Ok, questions for SY and JAck and whoever.. My whole system is still at my brother's house (for Thanksgiving!) so I can't look.
-Does Jack's board have the attenuator at the output or input? If I remember, its located close to the input.
-I have a 50k pot for now , but the attenuator will be 100k soon as you spec'ed
-I drive two amps with the output. For now that will be 2 stereo F-4's with 100k input impedance (not balanced)
-How about the impedance of 2 100k amp channels in parallel..I 50k input impedance I guess.. Is that OK with the Impasse?
Seems fine even with the 50k attenuator, but is it not optimal?
Additionally, one amps inputs will need to be attenuated. At the moment I am attenuating that amp with a 100k pot each channel which when set right measures about 80k to ground 20k to the speakers.
-Would a 10k or 20k pot or the 2 resistor equivalent be better than 100k?
-Does Jack's board have the attenuator at the output or input? If I remember, its located close to the input.
-I have a 50k pot for now , but the attenuator will be 100k soon as you spec'ed
-I drive two amps with the output. For now that will be 2 stereo F-4's with 100k input impedance (not balanced)
-How about the impedance of 2 100k amp channels in parallel..I 50k input impedance I guess.. Is that OK with the Impasse?
Seems fine even with the 50k attenuator, but is it not optimal?
Additionally, one amps inputs will need to be attenuated. At the moment I am attenuating that amp with a 100k pot each channel which when set right measures about 80k to ground 20k to the speakers.
-Would a 10k or 20k pot or the 2 resistor equivalent be better than 100k?
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My board has provision for a pair of Molex 0.100" headers -- one from the transformer, the other for the "volume" potentiometer. In my case I have a 100K ALPS audio pot in parallel with a 100K ALPS "balance" pot. To adjust the shunt on the input of the 6SN7 you need to simultaneously examine the square wave on the 'scope and the bandwidth on a sound card (or more expensive) analyzer. It's also a good idea to let the preamp warm itself up as there is a huge momentary DC transient on the sending end of the caps until they are bled off.
Why do you have to attenuate one of the amps?
In any event, it is absolutely vital that the loads from each polarity of the output be identical, so anything you do on the amp end, keep that in mind. With a FET input in the amp, you can make that input impedance higher, 100-200k would be fine.
In any event, it is absolutely vital that the loads from each polarity of the output be identical, so anything you do on the amp end, keep that in mind. With a FET input in the amp, you can make that input impedance higher, 100-200k would be fine.
Been enjoying the Impasse back at my place again. Here is a photo. Not really finished, but one input is all I need ATM. Still sounds great. Jack, thanks for making those boards!! You still have a box of them? I'm very pleased that I used the monster chassis from an old B&G power amp. Having everything with lots of space around it helped make assembly easy..and its really quiet.
SY, yes it did cross my mind whether I could hook up a screwy combo of single ended and not, but I guess I'm catching on, it seemed
unwise considering all the matching done in the assembly..
The reason I want to attenuate one amp would be that my bass drivers have their own amp and are less efficient. so I would turn down the amp for mid/highs to get the correct response.
Jack, Ohhh,
so those are spaced for Molex connectors! That explains the eeensy holes. Doh! Wiring that was the job of the
Assembly Department- Jan Didden wired the boards to the inputs and outputs and to each other.. 🙂 I think he just gooped on solder and stuck the wires in the puddle..
In the photo you will see the "Pass DIY" sticker. While this isn't exactly correct, it IS for a Pass amp and I didn't have "SYdiy" stickers, and I
had to cover the old power switch hole with something!
SY, yes it did cross my mind whether I could hook up a screwy combo of single ended and not, but I guess I'm catching on, it seemed
unwise considering all the matching done in the assembly..
The reason I want to attenuate one amp would be that my bass drivers have their own amp and are less efficient. so I would turn down the amp for mid/highs to get the correct response.
Jack, Ohhh,
so those are spaced for Molex connectors! That explains the eeensy holes. Doh! Wiring that was the job of the
Assembly Department- Jan Didden wired the boards to the inputs and outputs and to each other.. 🙂 I think he just gooped on solder and stuck the wires in the puddle..
In the photo you will see the "Pass DIY" sticker. While this isn't exactly correct, it IS for a Pass amp and I didn't have "SYdiy" stickers, and I
had to cover the old power switch hole with something!
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I started to read this thread near at beginning and have only just looked at it again. Could someone point me to where I could find a copy of the schematic please? I assume it's available by now.
In respect of the Molex connectors -- I do, in fact, use ribbon cables when I have ones of the correct length. It makes life (and testing) so much easier. I also use CAT5 and have some teflon insulated #28 which I purchased decades ago at Electronics Surplus in Cleveland.
To what I know, the schematic isn't available on line.
To what I know, the schematic isn't available on line.
I DID NOT! However, come to think of it, it was like a search-and-destroy operation. You need another solder iron, remember 😉
jan didden
This isn't the original schematic from the article, but a pretty accurate redrawing of the signal circuit portion from fellow diyer and neighbor luvdunhill.
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Good point! HE had to use my $4 soldering iron! My beloved Hakko setup seems to have died. The question now is whether to buy a new tip or not. For the old Hakkos, a new tip costs about $30 and these days there are some nice looking irons for about 2x that.. and who knows if the tip is the only problem..
Check to see if there is power to the tip through the contacts to the heater. I have to say, that after using other cheaper irons at work, I will do what it takes to keep my Hakko 929-903 working. I've never used a better iron.
