Well, did you not? Those TH pads were included for a reason. If you used 2SK170s, you did not deviate from the design. It will work great, as designed, if you built it properly.
Have you listened to it yet?
Indeed.
My brother had a baby grand in the same room as his massive speakers, so comparisons were quick and easy to make. Much of his life was spent trying to find gear that sounded like the real piano, and for many years until the speakers died, he achieved that goal to a great extent (and cost).
My brother had a baby grand in the same room as his massive speakers, so comparisons were quick and easy to make. Much of his life was spent trying to find gear that sounded like the real piano, and for many years until the speakers died, he achieved that goal to a great extent (and cost).
I have been playing the Pearl3 through my Linkwitz LXMinis+Subs and Nelson’s balanced crossover using the Whammy as a preamp until I build Wayne’s line stage. The speakers don’t look at all impressive, but the dispersion of sound with a dipole speaker using the SEAS drivers is surprisingly realistic.
I would personally want to see the cascode operating properly with a little Vce margin. Sure, the circuit will gracefully continue working while the cascode is saturated, and it might even sound fine that way. But then it seems to me you're not getting the full potential out of your P3. Try soldering 2kΩ or thereabouts in parallel with R1. This should give you ~6V of drop for your 11mA FET current, and you can always remove it later if you choose. Or take the 750 right out and stuff something around 550Ω in it's place. Lowering the value of R1 is also a Wayne-approved mod if you want to feel better about changing something.
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Hmm... if they're whistling at all, that means they are unstable and giving you a clear indication that they're unhappy in this circuit. They could be oscillating at some ultrasonic frequency part time, and you won't hear that. I agree with 6L6 - I wouldn't use 'em unless you have a scope on hand to diagnose what's going on and solve it. They might get damaged over time, or punish something downstream with high-level ultrasonic signal. Caution advised...
The kit was designed and intended to be used with 2SK209GR in the Jfet positions, as they are in-production, available for purchase through normal channels, and work wonderfully in the circuit. This is why they are included in the kit. There are also a number of other jfets useable in the front-end, which are conveniently listed on the schematic, this includes K170s and more.
The bipolar transistors in the front-end were originally ZTX851 as shown in the schematic, but they have been very difficult to purchase over the last handful of months, so analysis was used to see if there was a suitable part that could be used in lieu of the 851, and it was discovered that the ZTX457 is actually better in the cap multiplier position (Q8). So ZTX457 are supplied for that position, so that more kits could be made available due to the very limited amount of 851s.
The bipolar transistors in the front-end were originally ZTX851 as shown in the schematic, but they have been very difficult to purchase over the last handful of months, so analysis was used to see if there was a suitable part that could be used in lieu of the 851, and it was discovered that the ZTX457 is actually better in the cap multiplier position (Q8). So ZTX457 are supplied for that position, so that more kits could be made available due to the very limited amount of 851s.
Doing a little test fit today...
These are vintage Jensen quadfilar output transformers, salvaged from an old mixing desk. Close if not identical to Jensen JT-123-FLPCH or Cinemag CMOQ-4. Core dimensions and measured winding DCR are an exact match. If the Q6-Q7 discrete output stage has enough grunt to drive these, I plan to use 'em for the balanced outs, in lieu of the DRV135 active solution. They'll add a wee touch of color to the sound, so TBD if they stay.
There is juuuust enough room to squeeze 'em between the P3 boards and the XLR jacks.
These are vintage Jensen quadfilar output transformers, salvaged from an old mixing desk. Close if not identical to Jensen JT-123-FLPCH or Cinemag CMOQ-4. Core dimensions and measured winding DCR are an exact match. If the Q6-Q7 discrete output stage has enough grunt to drive these, I plan to use 'em for the balanced outs, in lieu of the DRV135 active solution. They'll add a wee touch of color to the sound, so TBD if they stay.
There is juuuust enough room to squeeze 'em between the P3 boards and the XLR jacks.
Attachments
Hello,
The Jfet part of the cascode is a transconductance amplifier, volts input controls current output. R1 converts current to volts output.
Reducing the number of 2SK170 to 3 will reduce the current and voltage output. Q5 will see less current as part of the deal. Less gain as well.
3 2SK170 is still quieter than 4 2SK209.
Thanks DT
The Jfet part of the cascode is a transconductance amplifier, volts input controls current output. R1 converts current to volts output.
Reducing the number of 2SK170 to 3 will reduce the current and voltage output. Q5 will see less current as part of the deal. Less gain as well.
3 2SK170 is still quieter than 4 2SK209.
Thanks DT
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Technically, yes. But not by much. Q5 emitter current should stay nearly the same.
If Q5 is saturated, then it's conducting more current than normal (beta becomes low) through the b-e junction, diverting some away from the collector and R1. This increased base current in turn pulls down the R2-R3 divider bias voltage a bit, in turn lowering the drain voltage on Q1-Q4, causing them to conduct a bit less until an equilibrium is reached. Restoring adequate Vc-e to bring Q5 out of saturation, beta returns to normal and the excess diverted base current will once again flow to the collector where it's supposed to go. That'll raise the collector current a fraction, and the increase in the JFET drain voltage due to R2-R3 bias being restored to normal will also cause the FETs to conduct a smidge more.
All of this should amount to a single-digit percentage current change, I'd guess (assuming Q5 is only slightly dipping into saturation, as appears to be the case for mworthin).
If I am on my way to converting this to all 2SK209GR (GR grade, right? I am not sure what was in the kit), then I might as well try all of these and see what works. I must have a 2K resistor somewhere--if not, will place a Mouser or Digikey order--and if it doesn't appreciably change, I can pull the first 2SK170 and see what happens. I have the Pearl2 boards, and those came with 2SK170BLs, so that isn't possible as a source. I don't see any source, Punkydawgs or otherwise, for an octet of 2SK170s in the 2-6 ma IDSS range.
Soldering those 2SK209 on an otherwise completed board will be a new level of fun.
@6L6, what did you use for your thru-hole FET Pearl3? (I think I remember you making one, but I could be wrong).
Soldering those 2SK209 on an otherwise completed board will be a new level of fun.
@6L6, what did you use for your thru-hole FET Pearl3? (I think I remember you making one, but I could be wrong).
Just received an order of Mogami W2330 - nice stuff ... thanks for the recommendation!
I'll toss out my go-to choices for balanced hookup cable:
- Mogami W2799 mini-quad balanced console cable - my favorite chassis audio cable for almost 20 years now, the XLPE dielectric is really nice to work with, no shrink back when soldering.
- Mogami W2944 miniature balanced console cable - smaller diameter than the 2799; same internal wire specs, but twisted pair instead of star quad. Yet another excellent choice from Mogami's catalog.
My usual source for bulk cable and Neutrik connectors is either Markertek or HAVE Inc... Broadcast industry supply houses, they typically have better prices than elsewhere.