The Powells assert that the district court acted improperly (1) in limiting Dixie Powell's ability to object to witnesses; (2) in limiting Dixie Powell's ability to cross-examine witnesses; (3) in denying the Powells' discovery motion; (4) in its conduct of voir dire; (5) in limiting the testimony of the Powells' character witness; and (6) in appointing only one attorney as advisory counsel for both Dixie and Roy Powell.1 We find no merit in any of these contentions.

a. Objections

During the examination of the custodian of records of Roy Powell's employer, Ms. Bailey, Dixie Powell stated "Objection, Your Honor, as to whether this witness' name is Bailey." The court instructed Dixie Powell that she could object as her own attorney, but that she could not make objections on behalf of her husband against witnesses testifying solely against him. The Powells assert that the district court's ruling is error.

The district court's ruling was correct. Ms. Bailey's testimony was offered only against Roy Powell. The prosecution brought in a second witness to establish that Dixie Powell's income was above the minimum required to file an income tax return. Roy Powell does not have the right to lay counsel. United States v. Turnbull, 888 F.2d 636, 638 (9th Cir.1989), cert. denied, --- U.S. ----, 111 S.Ct. 78 (1990). Therefore, the court did not abuse its discretion in informing Dixie Powell that she could not object to evidence offered against Roy Powell. See United States v. Bonanno, 852 F.2d 434, 439 (9th Cir.1988), cert. denied, 484 U.S. 1016 (1989) (we review for abuse of discretion the district court's limiting of cross-examination).

Even if Dixie Powell could object for her spouse, there was no basis for this objection. Ms. Bailey testified only to demonstrate Roy Powell's income was greater than the minimum requiring Roy Powell to file an income tax return. Whether the witness's name was Bailey had no relevance to this case. Therefore, the district court did not err in overruling Dixie Powell's objection.

b. Cross-examination

The Powells raise as error that the district court restricted Dixie Powell in the cross-examination of her husband. However, the district court did not abuse its discretion in sustaining the government's objections to Dixie Powell's line of questioning.

The government objected to Dixie Powell's question to her husband about a $23,000 assessment which had been assessed for the 1979 and 1980 tax years. The district court sustained the government's objection on relevance grounds. This question had no relevance as to Roy Powell's or Dixie Powell's intent with regard to their 1982, 1983, or 1984 tax returns. Dixie Powell also asked about Roy Powell's "feeling" about the tax court and whether he owed the taxes assessed in the $23,000 assessment. Again a relevance objection was sustained. The prosecution objected to Roy Powell's statement that he felt he had been "stomped on" because he had been denied deductions in prior tax years. These statements were not relevant to the Powells' state of mind with regard to filing tax returns in 1982, 1983 and 1984. Roy Powell's feelings about the tax court and whether he felt "stomped on" do not tend to establish whether he believed he was required to file tax returns nor whether he filed the returns or whether he was required to file the returns. Therefore, they bear no relevance to any of the issues in this case. The district court did not abuse its discretion in sustaining the government's objections.

The Powells assert that the district court erred in refusing to allow the Powells access to the documents they wanted from the government's open file without signing the standard release required by the government. The government provided all of the documents to the Powells on the first day of trial.

Even if there was some misconduct on the part of the government, the Powells must show some prejudice to this court to demonstrate that the district court abused its discretion. See United States v. Abascal, 564 F.2d 821, 831 (9th Cir.1977), cert. denied, 435 U.S. 942 (1978). The Powells assert that they were harmed by the failure of the government to provide documents to them. They argue that the documents would have been far more useful to the Powells during their pre-trial preparation. Beyond their bare assertions of harm, the Powells have not demonstrated prejudice. The district court did not abuse its discretion in refusing to compel production of the documents earlier.2

The Powells challenge the district court's conduct of voir dire. Where, as here, neither party objected to the scope of the judge's questions, we review the district court's conduct of voir dire for plain error. United States v. Anzalone, 886 F.2d 229, 234 (9th Cir.1989). A plain error is a highly prejudicial error affecting substantial rights. Id. Reversal for error in voir dire "requires a showing that 'the procedures used and the questions propounded were so unreasonable as to constitute an abuse of discretion.' " Id. (quoting United States v. Flores-Elias, 650 F.2d 1149, 1151 (9th Cir.), cert. denied, 454 U.S. 904 (1981).

The Powells argue that the district court's questioning of the prospective jurors about memberships in groups which have taken a position on the tax system and their participation in tax seminars unfairly prejudiced the Powells. The Powells argue that their defense had nothing to do with these groups. Thus, they conclude, the district court's questions constituted error.

The purpose of voir dire is to help ensure that the defendant is tried by an impartial jury. United States v. Giese, 597 F.2d 1170, 1181 (9th Cir.), cert. denied, 444 U.S. 979 (1979). Membership in organizations which have attitudes on the legality of the taxation system and a juror's knowledge of the tax system derived from meetings and seminars is relevant to determining the potential bias of prospective jurors. Cf. United States v. Wolters, 656 F.2d 523, 525 (9th Cir.1981) (the record did not establish that the district court abused its discretion in refusing to ask prospective jurors if they belonged to the Morman Church, a group which is strongly committed to upholding the tax laws). It does not appear that the procedures the district court used or the questions it asked were unreasonable. We hold that the district court did not commit plain error in conducting voir dire.

The Powells argue the district court improperly limited them in questioning their daughter whom they called as a character witness. After Denise Hamilton testified as to the honesty of her parents and their reputation as honest people, Dixie Powell attempted to elicit testimony about whether her parents are law abiding or whether they had ever broken the law. The trial court did not allow Ms. Hamilton to answer. Dixie Powell asked Denise Hamilton if there was anything else she would like to say. The court sustained the government's objection. Denise Hamilton attempted to say that her parents had "research[ed] what they [o]ught to probably do--," at which point the district court halted Denise Hamilton's testimony again.

On direct examination of a character witness, evidence of specific instances of conduct are not admissible. Fed.R.Evid. 405(a); United States v. Giese, 597 F.2d at 1190. Ms. Hamilton was called for the limited purpose of establishing the Powells' character. The trial court properly limited Ms. Hamilton's testimony and did not abuse its discretion. See id. at 1170 (district court's rulings on the admissibility of character evidence reviewed for an abuse of discretion).

The Powells argue that the district court erred in appointing only one advisory counsel for both of them. The district court appointed counsel for the Powells. They declined that attorney in favor of defending this matter themselves. The Powells do not allege that their waiver of counsel was invalid.

The district court's decision to appoint advisory counsel is discretionary. Locks v. Sumner, 703 F.2d 403, 407-08 (9th Cir.), cert. denied, 464 U.S. 933 (1983). Advisory or standby counsel's role is " 'to steer a defendant through basic procedures of trial' and 'to relieve the judge of the need to explain and enforce basic rules of courtroom protocol....' Having refused this assistance, however, [the defendants] may not be heard to complain later that the court failed to protect [them] from [their] own ineptitude." United States v. Flewitt, 874 F.2d 669, 675 (9th Cir.1989) (quoting McKaskle v. Wiggins, 465 U.S. 168, 184 (1984)). Having refused the appointment of trial counsel, the Powells may not attack the quality of their advisory counsel. We conclude that the district court did not abuse its discretion in appointing only one advisory counsel for both Roy and Dixie Powell.

We conclude that the district court did not err in its rulings on the above issues. Those rulings are therefore AFFIRMED.