View previous topic :: View next topic |
Author |
Message |
Boilermaker
Joined: 21 May 2006 Posts: 527
|
Link Posted: Sun Sep 02, 2012 2:41 pm Post subject: RESTOMOD PROJECT #2 - Citation IV |
|
|
I had so much fun redoing that old Knightkit repro amp, I thought that this time I would up the ante to an old classic.
As I told you, my best music source are a bunch of 1/2 track, 15ips master tapes. Sorry digiphobes, but the sound quality is better than the best SACD's that you can buy.
Since virtually all R2R's available have 1970's vintage first generation solid state repro amps, there is not much doubt that they can be improved by using the tape head amps built in to most of the preamps built before the early 1960's.
As a high school kid during this time that the most desired preamps were the Macintosh, Marantz 7, and the Harman Kardon Citation I. All of these had low level tape head amps but even the Citation I in kit form was out of my price range, so I ended up with a Dyna PAS.
Looking on Ebay for some of these three models, I found that the prices that they bring are unbelievable! Have to be driven by nostalgia, and I'll admit that they all have an effect on me.
Fortunately, I was was lucky enough to pick up a Citation IV which is functionally similar to the Citation I but does not have the custom vinyl curves to handle some of the old eq's used before the RIAA standard was developed. Since I would not have a need for this, I got the Citation IV and saved some money.
My goal was not to just bring it back to its original form, but to bring its performance up to modern day high end levels. Especially since it has the NAB tape head input, I saw no need to change any of the circuit topology and decided to do the following enhancements:
1 - All capacitors would be upgraded to either polystyrene or polypropolene depending upon value. As it turned out, I had to parallel some to get the proper values.
2 - Replace all lo level (RIAA and NAB) wiring with shielded Mogami.
3 - Replace all other wiring with #20 stranded plated teflon hookup wire (love that teflon!)
4 - Replace all resistors with 1% metal film. There were a couple high value that I had to use carbon films instead.
5 - Utilize a "Star" grounding scenario. I felt that the original grounding scheme relied too much on the chassis.
6 - Replace the old steel RCA jacks with high quality gold plated new ones. I used a thick double sided blank circuit board (2oz. copper) to mount them on. It also became part of the new grounding system.
7 - Cleaned all the switches perfectly and applied Deoxit. The wipes on all these were black when I got it, but they all shine like new now!
8 - For the biggey, I decided to use a regulated B+ supply. There were several available that would work, but the one kit I decided on just the right size. If it was 1/4" larger, it would not have fit in the chassis. I selected 270 volts as the voltage. This regulated supply probably has an output impedance 1/1000 of the original at all frequencies! SHould make a hugh difference.
Now, for the "before" and "during" pictures:
Description: |
|
Filesize: |
177.64 KB |
Viewed: |
11713 Time(s) |
|
|
|
Back to top |
|
|
Boilermaker
Joined: 21 May 2006 Posts: 527
|
Link Posted: Sun Sep 02, 2012 4:20 pm Post subject: |
|
|
Having a problem loading the pictures. I'll try again later.
Bob
|
|
Back to top |
|
|
Boilermaker
Joined: 21 May 2006 Posts: 527
|
Link Posted: Fri Sep 07, 2012 11:21 am Post subject: |
|
|
Here are the rest of the before/during pic's:
Description: |
|
Filesize: |
163.78 KB |
Viewed: |
11667 Time(s) |
|
Description: |
|
Filesize: |
184.75 KB |
Viewed: |
11667 Time(s) |
|
Description: |
|
Filesize: |
148.61 KB |
Viewed: |
11667 Time(s) |
|
Description: |
|
Filesize: |
220.69 KB |
Viewed: |
11667 Time(s) |
|
|
|
Back to top |
|
|
Boilermaker
Joined: 21 May 2006 Posts: 527
|
Link Posted: Fri Sep 07, 2012 11:34 am Post subject: |
|
|
Ok - Here are the "after" pic's. The circuit board that you see is the voltage regulator for the 280 volt B+ supply. It took the space that the old power supply was and just barely fit inside the side of the chassis.
Bob
Description: |
|
Filesize: |
153.15 KB |
Viewed: |
11665 Time(s) |
|
Description: |
|
Filesize: |
144.22 KB |
Viewed: |
11665 Time(s) |
|
Description: |
|
Filesize: |
158.34 KB |
Viewed: |
11665 Time(s) |
|
Description: |
|
Filesize: |
150.43 KB |
Viewed: |
11665 Time(s) |
|
Description: |
|
Filesize: |
201.41 KB |
Viewed: |
11665 Time(s) |
|
Description: |
|
Filesize: |
155.13 KB |
Viewed: |
11665 Time(s) |
|
|
|
Back to top |
|
|
kal Forum Administrator
Joined: 06 Mar 2006 Posts: 17860 Location: Ottawa, Canada
TV/Projector: JVC DLA-NZ7
|
Link Posted: Fri Sep 07, 2012 12:14 pm Post subject: |
|
|
Very cool!
