology suggesting some similarity to the Blackgate which used graphite.
"MUNDORF electrolytic capacitors with black cathodes feature a real cothode foil! This enables extremely fast and almost lossless ion movements, reducting the ESR, distortions and noises it produces itself to an absolute minimum. The positive effects are comparable to when modified electrolytes are used, which are produced for example with the addition of graphite, although the effects of the former are more pronounced. The result is a holographic music playback with a wide and deep on-stage representation and a completely stable focus."
Jac
Hi Jac,
the audiotuning eBay auction I was referring to is still open and 8 pieces still available...
I don't think I'll ever do a board that can accept such large axial caps... maybe I'll add a bypass position for FKP2s or KP1830.
Dario,
Thanks. You were right as usual. I forgot to click "worldwide" when I searched and nothing came up. As you say, still some available. I may give it a try.
Bob,
You picture is exactly what I imagined. I may give the Mundorf's a try since the price is not too bad.
Jac
I cannot vouch for sonic comparisons to Mundorf or anything else, but I know for a fact that Jensen makes a bipolar 'lytic that is quite a bit smaller. It will fit decently on the FE board if R10 is connected directly to one lead instead of using PCB mounting holes. Difficult to explain, but have a look and you'll figure it out. Jensen part is considerably more expensive. I have a pair here but never got around to trying them because I got tired of experimenting. If anyone is interested, I'll give them a deal.
Dario, the pads for bypass on the TP boards was not a bad idea, and some cap combinations sounded okay. Adding them to FE would not be difficult and would provide options for future builders.
Peace,
Tom E
Dario, the pads for bypass on the TP boards was not a bad idea, and some cap combinations sounded okay. Adding them to FE would not be difficult and would provide options for future builders.
Peace,
Tom E
As I continue to think about this subject and all the approaches to C9, exploring bypassing seems interesting too. As you know, I'm not opposed to getting lucky with the right bypass cap. I'm sure some of you have bypassed C9 in earlier versions of My_Ref. What kind of bypass value is typically used with C9? I would guess something in the range of 0.1 uF?
I gather from earlier discussion that BGs, even STD and PK don't seem to benefit from a bypass cap. Is that the right conclusion, or would it be interesting to try a bypass on a BG PK?
I think I'm going to have to study up on the compensation circuits in the feedback loop of the My_Ref. It would be interesting to try to get C9 into the range where a film cap were possible. I remain curious about trying to shift the value of C9 down by increasing the value of the gain resistor pair, but would have to truely understand the function of the compensation circuits before even trying it.
Thanks in advance for any experience or thoughts on the subject.
Jac
I've used values in the range of 6.8nF to 22nF, types ranging from FKP2, MKP1830 and MKP10. It's also worth trying out polycarbonate and polyester film/foils like KC1850 and FKS2.
From my experience, it's not beneficial to sonics to bypass a BG PK at C9, but you can try a film/foil or a styroflex.
Hey Jac, since you are an obvious proponent of bypassing, I'm going to lean on (read - pick on 😀) you for some focus information. I understand the basics but am not clear on the target as applied to the MyRef and FE specifically. I went to Mr. Google to brush up on the concept and came away with the impression that filtering out an AC component, which causes noise in the signal, is the most likely function of a bypass here. I'm not clear on why C9 - and its local circuit - needs that modification. It may well be that this type of bypassing is more like 'tuning" rather than "cleaning" the input, as my limited knowledge would suggest bypassing is incorporated at many other locations in the amp.
Can you or anyone clarify the goal in the process here?
Dario - If you adjusted a new version of the FE to allow for bypassing, would that most likely be a surface mount item?
References:
Choosing and Using Bypass Capacitors
The Basics
Can you or anyone clarify the goal in the process here?
Dario - If you adjusted a new version of the FE to allow for bypassing, would that most likely be a surface mount item?
References:
Choosing and Using Bypass Capacitors
The Basics
OK Bob, I'm going to try to explain how I understand this, but I may miss here and there, so others, please feel free to correct me.
In a My_Ref, the gain is set by R7 and R10, that is R7/R10 = 12k/390 ~ 30.8:1 voltage ratio. The problem is that the LM318 opamp has some stability issues as the frequency approaches DC. To make sure that the 318 remains stable, Mauro added C9 to R10, the combination making a high pass filter that acts like an open circuit at DC and causes the gain of the circuit to decrease as the frequency goes lower. That helps the low frequency stability.
To avoid affecting the sound quality, he selected the corner frequency of the filter at 1.8 Hz which meant that we need a 220 uF C9 to go with the 390 Ohm R10. If he had selected R7 at 120k and R10 at 3.9k, we would have only needed C9 to be 22 uF, but he didn't and the other circuit compensations have been developed at the current R7/R10 ratio, so changing the value of C9 requires a lot of retuning.
C9 affects the sound quality because it affects the amount and phase of the feedback signal and that affects the output. Because C9 is a relatively large value, the only reasonable capacitor is an electrolytic. The problem with electrolytic capacitors is that they provide capacitance through ion transfer where film caps use electron transfer. In comparison, ion capacitors are slow (phase errors) and have high ESR and ESL. The combination of the capacitance, ESR, and ESL will combine in an internal resonance that means a capacitor reaches a frequency where it responds like a resistor, then above that frequency it responds like an inductor.
All capacitors have that resonance, but in large electrolytic capacitors, the resonance can occur at a few thousand Hz. Ideally, we would like that resonance to happen at 100 kHz or higher whenever a capacitor is exposed to the signal so that we don't introduce uncontrolled attenuation or phase shifts. In my opinion, phase shift are likely what causes the differences we can hear in clarity and sound stage.
