I was missing the 18v zener Z1 per the CodyT/ra7 schematic on this amp so got that delivered today and was able to power up the amp.
Thanks Eric for all your help. I replaced one of the 2.2R with 3.3R and now I get 2.095vdc voltage drop with the total resistance of 1.3R so very close to 1.6A bias and yes my klipsch too are rated 8ohm and 97-99db sensitivity đź‘Ť
I did hear the music too
I decided to fiddle with my TDV and swapped in a pair of Lundahl LL1694 for my Hammond 159ZC, raising inductance from 60mH to 160mH. Another neat thing about the swap is that I was able to drop my bias resistors and rely exclusively on the DCR of the Lundahl’s (1.8R). The extra inductance has filled in the bottom end nicely and tightened things up a bit. A nice improvement overall.
I wouldn’t recommend using the Lundahl’s unless you already know the amount of resistance you’re after for your specific devices and can work with the 1.8 DCR these specific chokes offer. I’m lucking enough to have a somewhat matched pair of 2087’s, which made things a bit easier.
I wouldn’t recommend using the Lundahl’s unless you already know the amount of resistance you’re after for your specific devices and can work with the 1.8 DCR these specific chokes offer. I’m lucking enough to have a somewhat matched pair of 2087’s, which made things a bit easier.
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I've done a bit more tweaking and have settled on some preferred operating points (for my specific devices). With the 159ZC's I was using rails around 26v and 1A4 Iq and I really liked that combo. With the LL1694's, I settled on a 28v transformer, getting my rails to 36-37v and a final Iq around 1A7. This lands me at roughly the same THD and spectra as the previous operating point, but the additional mH's and power have really transformed the bottom end. It's the same palpable bass and midrange, but with some serious grunt and control. I'd call it my absolute favorite in terms of the LF sound and definitely near/at the top for HF and overall sound. Granted, its not apples to apples, this being a follower and driven by a tube pre (whereas most of my other amps are common source.)
All in all, a successful experiment. At some point I'll have to tackle the PSU harmonics. I imagine there's not much PSRR to speak of, so maybe a cap multiplier would help. Of course I can't say that I hear any of that noise, so fixing is not especially high on my list.
All in all, a successful experiment. At some point I'll have to tackle the PSU harmonics. I imagine there's not much PSRR to speak of, so maybe a cap multiplier would help. Of course I can't say that I hear any of that noise, so fixing is not especially high on my list.
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The higher rail voltage is definitely a plus. It makes use of the Tokin's power capacity - there is no replacement for displacement.
My Hammond 193V choke loaded 2SK180 follower runs on 38V or so rail and it sounds great. Distortion is similar.
One way to lower the power supply ripple is to change the CRC filter to CLC. That is what I have in my amp.
My Hammond 193V choke loaded 2SK180 follower runs on 38V or so rail and it sounds great. Distortion is similar.
One way to lower the power supply ripple is to change the CRC filter to CLC. That is what I have in my amp.
My TDVs continue to give me great pleasure. I am using the "51"s.
Mine have the power supplies "flipped".
One wonders how much more rail voltage one can get away with? Mine are in the 38 volts range.
One of these days I am going to learn how to use REW to take measurements - I guess I need to make a resistor bank and the AKITIKA oscillator, first.
Any advice would be appreciated.
Mine have the power supplies "flipped".
One wonders how much more rail voltage one can get away with? Mine are in the 38 volts range.
One of these days I am going to learn how to use REW to take measurements - I guess I need to make a resistor bank and the AKITIKA oscillator, first.
Any advice would be appreciated.
With adequate cooling, whether free air or forced air, you can probably power the Tokin to one quarter or even one third of its rated power dissipation. The THF-51S is rated at 400W so if one quarter of rated power, that would be 100W. So if say @2A, that would give 50V of Vds. The choke will drop some voltage, so that can be added to the Vds to get the rail voltage. Or even higher, depending on how much you want to push it.
Ed: At higher rail voltage, 2A might be on the low side, so perhaps 2.5A or even higher to take advantage of the higher rail voltage. So that will factor into the voltage calculation.
Ed: At higher rail voltage, 2A might be on the low side, so perhaps 2.5A or even higher to take advantage of the higher rail voltage. So that will factor into the voltage calculation.
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Thanks for the ideas regarding supply noise. I do have a pair of chokes I could try for CLC, but space is at a premium in this specific chassis. I'll start thinking about flipping the supply too.
Regarding dissipation, I don't quite know what the 2087's are capable of handling. I'm pushing my comfort level at 60W, but I do have pretty big sinks to handle the heat. Top of device is at 60C right now. If I ever go higher, I'll swap in some THF51's.
Regarding dissipation, I don't quite know what the 2087's are capable of handling. I'm pushing my comfort level at 60W, but I do have pretty big sinks to handle the heat. Top of device is at 60C right now. If I ever go higher, I'll swap in some THF51's.
Hey Cody, what power level into what load is that spectrum snapshot? If it's 1 watt into 8 ohms, that's a great THD for this type circuit.
I totally agree with higher inductance making the bass sound just "right". I've been using Hammond 193U which are 200mH, 1.8ohm DCR, 2A max. I think I'll have to try some of these Lundahl LL1694's though as a step up from the Hammonds.
Nice work.
I totally agree with higher inductance making the bass sound just "right". I've been using Hammond 193U which are 200mH, 1.8ohm DCR, 2A max. I think I'll have to try some of these Lundahl LL1694's though as a step up from the Hammonds.
Nice work.
Thanks @Cinco! The spectrum is 1W into 8R. I've tried a number of different operating points and have seen as low as .018% and as high as .12%. This middle spot has been my preference, probably somewhat based on the 2nd to 3rd ratio. The distortion spectrum is nearly identical to what I'd settled on with the smaller Hammonds, but I much prefer this new configuration.
I'll have to take another look at the 193U's – those are nearly the same as the Lundahl, but with even more inductance and current rating. The main reason I chose the Lundahl was because they fit the designated spot in my chassis. I'm not necessarily convinced that the fancy nature of the lundahl's improved sound quality, but rather the simple increase in inductance and voltage. Who knows though.
Attaching all the distortion shots I've taken. All are with the Hammond except the last.
I'll have to take another look at the 193U's – those are nearly the same as the Lundahl, but with even more inductance and current rating. The main reason I chose the Lundahl was because they fit the designated spot in my chassis. I'm not necessarily convinced that the fancy nature of the lundahl's improved sound quality, but rather the simple increase in inductance and voltage. Who knows though.
Attaching all the distortion shots I've taken. All are with the Hammond except the last.