If you're going to build an Impasse on perf board make sure you have enough finger room to adjust the shunt resistor across the input transformer. I used a 25K pot and a variable cap from an old AM receiver. The value of the resistor will depend upon the transformer --
To contribute to this awesome thread and device, I just whipped together a BOM from the original info. It would be great if someone could proof it for me.
Impasse Preamp Circuit Bill of Materials
Resistors
R1 18k Metal Film, See Text
R2, R9, R13, R14 1M 0.125w
R3, R10 1k 0.25w Carbon Composition
R4 12k5 2w Metal film or Wirewound
R5 300R 0.125W Metal film
R6, R7 120R 0.125W Metal Film
R8 560k 0.5W Metal film
R11, R12 15k 1W Metal film (matched to 0.1%)
Capacitors
C1 Not Used Jumpered, See Text
C2, C5 0.1uF 630v Polypropylene
C3, C4 0.47uF 400v Polypropylene
Semiconductors and Lamps
D1, D2 Red LED 1.7v Allied # 670-1216
Q1, Q2 DN2540N5 MOSFET, Depletion Mode
NE-1 NE2 Neon Bulb
Transformers for Signal Circuit- One per channel
T1 Jenson JT11P-1, Cinemag CMLI-15/15B, or other equivalent 1:1 Input Transformer
Controls
P1 100k Stereo Potentiometer, Audio Taper
S1 2 Pole, 4 or 5 Position Rotary Switch
Impasse Power Supply Bill of Materials
Power Supply Resistors
R101, R102 47R 0.5w
R103 470R 3.0w Metal Oxide or Wirewound
R104 1k 3.0w Metal Oxide or Wirewound
R105 20k 0.5w
R106 100R 0.5w
R107 47R 0.5w
R108 56k 5.0w Wirewound
R109 200R 0.5w Wirewound
R110 4R7 0.25w
R111 270k 0.5w
R112 47k 0.5w
Power Supply Capacitors
C101 1uF 630v Polypropylene
C102, C103 100uF 450v Polypropylene
C104 47uF 400v Polypropylene
C105 Not Used
C106, C107, C108 0.01uF 600v Ceramic Disk Allied#507-0721
C109 1uF 630v Polypropylene
Power Supply Semiconductors
D101, D102, D104, D105 UF4007 Fast Recovery Rectifiers Allied# 950-0321
D103 Zener Diode 12v 1w
Q101 TIP 50A or equal
IC1 LM317 Adjustable Regulator
Power Supply Transformer, etc.
T2 Allied 6K3VG, 650vct @ 2A Allied # 227-0005
PEM Power Entry Module w/ Switch, Fuse & IEC Cord Connector, or separate equivalent parts
Impasse Preamp Circuit Bill of Materials
Resistors
R1 18k Metal Film, See Text
R2, R9, R13, R14 1M 0.125w
R3, R10 1k 0.25w Carbon Composition
R4 12k5 2w Metal film or Wirewound
R5 300R 0.125W Metal film
R6, R7 120R 0.125W Metal Film
R8 560k 0.5W Metal film
R11, R12 15k 1W Metal film (matched to 0.1%)
Capacitors
C1 Not Used Jumpered, See Text
C2, C5 0.1uF 630v Polypropylene
C3, C4 0.47uF 400v Polypropylene
Semiconductors and Lamps
D1, D2 Red LED 1.7v Allied # 670-1216
Q1, Q2 DN2540N5 MOSFET, Depletion Mode
NE-1 NE2 Neon Bulb
Transformers for Signal Circuit- One per channel
T1 Jenson JT11P-1, Cinemag CMLI-15/15B, or other equivalent 1:1 Input Transformer
Controls
P1 100k Stereo Potentiometer, Audio Taper
S1 2 Pole, 4 or 5 Position Rotary Switch
Impasse Power Supply Bill of Materials
Power Supply Resistors
R101, R102 47R 0.5w
R103 470R 3.0w Metal Oxide or Wirewound
R104 1k 3.0w Metal Oxide or Wirewound
R105 20k 0.5w
R106 100R 0.5w
R107 47R 0.5w
R108 56k 5.0w Wirewound
R109 200R 0.5w Wirewound
R110 4R7 0.25w
R111 270k 0.5w
R112 47k 0.5w
Power Supply Capacitors
C101 1uF 630v Polypropylene
C102, C103 100uF 450v Polypropylene
C104 47uF 400v Polypropylene
C105 Not Used
C106, C107, C108 0.01uF 600v Ceramic Disk Allied#507-0721
C109 1uF 630v Polypropylene
Power Supply Semiconductors
D101, D102, D104, D105 UF4007 Fast Recovery Rectifiers Allied# 950-0321
D103 Zener Diode 12v 1w
Q101 TIP 50A or equal
IC1 LM317 Adjustable Regulator
Power Supply Transformer, etc.
T2 Allied 6K3VG, 650vct @ 2A Allied # 227-0005
PEM Power Entry Module w/ Switch, Fuse & IEC Cord Connector, or separate equivalent parts
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Great! It seems I deleted a bunch of resistors in the transfer, plus invented a 112k5 resistor. Thanks for the review.
R5 is listed as 200R in the schematic and 300R in the article... I have it as the 300R
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I finally got off my butt this week and got my impasse running. Thanks so much to you guys for your support. It sounds great and for once has plenty of gain. I haven't gotten a chance to give it a good long listening session yet, but maybe tonight.
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Completely non-critical. It can even be 1k and make no difference to the circuit operation- strictly there to prevent oscillation of the MOSFET.