AFAIK, the servo works and settles perfectly on Spooky, the settling time issue was with the Symasui IPS. The offset fix I'm pretty sure does not apply to Spooky, but rather Symasui.
The Value of R36 just limits the servos influence and provides some isolation between the servo and the feedback node. The actual value isn't really critical as this IPS doesn't produce much offset even without the servo, so the servo doesn't have much work to do.
The Value of R36 just limits the servos influence and provides some isolation between the servo and the feedback node. The actual value isn't really critical as this IPS doesn't produce much offset even without the servo, so the servo doesn't have much work to do.
Thanks guys. That makes sense.
I'll use the values that are on the schematic but I need to finish my Statement speakers first. They are taking far too long to complete.🙁
I'll use the values that are on the schematic but I need to finish my Statement speakers first. They are taking far too long to complete.🙁
The changes in the BOM vs the schematic aren't critical. Most of the differences are to have the gain more closely match the other IPS designs. If you aren't directly comparing with the other IPS designs, the original values would be just fine.
Since fixing the Symasui, Ostripper has since recommended adding the same "Rsl" resistor to the Spooky. See post 5110 in the Slewmaster main thread. http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-511.html#post4114348
All this extra resistor dose is give the servo a better ground reference.
However; the Servo fix "Rsl" resistor isn't truly needed on the Spooky. I could see this added resistor being helpful on a build that has really mismatched transistors.
Since fixing the Symasui, Ostripper has since recommended adding the same "Rsl" resistor to the Spooky. See post 5110 in the Slewmaster main thread. http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-511.html#post4114348
All this extra resistor dose is give the servo a better ground reference.
However; the Servo fix "Rsl" resistor isn't truly needed on the Spooky. I could see this added resistor being helpful on a build that has really mismatched transistors.
Transistor Selection
1. The recommended Spooky transistors for Q1, Q2 & Q5, Q6 are KSC1815 and KSA1015. As I can only can find these in Y ranking (hFE120-240) am I better off in using the Toshiba 2SC2240BL & 2SA970BL (hFE 350-700) which I have plenty of?
2. For the 10 output transistors, my first choice would have been the Sanken 2SC3264/ 2SA1295 until I saw the price.
I looked up the very useful post on "Output Transistor Choices" that akimmet kindly posted and found the Semelab MG6331/ MG9411 300W transistors were also recommended but not used.
These are half the price and as far as I can tell (i'm not an engineer) are slightly better at 60V rails.
The Sanken are generally recommended as "very good" audio transistors in many of the threads on diyAudio. Can anyone see any issues/ compromises if I use the Semelab MG transistors?
3.Also I would like to use the Toshiba 2SC5200/ 2SA1943 transistors that I have as drivers.
1. The recommended Spooky transistors for Q1, Q2 & Q5, Q6 are KSC1815 and KSA1015. As I can only can find these in Y ranking (hFE120-240) am I better off in using the Toshiba 2SC2240BL & 2SA970BL (hFE 350-700) which I have plenty of?
2. For the 10 output transistors, my first choice would have been the Sanken 2SC3264/ 2SA1295 until I saw the price.
I looked up the very useful post on "Output Transistor Choices" that akimmet kindly posted and found the Semelab MG6331/ MG9411 300W transistors were also recommended but not used.
These are half the price and as far as I can tell (i'm not an engineer) are slightly better at 60V rails.
The Sanken are generally recommended as "very good" audio transistors in many of the threads on diyAudio. Can anyone see any issues/ compromises if I use the Semelab MG transistors?
3.Also I would like to use the Toshiba 2SC5200/ 2SA1943 transistors that I have as drivers.
Today I have fired up my second chanel of my Slewmaster after I have mounted Q104 on the main heatsinkt (and without the bulb). The bulb test went well a couple of weeks ago, but now both fuses blowed (3.15 A fast). I tried with 5.0 A. This time only one fuse blowed.
Since the bulb test went so postive, this confuses me. The other chanel works fine with 3.15 A. I have not changed on the bias pot after moving Q104. With the bias pot in this position, I measured 30mV over one emitter pair before moving Q104. Is there a connection with how the bias pot is set, and the fuses blowing?
Since the bulb test went so postive, this confuses me. The other chanel works fine with 3.15 A. I have not changed on the bias pot after moving Q104. With the bias pot in this position, I measured 30mV over one emitter pair before moving Q104. Is there a connection with how the bias pot is set, and the fuses blowing?
Did you set the bias pot with the bulb limiter installed? If so the bias setting will be way too high. Did you test for shorts between output transistors emitters and the heat sink? Same goes for Q104 emitter.
