Well, I already uploaded these servicemanuals to Jan Duponts great site:
Audio Circuit Denmark
Give him a few days to check the integrity of the files, then they will be online.
BR
Gary
Audio Circuit Denmark
Give him a few days to check the integrity of the files, then they will be online.
BR
Gary
K H 4400A, 4402B:
THD ca. 0.0001%, fmax 100kHz
K H 4200:
Krohn Hite 4200A | Used Signal Generator | Used Test Equipment | Refurbished Test Equipment
THD 0.1%, fmax 10MHz
Hard to modify without schematics ...
THD ca. 0.0001%, fmax 100kHz
K H 4200:
Krohn Hite 4200A | Used Signal Generator | Used Test Equipment | Refurbished Test Equipment
THD 0.1%, fmax 10MHz
Hard to modify without schematics ...
I've got a dead 4400 also and could use help with a schematic /manual. The -15V supply is shorted so it may be simple to resolve with a schematic- or maybe not if something else was damaged. It looks like the unit has a load of 1980s vintage tantalums- are they a known problem?
Thanks for any help
Ed
Thanks for any help
Ed
Demian is the KH4400 guru!
Here's a screenshot after letting the KH4402 (dual 4400) settle for a few minutes -- obviously the 400Hz HPF and 22kHz LPF were used. You might find it worthwhile to not perform any surgery on the unit:
Attachments
Let me dig out my notes. I have a partial rev worked out but still need some revisions.
The 4400 has a single 50 Ohm output and a JFET AGC. The 4402 has balanced outputs and an analog multiplier for the AGC. however its quite possible to improve the 4400 but you will need instrumentation to make sure you are getting it all working right. Patience with a passive twin tee may be good enough.
I'll try to find my marked up schematic or reverse the unit I tweaked.
The 4400 has a single 50 Ohm output and a JFET AGC. The 4402 has balanced outputs and an analog multiplier for the AGC. however its quite possible to improve the 4400 but you will need instrumentation to make sure you are getting it all working right. Patience with a passive twin tee may be good enough.
I'll try to find my marked up schematic or reverse the unit I tweaked.
I opened my box and pulled the schematic to see what to do. I have a few tweaks since I last looked at it which I will try. I have the currently extinct LME49990 in mine which may be a limitation. I'll try a trick with the LME49710 first since its currently available. Once I know these work I'll post.
One discovery is that the internals of the 4400 won't drive 50 Ohms on the 7V setting. You need the .7V setting to get that working. I looked briefly at grafting a buffer but it would be too much of an undertaking. It will drive 600 Ohms with no problem.
One discovery is that the internals of the 4400 won't drive 50 Ohms on the 7V setting. You need the .7V setting to get that working. I looked briefly at grafting a buffer but it would be too much of an undertaking. It will drive 600 Ohms with no problem.
The osc IC can be improved over the original..... The freq range is fairly wide... I have sacrificed some higher thd at the very highest freq (>20KHz) for lowest thd at <20Khz.
Replace the fixed r value with a 22 turn trim pot for the control jFET gate to drain resistor and adjust for lowest 2H.
Upgrade the output opamp.
THx-RNMarsh
Replace the fixed r value with a 22 turn trim pot for the control jFET gate to drain resistor and adjust for lowest 2H.
Upgrade the output opamp.
THx-RNMarsh
I went through my KH4400 this morning and did some updates and calibration. I have a marked up schematic but its too big to post so PM me for a copy.
The mods are pretty simple. Tuning and calibrating is easy with the right instruments. probably impossible without. You will need an accurate AC voltmeter good for 100KHz, a frequency counter, and a distortion analyzer with harmonic resolution below -120 dB (Shibasoku 725 or ??)
The distortion null only affects the 2nd harmonic. 3rd is untouched by the tuning.
I looked at increasing the output drive. Its only good for 50 Ohms on the -20 dB step. It doesn't have enough drive for 50 Ohm load at full output. I don't think the supplies are big enough to support that (an extra 200 mA * 30V or 6W).
The mods are pretty simple. Tuning and calibrating is easy with the right instruments. probably impossible without. You will need an accurate AC voltmeter good for 100KHz, a frequency counter, and a distortion analyzer with harmonic resolution below -120 dB (Shibasoku 725 or ??)
The distortion null only affects the 2nd harmonic. 3rd is untouched by the tuning.
I looked at increasing the output drive. Its only good for 50 Ohms on the -20 dB step. It doesn't have enough drive for 50 Ohm load at full output. I don't think the supplies are big enough to support that (an extra 200 mA * 30V or 6W).
?? Mine has no resistor between the JFET gate and the drain. None on the schematic either. There is a distortion trimpot, that does that function but on the other side of an opamp if that's what you mean. I would'n swap it since its not that tweaky. The AVC trimmer may be a better candidate for a multiturn trimmer. It can be tweaking to adjust.
i am still in asia.... been here for the past 3 months. But I return in a few days and maybe I can take a look to see exactly what the details of the 4402B mod is. Been 3 years ago or more. As results show, the mods worked very well.
If you have model with jFET, make R from gate to drain variable. I have had three KH 44xx models. The 4402B was the best, I think.
THx-RNMarsh
If you have model with jFET, make R from gate to drain variable. I have had three KH 44xx models. The 4402B was the best, I think.
THx-RNMarsh
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.