In comparison to electrolytic caps, film caps have low ESR and high resonant frequencies. It is also true that the smaller the capacitance value, the higher the resonant frequency.
The links you provided on bypass capacitors were referring to bypassing the power supply of a circuit or IC. For example, C2 and C4 on the My_Ref bypass the power supply of the LM3886. What I was talking about was a small capacitor bypassing a large capacitor. In that case, a large electrolytic capacitor may have a self resonance that is lower than we want and, therefore, doesn't act like a capacitor at high frequencies. If we can add a small film cap in parallel without adding too much inductance with extra leads, the small film cap will still be acting as a capacitor in the high frequency range. The theory is that the high frequencies will be passed through the small cap and the low frequencies dominated by the large cap. The value of the combined cap won't be changed significantly because we will select the small cap to be less than 10% of the big cap. In fact, cap size ratios of 1:100 or even 1:1000 seem to work well.
The trick with bypassing caps is to find two caps that work well together. Otherwise, the sound doesn't seem blended or coherent. If I understand Dario correctly, that is why he prefers one single high quality cap over a cheaper cap with a bypass. He realizes how hard it is to get a good combined cap. In the case of C9, Blackgate caps seem to be the best sounding single caps with the NX as the best of those. One of the keys to Blackgate's sound quality was that they added graphite to provide some electron transfer and improved the high frequency performance. Alas, only leftover Blackgates are available which is why we are having the discussion on what might replace it, a big axial or a normal sized radial, possibly with a bypass.
Sorry for the long post, but I will add one more unproven theory. Some cap materials seem better at high frequency than others, for example teflon. Because of that, a lot of people choose a small teflon cap to bypass their electrolytic or paper-in-oil cap. I suspect that the material differences may be providing some of the lack of coherence in those combinations. Since a smaller size increases the self resonance frequency in any cap, I like to try caps of similar materials, just smaller size, when bypassing a bigger cap. So when bypassing an electrolytic in C9, I might try a small paper-in-oil as well as a polypropylene, just to see how it sounds.
Bob,
Did I answer your question or did I just ramble on?
In a My_Ref, the gain is set by R7 and R10, that is R7/R10 = 12k/390 ~ 30.8:1 voltage ratio. The problem is that the LM318 opamp has some stability issues as the frequency approaches DC. To make sure that the 318 remains stable, Mauro added C9 to R10, the combination making a high pass filter that acts like an open circuit at DC and causes the gain of the circuit to decrease as the frequency goes lower. That helps the low frequency stability.
To avoid affecting the sound quality, he selected the corner frequency of the filter at 1.8 Hz which meant that we need a 220 uF C9 to go with the 390 Ohm R10. If he had selected R7 at 120k and R10 at 3.9k, we would have only needed C9 to be 22 uF, but he didn't and the other circuit compensations have been developed at the current R7/R10 ratio, so changing the value of C9 requires a lot of retuning.
C9 affects the sound quality because it affects the amount and phase of the feedback signal and that affects the output. Because C9 is a relatively large value, the only reasonable capacitor is an electrolytic. The problem with electrolytic capacitors is that they provide capacitance through ion transfer where film caps use electron transfer. In comparison, ion capacitors are slow (phase errors) and have high ESR and ESL. The combination of the capacitance, ESR, and ESL will combine in an internal resonance that means a capacitor reaches a frequency where it responds like a resistor, then above that frequency it responds like an inductor.
All capacitors have that resonance, but in large electrolytic capacitors, the resonance can occur at a few thousand Hz. Ideally, we would like that resonance to happen at 100 kHz or higher whenever a capacitor is exposed to the signal so that we don't introduce uncontrolled attenuation or phase shifts. In my opinion, phase shift are likely what causes the differences we can hear in clarity and sound stage.
In comparison to electrolytic caps, film caps have low ESR and high resonant frequencies. It is also true that the smaller the capacitance value, the higher the resonant frequency.
The links you provided on bypass capacitors were referring to bypassing the power supply of a circuit or IC. For example, C2 and C4 on the My_Ref bypass the power supply of the LM3886. What I was talking about was a small capacitor bypassing a large capacitor. In that case, a large electrolytic capacitor may have a self resonance that is lower than we want and, therefore, doesn't act like a capacitor at high frequencies. If we can add a small film cap in parallel without adding too much inductance with extra leads, the small film cap will still be acting as a capacitor in the high frequency range. The theory is that the high frequencies will be passed through the small cap and the low frequencies dominated by the large cap. The value of the combined cap won't be changed significantly because we will select the small cap to be less than 10% of the big cap. In fact, cap size ratios of 1:100 or even 1:1000 seem to work well.
The trick with bypassing caps is to find two caps that work well together. Otherwise, the sound doesn't seem blended or coherent. If I understand Dario correctly, that is why he prefers one single high quality cap over a cheaper cap with a bypass. He realizes how hard it is to get a good combined cap. In the case of C9, Blackgate caps seem to be the best sounding single caps with the NX as the best of those. One of the keys to Blackgate's sound quality was that they added graphite to provide some electron transfer and improved the high frequency performance. Alas, only leftover Blackgates are available which is why we are having the discussion on what might replace it, a big axial or a normal sized radial, possibly with a bypass.
Sorry for the long post, but I will add one more unproven theory. Some cap materials seem better at high frequency than others, for example teflon. Because of that, a lot of people choose a small teflon cap to bypass their electrolytic or paper-in-oil cap. I suspect that the material differences may be providing some of the lack of coherence in those combinations. Since a smaller size increases the self resonance frequency in any cap, I like to try caps of similar materials, just smaller size, when bypassing a bigger cap. So when bypassing an electrolytic in C9, I might try a small paper-in-oil as well as a polypropylene, just to see how it sounds.
Bob,
Did I answer your question or did I just ramble on?