The thing I find neat/interesting is that components are so much better today that you can actually take a device like this and have it perform better than when it was first new.
The power supply replacement is probably one of those things that will help a lot. I'm a firm believer in good power supply design - in analog devices IMHO it's the critical "root" item you need to get right that affects everything.
Do you have to replace any of the pots (variable resistors) at all too? How about the switches? Or was some contact cleaner enough like you mentioned? Sometimes the traces wear right through from years of use...
Kal
_________________
Support our site by using our affiliate links. We thank you!
My basement/HT/bar/brewery build 2.0
|
|
Back to top |
|
|
Curt Palme CRT Tech
Joined: 08 Mar 2006 Posts: 24301 Location: Langley, BC
TV/Projector: All of them!
|
Link Posted: Fri Sep 07, 2012 12:35 pm Post subject: |
|
|
Don't you love it when input and output jacks are SCREWED into place so you can take them out without any hassle? Never mind the point to point wiring. Nice work! When you say you 'restore', you ain't kidding!
|
|
Back to top |
|
|
Nashou66
Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY
|
|
Back to top |
|
|
Boilermaker
Joined: 21 May 2006 Posts: 527
|
Link Posted: Fri Sep 07, 2012 2:30 pm Post subject: |
|
|
Quote: | The thing I find neat/interesting is that components are so much better today that you can actually take a device like this and have it perform better than when it was first new. |
I couldn't agree more. The quality and availability difference is huge. For example, the final output DC blocking cap was an electrolytic!! They didn't have a choice at the time, but it now has a nice polypropolene. Gone are all the lousy ceramic's which have mostly been replaced with polystyrene. My goal was to rival the performance of the best tube preamps available today such as Audio Research, etc., and also have a tape head input for all my tapes. There probably hasn't been a tape head repro input on a preamp since the mid 1960's.
Quote: | The power supply replacement is probably one of those things that will help a lot. I'm a firm believer in good power supply design - in analog devices IMHO it's the critical "root" item you need to get right that affects everything. |
Absolutely. That's why I went with a regulator in addition to a bypass cap at each tube. I don't know how much this had to do with it, but I hooked up my ancient Heathkit audio generator to check it out and was amazed with the performance.
The original specs state a -3db at 80Khz. My old generator only goes out to 100Khz, but it was only down 0.4db at that point! and that was into a 100Kohm load which is probably lower than the original since it was set up for tube amps at the time.
I then fed it a square wave and could not detect any roll off until about 10Khz, which puts it in a league with the best today. There was also absolutely no ringing or over/undershoot visible. Very stable.
Quote: | Do you have to replace any of the pots (variable resistors) at all too? How about the switches? Or was some contact cleaner enough like you mentioned? Sometimes the traces wear right through from years of use... |
I got lucky here. I was able to clean every wiper surface with alcohol and then apply Deoxit. They were all in excellent shape and are all noise free. I was prepared to replace the all the pots, but the volume pot is a special unit with dual wipers and no longer available anywhere. I did find a source of some used ones, but fortunately did not need it.
Quote: | Don't you love it when input and output jacks are SCREWED into place so you can take them out without any hassle? |
Yes! It is just like our CRT's, built to last forever and fun to work on. We will never see it again, unfortunately. We are not the only ones who appreciate it though - Have you seen the prices these old tube amps and preamps are bringing on e-bay?
I saw a listing recently for a combined set of two Marantz model 9 amps, one model 7 preamp and a 10B tuner in pristine condition with a reserve price of $45K!!!!! I doubt he got it, but he probably wasn't far off.
Bob
|
|
Back to top |
|
|
Tapp
Joined: 20 Apr 2021 Posts: 2
|
Link Posted: Tue Apr 20, 2021 7:25 pm Post subject: |
|
|
Bob, are you still around. I'm new and just read your HK Citation IV resto info. I'm really curious how it turned out and if you still own/use the pre? I have one myself that I want to restore.
|
|
Back to top |
|
|
AnalogRocks Forum Moderator
Joined: 08 Mar 2006 Posts: 26690 Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
|
Link Posted: Tue Apr 20, 2021 10:42 pm Post subject: |
|
|
He last logged in in 2015.
_________________ Tech support for nothing
CRT.
HD done right!
|
|
Back to top |
|
|
Tapp
Joined: 20 Apr 2021 Posts: 2
|
Link Posted: Wed Apr 21, 2021 3:23 am Post subject: |
|
|
Thanks; it's rare to find someone that has experience with the Citation IV. Seems like the Citation 1 gets more attention.
|
|
Back to top |
|
|
AnalogRocks Forum Moderator
Joined: 08 Mar 2006 Posts: 26690 Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
|
Link Posted: Thu Apr 22, 2021 8:26 am Post subject: |
|
|
I sent Bob a message. Not sure he'll get it or not. Let's see if he pops in.
_________________ Tech support for nothing
CRT.
HD done right!
|
|
Back to top |
|
|
|
|