1. I really don't see anything obvious in the data sheet to make me think the Toshiba transistors wouldn't work. Ostripper chose KSC1815/KSA1015 because you can easily get them. The same can not be said about the obsolete 2SC2240/2SA970.
2. If you can get Semelab outputs cheaper, by all means get them! They have excellent specs.
3. Toshiba 2SC5200/2SA1943 is an excellent choice for the drivers.
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jwilhelm
New test today. Back to the bulb connected. It started up with 26mV. I was unsure what way to turn trim pot. Turning the pot to the right the measure increased to 26.7 mV as max. Then I turned the trimpot the other way, and also here I could not get lower than 25.1mV. In this lowest position and with the trim pot fully anticlock I have not tried without the bulb.
There is no shortcut between the heatsinks and the output transistors. With the bulb connected I measures 0.42V between B-E on Q104.
Eivind S
New test today. Back to the bulb connected. It started up with 26mV. I was unsure what way to turn trim pot. Turning the pot to the right the measure increased to 26.7 mV as max. Then I turned the trimpot the other way, and also here I could not get lower than 25.1mV. In this lowest position and with the trim pot fully anticlock I have not tried without the bulb.
There is no shortcut between the heatsinks and the output transistors. With the bulb connected I measures 0.42V between B-E on Q104.
Eivind S
It sounds like Q104 isn't passing any current. With the bias pot adjusted to it's maximum resistance, Q104 should be passing all VAS current available, leaving none for the drivers.
It's not safe to connect this board without the bulb limiter in place. It will blow output devices quickly. Once you do have it sorted out, turn your bias setting to minimum again before connecting without the bulb limiter. Always set bias with the amplifier connected how it is going to operate.
It's not safe to connect this board without the bulb limiter in place. It will blow output devices quickly. Once you do have it sorted out, turn your bias setting to minimum again before connecting without the bulb limiter. Always set bias with the amplifier connected how it is going to operate.
With the bulb connected for one hour and the tripot max clockwise, I have measured this on the emitters:
25.9mV
22.3mV
29.5mV(!!)
25.6mV
24.4mV
It is obvios that my try with the bulb disconneted have not harmed the output transes(Sanken). Jwilhelm, you said it would not be safe to try withot the bulb.
My measurement with the bulb connected on Q104 (0.42V) seems to me to be quite normal. With full power (+/-64V DC) I suppose this will rise to a normal value of 0.6V. Could the trimpot be the "sinner"?
It is curious that this problem was not there before I moved Q104.
Eivind S
25.9mV
22.3mV
29.5mV(!!)
25.6mV
24.4mV
It is obvios that my try with the bulb disconneted have not harmed the output transes(Sanken). Jwilhelm, you said it would not be safe to try withot the bulb.
My measurement with the bulb connected on Q104 (0.42V) seems to me to be quite normal. With full power (+/-64V DC) I suppose this will rise to a normal value of 0.6V. Could the trimpot be the "sinner"?
It is curious that this problem was not there before I moved Q104.
Eivind S
Where are you measuring .42V? If this is base to emitter, the transistor is not being turned on at all, so it is not functioning.
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Yes, I measured between base and emitter on Q104. With the bulb connected, all measured voltage are lower that with full power. With full power I was quite sure that B-E should be 0.6V(????)
I could of course have mixed the pinout on Q 104(it would not be the first time). Looking at Q104 from the "front" the pins are from left to right: E-C-B. Q104 is connected with short wires to the PCB in the same way.
Eivind S
I could of course have mixed the pinout on Q 104(it would not be the first time). Looking at Q104 from the "front" the pins are from left to right: E-C-B. Q104 is connected with short wires to the PCB in the same way.
Eivind S
ECB is the correct pinout. it doesn't matter what voltage you are working with, a transisor won't conduct unless it sees around .6V base to emitter. You have at least 3.6V between PD+ and ND-, otherwise you would have no current flow in the output devices, so there must be a reason why VBE is so low on Q104. Either resistance is too high between PD+ and the base, or resistance is too low between ND- and the base, or Q104 is damaged/connected wrong.
Can you confirm the value of your trim pot? In my first slewmaster attempt I built it with 200r trimpot, leaving me with way to high bias current. Using light bulb it seemed ok since the light bulb limited the current.
With 500R trimmer, I need multiple turns before the bias current start increasing.
Monitor the bias voltage generated by the Vbe multiplier.
You will see the bias voltage change with every change of the Vr.
Does anyone have layout files for a 2p ops?
I would like to try etching my own PCBs. I think the 2p ops would be perfect to re-use some parts from my HK690 that fell down from a shelf in my garage.
I would like to try etching my own PCBs. I think the 2p ops would be perfect to re-use some parts from my HK690 that fell down from a shelf in my garage.
The file is available here. http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-51.html#post3830832 Post 502